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Here we go again. Round 3 of this severe weather outbreak will unfold on Monday afternoon across the Midwest as the troublemaking low pressure system begins to very slowly make its way off to the east.

This weekend demonstrated a classic springtime tornado outbreak across the Plains. Multiple violent tornadoes touched down from Nebraska to Oklahoma, destroying entire communities and leaving at least one person dead in Shawnee, OK. For pictures and radar updates from Sunday's severe weather as it happened, visit yesterday's liveblog.

Here's the risk for severe weather today. The red shaded area is a moderate risk for severe weather. Yellow is a slight risk. Green is a risk for general, non-severe thunderstorms.

Here are the probabilities for severe weather on Monday. The percentages mean there is an xx% chance for severe weather within 25 miles of any point within the shaded region. CAUTION: the below maps were issued at 1AM Central Time. They update them again early in the morning, and again around noon. Check the Storm Prediction Center for the latest forecasts.

TORNADO risk for Monday. 2% warrants concern. Black hatching indicates risk for violent, long-lived tornadoes much like we saw on Sunday.

HAIL risk for Monday. 15% warrants concern. Black hatching indicates risk for hail larger than golf balls.

SEVERE WIND (60+ MPH) risk for Monday. 15% warrants concern.

Here's the basic setup that's causing the severe weather:

A strong mid-level jet stream between 18,000 and 19,000 feet above ground level is expected to move over Oklahoma and Kansas on Monday afternoon, packing winds of about 60-70 knots (the filled-in shaded region).  These winds are generally going to be from the west-southwest (the skinny part of the barbs points in the direction of the winds).

At the surface, the low pressure system will draw in very warm and moist air directly off of the Gulf of Mexico. The following image depicts surface winds tomorrow afternoon around the same time as the mid-level jet above. The winds across eastern Oklahoma are almost straight out of the south.

The clash between fast west-southwesterly winds at 18,000 feet and slower low-level winds from the south will produce horizontal rotation in the atmosphere due to vertical wind shear -- winds that increase with speed with height. Think of the cardboard tube in a roll of paper towels, laying on its side, spinning above you. That's what happened Sunday over Oklahoma and Kansas, and that's what's going to happen again today over Oklahoma, northwest Arkansas, and southwestern Missouri.

The horizontal tube of rotation caused by vertical wind shear (winds increasing in speed with height).
The next ingredient is the thunderstorms. The air is going to be a soupy mess -- it is almost the end of May, after all. Very warm temperatures with ample moisture will create an unstable airmass as we get into the afternoon hours across the eastern half of Oklahoma. Very cold mid- and upper-levels will allow the air at the surface to begin rising rapidly once something sets off the spark, so to speak.

This spark will come in the form of a front. A sharp cold front will serve as the focus to fire off thunderstorms. The boundary acts as a ramp of sorts, allowing the surface air to rapidly rise into the upper atmosphere -- an updraft -- generating massive thunderstorms.

Jump back to the horizontal tube of rotation. When these updrafts run into this horizontal rotation, it starts to bend it. One half will tip vertical and begin spinning counter-clockwise; the other, clockwise. The counter-clockwise spinning rotation almost always wins out in the northern hemisphere (depending on the winds, but that's another story), and this now-vertically oriented tube of rotation sort of absorbs the updraft.

The horizontal tube of rotation is titled vertically by the updraft, denoted in this image by the orange arrow. The resulting vertical rotation is the heart and lungs of a supercell thunderstorm.
The result is something called a mesocyclone -- a somewhat broad area of rotation that serves as the heart of a supercell thunderstorm. This mesocyclone is like a "super updraft" of sorts, to use a term that would get me kicked out of a meteorology course. Those strong winds 18,000 feet above the ground has a hard time penetrating this rotating updraft and killing it. In fact, it tilts the updraft. This tilted updraft is really hard to kill, so the supercell lives on for dozens (and sometimes, hundreds) of miles.

The stronger this mesocyclone rotates, the higher the likelihood of a tornado.

The atmosphere in eastern Oklahoma tomorrow is ripe for supercellular development. In addition to the risk for violent, long-lived tornadoes (like we saw on Sunday), very large hail (to the size of baseballs) and damaging winds in excess of 60 MPH are possible.

As was the deal today, I'll post a severe weather liveblog if things start getting nasty. Remember...even though these are deeply red states, people are people. Many DailyKos readers live in these areas. Think before you post -- we're supposed to be the compassionate ones.


National Weather Service Main Page
National Weather Service -- Central Oklahoma
National Weather Service -- Tulsa OK
National Weather Service -- Springfield MO
National Weather Service -- Arkansas (whole state)

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.

ChaserTV-- live streaming video from storm chasers.

News9 in Oklahoma City provides extremely thorough severe weather coverage. This is Gary England's station -- the pioneers of on-screen weather warnings and chasing tornadoes with helicopters. Their efforts, along with those of storm chasers, have saved thousands of lives.

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

Sun May 19, 2013 at 11:10 PM PT: Updated the severe weather risk maps at 1AM CDT to reflect the new maps from the SPC. Always check the SPC for the latest updates.

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