Severe Weather Threat Day 1 Wed May 22

The Prominent Blocking Pattern Now Present Across Much Of Western And Central North America May Begin To Weaken During This Forecast Period.

As A Significant Short Wave Trough Continues To Dig Southeast Of The Hudson Bay Region...The Closed Low Over The Upper Mississippi Valley Appears Likely To Transition To An Open Wave And
Shift Eastward Into The Ohio Valley.

A Smaller Scale Impulse Currently Pivoting Around The Southern/ Eastern Periphery Of This Remnant Cyclonic Circulation Is Expected To Shift Northeastward Toward The Upper Ohio Valley And Lower Great Lakes Region Through Late Afternoon...Before Weakening And Becoming Increasingly Sheared Within A Confluent Regime Into The Canadian Maritimes.

At The Same Time...
Little Movement Is Expected With A Large And Cold Mid/Upper Low Now Centered Over The Northern Pacific Coast States. While Some Deviation Of The Circulation Center Is Likely...This Will Mostly Be In Response To Short Wave Impulses Rotating Around Its Periphery.

Oh/Tn Valleys Into The Lower Great Lakes And New England...

Extensive Convection And Associated Outflow From Yesterday Has
Impacted A Significant Portion Of The Warm Sector Of The Surface Low Now Centered Over The Upper Midwest...From The Mississippi Valley Eastward To The Appalachians. And The Focus For Storm Development Later This Afternoon And Evening Remains A Bit Unclear.

However...Models Continue To Suggest Strengthening Of Lower/Mid
Tropospheric Flow Fields /To Around 40 Kts Or So/ In A Southerly
Belt Across Parts Of The Upper Ohio Valley Into The Lee Of The Lower
Great Lakes By Late This Afternoon...Which Should Enhance Any Storm Development Occurring In The Peak Heating.

Shear Will Be Sufficient For Organized Storm Development...Which May Eventually Consolidate Into Clusters Or Lines With An Enhanced Risk For Damaging Wind Gusts. But Discrete Storm Development Also Will Be Possible...Particularly Near The Crest Of Broader Scale Upper Ridging Across Upstate New York...Where Mid/Upper Flow Will Be Slower To Back To A Southerly Direction. Mid-Level Lapse Rates
Appear To Have Stabilized Some Over The Past Day Or So...But Severe Hail Still Seems Possible...Along With A Risk For One Or Two
Tornadoes...Before Storms Weaken By Late Evening.

Northern Rockies...

Moisture Appears Marginal For Vigorous Storm Development...But
Stronger Heating Along An Axis From Northeast Wyoming Through
Western Montana May Contribute To Sufficient Destabilization For
Scattered Storm Development This Afternoon. Orographic Lift Will Be
Aided By Large-Scale Ascent Beneath Strongly Difluent And Divergent
Upper Flow. Given The Favorable Shear Beneath Strong Cyclonic
Mid/Upper Flow...It Does Not Appear Completely Out Of The Question
That Instability On A Very Localized Basis Could Become Enough For A Supercell Or Two With The Risk For Severe Hail Or Wind.


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