November 11, 2019

Mother Nature Cashes In On Your Heat Relief Pleas With A Bitter November Cold Snap



Remember all those tweets and posts about how you'll do anything to make the summer heat stop? Time to pay up. The season's first deep shot of cold air will cover much of the United States and Canada this week. Temperatures will plunge firmly into winter territory for most areas east of the Rockies, but not before a significant early-season snowstorm blankets parts of the Great Lakes and Northeast.

The pattern we'll see this week is more common in the winter than in the middle of November. A strong trough will move south from northern Canada, allowing a pent-up pool of Arctic chilliness to flow toward lower latitudes.

Here Comes The Cold

An animated look at NWS forecast high temperatures between Monday (Nov 11) and Thursday (Nov 14).


The leading edge of the cold air is already draped over the northern Plains and Upper Midwest, where lows on Monday morning will dip below zero in some areas.

An animated look at forecast high temperatures this week makes it pretty easy to follow the track of the upper-level trough as it pivots south from Canada. This won't be a sustained cold outbreak like we'd see in the dead of winter, but it's going to be pretty darn cold nonetheless.

Our cold front will race all the way to the Gulf of Mexico by Tuesday, leaving only southern Florida untouched by the chilly weather. High temperatures on Tuesday and Wednesday could break dozens of record low maximum temperatures, or the coldest high temperature on record for the date.

Temperatures will struggle to climb above freezing during the day on Tuesday as far south as Memphis, and the season's first freeze will reach all the way to the Gulf of Mexico a couple of weeks ahead of schedule. The average first freeze in Mobile occurs on November 25.

A stiff wind behind the cold front lead to below-zero wind chill values across the northern states, with wind chills dipping into the teens in the southeast.

This is a solid chill for so early in the season. It may not seem like too big of a deal to most of us, but consider how the cold temperatures and even colder wind chills will affect vulnerable populations like those who are homeless, folks who live without heat, and children who have to walk to school without warm clothing. This kind of cold can lead to hypothermia in short order.

Northern Border Snowstorm



A low-pressure system developing along the cold front will produce a swath of heavy snow across the Great Lakes and New England, largely straddling the U.S./Canadian border. Communities from Lake Erie to Atlantic Canada could see double-digit snowfall totals by the time the storm winds down on Wednesday and Thursday.

The latest forecast from local National Weather Service offices shows heavy snow along the northern borders from Ohio to Maine. While it doesn't show up on this NWS-generated forecast, snowfall totals will be just as high across the Canadian border in Ontario, Quebec, and New Brunswick.

Forecasters expect significant snowfall totals in places like Cleveland, Erie, Buffalo, and Burlington. It's not too unusual to see heavy snow along the lakes in November, but this will be more widespread than a true lake effect event. Burlington, Vermont, could see a storm total snowfall accumulation of 9 inches, which would be one of the greatest snowfalls ever recorded this early in the season.


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October 31, 2019

Dangerous T'storms Will Roll Through The Mid-Atlantic Just In Time For Trick-Or-Treating


A round of severe thunderstorms will move across the southeast and Mid-Atlantic states through the afternoon and evening hours on Thursday, bringing the potential for widespread damaging wind gusts and possibly even some tornadoes. The greatest threat for storms along and east of the Appalachians will coincide with kids trick-or-treating for Halloween in some populated areas. Please stay mindful of approaching storms and avoid going out tonight if you're under a risk for severe weather.



Broken lines of thunderstorms are already developing along the Appalachian Mountains as a strong cold front pushes into a warm, muggy airmass parked over the eastern United States. Conditions are downright tropical right now east of the front. Dew points were all the way up in the 70s as far north as Washington D.C. by 2:00 PM, which is a level of tropical humidity more common in August than the last day of October.

The thunderstorms will coalesce and strengthen as they move over the Appalachians and start ingesting all that unstable air. Severe thunderstorms are possible from central Alabama to southern Quebec, but the greatest risk for severe thunderstorms today exists across the Mid-Atlantic states. The Storm Prediction Center has issued an enhanced risk for severe weather, or a 3 out of 5 on the scale used to measure the threat for severe thunderstorm, from Greensboro/Raleigh in North Carolina up to the Scranton area in northeastern Pennsylvania. 

The main threat will be damaging winds and tornadoes. Winds are ripping just a few thousand feet above the ground. Winds at the surface are pretty strong as well—I can hear the gusts thunking against the window as I write this near Greensboro. It won't take much of a thunderstorm to shove those winds down to the surface and produce wind gusts of 60+ MPH.


The strong southerly winds giving us those warm, muggy conditions will also provide the low-level shear necessary for some storms to produce tornadoes. The greatest risk for tornadoes will exist in and around the area under the enhanced risk. The threat appears maximized up around the D.C. area, but the threat will exist anywhere along the squall lines that form today.

Tornadoes in squall lines can happen quickly—often with reduced tornado warning lead time—but duration doesn't relate to intensity. Any tornado is dangerous if it hits you...I know it sounds simplistic to say that, but even an EF-0 can send debris flying around at lethal speeds.

Please reconsider taking kids out trick-or-treating tonight if you're under a risk for severe weather. These storms will move fast and you may not have enough time to get to safety if the storms approach while you're out walking the neighborhood.

I look at it this way: if parents are willing to sit there and check each individual piece of candy to make sure nobody tampered with it, then they should be willing to say "no go" when there's the threat of dangerous thunderstorms on the evening of Halloween. You're much more likely to get hurt by lightning/falling trees than you are to get a piece of candy with a pin or poison in it. Kids will get over the disappointment, and many communities may even push back trick-or-treating to this weekend.


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October 27, 2019

An Extreme Wildfire Danger Will Develop In Northern California On Sunday



Dangerous fire weather conditions will develop across much of northern California on Sunday. A period of powerful winds and bone-dry humidity could allow even a tiny spark to grow into an out-of-control fire in short order. Authorities have issued a mandatory evacuation order across a significant portion of Sonoma County as worsening weather conditions could allow the Kincade Fire to rapidly grow and spread toward the Pacific Ocean.

The Storm Prediction Center's fire weather forecast for Sunday highlights an area of extremely critical fire weather conditions north of the Bay Area—including Santa Rosa, Napa, and Davis—with critical fire weather conditions existing along a swath from Fresno County to Shasta County. The agency used the term "potentially historic" to describe the fire weather threat in this area on Sunday, language they don't use lightly.

Forecasters also expect critical fire weather conditions to develop in southern California along the Transverse Ranges near Los Angeles.

High winds are likely across California on Sunday as a tight pressure gradient develops over the state. The strongest winds are likely in northern California, where we could see a widespread area of sustained winds of 40+ MPH with gusts reaching 60 MPH or higher beginning Sunday morning and lasting through the evening hours.

Winds descending on the leeward side of the mountains will warm and dry as they reach lower elevations, leading to the warm temperatures and extremely low humidity that will contribute to favorable conditions for rapid fire growth on Sunday.

Sonoma County's evacuation map around 11:00 PM PT on October 26, 2019. Areas in purple are under a mandatory evacuation. Areas in blue are under a voluntary evacuation. The area in red is the extent of the Kincade Fire.


This is a dangerous situation. Authorities have issued mandatory evacuation orders to everyone near and downwind of the Kincade Fire, stretching all the way to the coast. The situation on the ground in the evacuation area is otherworldly, with air raid sirens blaring across a moonlit horizon darkened by PG&E's blackout.

More than a million people are without power tonight as part of PG&E's Public Safety Power Shutoff program, and more power outages are likely as the winds pick up on Sunday. The goal of the intentional blackouts is to prevent downed lines or equipment failures from igniting fires on windy days; however, this may not have been enough to prevent the Kincade Fire, which reportedly started near a set of powered transmission lines during Wednesday night's blackout.

Weather conditions in northern California should become less favorable for major fire development by Monday morning as winds begin to die down.

[Top Image: Smoke from the Kincade Fire on October 24, 2019 via NOAA]


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October 24, 2019

Extreme Fire Weather Conditions Will Exist Across Parts Of California On Thursday



Strong winds and low humidity will create favorable conditions for wildfires across portions of California on Thursday. An intense fire had already broken out in Sonoma County on Wednesday night, where winds are gusting as high as 76 MPH. More fires could ignite before weather conditions slowly begin improve on Thursday night.

The combination of strong winds, low humidity, and dry vegetation will allow dangerous fire weather conditions to persist through the day on Thursday across southern California, with the the greatest risk existing in the Transverse Ranges surrounding the Los Angeles area. Critical fire weather conditions will also exist on Thursday in portions of northern California, including the northern Coast Ranges and the Chico area.
An intense fire broke out Wednesday night near Geyserville in Sonoma County, about 20 miles north of Santa Rosa on Highway 101. The Kincade Fire had consumed 1,000 acres in just a couple of hours, with no containment as of the publication of this post around midnight Pacific Time. Several folks published webcam snapshots of the fire on Twitter, showing a sea of flames on the nearby hillsides.

As we see so often during the autumn months, the greatest fire risk today will come from a Santa Ana wind event in southern California. Santa Anas develop when northeasterly winds blow across southern California. Winds cresting the mountains speed up as they race downslope toward the coast. Since sinking air compresses as it descends, these winds grow very hot and very dry by the time they reach lower elevations. This leads to an extended period of strong winds—often in excess of 40-50 MPH—hot temperatures, and bone-dry humidity levels, all three conditions necessary for explosive fire development.

More than 180,000 people in northern California were without power late Wednesday night as part of PG&E's Public Safety Power Shutoff program, designed to prevent wildfires if strong winds damage power equipment. Investigators found that PG&E's power lines sparked the November 2018 Camp Fire, which killed 85 people and destroyed most of the town of Paradise, California.

SoCal Edison warns that 308,000 customers could lose power as a safety precaution when the Santa Ana winds crank up on Thursday.

Conditions should improve on Thursday evening, though critical fire weather conditions could extend into Friday across parts of southern California.

The Storm Prediction Center issues fire weather outlooks much as they issue severe weather outlooks. The three categories—elevated, critical, and extremely critical—convey how favorable conditions are for the development and spread of wildfires. Fires can spark more easily and grow more quickly as you get into "critical" and "extremely critical" territory.

Forecasters issue the "extremely critical" category when sustained winds of 30+ MPH, very low humidity, and warm temperatures are all expected to coincide for three or more hours across an area with dry vegetation. The SPC has an extended rubric on its website explaining the criteria necessary for a forecaster to issue each fire weather category.


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October 19, 2019

Tropical Storm Nestor Set To Hit Florida Saturday With Heavy Rain, Gusty Winds



Tropical Storm Nestor is hauling tail toward Florida's Gulf Coast this evening. The lopsided storm should make landfall near Apalachicola, Florida, sometime early Saturday morning, bringing much-needed rain to the southeast over the next couple of days. The storm's winds could lead to power outages and potentially a life-threatening storm surge along parts of the Florida coast.
Nestor around midnight on October 19, 2019. || College of DuPage


Nestor isn't exactly a "classic" tropical storm. The system is lopsided, for one, and it's right on the line between tropical and extratropical, or the more common type of low-pressure system that's powered by upper-level lift. This is one of those cases where we have to focus on the storm's impacts rather than the storm itself.

Rain



We won't see a ton of rain from Nestor, but the southeastern United States is mired in a growing drought and any little bit of rain will help.

The latest forecast from the Weather Prediction Center shows the potential for a couple of inches of rain across most of the southeast over the next week, with the heaviest totals expected around Tallahassee where Nestor's core comes ashore. Some areas in the Florida Panhandle could see 5 or more inches of rain, which could lead to flash flooding in vulnerable areas.

Storm Surge

The unique shape and composition of the coast along Florida's Big Bend can expose coastal communities to a potentially life-threatening storm surge as Tropical Storm Nestor comes ashore. If the storm remains at its predicted strength on its predicted track into Florida, the latest advisory from the National Hurricane Center shows the potential for:



—a storm surge of 3 to 5 feet above ground level is possible from Indian Pass to Chassahowitzka
—a storm surge of 2 to 4 feet above ground level between Chassahowitzka to Clearwater Beach
—a storm surge of 1 to 3 feet above ground level in Tampa Bay.

I've highlighted the NHC's maximum surge potential on the map above, even though we all obviously know where Chassahowitzka is, right?

Wind

Power outages are likely along and to the east of Nestor's point of landfall as strong winds knock down trees and power lines. Sustained winds of 60 MPH winds don't sound like much, but keep in mind that severe thunderstorm warnings are issued for thunderstorm wind gusts of 60 MPH.

Tropical storm watches and warnings don't extend inland since the storm is expected to lose its tropical characteristics not long after landfall. However, wind advisories are in place for much of Georgia as gusts as high as 50 MPH could accompany the storm as it moves through on Saturday.

Make sure you keep your phone on the charger tonight, and keep a flashlight—a real flashlight, not your cell phone's flashlight—handy in case you lose power in the middle of the night.

Tornadoes

Radar image of a tornado northeast of Tampa, Florida, on October 18, 2019. || Gibson Ridge


Tornadoes are in progress across the Florida peninsula as I publish this article. Conditions are usually favorable for tornadoes to develop in thunderstorms embedded on the eastern side of landfalling tropical systems. Some of the tornadoes can be rather strong; we've already seen one classic supercellular tornado between Tampa and Orlando, complete with a well-defined hook echo and strong debris signature on radar (shown above).

The threat for tornadoes will continue across Florida through Nestor's landfall on Saturday morning, with the threat following the storm into Georgia and South Carolina through Saturday.

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October 16, 2019

A Strong Nor'easter Will Rapidly Strengthen Over New England On Wednesday Night


A potent but quick-hitting nor’easter will move into New England through Thursday afternoon, bringing a period of rough weather to the northeastern states that could result in some flooding issues and power outages. Aside from potential issues caused by heavy rain and gusty winds, much of the hullabaloo surrounding this storm stems from the term “bomb cyclone,” a hypetastic phrase that appears in just about every news article about the storm. Here’s a quick look at how the storm will strengthen so quickly.

Gusty Winds and Heavy Rain

Wind advisories are in effect from New Jersey to Maine ahead of tonight’s storm. Winds are gusting as high as 50 MPH in spots as the storm moves through the area; the combination of wet soil and full foliage will stress trees to their tipping point, potentially leading to power outages, home damage, and blocked roads. Don’t forget to stick your phone on your charger before going to bed tonight, and be mindful of large limbs or trees looming over your home.

Several inches of rain could fall during the storm, which could lead to flooding issues in low-lying areas. Roads that are normally fine during heavy rain at other times of the year could see standing water or outright flooding due to fallen leaves clogging up drains and sewers.

Bomb Cyclone

This storm is a “bomb cyclone.” The term is everywhere. Always. We can’t escape it. It’s like “polar vortex” and “wedge tornado.” It’s just there and we’ll have it forever and it’ll be used to get clicks until the internet dissolves in the fiery inferno of the Sun’s…wait, what was I talking about?

Sorry. 

Anyway.

A low-pressure system undergoes bombogenesis when its minimum central pressure drops 24 mb in 24 hours. The resulting storm—a “bomb cyclone,” if you will—is usually pretty impressive in both its effects and its appearance on satellite imagery
Record low air pressure records for the month of October. | Source: NOAA/WPC
This storm’s minimum pressure dropped in a hurry. The low had a minimum central pressure of 998 mb as it passed over the Delmarva Peninsula at 2:00 PM on Wednesday. Its pressure had dropped to 988 mb six hours later as it approached New York City. Most weather models have the system’s minimum pressure falling below 975 mb as the storm moves into interior New England during the day on Thursday. A pressure that low would set some all-time minimum pressure records at some weather stations in New England; air pressure records for the month of October are shown above.

How does a storm strengthen that quickly, anyway? Divergence.

Divergence describes winds fanning out in the upper levels of the atmosphere. Winds tend to spread apart as they leave the base of a trough or as they enter and exit stronger parts of the jet stream, known as jet streaks. Air has to rush upward to fill the void left behind by the diverging winds, leaving less air—a center of low pressure—at the surface.

An analysis of the jet stream at 8:00 PM on Wednesday. | Image: Tropical Tidbits, with my annotations


We have three sources of lift working on tonight's nor'easter as it revs up off the coast of New Jersey. The above model image shows an analysis of the jet stream at 8:00 PM on Wednesday.

A strong trough, combined with two different jet streaks, are all working together to lift massive amounts of air from the surface. If multiple sources of divergence align with each other like we're seeing right now, air has to rush upward from the surface really fast to compensate for the void left by the winds spreading out. This leads to the rapid strengthening of a low-pressure system at the surface. The storm will begin to weaken once it starts to lose that lift from above. In this case, the storm will slowly lose steam as it meanders toward Atlantic Canada on Friday.



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October 10, 2019

Two Feet Of Snow Is Possible In North Dakota As The Season's First Cold Air Arrives



A major winter storm could bring several feet of snow to the northern Plains over the next couple of days, bringing the first widespread shot of winter to much of the continental United States. Temperatures are falling like a rock behind the developing storm, dropping as much as 30°F in just a couple of hours. The chill will continue to sag south through the weekend, eventually reaching the Mississippi River before it starts to taper off.



A strong upper-level low swinging across the northern Rockies is to blame for this early-season taste of winter. A cold front moving across the Rockies on Wednesday sent temperatures falling off a cliff through the afternoon hours. Take a look at these temperature drops on the Front Range as the cold front swept through:

Chart: me | Source: Iowa State/IEM
Denver fell from 82°F to 47°F in just four hours on Wednesday afternoon. Cheyenne, Wyoming, saw an equally impressive drop, falling from 70°F to 38°F between 1:00 PM and 5:00 PM on Wednesday. The cold front sent temperatures plummeting from 80°F to 45°F in just three hours in Fort Collins, Colorado.



The cold air will continue to spread across the Plains on Thursday and Friday, eventually crossing the Mississippi River this weekend as a weaker (but still much cooler) burst of fall chilliness. The animation above shows the National Weather Service's forecast low temperatures between Thursday and next Monday. Low temperatures could reach the upper 30s as far south and east as the Tennessee River Valley.

Such an intense blast of early-season cold is almost always followed by snow somewhere, and it's going to get cranking in a hurry.



Above is the National Weather Service's snowfall forecast as of Wednesday evening, stretching through Saturday night. These forecasts were generated by individual NWS offices, so some of the borders and gradients may look a little bit wonky.

Overall, the latest forecasts show more than a foot of snow falling on a significant portion of North Dakota and South Dakota, with the greatest totals likely throughout central North Dakota where totals could easily exceed two feet. The highest totals are likely closer to the Canadian border.

Snow is already underway along the Front Range as I write this post late Wednesday night—including reports of thundersnow!—and the snow will continue spreading toward the Dakotas through the day on Thursday. Snow should slow down in North Dakota on Friday night, coming to an end on Saturday morning as the storm system pulls away from the area.

Now, about Canada. I know quite a few of you live in Canada or have family and friends up there. Every time we have a major weather event near the northern border, I get emails/tweets asking me why we discriminate against our polite neighbors.

There are a few reasons most American weather maps stop at the border. It's a sovereignty issue, for one, given that official American government forecasts could clash with an official Canadian government forecasts. The second is that NWS offices can only forecast for their area of responsibility—their forecasts come to a hard stop at a county border, let alone the dividing line between the U.S. and Canada.



Thankfully, snow is one of those events where we can look at products issued by NOAA's Weather Prediction Center, which actually do transcend international borders. The forecast is a little different from how local NWS offices arrive at their numbers, but it's usually close enough to give us a good regional overview.

The two-foot snow totals will extend deep into southern Manitoba, not too far from the Winnipeg metro area, which is home to about 800,000 people. The city could see more than a foot of snow if the forecasts verify. That much snow is more than enough to mess things up for a day since it's the first snow of the season and, no matter how used to it you are, that much snow is tough to deal with.


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October 4, 2019

Historic Heat Wave Produces Some Of The Hottest Temps Ever Recorded In October



Temperatures soared into the triple digits across parts of the southeastern United States this week at the peak of a historic late-late-season heat wave. Cities from the Gulf to the Great Lakes shattered all-time October high temperature records on Wednesday and Thursday, and many of those spots recorded temperatures hotter than any they saw during the summer.

It's been hot. Really hot. It's easy to forget that it's the beginning of October with temperatures this darn hot. It's funny...abnormally warm weather and shattered high temperature records are so common nowadays that we hardly notice them anymore. (Compare that to, say, the frenzied reaction to the major snowstorm that hit Montana and Alberta earlier this week.)

This major heat wave closes out what's been a long and dry summer in much of the eastern part of the country. Some cities saw their earliest and latest 100+°F readings this year, beginning with a major heat wave in May and ending with this nonsense here in October.

It's been a daunting task to keep up with all the records over the last couple of days; not just daily record highs, mind you, but all-time monthly high temperature records (which appear as pink dots on the following maps). Those are the hottest temperatures ever recorded at those stations during the month of October, with records stretching back more than 100 years in many locations.

Here's a look at where high temperature records fell on Wednesday:
Source: CoolWx.com



...and a look at Thursday's heat:

Source: CoolWx.com

Dozens of reporting stations broke their all-time high temperature for the month of October on Wednesday, and many of those stations re-broke their all-time monthly high on Thursday. Some of those records weren't close calls, either.
  • Huntsville, Alabama, hit 100°F on both Wednesday and Thursday, which is the latest triple-digit readings—and the hottest October days—on record there.
  • Raleigh, N.C., hit 100°F on Thursday, which is the latest triple-digit reading on record there.
  • Birmingham, Alabama, broke its record high on each of the 9 days between September 26 and October 4.
  • Charlotte, N.C., broke its record high on 7 out of the last 8 days, which, according to Brad Panovich, is the city's longest streak of broken high temperature records in 140 years of recordkeeping.
  • The summer began and ended with the earliest and latest 100°F readings on record in Augusta, Georgia. The city saw its earliest 100°F back at the end of May, and their latest 100°F occurred on Thursday. Columbia, S.C., also saw its earliest 100°F on record back in May, but missed its latest triple-digit reading by just two days this year.
The heat will wane through the weekend as the first major cold front of fall continues to push through the Mid-Atlantic and southern states. Seasonable temperatures could reach as far as the northern Gulf Coast by early next week—and, really, hoping for average highs shouldn't be such a reach in October.

500 mb normalized height anomalies. Source: Tropical Tidbits




A significant upper-level ridge parked over the eastern half of the United States is responsible for the excessive heat. Sinking air beneath a ridge of high pressure compresses as it reaches the surface, leading to the unpleasant warmth we've felt for the last couple of days. That sinking air also serves to put a lid on any convection or clouds, which is why you hardly get any relief from a passing cloud or afternoon shower.

Extremes beget extremes; the intense ridge over the eastern United States was directly related to the sharp trough over the Rockies earlier this week that brought historic early-season snows to parts of Montana and Alberta. Some spots saw as much as three feet of snow to begin the month of October, which is among the highest snowfall totals ever recorded during the month in those communities.

Speaking of extremes, it's important to address the elephant in the room. Climate change increases the probability of seeing heat waves like this in the future. It's hard to link directly link any one specific event to climate change; climate consists of patterns and trends, after all. Abnormal heat is certainly a trend. The five hottest years on record were 2016, 2017, 2015, 2018, and 2014. It's likely that 2019 is going to rank high on the list at the rate things are going. Climate change exacerbates the extremes, meaning we're likely going to see longer and more intense heat waves as the atmosphere warms and it begins to affect weather patterns.


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September 19, 2019

Texas Reels From Another Historic Flood After Imelda Drops Nearly Four Feet Of Rain



The remnants of Tropical Storm Imelda triggered yet another flash flood emergency in southeastern Texas, the fourth time this region has had to deal with historic, devastating floods in the last four years. Since Tuesday, the Beaumont area has seen bands of intense thunderstorms redevelop and sit over the same areas for hours at a time, producing nearly four feet of rain in some areas. The rain will slowly wane over the next day, but the damage is done.

A tropical wave moving across the northern Gulf of Mexico quickly strengthened into Tropical Storm Imelda on Tuesday as it made landfall. The disturbance organized into a tropical depression, strengthened into a tropical storm, and made landfall near Freeport, Texas, all within a two-hour window on Tuesday afternoon.

Imelda came ashore beneath a large ridge of high pressure over the eastern two-thirds of the United States; the storm's weak structure and the lack of steering currents meant that there was nothing to keep the storm moving north and away from the Houston/Beaumont areas. As a result, the system and its remnants have meandered over southeastern Texas for three full days. Ample tropical moisture and several sources of forcing allowed bands of thunderstorms—which produced 500,000 lightning strikes (!!!) in ten hours on Wednesday—to train over the same areas for hours at a time.


Some observing stations around Beaumont have seen more than three-and-a-half feet of rain since this all began on Tuesday. A foot of rain in one afternoon can trigger significant flash flooding just about anywhere; once you climb up two, three, four feet of rain, there's just no way to handle that even if you have the best infrastructure possible. The ground can't handle it. Natural waterways can't handle it. Man-made sewer systems can't handle it. Since it has nowhere else to go, the water just builds up and floods neighborhoods that have never experienced significant flooding before. This is why we hear "we've never flooded around here" after each of these events. Areas you don't think can flood really can flood if it rains hard enough for long enough.

Despite the system's rapid development, residents had plenty of warning that heavy rain would lead to flash flooding across southeastern Texas regardless of whether or not the disturbance became a named storm. Flash flood watches went into effect while the system was still over the Gulf. Local meteorologists went out of their way to make sure everybody knew the risks. However, there were few indications beforehand that rainfall totals would rival some of those seen in Hurricane Harvey just two years ago.

According to the National Weather Service office in Houston, the highest preliminary rainfall total from this event was 43.15" near Beaumont in Jefferson County, Texas. If that total verifies, the office said, it would make Tropical Storm Imelda the seventh-wettest tropical cyclone on record in the United States, and the fourth-wettest on record in Texas. This would also beat out Tropical Storm Allison's highest rainfall total of 40.68 inches; that storm in June 2001 served as the benchmark for tropical cyclone flooding for all subsequent storms until Harvey.

Tropical Storm Imelda is the fourth historic flood event in southern Texas in the last four years, following Memorial Day 2015, Tax Day 2016, and Hurricane Harvey in 2017. The Carolinas suffered tremendously in the flooding left behind by Hurricanes Matthew (2016) and Florence (2018). It's easily forgotten that Hurricane Barry, which made landfall (and produced two feet of rain) in Louisiana this past July, broke the all-time tropical cyclone rainfall record for the state of Arkansas after producing 16.17 inches of rain in the town of Dierks.

It's a common comment among meteorologists and weather enthusiasts during this event that there are few weather maps with a color scale large enough to cover the spread of rainfall totals. Topping-out the color scale on a rainfall map is a fairly arbitrary marker, but it demonstrates how unusual it is to see so many extreme rainfall events in such a relatively short period of time. We could go years without ever seeing another tropical system produce more than three feet of rain, or we could have another next month.

It's hard to link any one weather event directly to climate change, but it's also hard not to look at all these heavy rain events and ignore the influence climate change may play in current flood disasters and future storms. A warmer atmosphere is able to hold more moisture, which creates more opportunities for thunderstorms to produce heavier downpours. A changing climate will accentuate the extremes—dry spells will grow drier and flooding rains will grow even heavier.


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September 13, 2019

Tropical Storm Humberto Will Likely Develop And Approach Florida This Weekend

Tropical storm warnings are up in the northwestern Bahamas ahead of "Potential Tropical Cyclone Nine," a tropical disturbance that will likely develop into Tropical Storm Humberto over the next day or two. Its ultimate strength and track remains to be seen, but conditions are favorable for strengthening and the potential storm could bring foul weather to areas devastated by Hurricane Dorian last week.

Don't focus too much on the name of the storm right now. "Potential Tropical Cyclone" is a bureaucratic thing that lets forecasters issue watches and warnings before a disturbance becomes a tropical cyclone. The system is likely going to develop into a tropical depression on Friday and a tropical storm by this weekend.

A tropical storm warning is in effect for the northwestern Bahamas, including Great Abaco and Grand Bahama, the two islands devastated by category five Hurricane Dorian last week. Gusty winds and 2-4 inches of rain are possible in the northern Bahamas as the future tropical storm moves through the area. Tropical storm force winds (39+ MPH) are possible in the vulnerable northwestern Bahamas as early as Friday morning.



The official forecast from the National Hurricane Center brings future-Humberto into Florida as a tropical storm. The main impacts right now look to be gusty winds—some strong enough to down trees and power lines—and heavy rain, which could lead to flooding issues across areas that saw heavy rain from Dorian last week. Based on the current forecast track, the Weather Prediction Center expects a broad potential for 3-6 inches of rain across coastal parts of the southeast, with higher totals in some areas. Rainfall forecasts will likely change as forecasters get a better handle on the organization and ultimate track of the storm.

There's considerable uncertainty in forecast track for this potential storm. It's important to remember that this system isn't a fully-formed tropical cyclone. There's no center of circulation at the surface and the system hasn't developed the core that's necessary for a tropical cyclone to sustain itself and grow. The organization of a system heavily influences its future track; a weak and unstable system is more susceptible to sudden shifts, while a stronger and more well-rooted system can tap into deeper atmospheric steering currents.

We'll know much more about the future of this system once it actually develops. I know it seems like a million years ago, but we had a similar problem during the early days of Dorian. It wasn't a sure thing that the storm would survive beyond the Greater Antilles because of the young system's weak and fragile structure. Future-Humberto is a different system and it's rooted in a much different environment than the one that supported Dorian. That said, the ex-storm's first days in existence are a great example of how the internal structure of a storm can have a big influence on what it does in the future.

Now, about that name...

A "potential tropical cyclone" is a disturbance that's on the cusp of developing into a tropical depression or tropical storm, but it's close enough to land that watches and warnings are needed to give people adequate time to prepare for tropical storm conditions.

The old rules used to forbid the NHC from issuing watches or warnings until the system actually developed into a tropical depression or tropical storm. Sometimes it's too late to issue warnings by the time the storm actually develops.

One infamous example of this was Tropical Storm Bill back in 2015. Bill made landfall in Texas with 60 MPH winds just 12 hours after a tropical storm warning went into effect. If you went to bed early on June 15 and woke up late on June 16, you could have missed the entire warning ahead of the storm. That issue is remedied by the existence of "potential tropical cyclones."

Thankfully, the NHC usually doesn't have to use this designation for very long. These systems are so close to the line that they're typically upgraded to a depression or a storm within a couple of advisories, limiting the time that this newfangled term is thrown around in weather forecasts.


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September 11, 2019

Weather Forecasts Were Under Attack Well Before Trump. Fighting Back Is Long Overdue.



It’s been a heck of a couple of weeks for meteorologists. Expert forecasters had to juggle the precise path of a category five hurricane while the President of the United States led a bizarre campaign to undermine those very forecasts to avoid admitting he made a mistake on Twitter. The deep mistrust sowed in forecasts and forecasters in recent days will take years to undo, but don’t for a second think this eroding trust is a new phenomenon. It’s been stewing for years, and we’re all worse for it.

The National Hurricane Center accurately predicted the path of category five Hurricane Dorian as it came perilously close to Florida, nailing almost a week out that the storm's destructive core would curve within a hundred miles of the Florida coast. Dorian’s forecast path was one of the highest-stakes forecasts in recent years, and it’s a coup of both meteorology and human forecasting that they successfully predicted the path of a scale-topping hurricane.

A Mistake Becomes The Government Line

Not everyone appreciated the forecasting success. We’re all familiar with the flap about Hurricane Dorian “threatening” Alabama. The president tweeted on Sunday, September 1 that Alabama would “most likely be hit (much) harder than anticipated” by Hurricane Dorian, even after expert forecasters had ruled out impacts to Alabama.

The statement drew a mixture of confusion and anger from meteorologists, who correctly pointed out that the weekend forecast updates spared Alabama from any of the storm's hazards. 
The official forecast for Hurricane Dorian at the time of Donald Trump's first "Alabama" tweet on September 1, 2019. | NOAA/NHC


The president reportedly received hourly hurricane updates on the golf course over the weekend, which likely kept him aware of the forecast keeping Dorian east of Florida. The map above shows the forecast from Sunday morning when Trump sent his first "Alabama" tweet.

Trump, who would legally change his name to Donall if he spelled it wrong to avoid having to admit an error, didn’t take kindly to the corrections in the days that followed. The president kept doubling-down on the mistake with increasing intensity in order to save face.

During a public Oval Office briefing on Wednesday, September 4, the president displayed an outdated forecast from August 29 to justify his tweet from September 1. Trump had drawn on the map with a Sharpie to falsely extend the cone of uncertainty to include a portion of Alabama, a transparent attempt to justify his false tweet.

The falsely altered map drew even more intense criticism, and the president's one-off mistake turned into a full-blown Thing. Enraged by the added criticism of his falsified map, Trump tweeted an even older computer model image to justify his warning to Alabama, then commanded an adviser to release a statement that the president’s false claims weren’t false at all.

Again not satisfied with the intensifying criticism, the White House Chief of Staff reportedly ordered the Secretary of Commerce to threaten to fire top officials at NOAA if they didn’t issue a statement refuting a tweet from the National Weather Service office in Birmingham, Alabama, which accurately said their state would “NOT see any impacts from #Dorian."

NOAA's subsequent unsigned statement throwing their own forecasters under the bus to satisfy the president was widely derided, galvanizing support among meteorologists to call out the administration for warping the weather to suit the president's political needs.

It's Transparently Ridiculous

It’s all absolutely ridiculous, and what stings the most is that it’s so transparently ridiculous.
If the expert meteorologists at the National Weather Service can’t speak authoritatively on a major weather event because it might upset the fragile sensibilities of those in charge, then we’re longer lost as a functioning country than anyone cares to admit.

The weird defenses and justifications we’ve seen over the last week are just as concerning as the bad information itself. We all know what’s going on. We all know what happened. Contrary to every principle that's supposed to guide government officials in the United States, the president successfully mobilized the executive branch to lie about weather forecasts in order to defend a single incorrect tweet despite the fact that they all knew it was the wrong thing to do.

This is a protracted struggle to never admit a mistake. Saying “oops” is a weakness. If the facts don’t conform to what you said, just issue threats and make stuff up until people are too confused to tell the difference.

No amount of days-old backfilling can change the fact that there was no threat to Alabama by the time Trump tweeted on September 1, much less the state at risk of being “hit (much) harder than anticipated.”

Weather Has Been Under Attack For A While

We’re rapidly losing our ability to use basic reasoning to determine what’s real and what’s not.  Dorian was not a threat to Alabama on September 1. But after just one week of this partisan jackhammering, you could probably run a national poll and find a double-digit response who would all swear Alabama was in grave danger.

This didn’t start with Trump. This didn’t even start with Twitter. The nonsense we’re living through right now is why I’ve expended great effort trying to debunk conspiracy theories and blatantly fake weather forecasts put out by attention-seeking weenies.

Conspiracy theories, made-up weather forecasts, and the instinct to go full-hype on social media has primed people for the reality-adjacent bizarroworld we’re living in right now.

I’ve argued for years that conspiracy theories about the weather—kooky as they sound—will become extremely dangerous when enough people believe them for a long enough time. We seem to have reached that tipping point.

The wispy clouds behind cruising jetliners aren't weather- or mind-controlling chemicals. Antennas can't control the weather. Doppler radar dishes can’t control the weather. Meteorologists don't fake weather forecasts to scare people or drive up grocery sales. Meteorologists don’t rip their forecasts from a computer—oh, and they’re right a heck of a lot more than just half the time.

All that stuff is really easy to believe once you’ve lost trust in all things outside of your bubble. Once you’re convinced that the world around you is all an elaborate play and everything is controlled by just a couple of people, it doesn’t take much of a spark to flip you out. We’ve seen too many people, intoxicated by conspiracy theories, decide to take up arms and act on their twisted view of reality.

The vast majority of people who subscribe to those outlandish ideas believe it peacefully; or, as peaceful as you can be while screaming at nonbelievers via email. But words alone can cause serious damage.

If someone has lost so much trust in the world that they believe the government controls the weather, what are they telling their friends and family about the forecast for Hurricane Dorian? How many Facebook pages out there have hundreds of thousands of gullible fans lapping up the idea that an antenna array in Alaska can create storms on command? How often do you hear a cashier at the grocery store or a colleague at work brush off a weather forecast because “they’re always wrong” or “they don’t know what they’re talking about?” Yes, that banal small talk does damage after a while.

It’s not just the conspiracy theories we have to worry about. Fake and misrepresented weather forecasts are also a huge problem on social media. Have you ever seen a weather model image on Facebook that showed an enormous blizzard or hurricane racing toward a populated area in a week or two?

There’s a patchwork cottage industry of amateur weather enthusiasts and less-than-level meteorologists looking for clicks who all gleefully share horrifying and outlandish weather model runs on social media. Some folks even flat-out issue fake "forecasts" for clicks—this was such a big issue at one point that the NWS had to issue a statement in June 2011 calling out a single weather hoaxer by name to distance themselves from his faux-official products. And, no, it wasn’t Donald Trump.

We’ve been dealing with this trend of—apologies for the term—fake weather news for years. It’s not a new­ thing. It’s been a long struggle and it’s not one easily won in the social media era. You can’t stop Tri-County Weather Authority 3000 from screaming that the entire tri-county area is going to get buried in a blizzard that was never going to happen. You can’t stop Chief Meteorologist Chad Cheesebog from sharing a weather model showing a 934 mb hurricane hitting New York City in 15 days.

But we can call it out.

Speak Out

The one thing we can do to preserve the character and integrity of weather forecasting, the expert scientists who issue those forecasts, and the very foundation of the science of meteorology itself, is to speak up and fight back. This is no time for “stick to the weather” or “I don’t really like politics.” If you haven’t felt the pain or seen an attack on your little slice of life yet, trust me—it’s coming. I can only wonder how many proudly apolitical meteorologists never envisioned having to speak out against the president's statements before last week.

It’s on you to call out nonsense when you see it. Put people on the spot for peddling fake or inaccurate weather information. Call out inappropriate use of weather models on social media. Don’t politely nod when someone at the grocery store says “weathermen get paid to be wrong all the time.” Don’t stay out of the fray when the president draws on a hurricane forecast to make himself look right. If the president can successfully try to bully and bury official weather forecasts to fit his worldview, how can anyone ever trust a forecast again? 

Meteorologists have done a fantastic job of pushing back against the administration's political meddling since this whole ordeal began. A top scientist at NOAA denounced the statement issued by the agency's political leadership and vowed to launch an investigation. NWS Director Dr. Louis Uccellini strongly defended his agency's forecasters in a speech at this week's National Weather Association's annual meeting in—go figure—Alabama. Just about every meteorologist and weather enthusiast with an audience spoke out against the nonsense and held nothing back speaking to those who tried to defend it. 

That trend needs to continue. We need to make it loud and clear that you cannot mess with the integrity of weather forecasts, because once that trust is gone, it's gone for a generation. Lives are at stake when people start to believe that there are different versions of reality and the warnings and statements of expert meteorologists are issued under duress or with an ulterior motive. The only way the integrity of weather forecasting can withstand political spin and deep mistrust is if we stand up and speak out. Anything less is unacceptable.

[Top Image: Twitter/@WhiteHouse]


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September 6, 2019

Hurricane Warnings Issued For Nova Scotia As Hurricane Dorian Races Toward Canada

Nova Scotia will likely experience hurricane conditions on Saturday as Hurricane Dorian makes its final run as a named storm. Tropical storm conditions are likely in Prince Edward Island, eastern New Brunswick, and western Newfoundland before the hurricane races toward the Arctic and dissipates.

Hurricane Dorian made landfall on Cape Hatteras, North Carolina, early on Friday morning, bringing hurricane force winds and a major flooding to the state's Outer Banks. Some communities on the barrier islands recorded a significant storm surge, which was enough to inundate neighborhoods and cover roads in feet of sand and debris.

The hurricane continues to accelerate through the western Atlantic Ocean this evening as a trough over the northeastern U.S. scoops the storm toward higher latitudes. At 8:00 PM EDT, Hurricane Dorian still had formidable maximum sustained winds of 90 MPH with higher gusts.

A tropical storm warning is in effect for Cape Cod, Martha's Vineyard, and Nantucket as the storm passes off to the east. Heavy rain and wind gusts as high as 60 MPH are possible through Saturday morning as Dorian passes well to the east of the area.

Dorian will begin to affect Nova Scotia on Saturday morning, with conditions quickly deteriorating through the afternoon hours. A hurricane warning is in effect for central and northern Nova Scotia. A tropical storm warning and a hurricane watch are in effect for southern Nova Scotia and Prince Edward Island. Hurricane and tropical storm watches are in effect for western portions of Newfoundland.

The greatest risk for hurricane force winds (119+ km/h, or 74+ MPH) will occur around the center of the storm, likely bringing a period of dangerous conditions to central and northern Nova Scotia as well as eastern Prince Edward Island, including the cities of Halifax, NS, and Charlottetown, PEI. Widespread power outages and tree damage are possible in these areas. Soggy soil from heavy rain could make trees more susceptible to toppling in the strong winds.

Environment Canada warns of the potential for 50-100 mm [2-4 in.] of rain in Nova Scotia and Prince Edward Island, where some totals could reach as high as 150 mm [6 in.]. This much heavy rain in a short period of time could lead to flash flooding in low-lying areas. The National Weather Service's flood safety motto is "turn around, don't drown." It takes a surprisingly small amount of moving water for a vehicle to lose buoyancy and get washed downstream, and you can't reliably tell how much water actually covers the road ahead of you.

It's worth noting that the 5:00 PM forecast from the NHC keeps Hurricane Dorian a tropical cyclone as it crosses the Maritimes. Hurricane Dorian could soon undergo a process called "extratropical transition." After this occurs, the storm will be called "Post-Tropical Cyclone Dorian" in official forecasts and warnings. Don't let the new title throw you. It'll still be the same storm with the same hazards.

Extratropical transition has to do with the internal structure of the storm. Tropical cyclones are fueled by thunderstorms around the center of circulation. Tropical cyclones racing toward higher latitudes often lose that energy source and begin to derive their energy from the jet stream instead. This causes the tropical cyclone to become an extratropical cyclone, or the type of low-pressure system that develops cold and warm fronts. A storm's wind field grows larger as it undergoes extratropical transition. This would expose more of Atlantic Canada to damaging winds.

Dorian will remain a dangerous storm even after it experiences this structural change. As such, the National Hurricane Center will continue to issue forecasts, watches, and warnings as they are now, so long as the storm poses a threat to land.

[Satellite: NOAA]


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September 5, 2019

Dorian Producing Hurricane Conditions In North Carolina; Atlantic Canada Next In Line

Hurricane Dorian's eyewall will continue scraping along the North Carolina coast on Thursday night after bringing high winds and coastal flooding to South Carolina earlier in the day. Hurricane force winds and a life-threatening storm surge are possible tonight and through the first half of Friday as the hurricane makes its way up the North Carolina coast toward open waters. Atlantic Canada will likely see hurricane conditions on Saturday and Sunday as Dorian races toward higher latitudes.

Dorian's Holding Steady

Radar image of Hurricane Dorian at 9:10 PM EDT on September 5, 2019 | GREarth/AllisonHouse
We've still got a strong hurricane this evening. The 8:00 PM EDT update from the National Hurricane Center found maximum sustained winds of 100 MPH with higher gusts. Charleston, S.C., experienced sustained winds of 52 MPH and a wind gust of 69 MPH just before noon on Thursday. A station along the coast near Georgetown, S.C., reported sustained winds of 77 MPH with a gust to 85 MPH as the core of the storm approached the region around 4:00 PM. We're likely to see more reports of sustained hurricane force winds on the North Carolina coast tonight.

Current Forecast

Dorian is moving northeast right now, and its eye could make landfall somewhere along the North Carolina coast this evening. Regardless of whether a technical landfall occurs, hurricane force winds in the eyewall will continue to spread over land as the storm moves up the coast.

The hurricane's wind field continues to grow larger as it begins to feel the effects of the jet stream to its north. Tropical storm force winds extend 170 miles from the center of the storm—stretching as far inland as Fayetteville—with hurricane force winds stretching 70 miles from the center. This expansion will likely expose the Virginia Tidewater and the southern half of the Delmarva peninsula to tropical storm conditions on Friday morning.


According to PowerOutage.US, the storm has caused about 260,000 power outages across the Carolinas as of 9:20 PM EDT. This number will likely climb through Friday as strong winds move over populated areas.

Flooding

Radar rainfall estimate between 9:00 AM and 9:00 PM on Thursday. | GREarth/AllisonHouse
Multiple flash flood warnings are in effect across North Carolina as the storm wrings out every drop of tropical moisture in its rainbands. Radar estimates show widespread totals of 3-5 inches over the last 12 hours—with isolated totals as high as 7 inches—and plenty more heavy rain is on the way during the overnight hours. Remember, most flood-related fatalities are the result of motorists trying to drive across a water-covered roadway.

Tornadoes

Tornadoes are a threat with any landfalling tropical cyclone. There have been multiple confirmed tornadoes across North Carolina today, including in Carolina Shores and Emerald Isle on Thursday morning.

A tornado watch is in effect through the overnight hours in northeastern North Carolina and southeastern Virginia as thunderstorms in the outer bands tap into low-level wind shear and begin rotating. The tornado warning lead time on tropical tornadoes is lower than normal due to how quickly they form. Pay close attention to tornado warnings tonight and make sure the emergency alerts are activated on your cell phone.

Eastern Massachusetts

Once Hurricane Dorian clears the Mid-Atlantic on Friday afternoon, the next spot at risk is eastern Massachusetts.

A tropical storm warning is in effect for Cape Cod, Martha's Vineyard, and Nantucket as Hurricane Dorian races past the area on Friday night and Saturday morning. The center of the storm will pass well to the east of New England, but its wind field will grow so large by that point that a period of tropical storm conditions are possible in far-eastern Massachusetts.

NWS Boston warns of the threat for 30 to 40 MPH sustained winds—with wind gusts potentially as high as 60 MPH—across areas in the tropical storm warning. These areas could also see 2 to 4 inches of rain, which could lead to localized flooding issues.

Atlantic Canada

Hurricane Dorian will slowly lose its tropical characteristics as it approaches Atlantic Canada this weekend. Interaction with the jet stream will combine with cooler waters to force the hurricane to transition into an extratropical cyclone, or a "common" low-pressure system that derives its energy from the jet stream and features cold and warm fronts at the surface.

Despite the likely status change, ex-Dorian will still pack hurricane force winds, flooding rains, and the potential for a storm surge along the coast once it arrives in Nova Scotia on Saturday. Folks who live in Nova Scotia (especially around Halifax), eastern New Brunswick, and eastern Prince Edward Island should spend Friday preparing for a period of damaging winds on Saturday that could lead to widespread power outages, downed trees, and significant coastal flooding in vulnerable areas. The storm will move into Newfoundland on Sunday, bringing these hazardous conditions to communities on the western half of the island.


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