Severe Weather Threat Day 3 Sun Dec 9

Synopsis...

The Spread Among The Models And Model Ensembles Continues To
Increase Concerning Short Wave Developments Within Larger Scale
Troughing Encompassing Much Of The Interior Of North America During This Forecast Period. However...Most Guidance Does Indicate That At Least Some Phasing Of Embedded Impulses Will Lead To Sharpening Of The Upper Trough Along A Positively Tilted Axis Extending From Northwest Ontario Through The Texas Big Bend/Adjacent Mexican Plateau Region By 12z Monday.

This Is Forecast To Coincide With The Southeastward Advancement Of A Cold Intrusion Through Much Of The Remainder Of The Plains/Mississippi Valley...Into The Western Gulf Coast Region...And Significant Surface Cyclogenesis...Mainly Across Parts Of The Great Lakes Region Into Southern Ontario Late In The Period.

Aided By The Northward Advection Of Precipitable Water On The Order Of 1.0 To 1.25 Inches Along And Just Ahead Of The Front... Large-Scale Forcing For Upward Vertical Motion And Destabilization Probably Will Support Considerable Thunderstorm Activity From Portions Of The Southern Plains Into The Lower Ohio And Tennessee Valleys.

Parts Of Cntrl/Ern Texas Into Lwr Ms Valley...

Substantive Differences Exist Among The Models Concerning Surface
Cyclogenesis...But Primary Strengthening Of The Associated 850 Mb
Jet Appears Most Probable Across The Ohio Valley Into The Lower
Great Lakes Region Sunday Night. However...Deeper Layer Flow Fields And Shear Will Likely Still Be Strong Along The Front As Far South As The Rio Grande Valley. And Some Strengthening Of Southwesterly Pre-Frontal 850 Flow /To Around 30-40 Kt/ Appears Possible Across The Southern Plains Through The Lower Mississippi Valley...As A Short Wave Impulse Within The Base Of The Larger Scale Trough Begins To Accelerate East Of The Southern Rockies.

Variability Exists Among The Models And Model Ensembles When And How This Occurs...But It Does Not Appear Out Of The Question That Strengthening Of Forcing For Upward Vertical Motion Downstream Could Contribute To Initiation Of Storms To The Warm Side Of The Front By Sunday Evening.

At The Present Time...This Seems Most Probable Across Parts Of The Arklatex And Southern/Eastern Arkansas. In The Presence Of Moist Low-Levels With Modest Mixed Layer Cape Of 500 To Perhaps 1000+ J/Kg...It Does Not Appear Out Of The Question That Forcing And Strong Generally Unidirectional Shear Could Support The Evolution Of A Southeastward Advancing Squall Line Overnight.

This Will Include Potential For Severe Wind/Hail...Perhaps An
Isolated Tornado Or Two...But Lingering Uncertainties Remain Too
Large To Include An Outlook Of Slight Risk Probabilities.


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