Severe Weather Threat Day 2 Thu Apr 11

To The South Of A Prominent Higher Latitude Block...Models Suggest
That Upper Troughing Encompassing Much Of The Interior Of The U.S. Will Persist...But Cyclonic Flow May Begin To Become Less Amplified During This Forecast Period.

Only A Slow Eastward Progression Of A Mid-Level Closed Low From The Mid Missouri Valley Into The Upper Midwest Is Forecast Thursday And Thursday Night. But...A Significant Short Wave Impulse...Now Digging Into The Base Of Larger Scale Troughing Across The Northern Mexican Plateau...Appears Likely To Accelerate East Northeast Of The Lower Rio Grande Valley Through The Central/Southern Appalachians/Mid Atlantic Region By 12z Friday.

Uncertainty Lingers Concerning Timing...But The Most Rapid
Acceleration May Occur East Of The Lower Mississippi Valley Thursday Evening Into The Overnight Hours. As This Occurs...Increased Coupling Of An Associated 500 Mb Jet Streak With A Strengthening 850 Mb Speed Maximum Appears Probable Across The Eastern Gulf States Into The Carolinas...Accompanied By Secondary Frontal Wave Development Across Southeastern Mississippi And Central Alabama Into The Lee Of The Southern Appalachians.

Models Also Suggest That There Will Be Continued Slow Deepening Of The Primary Surface Cyclone Across Southern Portions Of The Great Lakes Region...West Of The Appalachians.

The Trailing Cold Front Is Expected To Advance East Of The Mississippi Valley...Into The Vicinity Of The Appalachians By The End Of The Period...As A Significant Preceding Intrusion Of Cold Air Is Slow To Modify Across The Lower Great Lakes Region And Much Of The Northeast.

Lwr Oh/Tn Valleys And Cntrl/Ern Gulf States Into Carolinas...

Deep Layer Shear Is Expected To Become More Than Sufficient For
Severe Storms Within The Warm Environment Encompassing A Large Portion Of The Eastern U.S...Ahead Of The Front Advancing East Of The Mississippi Valley...And South Of The Stalling Front Across The Upper Ohio Valley And Mid Atlantic Coast Region.

Some Aspects Of The Evolving Large Scale Pattern Appear Favorable For A More Significant Severe Weather Outbreak Than Indicated By The Current Categorical And Probabilistic Outlooks.

However...One Prominent Potential Limiting Factor Evident In Model Forecasts Is The Continuing Presence Of Drier Pockets Within The Warm Sector Into The Day Thursday...Particularly In The Boundary Layer...East Of The Central Appalachians...And Across The Cumberland Plateau Southward Into Eastern Gulf Coastal Areas. While This May Modify Some On Southerly Low-Level Flow...Richer Boundary Layer Moisture Characterized By Upper 60s/70s Dew Points Is Not Expected Inland Of Immediate Gulf Coastal Areas During This Period.

Early Period Pre-Frontal Convection And Associated Cloud Cover
Provide Additional Uncertainty Concerning Destabilization...
Particularly Across The Lower Ohio/Tennessee Valleys. However... At
Least A Narrow North/South Corridor Of Weak To Moderate Boundary
Layer Based Destabilization Appears Probable During The Peak
Afternoon Heating. In The Presence Of Wind Profiles...Which
Forecast Soundings Suggests Could Exhibit Pronounced Low-Level
Hodograph Size And Clockwise Curvature...Strong/Severe Storms Appear Probable...Including The Risk For At Least A Few Discrete Supercells Capable Of Producing Tornadoes And Large Hail.

Farther South...Probabilities For The Evolution Of An Organized
Severe Mesoscale Convective System Appear Higher As Forcing/Shear Increases In Association With The Accelerating Short Wave Impulse ... Across Alabama/Georgia By Early Thursday Evening. This May Be Accompanied By A More Substantive/ Widespread Damaging Wind Threat. Tornadoes And Large Hail Will Also Be Possible With This Activity.


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