The Storm Prediction Center is forecasting a major severe weather outbreak in the Central Plains and Midwest today, which could include strong tornadoes, damaging winds, and large hail. There's some uncertainty in the forecast, but severe weather indices are off the charts and if the storms form, they could mean business.
This morning's 730 AM update (above) from the Storm Prediction Center showed a moderate — 4 out of 5 — risk for severe weather across the Central Plains today. The moderate risk covers almost 3 million people over 70,000 square miles of real estate.
Here's the tornado risk for today. A 10% risk means that the odds of seeing a tornado within 25 miles of any point in the shaded area is 10x higher than normal. 5% usually warrants concern.
Here's the threat for damaging winds in excess of 60 MPH. 15% usually warrants concern, and the black hatching indicates the risk for wind gusts exceeding 75 MPH. Remember that the 45% risk zone means that areas in and around the shading are 45 times more likely to see damaging winds today than normal.
And here's the hail threat, with 15% again being the level where we start getting concerned. The black hatching indicates a risk for hail larger than golf balls.
The severe weather indices are truly off the charts. Here's the Energy Helicity Index (EHI) for this evening as of last night's run of the North American Model (NAM). The index takes into account both the instability and potential for rotation in the atmosphere to determine how conducive the atmosphere is to producing tornadic supercells. Values between 2 and 3 are cause for concern, and anything above 3 is indicative of an atmosphere capable of sustaining strong tornadoes. Values are exceeding 12 in Nebraska near sunset this evening.
Here's the supercell composite index, which looks at the how conducive the atmospheric wind shear (winds changing speed and direction with height) is to producing supercells. Values this high are pretty rare.
There are two big problems that these storms could (and hopefully do) encounter: 1) any storms that form in the morning/early afternoon could stabilize the atmosphere and kill the storm potential later this evening, and 2) a strong cap (inversion in the atmosphere that prevents air from rising beyond it) will be present and the air might not be able to break the cap, preventing thunderstorms from forming.
If and when the storms do form, supercells will be the main threat over Nebraska and Kansas at the beginning of the outbreak this afternoon and evening, and as the storms move eastward, they will start to merge with one another and form a dangerous squall line that could produce significant damaging winds — in excess of 70 MPH — from Kansas City straight into the Mississippi River Valley and even potentially areas in the western Ohio Valley overnight tonight.
It's going to be an interesting, dynamic, and potentially life-threatening severe weather outbreak today, and it's one to keep an eye on if you or someone you know lives in the affected areas. Below you can find my standard set of links to help you keep up with the forecast today. Stay safe.
- The Storm Prediction Center is the official agency in charge of predicting severe thunderstorms in the United States.
- The National Weather Service issues local forecasts, as well as severe thunderstorm/tornado warnings across the U.S.
- Wunderground provides excellent weather radar imagery — click on the + closest to your location.
- NASA's website provides excellent satellite imagery from the GOES weather satellites.
- Dr. Greg Forbes of The Weather Channel is a world-class meteorologist who developed the accurate TOR:CON index that evaluates the threat for tornadoes on a 0-10 scale. Dr. Forbes' TOR:CON forecasts are found on weather.com.
[Images via SPC and College of DuPage]
This post will be updated through the day to reflect the correct forecasts from the SPC. The next update from the SPC comes out at 12:30PM EDT.