June 4, 2020

Flooding Likely Along Gulf Coast And Miss. Valley As Cristobal Strengthens This Weekend


Tropical Storm Cristobal made landfall near Ciudad del Carmen in southern Mexico on Wednesday after several days of meandering and strengthening in the Bay of Campeche. The system will remain inland until Friday evening, when forecasters expect it to reemerge over the Gulf of Mexico and slowly strengthen as it heads for the northern Gulf Coast. The system will bring heavy rain, gusty winds, and a risk for tornadoes to portions of the Southeast and Midwest early next week.


The center of what's now Tropical Depression Cristobal spent Thursday moving along the Mexico/Guatemala border at walking speed. The storm is quite ragged looking now, having lingered over land for about a day now. The system will begin lifting north toward the Yucatan Peninsula and the Gulf of Mexico on Friday, reemerging over open waters by Friday night.

The latest forecast from the National Hurricane Center shows the system regaining some of its strength and making landfall along the northern Gulf Coast as a tropical storm on Sunday or Monday. While folks near the point of landfall will likely see the strongest winds and greatest potential for storm surge flooding, this will be a large system and the potential for flooding will extend many hundreds of miles from the center of the storm.

Rain


It's been raining for days in some parts of Central America and southern Mexico—remember, this system originally made landfall on Sunday as Tropical Storm Amanda over in the eastern Pacific—and some communities have measured several feet of rain as a result. Widespread flooding and mudslides will continue until the system lifts away this weekend.

We won't see that kind of intense rainfall in the United States, but this is a juicy storm and it's going to rain quite a bit across areas affected by Cristobal. The Weather Prediction Center's latest forecast calls for up to half a foot of rain along the Gulf Coast. It's easy to trace the predicted path of the storm by following the swath of heavy rain from the Gulf to the Midwest through the first half of next week.

Heavy rain that falls too quickly will lead to flooding issues in vulnerable areas. Flooding accounts for most deaths in a landfalling tropical storm. We've been through this time and time again in the last couple of years. The messaging should be driven home by now: the wind gets all the headlines, but it's the water that causes most of the problems.

Wind

While it's the water that causes the most problems, we can't completely ignore the threat for wind. Meteorologists warn severe thunderstorms for wind gusts of 60 MPH. A tropical storm with sustained winds of 60 MPH at landfall will certainly do some damage to trees and power lines, as well as blowing around objects outside that could cause injury or damage. The rain-soaked soil will make it easier for trees to come down in gusty winds.

Tornadoes

Tornadoes are a threat with any landfalling tropical system. The greatest threat for tornadoes lies in the right-front quadrant of a tropical system—in this case, to the east of the center of circulation. If the storm follows its projected path, a threat for tornadoes will exist on Monday and Tuesday in eastern Louisiana, Mississippi, Alabama, and possibly the Florida Panhandle.

Rough Seas

Rough seas across the Gulf of Mexico will lead to an increased threat of rip currents from Texas to Florida. A rip current is a swift channel of water that moves from the shore to the sea, induced by waves that hit the coast head-on.

Rip currents don't suck you under like you see in movies—they pull you out away from land. Folks susceptible to drowning include inexperienced swimmers or folks who quickly get exhausted from trying to fight against the pull. If you're ever caught in a rip current, it's wise to do one of two things:

1) swim parallel to the shore until you've left the current, then swim back toward shore, or;
2) calmly signal for help.

Rip currents often look appealing to swimmers since they look like oddly calm sections of the beach amidst otherwise raucous waves, but the calm you're seeing is the channel of water retreating out to sea.

It's always a good idea to check the rip current forecast and make sure it's safe to swim. The National Weather Service offers regular rip current forecast for shores in their service areas, and most public beaches post warnings when dangerous rip currents are possible.

[Satellite Image: NOAA]


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May 31, 2020

Heavy Rain Likely Along Gulf Coast This Week As A Tropical Disturbance Enters Gulf


The National Hurricane Center gives a tropical disturbance over Central America a 60 percent chance of developing into a tropical depression over the Gulf of Mexico later this week. Regardless of development, the system is going to be a heavy rain threat to much of the Gulf Coast. This is going to be a slow-burn event and we have several days to watch and wait for what happens next.

Heavy rain and widespread flooding are ongoing across much of Central America as the remnants of the eastern Pacific's first tropical storm of the year linger over Guatemala. The system, former Tropical Storm Amanda, has produced more than a foot of rain at higher elevations, bringing flash flooding and mudslides to vulnerable areas.

A large-scale circulation known as a "Central American Gyre" will foster unsettled conditions over the region throughout the week. The remnants of Amanda will continue to bubble over the next couple of days in that favorable environment, slowly drifting toward the Gulf of Mexico by midweek. It's in the Bay of Campeche that the National Hurricane Center sees a 60 percent chance for tropical development by the middle of the week.

Source: WPC

Regardless of tropical development, this is a rainmaker if there ever was one. The latest precipitation forecast from the Weather Prediction Center shows an enormous amount of rain falling over the Gulf of Mexico over the next seven days. The outer extent of the rain touches coastal areas from southern Florida to eastern Louisiana, potentially leading to flooding issues if too much heavy rain falls all at once.

The closer the system gets to the United States, the greater the potential for heavy rain over land. Everyone from Texas to Florida needs to keep an eye on the forecasts to see how this system develops and prepare now for potential flooding or wind-damage issues. Map out alternate routes to get to work, home, or to run errands. Areas that don't normally flood can wind up covered in water during exceptionally heavy rain events. It may be difficult to stock up on emergency supplies given the pandemic, but it never hurts to have a few extra non-perishables and batteries on hand in case the power goes out.

This is going to be a watch-and-wait situation. I know we hate those when it comes to the weather, but it's both a curse and a benefit of modern weather forecasting. It seems like a headache to watch something for a week to see if you'll be fine or if you need to invest in a pontoon boat, but hey, that's an improvement over the old way of finding out you'd get hit with a windswept flood once the waters started rising.

The Atlantic hurricane season officially begins on June 1, but we already saw two tropical storms during the month of May. The next name on the list is Cristobal.


Correction: I put the wrong date on the NHC outlook map above. The outlook was issued on May 31, not May 30 like I had in the original. Fixed. Sorry.


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May 26, 2020

The Worst Is Yet To Come For California's Central Valley Heatwave


An intense heatwave gripping California's Central Valley will continue through the end of the week. Forecasters expect high temperatures to crack 100°F across the region through Thursday before things tick closer to normal this weekend. 

Monday began the sweltering four-day slog as temperatures climbed into the 100s through California's Central Valley. Sacramento, Merced, and Bakersfield all reported a reading of 100°F at 4:00 PM on Tuesday, with temperatures in the 90s creeping as far west as San Francisco Bay.

The heat will keep on going through the end of the week. Here are the week's forecast high temperatures from the National Weather Service as of Tuesday afternoon.

Wednesday, May 27th:


Thursday, May 28th:


Friday, May 29th:


Temperatures will return to a more reasonable state by this weekend as the upper-level ridge responsible for the heat begins to weaken and move off to the east.

This week's heat wave is the result of a strong upper-level ridge that's parked over the western United States. The ridge intensified when it got pinched between two upper-level lows, one over Texas and the other over the eastern Pacific Ocean. The intensity of the upper-level ridge is the primary driver of the unusually intense heat. High pressure aloft fosters sinking air, which heats up as it descends toward the surface. The intense subsidence leads to crystal clear skies and an intense sunshine that roasts communities stuck under the pattern.

Some daily and monthly record highs are in danger of falling during this heatwave. There's a chance that Fresno will break its monthly high temperature record of 107°F on Wednesday. Sacramento will likely break a few daily records before the heat abates, and the capital could come close to tying its monthly record high of 105°F.

The geography of the Central Valley and the relatively dry air that dominates the region allows this part of California to get pretty toasty during the warm months. The average first triple-digit reading occurs on June 11 in Sacramento, June 2 in Fresno, and May 30 in Bakersfield.


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May 16, 2020

Tropical Storm Watches Issued For North Carolina Coast As Depression Forms In Atlantic


Tropical Depression One formed off the Florida coast on Saturday afternoon, starting this year's hurricane season early for an unprecedented sixth year in a row. Forecasters expect the system to strengthen into Tropical Storm Arthur by early next week as it brushes the North Carolina coast. Heavy rain, rough seas, and gusty winds are likely as the system approaches land.

We've been watching this tropical disturbance for the past couple of days as it slowly moved out of the Caribbean into the southwestern Atlantic. A cluster of heavy showers and thunderstorms persisted long enough for the disturbance to root itself at the surface with a closed low-level circulation. It's easy to see the tight swirl of the circulation on radar out of Melbourne, Florida, this afternoon. 


Environmental conditions are favorable—and its access to the Gulf Stream sufficient enough—that the National Hurricane Center expects the depression to strengthen into Tropical Storm Arthur overnight Saturday into Sunday. It should follow a general north-northeasterly track over the next couple of days, with the center of the storm passing quite close to North Carolina's Outer Banks on Monday.

There are several large-scale features pushing and pulling on the system that will guide its ultimate path. A ridge of high pressure over the western Atlantic will keep it from simply jogging out to sea, while an approaching trough should eventually weaken the ridge and allow the system to curve away from land. The strength of each feature and the timing of the trough's approach are both critical in the exact path of the storm.

A tropical storm watch is in effect for many of North Carolina's coastal counties given the projected path of the storm. It wouldn't take much of a westward deviation from the forecast track to bring the core of the storm closer to the coast. We're probably not looking at too many impacts either way—minor flooding from heavy rain and scattered power outages from gusty winds would be the biggest threat to most folks on land. Rough surf and rip currents will pose a threat to anyone at southeastern or Mid-Atlantic beaches through early next week.

Remember that the cone of uncertainty is the average margin of error in the National Hurricane Center's forecast track during previous hurricane seasons. The center of the storm stays within that cone about 66% of the time. 

The National Hurricane Center issues advisories on storms every six hours—at 5:00 AM/PM and 11:00 AM/PM EDT—with updates every three hours in between when watches and warnings are in effect.

[Satellite Pic: NOAA]


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May 14, 2020

A Preseason Tropical Storm Could Form Off The Florida Coast This Weekend


This year's Atlantic hurricane season could start early for the sixth year in a row. A tropical disturbance moving through the Florida Straits has a high likelihood of developing into a tropical or subtropical storm off Florida's east coast on Friday or Saturday. While it's likely that the system will stay offshore, it's still too early to say what—if any—impacts we could see in the United States from the potential storm.

Bubbling Disturbance


The disturbance is slowly moving northeast across the Florida Straits tonight. Radar imagery out of Key West shows broad rotation within a disorganized batch of showers and thunderstorms. The system should move over The Bahamas by Friday morning, where the disturbance could produce several inches of rain through the weekend. 

Forecasters at the National Hurricane Center give the disturbance an 80 percent chance of development through the weekend, and it's likely we'll have a full-fledged tropical or subtropical storm come Saturday night.

The system—which would earn the name Arthur—will encounter favorable conditions for organization and strengthening once it clears the Florida Peninsula to the east. The disturbance will move through an environment with relatively light wind shear, as well as the moisture and warm waters (it'll be over the Gulf Stream!) necessary to sustain thunderstorm development.

Impacts

Source: WPC
It's likely the system will remain out to sea for the duration of its life cycle, but it's close enough to the coast that anyone from Florida to New England should watch it carefully and prepare for heavy rain or power outages if it changes direction.

Here are the impacts we're likely to see as things stand right now:

—Heavy rain will affect southeastern Florida and The Bahamas. Several inches of rain could lead to flooding in vulnerable areas if heavy rain occurs in a short period of time.

—Rough seas and rip currents are likely up and down the southeast coast as this storm strengthens. The stronger the storm, the greater the likelihood for dangerous waves and rip currents. 

We'll have a clearer understanding of its impacts once the system develops and forecasters and models get a better handle on its structure and surroundings.

Tropical vs. Subtropical

This system could exist as a subtropical depression or subtropical storm for at least a portion of its life. A subtropical cyclone is a low-pressure system that exhibits characteristics of both tropical and non-tropical lows. A subtropical cyclone isn't fully tropical, but it's just tropical enough—and brings the same impacts—that it deserves a name and the full treatment from the National Hurricane Center.

A tropical cyclone consists of a tight-knit cluster of thunderstorms wrapped around a center of low pressure. These thunderstorms act as the engine that allows the storm to maintain itself and strengthen. A tropical cyclone has an intense core of winds that gradually decreases in intensity with distance from the center of the storm. Temperatures throughout a tropical cyclone are uniformly warm throughout the system. 

A subtropical cyclone can see its main cluster of thunderstorms develop many dozens of miles from the center of the storm, giving it a severely lopsided appearance on satellite and radar imagery. Most subtropical storms derive at least some of their energy from upper-level winds rather than solely from those thunderstorms. Subtropical systems also have some cold air wrapped up in the core of the system. These systems can (and often do) transition to fully tropical cyclones if they're in a favorable environment.

The differences between tropical and subtropical are mostly academic. The messaging and impacts are largely the same no matter what you call the system, so subtropical systems should be treated the same as any other named system.

Six Preseason Seasons In A Row


We're poised to see the the sixth Atlantic hurricane season in a row that saw its first named storm develop before the "official" start of hurricane season. The chart above shows all the preseason storms we've seen since 2003. 


Atlantic hurricane season runs from June 1 to November 30. As we've seen this year, last year, the year before that, the year before that, the year before that, and one more year before that, these dates are somewhat arbitrary. Hurricane seasons are based on a mixture of climatology and the simple fact that the first day of June and last day of November are cute cutoff points for messaging purposes. 

The concept of a preseason storm is almost entirely an Atlantic Ocean phenomenon. Preseason storms happen here from time to time but they certainly seem more common than they used to be. It's still unclear whether this is a function of more favorable environments for storms in May, a better ability to detect wayward storms, or looser qualifications for naming/advising on storms.


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May 8, 2020

Trump's Hurricane Sharpie Map Was A Warning Flare For The Federal Coronavirus Response


We hit the point of no return the moment Donald Trump took his Sharpie to a days-old hurricane forecast in the Oval Office.

It seems like we've passed a thousand of these inflection points over the last three years.

He issued a controversial pardon while Hurricane Harvey made landfall in Texas because people were already watching the news and his ratings would be higher.

His administration slow-walked aid to Puerto Rico in the wake of Hurricane Maria. The president himself lied about how much money the territory got from the federal government, then responded to criticism by saying Puerto Rico didn't sufficiently show its appreciation to him.

He stood amid the charred ruins of Paradise, California, and said the fire might have been prevented if only the state had raked the forests more often.

So it seemed like just another eyeroll when the president held up a National Hurricane Center forecast map so freshly altered by the ink of his pen that the black semicircle protruding from the expert forecast shimmered a bit under the lights of the cameras.


Three days earlier, the president had erroneously warned that Alabama (among other states) would be hit "much harder than anticipated" by scale-topping Hurricane Dorian. No forecast on September 1, 2019, placed the hurricane's projected path near Alabama. It seemed like a normal mistake he'd make and meteorologists quickly corrected the president's misinformation. The National Weather Service office in Birmingham even tweeted that the storm would steer clear of Alabama.

As it turns out, NWS Birmingham was unaware of the president's tweet at the time of their correction. They only reacted to the onslaught of phone calls and messages initiated by the president's false claim. The corrections incensed the president, who spent the next couple of days digging-in and doubling-down on his assertion that Alabama was at risk no matter how much the experts said otherwise.

The president's mistake consumed the White House, which suddenly found itself more concerned with Trump's image than the category five hurricane churning perilously close to Florida's coast. The issue seemed to come to a head on September 4 when Trump manually extended the cone of uncertainty on a days-old hurricane forecast to make it look like he was right all along, proudly holding up the altered map for cameras to see.

He presented outdated and falsified information to the public as a scale-topping hurricane loomed near the country's coast. That wasn't even the worst of it.

We'd soon find out that there was an intense behind-the-scenes campaign to force NOAA and the NWS to back up the president's faulty claims, including threats to fire NOAA leadership if they didn't issue a statement denouncing their own experts for contradicting the president's tweet. NOAA complied and issued an unsigned statement.

That fiasco—that wholesale demolition of expertise for the benefit of the president's personal image—foreshadowed the federal response to the coronavirus pandemic.
Image Source: New York Times
Today, the death toll from the coronavirus in the United States stands at 75,000 people and climbing, and it's likely that number is an undercount. That's a staggering number. It's more than double the average number of people who die of the flu every year. It's higher than the deadliest year on record for car crashes in the United States (56,278 in 1972). The coronavirus will likely register as one of the top causes of death in the United States in 2020, and it's only May.

And at every step of this pandemic—from the first confirmed cases on American soil to governors prematurely reopening their states—things were made worse by valuing political whims over expert assessments.

The first heads-up about the impending pandemic reached the upper echelons of the Trump administration in January. Warnings grew more dire through February as the virus spiraled out of control in other countries and it was clear the United States would follow a similar trajectory. The United States encountered persistent testing delays that compounded the crisis and let the virus spread undetected for weeks. 

No warning struck as hard as one that came during a briefing on February 25, 2020, when Dr. Nancy Messonnier, a vaccine expert with the Centers for Disease Control, warned that it was a matter of when—not if—a bad outbreak of coronavirus would start spreading in the United States. Dr. Messonnier punctuated her remarks by describing how she warned her own family that the virus' spread would lead to "significant disruption of our lives." 

An already-plummeting stock market fell even harder on news reports of Dr. Messonnier's warnings, hurting Trump's prized metric for gauging his success as president. The Trump administration said the doctor spoke out of turn, and the president threatened to fire her if she didn't walk back her warnings.

The following day, Trump insisted during a press conference that the 15 confirmed cases at that point would "be down close to zero" pretty soon.

One day after that, Trump said the virus would go away on its own. "It’s going to disappear. One day—it’s like a miracle—it will disappear."

Trump called criticism of his administration's coronavirus response "the new hoax" during a rally on February 28, 2020.

The country saw its first confirmed coronavirus death on February 29, 2020, though it's likely the first actual death occurred weeks earlier.

Case counts quickly multiplied as testing ability came online throughout the country, finally giving us a glimpse of the extent of the community spread that had occurred before most communities took mitigating actions.

On March 9, as states began to roll out their stay-at-home orders, Trump (now, falsely) tweeted that the flu was deadlier than the coronavirus:


As the number of cases exploded through the middle of March, most states instituted stay-at-home orders of varying strictness, pausing the national economy to the tune of millions of jobs and trillions of dollars. This sudden economic crash cut at the heart of Trump's reelection pitch.

Trump's daily coronavirus press conferences, which began as an effort to stabilize the economy, slowly turned into venting sessions and virtual campaign rallies as the days wore on.

He openly bragged about the ratings for his briefings. He tweeted on five different occasions that his coronavirus briefings got bigger ratings than The Bachelor (March 29, March 29 (again), April 8, April 9, and April 21). He only started reining in the televised events after he openly wondered if doctors should inject patients with disinfectant to cleanse their systems of the virus.

Flouting his own government's suggestions that states stay the course until there's a significant decrease in serious cases, the president started pressuring states to reopen for the benefit of the economy. "Reopen" protests broke out in some states. Pictures and footage from the rallies showed an unmistakable trend: the vast majority of protesters wore Trump hats, Trump shirts, waved Trump flags, or drove vehicles adorned with stickers and signs advertising the president's reelection campaign.


The president appeared to take notice that his own supporters dominated these protests. Trump began April 17 by tweeting "LIBERATE MINNESOTA," "LIBERATE MICHIGAN," and "LIBERATE VIRGINIA," firing the starter gun for supporters to congregate in each state's capital and demand that their governor allow life to return to normal even as the virus continues to spread. Men carrying rifles wandered the halls of Michigan's capitol building as elected officials attended a legislative session wearing bulletproof vests. A day later, Trump tweeted that Michigan's governor should relent to their demands.

Now, as the death toll surpasses each bracket Trump predicted we'd stay under for him to have done a good job, reports indicate that Trump and his surrogates are preparing to publicly question the veracity of the death toll and claim that it's overinflated so states and hospital systems can grab federal dollars and make the president look bad at the same time.

He downplayed the virus because he thought it would hurt him. He threatened to fire an expert because he thought her warnings imperiled him. He egged on the protests because the attendees supported him. He's on his way to questioning the death toll because it looks bad on him.

He altered a hurricane forecast and upended NOAA during a disaster to save face over a simple mistake he made in a tweet one morning.

A category five hurricane became him.

It seemed easy to brush it off at first because hey, it's just the weather, right?

The bad weather served as a warning of what came next.

[Top ImageTwitter/@WhiteHouse]

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May 7, 2020

A Festive Mid-May Cold Snap Will Make Things Interesting For A Change


It's almost the middle of May. Crops are germinating. Flowers are in bloom. Leaves are fully leafed. So of course we're talking about the potential for accumulating snow! Welcome to a topsy-turvy weather pattern that's sure to bring a festive verve to the monotony of staying at home. A burst of heat will build across the western United States while a late-season cold snap in the east brings frosty temperatures to many and snow to some.
Source: Tropical Tidbits

A wavy jet stream will allow a sharply divided weather pattern to develop across the United States by the end of the week. A steep ridge will build west of the Rocky Mountains while a hearty trough digs south through the Great Lakes. The above-average temperatures out west and below-average temperatures back east will threaten to break daily temperature records on both ends of the spectrum.


The National Weather Service's high temperature forecast for Saturday is a stark example of what a pronounced ridge-trough pattern looks like. The west will register a solid "balmy" with 80s reaching Seattle and upper 90s as far north as California's Central Valley. Some cities out west will see record high temperatures over the next few days. Outside the heart of the deserts, it usually doesn't get this warm for a while yet.


Back east, Saturday would be considered a beautiful day if it wasn't May 9th. Temperatures will dip well below normal for this time of year; folks on the northern Gulf Coast could see their breath on Saturday morning. Such a late freeze will threaten crops and gardens if they're not protected.

We'll see lots of comfort-related complaining about the sudden resurgence of cooler weather this weekend, but it's not all bad. This kind of forecast is a dream come true for cold weather folks like me. It won't be long until we're in a months-long slog of hot and muggy weather with occasional severe storms. Everyone will complain about that soon enough. Enjoy the chill while we've got it.

Where there's cold air and precipitation, there's a chance for...


A low-pressure system will swoop across the Mid-Atlantic and Northeast on Friday evening into Saturday morning, bringing the potential for snow on the northern edge of the system. Models are a bit wishy-washy on who might see what—it's May, give them a break—but the National Weather Service does paint some accumulating snow across interior parts of the Northeast on Friday.

The map above doesn't cover the entire period when snow is possible. The map stops at Friday evening, while the bulk of the potential snow could occur overnight into Saturday. The data is also a little off because NWS Buffalo hadn't issued their snowfall forecast when I created the map, hence the conspicuous emptiness in western New York. But it gives you a good idea at where there's a chance for wintry weather to end the week.

There's an outside chance that snowfall totals will wind up edging a bit higher and nudge closer to big cities like Boston. Any snow that does fall won't stick around very long given borderline temperatures and a sun angle that's equivalent to what we see in August.


The Climate Prediction Center's latest outlook shows that it's likely we'll see below-normal temperatures continue across much of the eastern United States through next week, although not to such an extent as we'll see this weekend. Things should return to a more May-like state by next weekend.

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April 23, 2020

A Powerhouse Supercell Managed To Travel 300 Miles Across Three States


A real powerhouse of a supercell thunderstorm rolled across hundreds of miles of southern woodlands on Wednesday evening, ramping up in east-central Texas on Wednesday afternoon before finally petering out nearly eight hours later over the Mississippi River near Natchez, Mississippi. The supercell produced multiple tornadoes along its path, even prompting a tornado emergency as it approached Fort Polk, Louisiana.



Wednesday saw a classic springtime severe weather event across the southern Plains and lower Mississippi Valley. A line of tornadic supercells developed along a dry line in central Oklahoma, including a tornado that killed two people and grew to frightening strength in a matter of seconds.


The environment was just as ripe for severe weather farther to the south in Texas. A single supercell managed to survive for eight hours as it tracked from College Station, Texas, to Natchez, Mississippi. The video above shows a radar loop (video by me, radar by College of DuPage) of the storm along its track from College Station to Natchez. It's the southernmost storm that begins on the bottom-left and ends just right of center in the frame.
The thunderstorm near College Station that'd grow into the long-track supercell. (Gibson Ridge)

A thunderstorm began to develop broad rotation near College Station, Texas, around 3:00 PM CDT, slowly growing more organized over the next couple of hours as it moved east of the town. Things got going in a hurry as the supercell moved south of Lufkin, Texas, around 5:30 PM CDT, producing the first in a series of tornadoes that would touch down between there and central Louisiana through the evening.

A tornado east of Jasper, Texas. (Gibson Ridge)


The supercell neared peak strength once it got into far eastern Texas, cycling through stronger and weaker phases as it moved into Louisiana. The radar image above shows the storm around 7:30 PM CDT, as it approached the Texas/Louisiana border. It's broken down into four panels:

  • The top-left panel shows reflectivity, or precipitation.
  • The top-right panel shows velocity, or wind. Green shows wind blowing toward the radar (to the east), while red shows wind blowing away from the radar. When you have a strong, tight cluster of red and green right next to each other, it shows strong rotation within a storm.
  • The bottom-left panel shows correlation coefficient. The radar beam can tell us how similar in shape and size the objects are that it's intercepting. Uniform objects like raindrops have a high correlation coefficient (red/purple), while mismatched objects like tornado debris have a very low correlation coefficient (blue). When you see a dark blue dot in the same spot as tight rotation, you're looking at debris swirling around a tornado.
  • The bottom-right panel is normalized rotation, or NROT. This is an algorithm within Gibson Ridge's radar program that helps you quickly spot areas of rotation. Higher NROT values can indicate stronger rotation.
A tornado approaching Fort Polk, Louisiana, on April 22, 2020. (Gibson Ridge)

This storm appears to have produced several strong tornadoes across eastern Texas and central Louisiana. The National Weather Service in Lake Charles, Louisiana, had to issue a tornado emergency for Fort Polk, a military training site that houses thousands of troops and their families, as a confirmed tornado moved very close to the heart of the base.

The storm continued producing possible tornadoes as it passed southeast of Alexandria, Louisiana, before the updraft weakened and the storm finally started falling apart as it crossed the Mississippi River south of Natchez, around 11:00 PM CDT. The storm powered along almost uninterrupted for eight hours (!!!) before it finally fell apart.

A supercell is powered by a rotating updraft. Strong wind shear can cause horizontal rolling motions in the atmosphere. If a strong thunderstorm can develop in that environment, the updraft will push that rotation into the vertical and the updraft itself will begin to rotate. This rotating updraft then tilts downwind, allowing the storm to ingest unstable air and vent cooler air without choking itself off like a "normal" thunderstorm would.

This was a rather unusual testament to the endurance of a supercell when it's in a near-pristine environment. We usually don't see this kind of a marathon run outside of major outbreaks.

We're used to hearing about supercells after a tragic tornado or major hailstorm, but the vast majority of supercells are relatively—relatively—weak and don't last for very long. Supercells can be extremely fragile, falling apart if their outflow moves too quickly or if nearby storms contaminate the environment ahead of them with stable air. It's quite something to watch a supercell on radar practically disappear in just a few frames.  But there was nothing in this storm's way and it took full advantage of the situation.

Update: I changed the headline from "Tornadic Supercell Travels Farther In One Day Than You've Gone In The Last Two Months" to "A Powerhouse Supercell Supercell Managed To Travel 300 Miles Across Three States" because...well, do I really need to explain? 


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