Severe Weather Threat thru Nov 27

Wed Nov 20 Convective Outlook
No Svr Tstm Areas Forecast...

Prevailing Zonal Flow Of The Past Two Days Will Become More
Amplified Over The Next 24-36 Hrs As A Positive-Tilt Split Flow
Pattern Gradually Becomes Established Over The West.

In The Mean Time...Upr Impulse Now Crossing The Cntrl Plns Should Continue Ne Toward The Upr Grt Lks Later Today As A Series Of More Poorly-Defined Upstream Disturbances Track Ene From The Srn Grt Basin Into The Srn/Cntrl Plns.

Moisture Return Will Continue Through The Period At Lwr Lvls From
Wrn/Srn Tx Nne Into Cntrl/Ern Ks...Wrn Mo...And The Wrn Ozarks. At
The Same Time...The Leading Edge Of A Shallow Polar Air Mass
Associated With A Passing Nrn Stream Disturbance Will Settle S
Across The Nrn Half Of The Plns.

Ern Tx Panhandle/Wrn-Cntrl Ok This Eve Through Early Thu...

In Wake Of Departing Cntrl Plns Impulse...Mid-Lvl Flow Will Back To
Swly Across The Srn And Cntrl Plns Today. In Response To Diurnal
Cycle And The Approach Of Upstream Disturbances Now Over The Grt Basin...Low-Lvl Sswly Flow Will Increase Tngt Across The Srn Plns ...With 850 Mb Speeds Increasing To Around 40 Kts From W Cntrl Tx Into Cntrl Ok.

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Thu Nov 21 Convective Outlook
No Svr Tstm Areas Forecast...

A Split Flow Regime Will Characterize The Synoptic Pattern Thursday
With An Upper Trough Dropping Swd Along The Wrn U.S. Coast And
Eventually Becoming Cutoff From The Nrn Stream While Evolving Into A Closed Low Over The Swrn States. Meanwhile...A Nrn Stream Trough Will Move Through The Nrn Plains And Upper Ms Valley Region. At The Sfc A Polar Front Will Surge Swd Into The Srn Plains. By The End Of The Period This Boundary Is Forecast To Extend From The Great Lakes Swwd Through Cntrl And Swrn Tx.

Srn Plains Area...

Sly Winds In Wake Of Retreating Sfc Ridge Will Advect 60s Boundary
Layer Dewpoints Through Tx With Low 60s Possible As Far North As Ok Thursday Afternoon.

Despite The Potential For Low Clouds Within The Moistening Warm Sector...An Axis Of Modest Instability /500-1500 J/Kg Mucape/ Will Likely Develop During The Afternoon. The Greater Instability Is Expected From Wcntrl Through Nwrn Tx Into Swrn Ok Where Ern Fringe Of Steeper Lapse Rates May Overtake Wrn Edge Of The Moist Axis And Where Some Diabatic Warming May Occur. A Belt Of 40-50 Kt Swly 500 Mb Winds Will Persist During The Day Across Nrn Tx Into Ok Resulting In 40-45 Kt Effective Shear...Though Flow In The 850-600 Mb Layer Is Expected To Weaken As Heights Rise In Wake Of An Ejecting Low Amplitude Shortwave Trough.

Storms Will Likely Initiate Along And Possibly Just Ahead Of The Swd Advancing Cold Front Across Ok And Then Swd Into Nwrn-Nrn Tx During The Afternoon And Evening.

Orientation Of The Winds Aloft With Respect To The Motion Of The Surging Front Suggests Storms Initiating On This Boundary Will Be Undercut. Some Of The Storms May Pose A Threat For Isolated Hail And Possibly Gusty Winds.

However...The Tendency For Storms To Be Undercut And Winds In The 850-600 Mb Layer To Weaken May Pose Limiting Factors For A More Robust Severe Threat.

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Fri Nov 22 Convective Outlook
No Svr Tstm Areas Forecast...

A Split Flow Regime Will Persist Through Friday. Closed Upper Low
Will Develop Slowly Swd...Becoming Situated Near Baja Ca...While A
Progressive Nrn Stream Trough Amplifies Across The Great Lakes.

A Shortwave Ridge Will Build Over The Srn Plains Downstream From The Evolving Swrn U.S. Upper Low Circulation. A Polar Front Should
Extend From The Lower Great Lakes Swwd Into Cntrl And Swrn Tx Early Friday. This Front Will Move Off The Tx Coast By Friday Night And
The Atlantic Seaboard Early Saturday.

Tx Through Lower Ms Valley Area...

A Moist And Modestly Unstable Pre-Frontal Warm Sector Will Reside
Across Scntrl And Srn Tx With 1000-1500 J/Kg Mlcape...But With Weak
Lapse Rates. Storms Will Likely Continue Developing Along The Swd
Advancing Front. However...Weak Vertical Shear Associated With A
Building Upper Ridge And The Marginal Thermodynamic Environment
Suggest The Threat For Severe Storms Should Remain Low.

Az...

Steepening Mid Level Lapse Rates Associated With Cold Temperatures Aloft Accompanying The Upper Low Circulation Will Promote Weak Instability As Boundary Layer Temperatures Warm During The Day.

Forcing For Ascent With Zone Of Upper Divergence East Of The Upper
Low Center Will Promote Development Of Thunderstorms From Srn Ca Into Parts Of Az. The Thermodynamic Environment And Vertical Shear From 30-40 Kt May Promote A Threat For Small To Marginally Severe Hail...Primarily During The Afternoon When Instability Will Be
Maximized.

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Nov 23-27 Convective Outlook
Storm Prediction Center Norman Ok

Days 4-6...Severe Potential Will Remain Low Through Day 6 Owing To A Couple Of Intrusions Of Cp Air Accompanying Expansive Areas Of High Pressure Building Sewd Through The Ern Half Of The Country.

Days 7-8...Though Some Timing And Amplitude Differences Still Exist ...Ecmwf...Gfs And Most Ensemble Members Have Generally Converged On Similar Solutions Regarding The Ejection Of Swrn U.S.
Upper Low Through The Gulf Coastal States.

Current Indications Are That This Wave Will Begin To Affect The Gulf Coast By Day 7.

The Attendant Cyclogenesis Should Result In A Return Of Partially Modified Gulf Air Into The Fl Panhandle...Srn Ga And Possibly The
Coastal Carolinas As The Low Redevelops Along The Sern Atlantic
Seaboard.

The Degree Of Any Severe Threat With This Ejecting Wave Remains Uncertain At This Time Frame Due To Lingering Questions Regarding The Quality And Extent Of Inland Moisture Return And
Resulting Instability.

However...This Area Will Continue To Be Monitored For A Possible Categorical Risk In Later Outlooks.


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