Severe Weather Threat thru Dec 14

Sat Dec 7 Convective Outlook
No Svr Tstm Areas Forecast...

Water Vapor Imagery Depicts An Elongated Warm Conveyor Belt That
Extends Across Nrn Mexico Into The S-Cntrl Conus And Then Newd Off The Mid Atlantic Coast On The Srn/Ern Periphery Of A Longwave Trough Covering The Wrn/Cntrl Conus.

A Plume Of 1.2-1.5-Inch Pw And Marginal Elevated Buoyancy Coinciding With The Warm Conveyor Is Supporting Scattered To Numerous Showers From Srn Al Newd To The Carolinas. An Isolated Thunderstorm Or Two Cannot Be Ruled Out With This Activity For This Morning Within An Anafrontal Flow Regime.

However...Thermodynamic Profiles Will Become Progressively More
Hostile For The Maintenance Of Deep Convection/Thunderstorm
Potential Following The Departure Of A Mid-Level Shortwave Trough
Off The New England Coast.

Upstream...A Low-Amplitude/Low-Latitude Impulse Currently Crossing The Nrn Gulf Of California Will Advance Enewd Through The Period. The Low-Level Response Will Favor A Ribbon Of Increasing Poleward Mass Flux Within The 850-700-Mb Layer From S Tx Newd To The Tn And Oh Valleys For Tonight.

In Turn...Strengthening Isentropic Ascent Is Forecast To Support A Blossoming Of Scattered Elevated Convection From The Mid South Enewd To Srn Ky. Forecast Soundings Suggest That Marginal Buoyancy -- Rooted Above The Sfc-Based Cold Dome That Has Become Established Across A Large Part Of The Conus -- Could Support Isolated Elevated Thunderstorms With This Activity. This Would Mainly Occur During The Overnight Hours Tonight. Limited Buoyancy And Weak Effective Deep Shear Will Preclude Any Svr-Thunderstorm Risk.

A Mid-Level Shortwave Trough Advancing Across The Cntrl Great Basin To The Cntrl Rockies Will Enhance Precipitation From Nv Ewd To Co...Though Limited Buoyancy Will Likely Preclude Any Thunderstorm Potential With This Activity.

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Sun Dec 8 Convective Outlook
Storm Prediction Center Norman Ok
No Svr Tstm Areas Forecast...

A Large/Longwave Trough Over Central Noam Will Make Gradual Ewd/Sewd Progress This Period...As One Embedded/Smaller-Scale Feature Ejects Newd Across The Central U.S. While A Second Digs Swd Out Of Canada And Across The Wrn Portion Of The Country.

Meanwhile...A Zone Of Fast Swly Flow Aloft Will Extend From The S
Central U.S. Newd Across The Ern Half Of The Country -- Along The
Ern Fringe Of The Main Trough.

As A Reinforcing Surge Of Continental Air Spreads Sewd Across The S Central And Sern States...Very Weak Low-Level Warm Advection / Isentropic Lift Across The Lower Ms/Tn Valley Region May Support Showers And A Few Embedded/Elevated Thunderstorms. Lack Of
Appreciable Cape...However...Precludes Virtually Any Severe Risk.

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Mon Dec 9 Convective Outlook
Storm Prediction Center Norman Ok
No Tstm Areas Forecast...

A Very Large/Positively Tilted Upper Trough -- Whose Axis Is Progged
To Extend From Central Canada And The N Central U.S. Swwd Into The Desert Sw Early In The Period -- Is Progged To Continue Shifting
Gradually Ewd With Time...While Several Smaller-Scale Features
Progress Through The Larger-Scale Flow Field.

With Cold Continental Air Prevailing Across The Majority Of The Conus ...Thunder Risk Should Remain Negligible In Most Areas.

One Exception Could Be Across The Southeast States...Mainly Within A Post-Frontal Regime Behind The Baroclinic Zone Shifting Across The Region. However...With Very Meager Instability And Likelihood That Convection Will Remain Low-Topped -- And Thus Likely To Produce Little Lightning...Will Not Highlight A 10% Thunder Area Attm.

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Dec 10-14 Convective Outlook
Storm Prediction Center Norman Ok

Medium-Range Models Depict A Slow Ewd Progression Of The Large-Scale Trough Affecting Most Of The U.S.

At The Start Of The Period. With Time...The Trough Is Forecast To Advance Across The Central And Ern Portions Of The Country -- As Multiple Smaller-Scale/Embedded Troughs Progress Through The Broader Cyclonic Flow Field.

Subtle Differences Exist Aloft Between The Different Models -- Even
At The Start Of The Period Where The Gfs Forecasts Weak Cyclogenesis Early Day 4 /Tue. 12-10/ Over The Sc Vicinity...Along A Baroclinic Zone Associated With An Advance Of Continental Polar Air Through The Southeast Portion Of The Conus.

Meanwhile...The Faster Ecmwf Shows This Boundary Farther To The Southeast...With No Frontal Wave Development Given The Subtly Different Orientation Of The Upper Troughing.

In Any Case...Any Severe Weather Risk Which May Evolve Onshore Near This Front -- And Possible Frontal Wave -- Would Be Quite Isolated At Best...Thus Not Requiring Areal Delineation.

After Day 4...As The Upper Trough Progresses Ewd And The Surface
Front Moves Off The Atlantic Coast...Any Severe Risk Should Likewise
Vacate The Conus.

As The This Trough Shifts Offshore Around Day 6...Model Differences Increase With Respect To A Srn Stream Trough Progged To Be Shifting Into The Swrn/S Central States.

Thus...Diminishing Forecast Confidence Will Extend Through The End Of The Period.


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