May 17, 2018

Spring Was a Lovely Week and Now It's Time to Deal With Summer

Did you enjoy spring? I had a pretty good week, too. The patterns quickly shifted gears late last week and it looks like we've started on June's greatest hits a little early this year. We're talking tropical weather outlooks, severe storms influenced by a ridge of high pressure, and an unrelenting slog of warm, wet weather. Lovely.

The Tropical Cyclone Thing That Wasn't

The National Hurricane Center kept watch over a sad sack of clouds over the eastern Gulf of Mexico for signs of tropical development earlier this week. The system had the chance to organize itself into a subtropical or tropical entity, but it couldn't take advantage of marginally-favorable conditions in time to develop into much of anything.

Even without the name and shiny cone of uncertainty, the disturbance has brought heavy rain to the southeast and the rain will keep falling up the coast through the weekend. The system's impacts would've been the same with or without a name.

It looks like we might make it to the end of May without a named system for the first time since 2014. It's not too unusual to see a named system develop before the official start of the Atlantic Hurricane Season on June 1. It happens once every couple of years. In fact, the past three years have all seen storms develop early.

2017's Tropical Storm Andrea formed in May. A freak hurricane formed in January 2016 and the year's second named storm (Bonnie) came around in May. Tropical Storm Ana formed in May 2015. These early-season storms are usually on the weaker side, but they can produce prolific rainfall if they form near the coast.

(*"S.T.S" on the above map stands for subtropical storm. The distinction between "tropical" and "subtropical" is interesting if you're into that sort of thing.)

Bermuda High

The polar jet stream has mostly retreated to northern Canada for the time being, which means that the majority of our weather in the United States over the past few days has been driven by smaller-scale features like the Bermuda High and the subtropical jet stream over the southern United States and Mexico.

The Bermuda High, a strong high-pressure system over the western Atlantic, opened the pipeline for warm, moist air from the Caribbean and Gulf to overspread much of the eastern and central United States. The heat we saw last weekend broke in favor of a cooler but muggier and wetter pattern. It's positively swampy out there in the southeast right now.

The animation above from Tropical Tidbits shows an analysis of surface dew points beginning on the evening of Sunday, May 13, and ends with the model's forecast for dew points on Friday, May 18. The wind barbs and isobars show the high over the western Atlantic and trough over the Gulf pumping a steady stream of tropical air over the eastern half of the country.

Showers and thunderstorms associated with the aforementioned tropical disturbance and small disturbances approaching from the west will continue to be a regular feature over the next couple of days.

The storms are widespread but hit-or-miss in their nature. It's hard to say in advance who will get poured on and who will be spared. If you get caught under one of those pop-up storms, high precipitable water values (a measure of the moisture in the atmosphere) will mean that heavy rain that sticks around over one spot for too long could lead to flash flooding.


Flooding has been a serious issue. Forecasters had to issue a flash flood emergency in Frederick, Maryland, on Tuesday night due to storms that dropped up to five inches of rain in a short period of time. The same squall line that blasted the Northeast with wind gusts up to 80 MPH on Tuesday afternoon kept going into the Mid-Atlantic after sunset. Thunderstorms associated with the squall line began training over northern Maryland, leading to life-threatening flash flooding that required several high-water rescues.

More heavy rain will overspread the Mid-Atlantic through the end of the week, leading to the potential for more flash flooding. The latest from the Weather Prediction Center indicates the potential for five or more additional inches of rain across the Mid-Atlantic—centered on the D.C. area—over the next seven days.

You can keep track of the threat for flash flooding by checking in with your local National Weather Service office and the Weather Prediction Center.

Severe Thunderstorms

The Mid-Atlantic and Northeast have taken the brunt of the nation's severe weather since last Thursday. There were more than 1,500 reports of severe weather between the morning of May 10 and the morning of May 16. A rather sharp stationary front across the Ohio Valley and Mid-Atlantic often served as the focus for the severe weather across the east.

In fact, you can even see the influence of the ridge of high pressure just by looking at the pattern of severe weather reports over the past week. Most of the storms occurred around the periphery of the ridge while those under the high were mostly spared save for a few rogue storms.

The threat for severe weather through the end of this week will move back to the Plains, where places like western Nebraska and northeastern Colorado could see severe thunderstorms produce damaging winds, large hail, and possibly a tornado or two. That doesn't rule out the potential for an occasional damaging wind gust or round of hail in the more vigorous storms that form out east.

[Maps: Dennis Mersereau | Model Animation: Tropical Tidbits]

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May 14, 2018

Severe Thunderstorms Likely in the D.C. Area This Evening

A line of severe thunderstorms is making its way toward the Washington D.C. and Baltimore metro areas and should arrive in the area around the end of rush hour on Monday, May 14. There is an enhanced risk for severe weather across much of the Mid-Atlantic ahead of the squall line moving southeast out of the Ohio Valley. The greatest threat this evening will be damaging straight-line winds.

The severe weather over the past few days has been the result of a stubborn stationary front that's hung around the area since the end of last week. The front has moved back and forth over the past few days, but it's been remarkably stationary even for a stationary front. This boundary served as the focus for several rounds of severe thunderstorms this weekend and it's set the stage for yet another burst of activity this afternoon.

An enhanced risk for severe weather—a three on a scale from one to five—exists across much of the Mid-Atlantic on Monday evening. The greatest hazard within the significant risk area is damaging straight-line winds. There's also a risk for tornadoes and isolated instances of large hail.

A severe thunderstorm watch is in effect ahead of the squall line. The watch mentions the chance for straight-line wind gusts up to 75 MPH, isolated large hail, and possibly a few tornadoes. Straight-line winds can cause as much damage as a weak tornado, downing trees and power lines and damaging roof, winds, and siding on homes and businesses.

While this system won't be a repeat of the derecho of 2012—that day saw the perfect mix of ingredients during a brutal heat wave—it's important to treat any threat for severe weather seriously. If you're under the threat for severe weather, it's a good idea to make sure you don't have anything loose outside that can become a projectile in high winds. It's also wise to stay away from parts of the house where tall trees or big limbs could pose a threat to your safety if they fall.

Stay aware of your surroundings this evening and make sure you always have a way to get warnings the moment they're issued.

[Satellite: NOAA | Maps: Dennis Mersereau]

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May 11, 2018

A Wildfire Likely Spawned a Severe Thunderstorm in Texas

The ground can influence the weather in ways we don't always realize are happening. Cities warm up the atmosphere around them. Air lifting over the sides of mountains can create rain and snow. Wildfires can cause billowing cumulonimbus clouds. And some of those fires can even trigger thunderstorms like the supercell that popped up over the Texas Panhandle on Friday afternoon.

Satellite and radar imagery showed smoke rising from a large wildfire southeast of Amarillo, Texas, on Friday afternoon. The fire grew in size through the afternoon and the heat generated by the fire spawned a rather hefty pyrocumulonimbus cloud.

There was enough instability over Texas and Oklahoma on Friday to support the development of thunderstorms, but only if the cap broke. A "cap" is a nickname for an inversion layer, or a layer of warmer air sitting atop a layer of colder air. An inversion layer can prevent air from freely rising through the atmosphere, stifling the development of showers and thunderstorms. Stronger caps are harder to erode.

Something needs to break the cap in order for a storm to form. Strong surface heating during the day can raise low-level temperatures enough that rising air can reach a speed at which it breaks through the cap like cheap aluminum foil. Sometimes it takes forcing from a feature like a cold front or a sea breeze to give rising air the extra oomph it needs to break through the inversion.

Today, the force that helped break the cap was the heat from the fire.

You can follow the progress of the wildfire using GOES-East's shortwave infrared product. The heat generated by the fire makes the affected area southeast of Amarillo show up as a black splotch on satellite imagery. Smoke billowing northeast of the fire starts off a darker shade of gray at first, but the smoke eventually becomes obscured by the pyrocumulonimbus clouds as the afternoon wears on.

The thunderstorm developed in the late afternoon. The storm was able to tap into the instability already present and organize into a supercell, complete with at least one report of quarter-size hail and a beautiful overshooting top and expansive anvil that shows up well on visible satellite imagery.

You can even track the smoke and thunderstorm on radar imagery out of Amarillo. The smoke appears on radar as the steady stream of returns flowing northeast on the eastern side of the radar. The thunderstorm develops around 5:00 PM CDT and continues to grow as it approaches the Oklahoma border as it feeds off of instability in the atmosphere.

While fire-induced thunderstorms are rare, it's not out of the question when there's a large fire in the right environment. The devastating fires in and around Fort McMurray, Alberta, back in May 2016 were strong enough to spawn pyrocumulonimbus clouds that caused lightning, which, in turn, started even more fires.

[Vis/IR Combo: Dennis Mersereau (data via AllisonHouse) | Radar/Sat.: College of DuPage | Model Image: PivotalWeather]

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May 4, 2018

Damaging Winds and Tornadoes Are Possible in the Northeast on Friday Afternoon

There's a moderate risk for severe thunderstorms on Friday across interior parts of the Northeast as intense storms develop during the afternoon and evening hours. A moderate risk is a 4 on a scale that runs from 1 to 5. Any thunderstorms that develop in the risk areas will form in an environment capable of sustaining destructive straight-line wind gusts, tornadoes, and some large hail.

Thunderstorms are already firing up ahead of a cold front extending off of a low-pressure system moving through southern Ontario and Quebec today. Temperatures in the upper 70s and some low 80s across the Northeast, combined with dew points in the low 60s, will provide the instability and moisture necessary to sustain the storms once they develop.

Severe thunderstorm watches are in effect from eastern Ohio to eastern New York ahead of the storms this afternoon. A tornado watch covers northern New York and much of Vermont through this evening. Thunderstorms are starting to pop up near Lakes Erie and Ontario as of the publication of this post, and storms will continue to develop and push east through the evening hours. The severe weather should clear out after sunset.

The latest forecast from the Storm Prediction Center shows an enhanced risk for severe thunderstorms across interior parts of the Northeast, with the greatest threat for damaging winds and tornadoes focused on New York, Vermont, and New Hampshire.

Wind is the greatest threat on Friday. Winds are racing just a few thousand feet above the surface. It won't take much for thunderstorms to mix some of those intense winds down to the surface.

The SPC's latest forecast shows an area of significant damaging winds possible; both the severe thunderstorm and tornado watches mention thunderstorm wind gusts up to 80 MPH possible. The black hatching on the map above shows the risk for significant damaging winds. Winds that strong will easily blow down trees and power lines and possibly cause some damage to roofs and windows.

The environment here is also capable of supporting tornadoes in any discrete thunderstorms or along the leading edge of squall lines that move through the region. The latest SPC forecast denotes a 10% risk for tornadoes near the Canadian border in New York, Vermont, and New Hampshire, with a lower risk radiating southward from there.

Such an elevated risk for severe weather in an SPC forecast is uncommon so far north in New England, occurring only once every couple of years on average. This is only the second 10% tornado probability for Burlington, Vermont since the IEM's records begin back in March 2002. The point is that the risk for severe weather today is much higher than normal for a part of the country that typically doesn't see much in the way of bad storms.

Weather doesn't stop at the border. (Wouldn't that be wild, though?) The risk for severe weather extends into the southern parts of Ontario and Quebec. Environment Canada has issued severe thunderstorm watches for parts of southern Ontario as the line of storms sweeps through this afternoon.

If you're in the affected areas, make sure you're close to safe shelter when storms threaten your area. It's a good idea to take mental note of supplies you have just in case the power goes out. An extended power outage around dinner time isn't the best if you don't have any ready-to-eat food and local restaurants are closed. Stay away from parts of your home where large trees or limbs may fall in high winds. Straight-line winds can cause as much damage as a tornado, just over a wider area.

If a tornado warning is issued, seek shelter on the lowest possible floor and in an interior room, putting as many walls between you and the outdoors as possible. You won't be able to see a tornado before it hits. Tornadoes in this part of the country are usually obstructed by terrain and trees, and tornadoes in the kind of storms we'll see today will likely be obscured by heavy rain—you won't see it until it's on top of you.

UPDATE: This post was updated at 4:30 PM EDT to reflect the latest forecast from the Storm Prediction Center, which upgraded some areas to a moderate risk and expanded the enhanced risk area.

[Maps: Dennis Mersereau]

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May 3, 2018

Living With Storm Anxiety as a Weather Geek

I get nervous before thunderstorms. Well, I get nervous before bad thunderstorms. For a couple of years now I've talked openly about my newfound struggle with storm anxiety. It's a weird thing to have to deal with when you love weather as much as I do and talk about it pretty much every day for a living. Publicly dealing with my storm anxiety has given me an interesting insight into how everyday people deal with thunderstorms and how meteorologists and weather enthusiasts have a giant blind spot when it comes to something they love.

I'm fine during run-of-the-mill thunderstorms. It's the wind—heck, even just the threat of wind—that gets to me. I've seen too many pictures of destroyed buildings. I've seen pictures of destroyed apartments that looked exactly like mine with a gaping hole where my bedroom would be. I've seen pictures of tornado victims. A few years ago I watched a warehouse's roof peel off across the street from me during a strong storm. I've seen tornado debris fall from the sky. Lightning and thunder and hail are unnerving but they don't bother me too much.

The wind bothers me.

I’ve had a love-hate relationship with storms all my life. I used to sit in the window as a toddler and watch lightning zap across the sky without so much of a twinge of fear. Storms started to terrify me in elementary school. I’m not sure if it was the movies Twister or Night of the Twisters (especially the latter), or the scary beeps and alerts that flew across the TV screen, but whatever spooked me as a kid grew into storm anxiety.

My storm anxiety got better once I hit high school. The fear eventually turned into a healthy obsession. I still got nervous ahead of tornadoes or bad squall lines but it was manageable. I was still excited to see storms. Going to college in Mobile, Alabama, intensified my love for storms. Even a few close calls with lightning strikes weren’t enough to completely shake me of my love for storms.

Starting in the summer of 2016, it seemed like every thunderstorm that passed through my town in central North Carolina reached its convective apogee directly over my apartment. Gone were the days of listening to the rain and rolling thunder and standing in the window for hours taking pictures of lightning. Almost every storm was severe and its worst attributes unfolded right over me.

I dubbed it #Rockinghaming on Twitter. That was my way of making light of the endless stream of sky-rage that seemed to inflict its pain specifically on our county and nowhere else in the area. Over the course of a year and a half, we've had two destructive microbursts, numerous extended power outages, a couple of hailstorms, lightning that destroyed a clock radio, two rounds of flash flooding, and a tornado that passed within a couple of miles of where I live and dropped a significant amount of debris on our apartment complex.

I know that my renewed fear of bad thunderstorms stems from living on the top floor of a wood-framed apartment building. It's the wind. I'm afraid that the roof is going to peel away or a tornado will scrub away everything I know. Even if I know that's probably not going to happen, the nervousness still takes hold.

I’ve always been an anxious person. Most of my fears have been and still are totally ridiculous. They all relate to emergencies in one way or another. I was terrified of the Emergency Alert System as a kid. I would have nightmares about the sound and the unnecessarily-apocalyptic screen Comcast chose to flash on every channel during an alert. I got over it (though the sound can still induce chills).

A fear of fire alarms that developed in elementary school has stuck with me the longest. (I know, right?) The best way I’ve found to describe it is an intense fear of being startled. A fear about fear! How odd. I learned to manage it a bit as I've gotten older, but I still struggle with it.

It makes my renewed storm anxiety feel like one of the more normal things about me. It’s also made me hyper-aware of how many other people get nervous when thunderstorms are in the forecast. I have a relative who sometimes sits in the bathroom during a bad lightning storm. I have friends on Facebook who can only bring themselves to post a worried emoji with a copy of the Storm Prediction Center’s latest outlook.

When we were under a risk for tornadoes a couple of weeks ago, I jokingly tweeted that my anxiety kept telling me that a delayed forecast by the SPC was the forecasters painting the highest tornado risk over me. Later that day, as I watched a confirmed tornado roll toward me on radar, I forgot all about being nervous and became laser-focused on staying safe. That’s not to say that I won’t be nervous during the next storms. But knowing that my mind switches into safety mode when I’m in actual danger feels like a positive step.

Blind Spots

My newfound (re-found?) storm anxiety informs the way I talk and think about the weather now. It makes storms more of a human event than a natural event for me. It's disappointing to see folks in weather speak about storm anxiety with derision or indifference.

Viewers and readers with storm anxiety are an enormous blind spot for meteorologists and weather reporters. It's more than just the jitters. Why would someone be nervous over something so cool? I get it.

I used to get a little excited when I saw a big severe weather outbreak on the horizon or a picture-perfect hurricane buzzsawing its way across the Atlantic. It’s instinctively thrilling for a weather enthusiast to witness the most furious conditions nature can produce. Nature is a beautiful force. But there's a human cost.

It’s upsetting to see weather enthusiasts cheer for tornadoes. Tornadoes are photogenic and tornadoes over open fields with a beautiful backdrop are gorgeous images. They’re still tornadoes. Openly hoping for a tornado outbreak isn’t the best optics for a field whose pitch to gain the public trust is predicated on serving and helping people. How are we serving or helping when we’re expressing delight over an event that could destroy homes and cost people their lives?

I'm well aware that people who get excited over bad weather aren't hoping that people die or lose their homes. But imagine being someone who actually lost a loved one or lost their home in a tornado or someone who lives with storm anxiety and follows a bunch of meteorologists to calm their nerves only to see a steady stream of posts excitedly hoping for big tornadoes or massive squall lines.

I’m also well aware that people who root for bad storms aren't jinxing it. The weather is going to happen whether or not those people cheer it or ignore it or even if those people didn’t exist.

It’s a matter of sensitivity and professionalism. Whether it's intended or not, they're actively conveying to people in the path of the storm—who may very well be looking to those professionals for information—that it's more a matter of personal entertainment and fascination than an issue of life or death seriousness.

The effect is more pronounced when someone in harm's way suffers from storm anxiety. Lots of people with storm anxiety follow lots of meteorologists and weather enthusiasts to keep up with weather and assuage their concerns by staying in-the-know.

What we say and do in public has an effect on other people and it reflects poorly on ourselves and our field when we express glee over something that could ultimately exact a human cost. We can’t and shouldn’t police people’s thoughts and emotions. At the same time, it's important to carefully measure our words when dangerous weather is on the horizon. It's a matter of what should and shouldn't be kept to ourselves.

It's natural for someone who loves the weather to stand in awe of a storm and gawk at radar and satellite. That shines through and everyone understands it. When we get eager for a severe weather outbreak and express delight at the chance for tornadoes, though, that negates so much of the seriousness and solemnity of the work we try to convince people is worth paying attention to.

I have no doubt that the folks who would benefit from heeding this advice the most are going to be the first to brush off my concerns and mock them. I can only hope that it's enough to give pause and maybe even some hesitation during the next severe weather outbreak.

Help Is Available

One of the most prominent meteorologists to discuss storm anxiety online is Rick Smith, the Warning Coordination Meteorologist for the NWS office in Norman, Oklahoma. Central Oklahoma is one of the most storm-prone regions of the country. The area has seen multiple devastating tornadoes in the past 20 years. Hail larger than baseballs and wind gusts stronger than 80 MPH aren't uncommon here.

The efforts of Smith and his office to help residents in central Oklahoma deal with their storm anxiety were recently covered in a fantastic article written by Nomin Ujiyediin for Oklahoma City's NPR station KGOU. The interview drives home just how many people are affected by storm anxiety:

Some people call several times a day, asking the same questions over and over. Others message the National Weather Service on Twitter and Facebook every few minutes for hours at a time.

“People are very clearly disturbed and bothered and upset by just the forecast of a severe storm. It’s not that they’re scared of the storm, they’re scared seven days before the storm ever gets here, and that’s prevalent,” Smith said.

These interactions happen so frequently that Smith and others in the Norman office decided they needed to address storm anxiety in the community. The Weather Service has begun posting mental health resources on its social media to a warm reception from followers. And the Norman office has reached out to specialists who see the effects of disasters on mental health, both immediately and over the long term.

There is help available for people who struggle with storm anxiety. You're not alone. Staying aware of the situation is the most important thing any of us can do. Completely ignoring the threat just puts you at risk of missing a critical warning. Talking about it helps. People who genuinely care about you will listen. Finding distractions helps. I listen to music to deal with bad storms. (Smooth jazz is a favorite, but it's a little on the nose.)

The Substance Abuse and Mental Health Services Administration (SAMHSA) is a federal agency that offers assistance and services for people who have storm anxiety or issues coping with the aftermath of a disaster.

If you're struggling to deal with storm anxiety or the aftermath of a disaster, you can reach SAMHSA's disaster distress helpline day or night by calling 1-800-985-5990. You can also text TalkWithUs to 66746 to speak with a counselor.

The agency's website has extensive resources available for folks who have trouble dealing with storms or other disasters, including warning signs and coping tips.

[both photos taken by me]

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April 26, 2018

Spring May Finally Start Acting Like Spring in May

Most of us have had it relatively easy when it's come to temperatures over the past few months. It's nice to be able to keep the windows open this late into April. It's nice to have a relative reprieve from severe thunderstorms—"relative" does a good deal of work in that sentence, of course. But the pattern keeping much of the United States east of the Rockies cooler than usual is having a negative impact in some places, and it will soon start to break and usher in a more seasonable setup over the next week or so.

East-West Divide

The cool weather of late is so deceptive that it's even easy to forget that you have to wear sunscreen if you're going to spend any length of time outside these days...not that I would know anything about that. You can see the stark difference in temperatures between west and east if you look at daily average temperatures so far this month.

The daily average temperature—the day's high and low averaged together—gives you a good idea of how abnormally warm or cool a day was on the whole. Since highs and lows alone can be deceiving, averaging daily average temperatures together for a period of time is the best way to determine whether it's been warmer or cooler than average during that period. The above chart shows the average of the daily temperatures between April 1 and April 24 for 17 cities across the United States.

All of the cities that have seen below-normal temperatures are east of the Rockies, while all of the cities above normal are west of the Rockies. The desert southwest has taken the brunt of the abnormal warmth so far this month; Phoenix hit 100°F on April 10, the fourth-earliest triple-digit reading at the city's airport since reliable records began there in the 1930s. The temperature usually doesn't hit 100°F in Phoenix until around May 7. 

Things were a bit chillier half a continent away in places like Minneapolis and Fargo, where temperatures this month have run more than 12°F below normal. Both cities saw low temperatures dip into the single digits early in the month, and Minneapolis has seen more than two feet of snow—a total of 26.4"—across 11 days since the beginning of April. Minneapolis usually sees around two inches of snow in a normal April.

The only part of the country that's really come in around normal for April has been the Pacific Northwest, where average temperatures this month have come in close to normal or even a little bit below in many locations across Washington and Oregon.


The track of storms in recent weeks and months has really taken a toll on the desert southwest and southern Plains in particular.

An exceptional drought—the worst level on the five-point scale—existed across parts of Texas, Oklahoma, and Kansas last week, as well as parts of the Four Corners region and a small part of northeastern Arizona.

Severe drought conditions blanket most the southwest and southern Rockies. There's also a severe drought in parts of the southeast, Florida, and a tiny part of the northern Plains in eastern Montana.

The next update of the drought monitor will come down today (Thursday), and it probably won't show much change across areas affected by drought. The biggest improvement would likely be seen across the southeast, where some areas have seen a few inches of rain over the past couple of days.

Severe Thunderstorm Drought

The lack of rainfall across the Plains also means there's been a lack of severe weather this season. The middle of the country is usually teeming with severe weather by this point in the spring, but there's been hardly anything to write home about so far. Most of the noteworthy severe weather this year has been confined to the southeast in states like Louisiana and Alabama.

The situation is so unusual that Oklahoma hasn't seen any tornadoes so far in 2018. Tornadoes have come close to the state borders, as you can see on the SPC's annual tornado reports map above, but there haven't been any confirmed tornadoes in Oklahoma so far this year.

April 26 is the latest date Oklahoma has recorded its first tornado in any year since reliable tornado records began in 1950. The state is poised to blow past that record by at least a couple of days, possibly even longer if next week's severe weather threat doesn't pan out. However, as NWS Norman's Rick Smith noted on Twitter, 2013 had an unusually late start as well and it turned out to spawn several devastating tornadoes in the state. A slow start doesn't mean anything for later storms.

What's to Come

It looks likely that temperatures will warm back up to around normal east of the Rockies as we head into the first week of May. Models are showing a tendency for more ridging than troughing in the upper-levels of the atmosphere starting next week, which would allow temperatures to rise to the level worthy of air conditioning before too long. The change in patterns could also bring some temporary relief from the heat in the southwest and possibly lead to chances for severe thunderstorms in the middle of the country. Finer details for next week will come into view after we get through the weekend, but it looks like things will start to change as the last vestiges of winter finally seem willing to give up.

[Model Images: Tropical Tidbits | Tornado Map: SPC | Drought Map/Temp Graph: me]

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April 19, 2018

The Anatomy of the April 15, 2018 Tornado in Greensboro, N.C.

One of the strongest and longest-track tornadoes to hit North Carolina's Piedmont Triad in years touched down on the evening of Sunday, April 15, 2018. The EF-2 tornado developed just east of downtown Greensboro shortly after 5:00 PM on Sunday and tracked north along a 33-mile path before dissipating south of Danville, Virginia. The tornado damaged more than 1,000 buildings in Guilford County, North Carolina, alone, and resulted in one indirect fatality and at least 14 injuries. The thunderstorm responsible for the tornado left behind a path of wind and tornado damage from central South Carolina through central Virginia.

The Setup

April 15 was the third day of severe weather in an outbreak that began on the Plains on the evening of Friday, April 13. The storms that formed over the two previous days resulted in at least one fatality in Louisiana and injured a dozen more people as strong winds and tornadoes caused a swath of damage focused on Louisiana, Arkansas, and Mississippi.

The system responsible for the previous severe weather continued into the Ohio Valley on the morning of Sunday, April 15. Strong southerly winds near the surface raised temperatures and dew points into the 60s and 70s across the southeast during the day on Sunday, helping to provide enough instability to fuel severe thunderstorms. Winds from the southwest in the middle- and upper-levels of the atmosphere provided the wind shear necessary to organize the thunderstorms into squall lines and allowed some storms to rotate and produce tornadoes.

The Storm Prediction Center issued a risk for severe thunderstorms across the southeast and Mid-Atlantic during the day on Sunday. The threat stretched from the foothills of eastern Ohio south through the Florida Peninsula. An enhanced risk for severe weather existed across portions of the Carolinas and south-central Virginia due to the elevated risk for tornadoes.

Forecasters noted that there was a 10% risk for tornadoes across an area stretching roughly from Savannah, Georgia, north through Martinsville, Virginia, in response to strong wind shear that could allow thunderstorms in or ahead of the squall lines to begin rotating. This was only the seventh time in the past ten years that the immediate Greensboro area found itself under a 10% or greater tornado risk in a SPC forecast.

The Thunderstorm

Most of the storms that formed on April 15 were part of squall lines moving west to east across the southeast. You can trace the individual thunderstorm that produced the Greensboro tornado from its formation around 10:30 AM in southern Georgia all the way until it produced another destructive tornado near Lynchburg, Virginia, almost eight hours later. 

This thunderstorm was the most persistent and destructive out of all the individual cells that formed in the southeast on April 15. The storm began as part of a squall line in southern Georgia around 10:30 AM, quickly strengthening as it moved toward Columbia, South Carolina. The airport in Columbia reported a 74 MPH wind gust as the storm moved through. 

The National Weather Service in central South Carolina confirmed four tornadoes west of Columbia as the storm moved through: one EF-2, two EF-1s, and one EF-0. These tornadoes all had a path length of 3 miles or less, which is common for storms that form as part of a squall line. The tornadoes occurred between 2:00 PM and 3:00 PM.

It appears that the storm gradually acquired characteristics of a supercell as it moved into North Carolina. It developed a sustained mesocyclone (rotating updraft) as it moved east of Charlotte and toward Asheboro. The storm in question eventually separated from its main squall line as it moved along Interstate 74 between Asheboro and Greensboro. 

The storm separating from the squall line appears to have allowed it to fully engage with the favorable environment it encountered—sufficient instability and strong wind shear—to produce the tornado near Greensboro. The rotation weakened as the storm once again merged into the squall line from which it came, and the storm regained its rotation when the storm yet again broke away from its parent squall line as it approached Lynchburg.

The Guilford-Rockingham Tornado

The tornado touched down just north of Interstate 40 on the eastern side of Greensboro, North Carolina, at 5:07 PM. The tornado damaged multiple homes and Peeler Elementary School as it strengthened and moved north.

Hampton Elementary School took a direct hit from the tornado as it reached its peak intensity with 135 MPH winds at 5:10 PM, producing damage that was right on the border between EF-2 and EF-3 intensity on the Enhanced Fujita Scale. Meteorologists from the National Weather Service in Raleigh estimated the tornado's peak intensity by the complete destruction of mobile classrooms at the elementary school.

Television station WFMY had to delay their live coverage of the tornado as their crew and staff sought shelter in a hallway while the tornado tore up neighborhoods not far from the station.

A tree fell on a car near the intersection of E. Cone Blvd. and Cesar St. in Greensboro. The driver passed away from his injuries. This was the only fatality caused by the storm, but it was far enough away from the tornado's track that it appears strong thunderstorm winds took down the tree rather than the tornado itself.

The tornado continued damaging hundreds of homes as it moved north away from the school and out of Greensboro city limits into unincorporated Guilford County. The path of damage shows the tornado slowly changed course toward the northeast until the storm eventually paralleled U.S. Highway 29.

Guilford County Emergency Services estimates that more than 1,000 structures were damaged by the storm in Guilford County alone; 199 homes and businesses suffered major damage (162) or were completely destroyed (37).

Raleigh's storm survey estimates that the tornado was an EF-0 with 80 MPH winds when it crossed into Rockingham County at 5:24 PM.

A significant amount of debris fell on southern Reidsville (where I live) as the tornado weakened and passed a few miles to the southeast of the city around 5:30 PM.

I witnessed several pieces of plywood and insulation fall from the sky before the winds picked up. I took a walk around my apartment complex after the storm and found a significant amount of insulation, large shards of plywood from buildings, many shingles, several large pieces of metal, a computer cable, a window screen, a six-foot strip of vinyl siding, and some other structural debris that fell during the storm. Several large pieces of sheet metal, presumably used as roofing material, also managed to make it up to Reidsville.

It's common to hear of light objects like papers or photographs traveling many dozens of miles after a strong tornado, but the amount of debris that fell on Reidsville surprised me. Most of the debris was able to make it the 15+ miles from Greensboro to Reidsville because it was light enough to easily float in the wind or its surface area was great enough that the debris caught the wind like a sail. Some of the pieces of metal were easily 10 or 20 pounds—so heavy that I couldn't throw them 10 feet let alone the 15 miles they were carried by the tornado—which is a testament to the power of both the tornado and its parent thunderstorm.

It appears that the reason so much debris from Greensboro fell on Reidsville is that the storm weakened as it approached Rockingham County and the tornado itself changed direction even as the winds in the lower- to mid-levels of the atmosphere stayed the same. Doppler radar data shows debris lofted nearly 20,000 feet into the atmosphere as it moved through eastern Greensboro. The radar data shows the debris moving with the thunderstorm over the next 20 minutes as it slowly descends before the bulk of the debris falls out over southern Reidsville.

A couple of minutes later, the tornado restrengthened and reached EF-2 intensity with winds of 125 MPH as it destroyed a mobile home and damaged multiple homes along Grooms Road in eastern Reidsville. The mobile home tumbled several hundred feet across the road, striking a moving vehicle and critically injuring the driver and his son.

The tornado continued through Ruffin, North Carolina, before finally dissipating at 5:46 PM.

Two more tornadoes would occur along the path of this storm for a total of seven during the thunderstorm's lifespan. The storm produced another tornado in the City of Danville shortly after the storm crossed into Virginia, leaving behind EF-1 damage along its 12-mile path. A little more than an hour later, the same storm produced an EF-3 tornado near Lynchburg, Virginia, destroying many homes and injuring at least 12 people along a 20-mile track.

The initial tornado warning for this storm was not issued by NWS Raleigh until 5:09 PM, two minutes after the tornado touched down. The warning was amended at 5:16 PM to indicate that a tornado was confirmed due to the presence of debris on radar. NWS Blacksburg issued a tornado warning for Rockingham County at 5:18 PM, six minutes before the tornado crossed the county line and 15 minutes before it injured people in Reidsville.

You can read the storm surveys conducted in Guilford County and Rockingham County, as well as the text of the tornado warnings for both Guilford and Rockingham Counties.

Triad Tornadoes

Significant tornadoes aren't common in the Piedmont Triad, which encompasses Greensboro, Winston-Salem, Burlington, and surrounding communities. Tornadoes that do form in the Triad are typically weak and short-lived. Before last week, only five tornadoes in the past 20 years to form in this area were rated F2/EF-2 or higher on the Fujita Scale.

Tornadoes are most common in the eastern part of North Carolina where the ingredients for outbreaks are more often present due to the flatter terrain and more favorable environment closer to the ocean. The presence of stable air and influence of the mountains typically reduces (but by no means eliminates) the tornado threat in central and western North Carolina.

Not only was the tornado uncommonly strong for its location, but the Guilford-Rockingham tornado remained on the ground for 33.6 miles—a rare feat for tornadoes in North Carolina. The National Weather Service recorded 1,255 tornadoes in North Carolina between 1950 and 2016. The average path length for tornadoes in North Carolina is just 3.55 miles. Only 18 of those 1,255 tornadoes (1.4%) had a path length of 30 miles or longer, and the vast majority of those long-tracked tornadoes occurred in the eastern part of the state. Sunday's tornado was the 19th such storm.

[Maps and Images by Dennis Mersereau | Radar: Gibson Ridge]

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April 14, 2018

A Race Between the Seasons: Battleground Pennsylvania

There was just a little bit of a temperature gradient across the Northeast and Great Lakes on Saturday. At 5:00 PM EDT, the temperature was 42°F in Boston, 54°F in New York City, and 81°F in Trenton, New Jersey. A strong low-pressure system over the Midwest on Saturday afternoon allowed warm air to surge northward along the East Coast while drawing cold air south from Canada.

The dividing line between "unseasonably cold" and "warm enough to use the A/C" was just a few dozen miles across at the afternoon's peak heating. The three features driving the sharp temperature gradient were an upper-level ridge over the East Coast, a potent low-pressure system located over Illinois, and an area of high pressure over eastern Canada.

The combination of southerly winds and subsidence caused by the ridge aloft brought May-like temperatures to the East Coast on Saturday afternoon. Temperatures in the Washington D.C. area got into the mid-80s today. BWI Airport hit 86°F, Dulles reached 83°F, and National Airport in Arlington made it up to 84°F. The 80s made it as far north as central Pennsylvania and New Jersey.

It's a completely different picture on the other side of those cold and warm fronts. Heavy snow, freezing rain, and sleet fell from from eastern Nebraska through interior sections of the Northeast. Forecasters expected the heaviest snow to fall in the Upper Midwest and northern Great Lakes, where some communities could see up to two feet of snow by the end of the storm. Significant ice accretion is possible in western New York—an ice storm warning includes the cities of Buffalo and Rochester, where up to half an inch of ice could form between this evening and Sunday afternoon, potentially downing trees and power lines.

The bulge of warm air won't extend as far into the Northeast on Sunday afternoon as the low-pressure system weakens, allowing the high in Canada to shove cold air deeper into areas bathed in warmth today. Sunday's forecast high in Trenton, New Jersey, is only 44°F, which is a 37°F drop from what the city saw today. Cold air coming in from the northeast (rather than the northwest) is often called a "backdoor cold front."

The warmth will break for the rest of us on the East Coast for a couple of days when a line of strong-to-severe thunderstorms sweeps through on Sunday afternoon and evening. The Storm Prediction Center has received hundreds of reports of severe weather over the past two days as thunderstorms have made their painfully-slow trek toward the east. A severe squall line over the northern Gulf Coast has barely moved through the day, leading to life-threatening flash flooding in eastern Louisiana and southern parts of Mississippi and Alabama.

A new squall line will develop with daytime heating on Sunday and bring the potential for damaging winds and tornadoes in the Southeast. Damaging winds will pose the greatest threat across areas at risk on Sunday, but tornadoes are possible, especially in any discrete storms that form before the main line comes through.

[Maps: Dennis Mersereau]

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