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SERIOUS STORMS POSSIBLE AGAIN...

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SIGNIFICANT SEVERE WEATHER THREAT...AGAIN!

Over the past week tornadoes and severe thunderstorms have produced more than 60 fatalities, injured hundreds, and destroyed numerous homes.

Last Friday alone 95 tornadoes were reported, most of those in the central U.S.

As of April 2nd, the nation was very close to its all time record for tornadoes to date with inflation adjusted totals at 350.

Preliminary LRS counts are higher with this years total of 412 topped only by 516 in 2008 and 462 in 2017.

The number is going to grow Tuesday around the central Midwest as another bi-modal outbreak of severe weather appears likely. SPC has two regions under moderate risk assessments (4 out of 5) Monday night.

The tighter perspective as of Monday night shows all of my area in the moderate level 4 risk outlook.

The level 4 threat category implies widespread, long lived, intense severe storms are likely around the region.

At least for now, SPC depicts a 15-29 percent hatched threat of a tornado within 25 miles of a point. The hatching indicates at least a 10 percent chance of a significant tornado EF2 or greater.

The Colorado State University Machine Learning Probability Model outlines risk areas for tornadoes, large hail, and damaging wind potential. This experimental model did a great job with Friday's outbreak. You can see how its tornado outlook on the left verified vs. the man-made SPC outlook. Actual tornadoes are plotted in red dots. Not bad for a model.

Here's its current outlook for tornadoes Tuesday

Here it is for large hail

And it has this for damaging winds.

When you consider all 3 of the parameters SE Iowa is the epicenter for the overall severe weather threat.


The big driver of all this is powerful upper air low which comes rolling at the Midwest late in the day. Out ahead of it southwesterly winds up to 100kts are fueling the storm with lift, energy, and warm moist air.

The big factor that will play an important role in how everything evolves is the strong warm front that approaches the region during the day. Near it winds will be strongly backed leading to significant shear and long looping hodographs supportive of strong tornadoes. Any updraft that goes up in that environment is going to rotate as evidenced by the RAP supercell composite near 30 near and north of I-80

That creates a virtual PDS sounding that is classic looking near Iowa City. PDS standing for particularly dangerous situation sounding. 0-6km shear is at 70 kts, that is cranking. Similar soundings are evident further east along the warm front.

The rap also shows a surface temperature of 77 over a dew point of 66. I wonder if the 3k, RAP, and HRRR are too aggressive pushing the warm front and that type of warmth and moisture so far into the region. The GFS and EURO hold it closer to I-80 and the 3k NAM, a real outlier has it way down closer to HWY 34 in SE Iowa. There is going to be a very big temperature gradient from north to south with the GFS showing 53 in Dubuque and 82 in Burlington at 3:00 in the afternoon. That could mean storms in some of my northern counties would be more elevated and more likely to produce large hail than tornadoes.


The bottom line is that these parameters are in flux and we won't know until early Tuesday how the set-up unfolds. There is certainly plenty of potential but heating and moisture and the eventual position of that warm front will tell the tale of how ugly the day gets (and where). Be sure and check the latest SPC risk outlooks from the NWS along with your local forecasts. The day has the potential to be a dangerous one if the right conditions are achieved, particularly in the area near and south of I-80


After this major system departs, the pattern is expected to turn quiet for awhile and if the GFS has its way, much warmer with a real springtime look to temperatures. Here's the average daily temperature departures for the period April 9th-19th. I love the look of that.

10 day precipitation departure are also below normal over that same period.

Wow, warm and dry. That's just what the doctor ordered. All we need to do is get through Tuesday. Seriously, there is the threat of significant severe weather in some part of the area as evidenced by the moderate risk from the Storm Prediction Center. I urge you all to pay extra attention to any NWS watches or warnings that might be issued for your area. Have a safe plan, especially with fast storm motions up to 50mph possible. I'll have more for you tomorrow. Roll weather...TS

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