Severe Weather Threat Fri May 31

A Closed Midlevel Low Over The Nrn Plains Will Drift Ewd And
Gradually Evolve Into More Of An Open Wave By Early Saturday...As
Embedded Speed Maxima Rotate Around The Srn Periphery Of The Low /Across The Central Plains To The Mid Ms Valley/. The Primary
Surface Cyclone Will Slowly Weaken Today Across The Dakotas/Mn ...While A Trailing Cold Front Drifts Sewd Into Se Ks And Nrn Ok...And Secondary Cyclogenesis Occurs Invof Cds This Afternoon. A Dryline Will Mix Ewd By Mid Afternoon To Nw And W Central Tx To The S Of The Secondary Low.

Mo/Il To Ok/Nrn Ar Through Tonight...

The Combination Of Low-Level Moisture Advection From The Wrn Gulf Basin And Some Evapotranspiration Will Support Boundary Layer Dewpoints In The Low 70s Into The Ok Warm Sector. This
Moisture...Along With Daytime Temperatures Warming Into The 80s
Beneath Steep Midlevel Lapse Rates...Will Support Strong-Extreme
Instability /Mlcape Values Of 3500-4500 J Per Kg/ In Ok This Afternoon ...With Somewhat Weaker Buoyancy Farther Ne Into Mo.
The Short-Term Model Forecasts Of Mid 70s Dewpoints And Mlcape In Excess Of 5000 J/Kg In Ok Appear A Little Overdone Based On Regional Observations.

Meanwhile...Deep-Layer Vertical Shear Will Be Favorable For Supercells From The Mid Ms Valley Swwd To Central Ok...Along The Sern Fringe Of The Stronger Mid-Upper Flow.

The Most Probable Scenario Today Is For The Morning Convection
Across Nrn Mo To Spread Into Ern Mo And Central Il. New Storm
Development Is Also Expected By Early Afternoon Across Central
Mo...Along The Srn Fringe Of The Morning Convection As The Low
Levels Recover From Overnight Convection That Is Weakening Across Wrn Tn. The Cap Will Delay Storm Development Farther Sw Into Ok Until Mid-Late Afternoon...With Rapid Thunderstorm Development Expected By 21-22z Along Or N Of The I-44 Corridor... And W Of I-35 Along The Dryline Where Intense Surface Heating Will Occur. The Strong-Extreme Cape And Effective Bulk Shear Aoa 50 Kt Will Favor The Production Very Large Hail /Baseball Or Larger/... Especially With The More Discrete Storms Earlier In The Convective Evolution.

The Tornado Threat Is A Bit More In Question Given The Necessary
Recovery Across Ern Mo/Il Where Low-Level Shear Will Be Stronger... And Rather Modest Low-Level Flow/Shear Farther Sw Into Ok.

Still...An Isolated Strong Tornado May Occur As The Extreme Instability Compensates To Some Extent For The Weaker Low-Level
Shear. Later During The Evening And Into Tonight...Storm Mergers/ Outflow Interactions Will Lead To Upscale Growth Of Larger Clusters /Bands Of Storms...And The Storms Will Be Maintained Overnight By A Strengthening Low-Level Waa Regime.

Ern Ia...Se Mn...Wrn Wi This Afternoon/Evening...

The Ongoing Storms In Nrn Mo Raise Some Questions About The Degree Of Recovery Today Farther To The N In Ia...Though The Dvn And Top Soundings Show The Potential For Somewhat Richer Moisture To Mix Downward Today With Some Surface Heating.

With Potentially Moderate Instability In The Warm Sector...Scattered Thunderstorm Development Will Be Posssible Along The Synoptic Cold Front As An Embedded Speed Max Rotates Newd Over Ia This Evening. Deep-Layer Speed Shear Will Be Strong...And A Few Organized Storms Could Produce At Least Isolated Damaging Gusts And Large Hail.

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