December 31, 2019

The April 27, 2011 Tornado Outbreak Shaped How We Viewed The Weather In The 2010s

This was the first decade that allowed us to track every weather event on social media in excruciating detail. We went into 2010 getting weather info from big companies, a few apps, and a handful of popular blogs. We're ending 2019 with more apps and Facebook and Twitter pages than any one person could ever hope to download or follow. The technological advances we've seen in the last ten years changed how we consume weather information, but the storms themselves—and one outbreak in particular—did just as much to shape how we approach future weather events.

April 27 was a seminal moment in meteorology. The peak of the generational tornado outbreak that unfolded that day shaped severe weather communication for every major outbreak since. Much of the day's legacy involves personal impacts and the emotional toll it took on people affected by the storms and the meteorologists who watched them unfold.

216 tornadoes touched down on April 27, 2011, setting the record for the most tornadoes ever recorded in a single day. National Weather Service meteorologists surveyed the damage left behind by dozens of major tornadoes, including 4 scale-topping EF-5s. More than 300 people died as a result of tornado-related injuries.

The tornado outbreak was a well-predicted event. Meteorologists sounded the alarm days in advance that an unusually potent tornado outbreak might take place that afternoon. Long-track tornadoes allowed meteorologists to give people hours of notice ahead of the storms. Just about every local television and radio station preempted programming to carry live coverage of the storms.

Despite the advanced warning and extensive live coverage of the storms, hundreds were killed and thousands more were injured in the day's tornadoes. The high death toll was a combination of infrastructure failures and the sheer strength and number of tornadoes.

A powerful squall line swept through Alabama early in the morning on April 27, causing widespread power outages across the state. Several weather radio transmission towers went offline during the power outages, leaving many Alabama residents with no electricity and no NOAA Weather Radio going into that afternoon's storms.

The raw power of the tornadoes also contributed to the immense death toll. Many homes in the path of the strongest tornadoes were scrubbed from their foundations. There's no amount of walls separating you from the outdoors that can save you when your entire house is simply swept away.

That single afternoon built a culture of weather awareness in the south. To this day, Alabama's most beloved living resident is probably James Spann. People who normally wouldn't care about the weather can decipher radar products without needing any help. The physical, emotional, and mental scars left behind by that day's tornado outbreak did more to instill weather awareness and storm education than just about any event before it.

That day's events also shaped how we cover the weather. That afternoon is the reason I write about the weather today. Every meteorologist and weather enthusiast who was around and paying attention uses that day as the benchmark for how to measure their coverage of potential tornado outbreaks.

Think back to Hurricane Sandy in 2012, the EF-5 tornado in Moore in 2013, blizzards, major flooding, Matthew, Harvey, Irma, Maria, Florence, Michael, Dorian...all the major weather events that came after April 27, 2011, were covered through a lens adjusted on that horrible day.

It strengthened the resolve to push back against hype-filled weather coverage. It taught millions of people to pay attention to the weather and take everything seriously. The closest that weather folks as a whole have come to ringing the alarm as loudly as April 27, 2011, was back on May 20, 2019, a day when the atmosphere appeared primed for an intense tornado outbreak in Oklahoma, but the storms ultimately had trouble forming.

We'll have historic disasters in the next ten years. It's likely that some of them will set new benchmarks for storms in the years that follow. Thankfully, technology today is better than it was back on April 27. Smartphones are more prevalent than ever and they're all equipped with wireless emergency alerts that receive tornado warnings instantly. Weather radar was upgraded with dual-polarization in the 2010s, giving us the ability to see tornado debris in a storm.

The next decade will see more advances in forecasting, detection, and alerting, progress that will help us stay ahead of storms even better than we can right now. People change. Tech changes. The weather is changing. It's up to all of us—meteorologists, reporters, the public—to learn the lessons of the past and apply them to whatever storms lie ahead.

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December 25, 2019

This Was The Warmest Christmas On Record For Much Of The Midwest

The sun just set on one of the warmest Christmases in recent memory. The abnormal blast of winter warmth stretched from the Rocky Mountains to the East Coast, with the bulk of the above-average temperatures focused on the central part of the country. Temperatures climbed as much as 30°F above normal in parts of the central United States on Wednesday afternoon, leading several cities to their warmest December 25 on record.

A strong ridge of high pressure over the eastern two-thirds of the United States is responsible for the current burst of above-average temperatures. The most significant and widespread warmth occurred on Wednesday afternoon, but the unseasonably comfortable temperatures will stretch into Thursday and Friday for some in the eastern part of the country.

This kind of warmth doesn't seem like much. It's pretty nice out! How often do you get to throw the windows open on Christmas and air out the house before the cold of winter sets in? However, just because it's comfortable doesn't mean that this isn't an unusually warm stretch for late December. It's easy to lose sight of the fact that it's not supposed to feel like late September in late December when that eye-popping temperature anomaly's practical effect is "ooh, this is comfy."

Dozens of reporting stations broke their daily high temperature record for December 25, cementing this as the warmest Christmas on record for many parts of the Midwest. The animation above shows the high temperatures that fell (in red) on Wednesday.

Moline, Illinois, saw its warmest December 25 on record, topping out with a high of 62°F. That doesn't seem like much until you consider that the city's average high for this date is 32°F. The high in St. Louis, MO, clocked in at 70°F, which is also a solid 30°F above what the city should see this time of year.
City Average High
for Dec. 25
Observed High
on Dec. 25, 2019
Departure From
St. Louis, MO 40°F 70°F +30°F
Moline, IL 32°F 62°F +30°F
Kansas City, MO 38°F 66°F +28°F
Chicago (MDW), IL 33°F 61°F +28°F
Wichita, KS 42°F 68°F +26°F
Indianapolis, IN 36°F 62°F +26°F
Oklahoma City, OK 49°F 70°F +21°F
Memphis, TN 50°F 70°F +20°F
Buffalo, NY 34°F 50°F +16°F
Mobile, AL 61°F 73°F +12°F
Sources: xmACIS2 / NWS
Extremes beget extremes. Folks east of the Rockies often have to endure relentless wintertime teasing from friends and family basking in California's mild winters. A strong ridge is usually paired with a strong trough nearby, and this ridge's companion found itself right over California on Wednesday. Chicago Midway recorded a warmer high temperature (61°F) than Los Angeles (58°F),

The ridge will slide east through the end of the week, briefly allowing more seasonable temperatures to wash across the Midwest before a ridge redevelops this weekend and pumps 50s and 60s back toward the Great Lakes. It's likely that above-average temperatures will continue across parts of the eastern U.S. through next week.

Here's a look at the National Weather Service's forecast high temperatures through Sunday.

Thursday, Dec. 26

Friday, Dec. 27

Saturday, Dec. 28

Sunday, Dec. 29

[Top Image: Tropical Tidbits]

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December 19, 2019

Those New 'Snow Squall Warnings' Are Designed To Prevent Deadly Pileup Accidents

Millions of smartphones across the Northeast flashed an unfamiliar warning on Wednesday afternoon. The message came across as a push alert with the iconic screeching tone and an abrupt vibration: "Emergency Alert. Snow squall warning until 4:15 PM. Sudden whiteouts. Icy roads. Slow down! -NWS" These alerts may seem a little excessive on first glance, but they're targeted at motorists who need to know that they're approaching a potential whiteout that could cause a deadly pileup accident like the one that occurred in Pennsylvania on Wednesday.

The National Weather Service created snow squall warnings as a way to warn people in the path of snow squalls that they could experience sudden whiteout conditions, giving them enough time to pull off the road and wait for things to calm down before driving again.
Source: NWS New York

A local NWS office can issue more than a hundred different types of watches, advisories, and warnings. Some of the products are more urgent than others. The most important warnings—the ones that require you to stop what you're doing and pay attention to the weather instead—are usually issued using polygons, which allow forecasters to target warnings to only the areas at risk for life-threatening hazards like tornadoes and severe thunderstorms.

There's a different target audience for each of those polygon-based warnings. Tornado warnings and severe thunderstorm warnings are "everyone" warnings, no matter who or where you are. Flash flood warnings are important to people who live in flood-prone areas and motorists who may approach a flooded roadway, but the vast majority of us can usually ignore them if we're going about our business at home or work.

Beginning in November 2018, the National Weather Service officially began issuing polygon-based snow squall warnings, giving forecasters the ability to instantly warn people that they could be in the path of a sudden burst of snow. Snow squall warnings are "driver" warnings. They're not targeted to people sitting in their living room or working at their cubicle. They're targeted at people on the road or those who are getting ready to head out.

Snow squall warnings are handled with the same urgency as tornado and severe thunderstorm warnings for good reason.
We hear about pileup accidents all the time during the winter. A chain-reaction crash is pretty much the worst-case scenario for anyone out on the roads when a sudden burst of snow turns the roads to ice and drops visibility down near zero. Pileups can involve hundreds of cars in the most serious incidents, amassing dozens of injuries and fatalities as people get stuck in the wreckage and absorb the blow of every car and truck careening toward them.

The warnings worked exactly as expected on Wednesday. Several snow squalls moved across portions of the Northeast today, bringing whiteout conditions and dropping up to two inches of snow in under an hour. It doesn't look like much on radar (shown at the top of the post), but the tweet above shows how abruptly a cloud of snow can drop visibility down near zero.

Unfortunately, a snow squall in central Pennsylvania actually did cause a deadly pileup on I-80 about 20 miles east of State College. The Daily Item reported that two people died and dozens more were injured during the chain-reaction crashes.

There's only so much meteorologists can do to warn people of what's on the horizon. Just like a tornado or severe thunderstorm warning, it's not always possible to pull off the road or avoid a wreck when you find yourself driving into a snow squall. The new warnings are designed to give you an opportunity to seek safety that wasn't available before. It's all worth it if each warning helps even a couple of people stay safe.

[Top Image: Gibson Ridge]

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December 16, 2019

A Quick-Hitting Storm Will Bring Midwest Snows And Severe Thunderstorms To South

A low-pressure system will develop over the Mid-South on Monday and dominate weather east of the Mississippi River for the next couple of days. The storm will start with a quick thump of snow across the Midwest and Ohio Valley, with severe thunderstorms developing in the storm's warm and humid airmass across the Deep South. Snow and ice will spread toward the Northeast on Tuesday before the storm races out to sea on Wednesday.

Wintry Weather

Winter storm warnings are in effect across central Missouri and central Illinois ahead of a period of heavy snow expected during the day on Monday. The snowfall forecast map above shows all the snowfall forecasts issued by local National Weather Service offices across the country. The NWS forecast shows up to five inches of snow across the winter storm warning, which isn't a whole lot, but it's enough to snarl traffic and make travel a headache when roads are at their worst.

Winter weather advisories exist from the central Plains to the Northeast, with more advisories and warnings likely as the storm moves east. It doesn't take much snow or ice to make travel difficult or even impossible. I've long argued that an inch of snow is more dangerous than a foot of snow, and the danger only grows when there's freezing rain, sleet, or roadway refreezing in the mix.

Severe Thunderstorms

It's not all cold and snow. Warm and humid air will rotate around the southern end of the low-pressure system, providing a decent amount of instability to fuel severe thunderstorms.

The Storm Prediction Center issued an enhanced risk for severe weather—a three out of five on the scale measuring the risk for severe thunderstorms—across portions of Louisiana, Mississippi, and Alabama, on Monday afternoon.

The greatest risk from the strongest thunderstorms is damaging wind gusts in excess of 60 MPH and the possibility for tornadoes. The threat for tornadoes appears maximized around central Louisiana and Mississippi, where the SPC painted a 10% risk for tornadoes on Monday. Tornadoes are most likely in discrete thunderstorms, while damaging wind gusts are favored in squall lines.

If you have any friends or family in the area, it's a good idea to give them a heads-up about the risk for severe thunderstorms on Monday and Monday night, especially since a decent number of the storms will roll through after sunset. Nighttime storms are dangerous both because people tune out as they wind down before bed and the fact that the urge to look for approaching storms and tornadoes can be overwhelming. Make sure you've got a way to receive severe weather warnings once you go to bed, and please trust that they're real and resist the temptation to look for the storm before seeking shelter.

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December 6, 2019

This Weekend Will See Heavy Rain In Northern California, Heavy Snow In The Sierra

A storm approaching California on Friday will produce plenty of heavy rain and snow across the northern half of the state this weekend. While the storm is nowhere near as strong as the record-breaking system we saw before Thanksgiving, which set California's all-time record low air pressure reading, it's bringing plenty of moisture ashore with it.

Unlike the system that came ashore the week of Thanksgiving, this storm will weaken as it approaches the northern California coast on Friday. Even though the approaching low-pressure system is much weaker than our previous storm, forecasters still expect the system to produce quite a bit of rain and snow through the weekend.

The latest forecast from the Weather Prediction Center shows up to five inches of rain falling across parts of northern California and southwestern Oregon, with the heaviest rain expected north of Santa Rosa. The Sierra could wind up with several feet of fresh snow by early next week, which is great news for both ski resorts and future water reserves.

It's also going to get windy. Coastal counties in central California could see wind gusts of 50 MPH as the storm comes ashore on Friday and Saturday, which could lead to (nature-induced) power outages and tree damage. Make sure you're prepared for a power outage—of course you are, thanks PG&E!—and stay mindful of large trees and tree limbs over your home/vehicle/smoking spot/what have you.

Flight delays are likely at SFO and other northern California airports over the next couple of days as pilots and air traffic controllers deal with rain, low ceilings, and gusty winds. Any delays or cancellations will cause a ripple effect of delays and cancellations down the line, as any slip in the schedule will affect all of an aircraft's future scheduled legs.

It's also worth noting that flash flood watches are in effect for the burn scar left by the Kincade Fire in northern Sonoma County, including areas downstream from the burned land. It's exceptionally difficult for rainwater to permeate soil burned by wildfires, forcing much of the rain to simply run off as if it had fallen on an asphalt parking lot. Debris flows are also common on and around burn scars in hilly areas as a result of fires destroying the vegetation that held the soil together.

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November 29, 2019

A Major Winter Storm Could Bring Blizzard To Northern Plains, Significant Snow To Northeast

A major winter storm will move across the northern United States through early next week, producing a solid blanket of snow from the northern Plains to the Northeast. The heaviest snow will fall on the Dakotas and across the Upper Midwest, where a huge swath of land could see more than 12" of snow by the time the storm is over. Disruptive snowfall totals are also likely across a large portion of the interior Northeast early next week.

The developing storm will come from the same trough that generated the record-breaking low-pressure system in California and Oregon earlier this week. The storm broke the all-time record low air pressure reading for the state of California, with a pressure of 973.4 mb recorded in Crescent City on Tuesday night.

Northern Plains and Upper Midwest

Heavy snow will continue to spread across the north-central United States on Friday night, ending from west to east by Sunday night as the storm scoots east across the Great Lakes.

The National Weather Service predicts more than a foot of snow for a decent chunk of real estate, including the cities of Pierre, Fargo, Grand Forks, and Duluth. Duluth could wind up "winning" the snowfall contest as a result of snowfall enhanced by lake effect snow off of Lake Superior. The city could see a foot-and-a-half of snow by the end of the storm.

Strong, gusty winds associated with the developing winter storm could lead to blizzard conditions in parts of Wyoming, Nebraska, and South Dakota, including Rapid City. A blizzard warning is also in effect in and around Duluth as a result of strong winds blowing off of Lake Superior. A blizzard occurs when sustained winds of 35 MPH and blowing snow reduce visibility to one-quarter of a mile for three consecutive hours. Not only is travel almost impossible during blizzard conditions, but a whiteout can easily disorient someone even on a short trip from the front door to the mailbox.


December will begin with the first major snowstorm of the season across much of the interior Northeast as a winter storm threatens to produce more than a foot of snow at higher elevations. This could be a long-duration winter storm, with precipitation beginning on Sunday evening and lasting through the first half of Tuesday in some areas. This is a winter-hardened part of the country, but more than half a foot of snow is difficult to deal with if road crews can't keep up with snowfall rates.

Heavy snowfall totals will come perilously close to the major cities along the I-95 corridor. The gradient between a lot and a little could be especially apparent in Boston, where the current forecast calls for minor accumulations along the coast, but more than 6" of snow just west of the city. A small nudge either way in the storm's track could have a big impact on who sees decent snowfall totals.

It's worth noting that the snowfall forecast above only runs through 7:00 PM EST on Monday, December 2. It's possible that accumulating snow may continue after that cutoff in some areas, so those additional accumulations aren't covered by the National Weather Service's forecast above.

Freezing Rain

It's not all going to be picturesque snow and fluffy drifts. Warmer air on the southern end of the system could allow precipitation to fall as freezing rain for a time, potentially leading to a crust of ice up to one-tenth of an inch thick on exposed surfaces. The greatest threat for freezing rain exists in central and western Pennsylvania, southwestern New York, southern Ontario, and parts of northeast Pennsylvania and northern Michigan.

Even the tiniest coating of ice can make travel by vehicle or foot almost impossible. A crust of ice beneath snow will make a snow-covered street deceptively slick, and freezing rain on top of snow can dramatically increase the weight of the snow and make shoveling a much more intensive task.

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November 25, 2019

Four Different Weather Headaches Will Snarl Thanksgiving Travel This Week

It wouldn't be Thanksgiving week without nasty weather. Several storms will move across the country through the holiday weekend, providing ample opportunities for disruption to airline and highway travel just in time for the holiday rush. It's a good idea to take the next day or two to prepare for travel snarls in advance so you're not stuck halfway between home and a turkey dinner.

Headache #1: Major Pacific Storm | Timing: Tues-Weds

GFS model guidance showing the strong low off the coast of Oregon on Tuesday evening. Source: Tropical Tidbits

A powerful storm will move across parts of Oregon and California on Tuesday evening, bringing the potential for damaging winds, heavy rain, and several feet of mountain snows through Thanksgiving. Heavy snow will make it difficult, if not impossible, to drive across the mountains on Wednesday, which will severely hamper traffic on one of the busiest travel days of the year.

The National Weather Service in Medford, Oregon, characterized the storm in unambiguous terms on Monday night: "this low is unprecedented in its strength and track." A strong jet stream diving south over the Pacific Northwest will allow a developing low-pressure system to rapidly strengthen over the next day or so. The low's minimum central pressure could get down into the low 970s, which would be impressive for a hurricane let alone an extratropical cyclone in this part of the country.

In fact, if the forecast air pressures come to pass, the storm could break all-time record low air pressure readings in southwestern Oregon and northwestern California. According to the Weather Prediction Center, the all-time record low air pressure at Medford, Oregon, was 978.0 mb, and 978.7 in Eureka, California. It's likely that these records would fall if the core of the low moved over or very close to one of these stations.

Source: NWS Medford

Damaging winds are a serious threat from a system this strong. Wind gusts in excess of 70 MPH are possible along and near the coast in southwestern Oregon and northwestern California. Higher gusts are likely at higher elevations. Winds this strong will easily knock down trees and power lines, potentially leading to widespread power outages. Trees and limbs falling across roads will pose a hazard to vehicles and homes.

Heavy Rain

This will be a fast-moving storm, which doesn't give it much time to drop a ton of rain all at once. (Remember, steady rain quenches the ground but torrential rain runs off before it can soak in.) The latest forecast from the Weather Prediction Center shows more than an inch of rain across most lower elevations in southern Oregon and northern California.

Heavy Snows

This storm will produce several feet of snow in the mountains of eastern California, which is great news for ski resorts but terrible news for travelers who are hoping to drive east for the long holiday weekend. It's worth considering alternate plans for Thanksgiving if you're planning to cross the mountains on a road like I-80.

Headache #2: Central U.S. Winter Storm | Timing: Tues-Weds

A classic winter storm developing along the Front Range on Monday evening will move toward the Great Lakes through Wednesday, blanketing a stretch between Denver and Marquette with a solid, shovelable snow. Thunderstorms and high winds will follow a cold front across the southern Plains through Tuesday evening, bringing the potential for severe thunderstorms to the lower Mississippi River Valley.

It's already snowing in Colorado and Wyoming, where communities like Boulder, Fort Collins, and Cheyenne, could wind up with a foot or more of snow by the time the storm is over on Tuesday evening. The storm will continue producing snow across the central Plains as it makes its way toward the Great Lakes. Another burst of 12"+ totals is possible in northern Wisconsin and Michigan's Upper Peninsula, where the storm's snow is enhanced by Lake Superior.

The warmer side of the system will produce high winds across the southern Plains, where high winds warnings are in effect for much of eastern New Mexico, western Oklahoma, and the Texas Panhandle in anticipation of wind gusts as high as 70 MPH after the cold front passes through on Tuesday. High winds and dry air will lead to an increased threat for wildfires across these areas.

Severe thunderstorms are possible in the lower Mississippi River Valley on Tuesday evening as the cold front pushes into warm, humid air. The Storm Prediction Center painted a slight risk across the area, which includes St. Louis, Little Rock, and Memphis. The storms are likely going to develop along the cold front in the form of one or more broken squall lines, posing the threat for damaging wind gusts and possibly a couple of tornadoes. Tornadoes are most likely in broken lines, where individual thunderstorms have an easier time tapping into low-level rotation.

Headache #3: SoCal Rain | Timing: Weds-Sat

Source: NWS San Diego

An inch or two of rain isn't too big of a deal for us east of the Rockies, but it's an errand-stopping ordeal in southern California. Heavy rain and maybe even a few rumbles of thunder are possible in southern California as a surge of moisture moves across the southwestern United States later this week. Several inches of rain could fall in southern California beginning on Wednesday and lasting through Saturday. Flash flooding is possible if the rain falls too quickly, especially in areas that saw wildfires in recent years.

It's likely that the rain will lead to flight delays at LAX just in time for the busiest flying day of the year. Rainy, gloomy weather requires air traffic controllers to slow down operations so they can safely maneuver the planes as they're arriving and departing. Pilots and controllers need a little breathing room in the rain, and it takes a little longer for planes to stop on wet runways. Even a small slowdown will cause a ripple effect of delays and cancellations down the line, since individual planes often complete so many legs in a day.

Headache #4: Southwest Snowstorm | Timing: Thurs-Fri

Source: NWS Flagstaff

A significant winter storm will unfold at higher elevations in Arizona, where several feet of snow could fall from the Grand Canyon to the White Mountains. Flagstaff could see more than two feet of snow by the beginning of the weekend. This kind of snow will snarl traffic along highways that traverse the northern half of Arizona. Crews should have the roads clear and open again in time for folks to head back home this weekend.

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November 22, 2019

Tropical Storm Sebastien Keeps Fighting The Odds To Survive In The Atlantic Ocean

Tropical Storm Sebastien is still trucking along in the central Atlantic Ocean with maximum sustained winds of 65 MPH. Forecasters expected the storm to absorb into a cold front by Thursday morning, didn't! It kept going, and going, and going. Thankfully, it's safe to gawk and laugh at the relative tenacity of this storm—it's far out in the middle of the Atlantic Ocean, and it poses no threat to land.

Sebastien formed on Tuesday morning from a tropical disturbance that found a pocket of favorable conditions a few hundred miles northeast of the Caribbean Sea. As I documented over at Forbes early Wednesday morning, the storm was originally expected to be a short-lived blip that just padded the 2019 hurricane season's numbers.

But it persisted.

We're now in day 4 of Tropical Storm Sebastien's joyride over the central Atlantic. It looked like the storm was going to absorb into a cold front moving across the western Atlantic Ocean and that would be that. What happened instead, however, is that Sebastien both slowed down and managed to stay ahead of the encroaching cold front, keeping it in a favorable environment much longer than expected.

The good folks at the NHC keep expressing their astonishment at the storm's persistence. The advisory headlines from Friday evening read "more of the same from Sebastien" and "tenacious Sebastien does not know it's November and refuses to weaken."

Tropical Storm Sebastien is still a fairly lopsided storm. Wind shear has kept all of its thunderstorm activity on northeastern side of the center of circulation, leaving a well-defined but totally naked surface swirl visible on satellite imagery.

The storm's luck will run out soon. Sebastien is running out of warm water to fuel its thunderstorms, and we'll eventually see the thunderstorms weaken enough that wind shear rips them away from the center of circulation, killing the storm once and for all. The NHC's forecast calls for Sebastien to weaken this weekend and finally dissipate on Sunday.

[Top Image: NOAA]

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November 17, 2019

A Coastal Storm Could Bring Freezing Rain To New England On Monday

A nor'easter that brought heavy rain, high winds, and coastal flooding to the Carolinas this weekend could produce a period of freezing rain in New England early next week. The latest forecasts don't call for a full-fledged ice storm, but even a thin crust of ice is dangerous on exposed surfaces.

The storm is quite the looker on satellite imagery today. You can clearly see the low-pressure system's center of circulation as the system wraps up and moves north. Sunday's 1:00 PM EST analysis from the Weather Prediction Center put the storm's minimum central pressure around 994 mb, and its pressure should hold steady or drop a little as it moves toward Atlantic Canada over the next couple of days.

Carolinas Rain And Wind

This is the same system responsible for all the cloudy, drizzly, rainy weather we've seen in the southeast for the past couple of days. The system managed to grow more organized once it left the coast, which is good news for folks in the eastern Carolinas, since double-digit rainfall totals occurred just a few dozen miles off the coast near the NC/SC border.

A cold rain is miserable enough, but this storm was downright windy, too. Winds gusted as high as 36 MPH in Greensboro, N.C., and gusts hit 60 MPH on the state's Outer Banks. The wind and waves led to coastal flooding in areas like Charleston; the water at the Charleston Harbor tide gauge came within a quarter of an inch of major flood stage at high tide on Sunday morning. The outer banks also saw significant storm surge flooding and beach erosion, with some roads in Rodanthe, N.C., completely covered by water and sand early Sunday.

Potential Freezing Rain In New England

The storm is picking up speed as it moves away from the Carolinas, eventually making a wide hook into Atlantic Canada over the next couple of days. The biggest threat from this storm is freezing rain, which could coat most of New England and parts of Quebec and New Brunswick through Tuesday. Winter weather advisories are in effect for most of New England in anticipation of freezing rain on Monday and Monday night.

The best chance for a glaze of ice near the coast will exist on Monday morning before temperature jut above freezing and it all turns to a cold, miserable rain. A greater chance for freezing rain exists inland, where temperatures near the surface should stay at or below freezing for the duration of the storm.

Steady freezing rain will begin in interior New England on Monday evening and continue through the night before changing over to snow. The Weather Prediction Center's most likely ice accretion forecast shows the potential for 0.10" of ice from freezing rain, which is enough to leave a solid, snappable crust on exposed surfaces. This won't rise to the level of a full-fledged ice storm, but even a thin glaze of ice is dangerous for motorists and pedestrians, especially when it's dark and you can't see the slippery surfaces.

Why Ice Instead Of Snow?

Why will the storm start as freezing rain even though temperatures are below freezing at the surface? As the storm draws closer, it'll begin to wrap around a layer of warm air a few thousand feet above the surface. You can see this pretty well in the weather models.

The above image is from a program called BUFKIT, which uses model data to simulate the SKEW-T charts that meteorologists use to plot out upper-air data from weather balloons. A SKEW-T chart shows the temperature, moisture, and wind speed through a column of the atmosphere. It's like looking at a cross-section with all the data plotted out for you.

The red line on the right traces the temperature through the atmosphere, while the green line traces the dew point through the atmosphere. The altitude on this chart is measured in feet above ground level. This particular graphic shows the GFS model's view of the atmosphere over Montpelier, Vermont, at 8:00 PM EST on Monday. I've highlighted the layers of the atmosphere that are above- and below-freezing.

If this model scenario pans out, the surface temperature in Montpelier at 8 PM on Monday would be about 28°F. However, the air temperature about 2,000 feet above ground level peaks at about 38°F.

Snow will fall until it reaches about 6,000 feet above ground level, at which point it'll start to meet air that's above freezing. Any snowflakes that fall into the thick layer of above-freezing air above Montpelier will completely melt into a liquid raindrop. The raindrop will begin to cool below freezing once it enters that shallow layer of 28°F air right at the surface, freezing on contact with any exposed surfaces.

This nose of warm air across interior New England will slowly erode through Monday night until the entire atmosphere is below freezing, at which point the freezing rain (and possibly some sleet) changes over to all snow. The National Weather Service expects that a couple of inches of snow will fall in northern Vermont and New Hampshire, with up to five inches of snow possible near the Canadian border in northern Maine.

[Top Image: NOAA]

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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.


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?


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.


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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