Severe Weather Threat Day 2 Sun Dec 16

Synopsis...

Broad Cyclonic Upper Flow Will Characterize The Synoptic Pattern
Sunday.

A Series Of Low Amplitude Progressive Shortwave Troughs Will Move Through This Regime. The Impulse Now Dropping Into Srn Ca Will Deamplify As It Continues Through The Oh Valley Sunday Morning. A More Substantial Srn Latitude Trough Will Move Into The Srn Plains During The Evening Before Reaching The Lower Ms Valley By Later Sunday Night.

A Cold Front That Should Stretch From A Weak Sfc Low Over The Great Lakes Sunday Morning Will Advance Sewd...Likely Extending From The Lower Great Lakes Swwd Into Nrn Tx By The End Of Period. Pacific Front Should Extend From Upper Great Lakes Swwd Through Ern Tx Sunday Morning And Subsequently Advance Through The Oh And Lower Ms Valley Regions.

Sern Tx Through Sern States...

Persistent Sly Low Level Winds Will Maintain Influx Of Modified Cp
Air Through The Sern U.S. With Sfc Dewpoints From Mid 60s Near The Gulf Coast To 50s Over The Tn Valley. Given Weak Lapse Rates And Limited Nwd Return Of The Richer Boundary Layer Moisture... Instability Will Likely Remain Marginal With Mlcape Aob 500 J/Kg.

Convection May Be Ongoing Sunday Along Conveyor Belt And Low Level Confluent Flow Regime From Sern Tx Into The Lower Ms Through Tn Valleys.

Most Of This Activity May Be Slightly Elevated Initially Except Possibly Over Sern Tx Into La. Continued Newd Advection Of Richer Moisture May Support Convection Becoming Sfc Based Later In The Day And Into The Overnight.

A Broad Swly Llj Will Shift Newd Through The Tn And Oh Valleys
During The Day With Weaker Low Level Flow Expected In The More
Unstable Portion Of The Warm Sector From Sern Tx Into La.

However...Most Of The Area Will Remain Embedded Within Strong Flow Aloft With Winds Increasing To 60+ Kt At 500 Mb With The Approach Of Srn Stream Mid Level Jet Supporting Strong 0-6 Km Shear.

Thunderstorms May Undergo Some Increase In Intensity During The Day From Sern Tx Into The Lower Ms Valley As The Boundary Layer
Destabilizes And In Association With A Deamplifying Srn Stream Wave.

A Stronger Shortwave Trough Will Move Into The Lower Ms Valley Later
Sunday Night With Attendant Strengthening Llj...Possibly Contributing To An Increase In Additional Convective Development Over The Gulf Coastal States.

A Marginal Thermodynamic Environment May Ultimately Serve As A Limiting Factor. However...Continued Moistening Of The Boundary Layer Coincident With Increasing Deep Layer Winds And Forcing For Ascent Will Support Potential For A Few Organized Storm Structures Including Bowing Segments With Embedded Supercells...Especially During The Evening Or Overnight Hours.

Oh Valley...

Despite More Limited Moisture Return With Only 40s Dewpoints
Expected...Cold Air Aloft /-20 C At 500/ And Diabatic Heating May
Contribute To At Least Weak Sfc Based Instability During The
Afternoon. Low Topped Convection Will Be Possible Ahead Of The Front Within A Strongly Sheared Environment. However...Coverage Of
Thunderstorms May Be Limited...As Current Indications Are That This
Region May Remain In Wake Of Deamplifying Lead Shortwave Trough
During The Day. Given Uncertainties Regarding Thunderstorm Coverage And Potential For Weak Instability...Will Maintain 5% Severe
Probabilities At This Time...But Continue To Monitor For A Possible
Slight Risk In Later Outlooks.


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