Skip to main content

(Originally posted to The Motley Moose.)

A strong cold front that is currently moving through the Central Plains states will act as the proverbial spark in the powder keg this afternoon, firing off severe thunderstorms across parts of the southern United States. Given the upper-level dynamics associated with this system, there is a moderate (several magnitudes higher than normal) risk of significant, long-track, violent tornadoes over a large area of real estate this afternoon and evening.

The Threat

The main threats today will be significant, long-track, violent tornadoes, as well as violent straight-line winds.

The SPC has issued a moderate risk for severe weather (red) across a large chunk of the south. The yellow area is a slight risk, and the green area indicates a risk for general, non-severe thunderstorms.

Here's the tornado probability chart. An area with a 15% chance of tornadoes means that there is a 15% chance that at least one tornado will touch down within 15 miles of any point in the shaded area. The black hatched area indicates the risk for significant (EF-2 or higher), long-track tornadoes.

Here's the severe wind (greater than 60 MPH) map. Percentages work the same as they do with the tornadoes. The black hatched area indicates a risk for severe thunderstorm winds greater than 75 MPH.

The Setup

A strong cold front is moving across the Central Plains states into a very warm, very soupy airmass being pumped in straight off the Gulf of Mexico:

Dew point map as of around 1130AM Central. The greener, the moister.

A cold front ramming into this warm unstable air will wreak havoc for the areas outlined by the Storm Prediction Center above. Winds at 850 millibars (about 5500 feet off the ground) are screaming along in what's called a low-level jet (LLJ), reaching speeds of almost 80 MPH. Winds at the jet stream level (30-35,000 feet off the ground) are moving along at almost 175 MPH.

This change in speed and direction with height is called wind shear, and along with the massive amounts of instability from the warm air, and the forced lift from the cold front, extremely strong storms are expected to develop this afternoon.

The storms are initially forming as individual supercells, which carry the greatest risk for tornadoes. Over time (probably later tonight) these supercells will start to merge with each other and create an intense squall line along the cold front as it heads into the southeastern and eastern parts of the United States.

CORRECTION: The supercells are forming out ahead of the main squall line along the cold front. The individual, more dangerous storms will come through first with the tornado threat, and be almost immediately followed by the damaging winds of the main squall line.

What we're most concerned about are the supercells that form before the squall line. The shear I mentioned before creates a horizontal rolling motion in the atmosphere -- think of a cardboard tube tilted on its side. This rolling tube of air can be tilted vertically by the strong updrafts in thunderstorms, making the entire storm begin to rotate.

This rotation is what facilitates the development of tornadoes. We measure this with something called "storm relative helicity." Essentially, the higher the number, the more likely we are to see strong tornadoes. The threshold changes based on a number of factors, but in this type of setup we typically see tornadoes begin to form with SRH values of around 250.

SRH values are expected to climb up beyond 500, especially over Arkansas, this afternoon.

The supercells, by nature, will eventually form into a strong squall line and move east. When this occurs, the tornado threat will die down and the damaging wind threat will ramp up.


National Weather Service Main Page
National Weather Service -- Central Oklahoma
National Weather Service -- Dallas/Ft Worth TX
National Weather Service -- Tulsa OK
National Weather Service -- Springfield MO
National Weather Service -- Arkansas (whole state)
National Weather Service -- Paducah KY
National Weather Service -- Shreveport LA
National Weather Service -- Memphis TN
National Weather Service -- Jackson MS
National Weather Service -- Huntsville AL
National Weather Service -- Birmingham AL

Storm Prediction Center Main Page
Storm Prediction Center -- Current Severe Weather Watches
Storm Prediction Center -- Convective (Severe Weather) Outlooks
Storm Prediction Center -- Mesoscale Discussions
Storm Prediction Center -- Storm Reports
Storm Prediction Center -- Mesoscale Analysis Pages

Wunderground's Detailed Radar (click the + nearest to you to see your local radar)

NOAA Weather Models's excellent GFS/NAM/RAP model website.

I'll continuously post updates to my Facebook page on this and most other major severe weather outbreaks.

Your Email has been sent.
You must add at least one tag to this diary before publishing it.

Add keywords that describe this diary. Separate multiple keywords with commas.
Tagging tips - Search For Tags - Browse For Tags


More Tagging tips:

A tag is a way to search for this diary. If someone is searching for "Barack Obama," is this a diary they'd be trying to find?

Use a person's full name, without any title. Senator Obama may become President Obama, and Michelle Obama might run for office.

If your diary covers an election or elected official, use election tags, which are generally the state abbreviation followed by the office. CA-01 is the first district House seat. CA-Sen covers both senate races. NY-GOV covers the New York governor's race.

Tags do not compound: that is, "education reform" is a completely different tag from "education". A tag like "reform" alone is probably not meaningful.

Consider if one or more of these tags fits your diary: Civil Rights, Community, Congress, Culture, Economy, Education, Elections, Energy, Environment, Health Care, International, Labor, Law, Media, Meta, National Security, Science, Transportation, or White House. If your diary is specific to a state, consider adding the state (California, Texas, etc). Keep in mind, though, that there are many wonderful and important diaries that don't fit in any of these tags. Don't worry if yours doesn't.

You can add a private note to this diary when hotlisting it:
Are you sure you want to remove this diary from your hotlist?
Are you sure you want to remove your recommendation? You can only recommend a diary once, so you will not be able to re-recommend it afterwards.
Rescue this diary, and add a note:
Are you sure you want to remove this diary from Rescue?
Choose where to republish this diary. The diary will be added to the queue for that group. Publish it from the queue to make it appear.

You must be a member of a group to use this feature.

Add a quick update to your diary without changing the diary itself:
Are you sure you want to remove this diary?
(The diary will be removed from the site and returned to your drafts for further editing.)
(The diary will be removed.)
Are you sure you want to save these changes to the published diary?

Comment Preferences

skybluewater, DeminNewJ, JR, northsylvania, filkertom, Odysseus, Timaeus, Trendar, Gooserock, Powered Grace, PeterHug, sphealey, Khun David, alicia, Shockwave, just another vet, Wintermute, missLotus, ATinNM, liberaldregs, mkfarkus, mrblifil, antirove, Kentucky DeanDemocrat, virginislandsguy, texasmom, defluxion10, Catte Nappe, BlogDog, zerelda, KayCeSF, oortdust, ExStr8, Tinfoil Hat, DianeNYS, BluejayRN, ArchTeryx, OpherGopher, Alice Venturi, MT Spaces, Dobber, teresab, owlbear1, cfk, SaraBeth, Pam from Calif, The Grace Kelly, Little Lulu, Steve in Urbana, Ozymandius, coolbreeze, kathny, xaxnar, Jim R, 417els, tonyahky, technomage, Loonesta, raincrow, wild hair, twigg, Rosaura, Crashing Vor, tapestry, sceptical observer, ER Doc, kkbDIA, doingbusinessas, Statusquomustgo, cpresley, pgm 01, zipn, edsbrooklyn, Mary Mike, terabytes, DWG, sfbob, Kentucky Kid, jayden, mudslide, jnhobbs, gchaucer2, Wreck Smurfy, Korkenzieher, chicago minx, MKinTN, JaxDem, ScottyUrb, Sixty Something, Youffraita, bythesea, lineatus, tofumagoo, royce, Cassandra Waites, Jake Williams, glendaw271, Al Fondy, savano66, Mrs M, Old Iowa Liberal, litoralis, LinSea, ewmorr, cantelow, TheFern, CanyonWren, maryabein, Norm in Chicago, janmtairy, War on Error, bfitzinAR, kevinpdx, stevenwag, louisev, spicecakes69, Leftcandid, Larsstephens, Railfan, Just Bob, Its the Supreme Court Stupid, Susan Grigsby, leftywright, luvsathoroughbred, addisnana, ericlewis0, Otteray Scribe, cocinero, progdog, wrpereir, Onomastic, Maximilien Robespierre, MidwestTreeHugger, I love OCD, coquiero, cv lurking gf, freesia, asterkitty, mrsgoo, badscience, Wolf10, Wheever, peregrine kate, Vatexia, Dbug, blue aardvark, joanbrooker, Prairie D, anodnhajo, leathersmith, cwsmoke, Siri, outspoken82, AnnieR, FloridaSNMOM, CA ridebalanced, Horace Boothroyd III, Lorinda Pike, jan4insight, Arahahex, pittie70, Vote4Obamain2012, Glen The Plumber, mumtaznepal, mythatsme, allensl, Lily O Lady, argomd, SanFernandoValleyMom, broths, PHScott, leeleedee, Aunt Pat, Ree Zen, evander, CJ WIHorse, ET3117, Hey338Too, footNmouth

Subscribe or Donate to support Daily Kos.

Click here for the mobile view of the site