Severe Weather Threat Tue May 7

In Mid-Upper Levels...Split-Flow Pattern Fcst To Continue Through
Day-3 Period...Bracketing Pair Of Increasingly Progressive Cyclones.

First Of Those Cyclones Currently Is Drifting Esewd Over Mid-South
Region...And Should Move Slowly Newd Over Carolinas Day-3.

Second Is Retrograding Across Nrn Ca Attm Toward Pac...Then Should Move Inland Day-2.

Accompanying 500-Mb Low Should Shift Ewd Across Great Basin To Ut This Period...Perhaps Centered As Far S And E As 4-Corners Area. Only Minor/Mesoscale Discrepancies Exist Among Avbl Operational Models Now...And Between Most Sref Members... Regarding Position Of This System Through Most Of Period.

Srn-Stream Shortwave Trough -- Now Evident Over Nern Pac Sw Of Ca Upper Low -- Is Fcst To Eject Newd Across Srn Rockies Day-2...Then Phase With Quasistationary/Pre-Existing Vorticity Field Over Dakotas And Nrn Neb Day-3.

At Sfc...Primary Low Associated With Sern Conus System Should Move From Nc Over Va...Generally In Step With Occluded Front Extending Ewd Over Atlc.

Meanwhile...Sfc Pressure Falls Will Lead To Lee Troughing Becoming Established Over High Plains.

Central-Nrn Plains...

Two Primary Convective Episodes Are Possible -- Diurnal/High-Based
Tstms And Elevated Convection Late Overnight. Lack Of More Robust / Shear / Moisture Keeps Svr Risk Too Conditional/Isolated For Probabilities Attm.

As Has Been True Most Of This Spring...Nmm-B Members Of Sref Appear Most Reasonable With Early-State Return-Flow Moisture. Meanwhile Remaining Sref Members And Operational Progs Appear Too Aggressive With Return Flow Once Again...Considering Antecedent Fropa And Low-Level Ridging Over Gulf.

Spotty Areas Of 50s F Sfc Dew Points Are Possible Across Plains States E Of Lee Troughing. This May Be Enough To Support High-Based/Late-Aftn Tstm Development Beneath Steep Midlevel Lapse Rates...Along And E Of Lee Trough Over Portions Ks/Neb/Sd.

Narrow Corridor Of Elevated Low-Level Waa And Moisture Transport May Contribute Enough Moisture/Lift To Support Elevated Tstm Development Late In Period Over Portions Ks/Neb...Ern Sd And Perhaps Wrn Mn As Well. However...In Each Instance...Strongest Midlevel Winds And Deep Shear Related To Wrn Conus Cyclone Still
Will Be Displaced From These Regions.

Great Basin...

Large Area Of At Least Isolated To Widely Scattered Diurnal Tstm
Potential Is Evident Over Wrn Conus. Steep Midlevel Lapse Rates
Accompanying Nrn Portion Of Cold-Core Region Of Cyclone Aloft ...Juxtaposed With Mrgl Low-Level Moisture And Pockets Of Diabatic Sfc Heating Of Higher Terrain...Should Concentrate Convection. Potential For Small Hail Exists In Some Tstms...But Buoyancy Appears Too Limited For More Organized Threat.

Srn Conus...

Broad Area Of Mrgl Tstm Risk Is Apparent Around Persistent
Deep-Layer Cyclone. Pockets Of Sfc Diabatic Heating And Relatively
Cold Air Aloft Will Support Convective Potential In Most Sectors Of
Cyclone Where Mrgl Moisture/Buoyancy Is Possible. Nern Sector Will
Contain Weakest Lapse Rates...But Also Deep Wly Fetch Of Atlc Waa
Conveyor Above Sfc...Supporting Sporadic Thunder Potential.


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