Severe Weather Threat Day 2 Sun Dec 9

Synopsis...

Within Large-Scale Upper Troughing Encompassing Much Of Interior
North America...It Still Appears That Some Phasing Of Embedded Short Wave Impulses Will Lead To Sharpening Along A Positively Tilted Axis Extending From Northwestern Ontario Through The Texas Big Bend Region By 12z Monday.

Sizable Spread Persists Among The Models And Model Ensembles Concerning The Details Of The Short Wave Developments...But It Appears That The Lead Impulse Shifting East Of The Northern Plains Early In The Period May Remain Most Prominent As It Continues East Northeastward Across The Upper Midwest And Great Lakes Region.

This Feature Is Expected To Support Primary Surface Cyclogenesis ...Mainly East Of The Middle Mississippi Valley Into Southern Ontario Late In The Period.

A Significant Cold Intrusion Probably Will Surge More Rapidly Southward Through The Southern Plains Than Eastward Into The Lower Mississippi Valley...As A Southerly Return Flow Off The Western Gulf Of Mexico Contributes To Pre-Frontal Moistening.

A Narrow Corridor Of Precipitable Water In Excess Of 1 Inch May Reach The Upper Ohio Valley/Lower Great Lakes Region By Late Sunday Night...With Values Of 1.25 To 1.5 Inches Across The Western Gulf Coast Into The Lower Mississippi Valley.

Coupled With Increasing Forcing For Upward Vertical Motion... Destabilization Probably Will Be Sufficient To Support Considerable Thunderstorm Activity From Portions Of The Southern Plains Into The Lower Ohio And Tennessee Valleys...And Perhaps Parts Of The Lower Great Lakes Region.

Cntrl/Srn And Ern Ar...Ne Tx...Nrn La...Nwrn Ms...Wrn Tn...

Although South/Southwesterly Low-Level Jet Strengthening Likely Will
Be Strongest To The Northeast Of The Region Late In The Period... Modest Strengthening Of 850 Mb Flow To 30-40 Kt Still Appears Possible Across Parts Of The Arklatex Region Into Upper Portions Of The Lower Mississippi Valley Sunday Evening.

This Is Expected To Occur As A Short Wave Impulse /Likely Digging Upstream Through Much Of The Day Sunday/ Finally Begins To Accelerate East Of The Southern Rockies. This May Also Contribute To An Increasingly Divergent Upper Flow Field Across Southern/ Eastern Arkansas And Adjacent States...Where Vertical Shear And Forcing For Upward Vertical Motion May Support Squall Line Evolution.

A Window Of Opportunity Appears To Exist For Potentially Damaging Wind Gusts...As Well As Large Hail...Before Activity Spreads Into A Less Stable Environment To The East And Weakens Overnight.

Peak Boundary Layer Destabilization Is Expected During The Late
Afternoon And Early Evening Hours Along A Pre-Frontal Corridor
Across The Arklatex Into Central Arkansas. Before Stronger Forcing
Develops...Scattered Discrete Storm Development Is Possible In The
Presence Of 500-1000 J/Kg Of Mixed Layer Cape. Forecast Soundings Are Suggestive Of Strong...But Mostly Unidirectional Vertical Shear. However...Low-Level Hodographs May Become Sufficiently Large To Support At Least Some Tornadic Potential.


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