Severe Weather Threat thru Dec 26

Thu Dec 19 Convective Outlook
No Svr Tstm Areas Forecast...

Southern Ca...

A Vigorous Shortwave Trough Is Digging Southward Along The Central Ca Coast. The Pocket Of Cold Temperatures Aloft And Steep Mid Level Lapse Rates Will Overspread Portions Of Southern Ca This
Afternoon...Providing Potential For Scattered Showers And Isolated
Thunderstorms. Small Hail Will Be Possible In The Stronger
Cells...But No Organized Severe Weather Is Expected.


Later This Evening...Increasing Large Scale Forcing For Ascent Will
Spread Into Portions Of Az...Where Another Round Of Showers And
Thunderstorms Will Be Possible.


Increasing Low Level Moisture Will Eventually Lead To Very Weak Cape Over Parts Of The Arklatex Region Late Tonight. However...It
Appears That Any Organized Thunderstorm Activity Will Likely Wait
Until After 12z Fri.

Otherwise...Dry/Stable Conditions Should Preclude Thunderstorms


Fri Dec 20 Convective Outlook
No Svr Tstm Areas Forecast...

A Progressive/Split Large Scale Pattern Will Exist Over The Conus On
Friday...Highlighted By Extensive Cyclonic Upper Flow Over Much Of
The Conus And The General Eastward Advancement Of A Potent Upper Trough/Polar Jet Over Northwest Mexico. Air Mass Modification Will Steadily Occur Especially Over The South-Central Conus...With An
Increasing Moist Boundary Layer Becoming Established Along/South Of A Frontal Zone From Parts Of Tx/Arklatex Northeastward Into The
Lower Oh River Valley.

Portions Of Tx/Arklatex...

As Southern High Plains Cyclogenesis Gradually Occurs Friday...The
Primary Surface Boundary Will Stall/Orient Southwest-Northeastward
From Southwest Tx To The Oh Valley...With A Frontal Wave/Surface Low Moving Eastward Across The Midwest/Oh Valley. Within The Nearby Warm Sector...Lower To Middle 60s F Surface Dewpoints Will Become Increasing Prevalent Across The Southern Half Of Tx And Adjacent Arklatex/Lower Ms River Valley.

In Spite Of Increasing Boundary Layer Moisture...The Majority Of The
Region Will Be Influenced By Weak Overall Forcing And Subtle Height
Tendencies /If Not Weak Height Rises/...At Least Through The
Daylight Hours. This Scenario...With An Increasingly Stout Elevated
Mixed Layer Across Tx...Should Generally Cap The Warm Sector With
The Possible Exception Of Friday Night Immediately Near The Front.

As Gradual Height Falls Begin To Influence Tx Friday Night Via The
Northwest Mexico/Southwest States Upper Trough...A Strengthening Low Level Jet/Associated Isentropic Uplift Focused Near/North Of The
Regional Surface Frontal Zone Will Result In A Nocturnal Increase Of
Tstms. This Includes A Corridor From Southwest/Central Tx
Northeastward To The Arklatex/Ozarks.

A Couple Of Near Surface-Based Storms Cannot Be Entirely Discounted Near The Front...But The Most Probable/Dominant Scenario Will Be For Storms To Develop/Increase On The Immediate Cool Side Of The Surface Front...With Storms Generally Rooted Above A Relatively Cool/Stable Boundary Layer. Strong Shear Through The Cloud Layer/Sufficient Elevated Instability Suggest That
Marginally Severe Hail May Occur With A Few Of The Storms.

In Spite Of Increasing Deep Layer Shear/Lengthening Low-Level
Hodographs...Any Severe Wind Gust And/Or Brief Tornado Potential
Will Be Contingent Upon Near Surface-Based Development Within The Warm Sector Friday Night...Which Appears Relatively Low/Uncertain At This Time.


Sat Dec 21 Convective Outlook
Slgt Risk Of Svr Tstms For Wrn/Cntrl Gulf Coast...Arklatex...Lower Ms Valley...

A Vigorous Upper Trough Will Eject Newd From The Srn Rockies And
Acquire A Negative Tilt As It Crosses The Great Plains Into The Mid-Ms Valley.

A Sfc Low Associated With This Feature Will Deepen Over Cntrl Tx And Track Newd Into Ar By Late Afternoon Along A Stalled Antecedent Front...Before Approaching The Great Lakes By Early Sun Morning.

A Cold Front Will Move Ewd Out Of E Tx Across The Wrn/Cntrl Gulf States...Which Is Likely To Be Accompanied By An Organized Convective Line Into Early Sun Morning.

Parts Of The Wrn/Cntrl Gulf Coast...Arklatex...Lower Ms Valley...

Convection Is Expected To Be Ongoing At The Start Of The Period
Along A Stalled Front Extending From Cntrl Tx Newd Across Ar To The
Lower Ms Valley...Aided By Isentropic Ascent Along The Nose Of A
Strong Low-Level Jet.

Meanwhile...A Sfc Low Is Forecast To Deepen As It Progresses Newd Out Of Cntrl Tx Towards Ar...And An Attendant Cold Front Will Extend Ssewd.

As Deep-Layer Forcing For Ascent Increases Via Midlevel Height Falls /Dcva...Additional Tstm Development Is Likely To Occur Along The Cold Front Across E Tx By Early Afternoon.

Mid-Upper 60s F Dewpoints Will Already Be In Place Early Sat Morning Throughout The Warm Sector. Widespread Cloud Cover May Limit Diurnal Heating And Destabilization...But Rich Boundary Layer Moisture And Moderate Lapse Rates Will Likely Yield Mlcape Values Generally Ranging From 1000-1500 J/Kg.

Further Strengthening Of The Low-Level Jet Is Also Forecast To Occur Throughout The Day...Resulting In Enlarged Hodographs. Significant Meridional Component To The Deep-Layer Flow Combined With Strong Low-Level Frontal Convergence And Upper Forcing For Ascent Will Likely Favor A Linear Convective Mode Evolving Along The Cold Front.

The Primary Threats Associated With This Likely Will Likely Be Dmgg Wind Gusts And Possibly A Few Embedded Tornadoes.

Isolated Tstms May Also Develop Within The Pre-Frontal Warm Conveyor...With Deep-Layer Shear Sufficient For Supercells And A Few Tornadoes.

Latest Forecast Model Guidance /Nam In Particular/ Is Inconsistent
With The Speed Of The Upper Trough And Associated Synoptic-Scale

However...The Most Probable Scenario Is For An Mcs To Evolve And Quickly Spread Ewd Through The Lower Ms Valley And Across Tn/Ms Into Early Sun.

With The Primary Sfc Low And Upper Trough Pulling Newd Away From The Region...Instability Will Likely Decrease With Ewd Extent...But Should Remain Sufficient To Maintain Strong-Svr Wind Gusts And Potentially An Isolated Tornado Threat Overnight.


Dec 22-26 Convective Outlook

Portions Of The Southeast And Mid-Atlantic...

Widespread Showers/Tstms /Most Likely In The Form Of A Pre-Frontal
Convective Line/ Will Be Ongoing At The Start Of The Period From The
Oh/Tn Valleys Swd Towards The Cntrl Gulf Coast.

The Primary Upper Trough And Sfc Low Will Continue Ejecting Newd Away From This Area...But An Associated Low-Level Jet Will Extend Down To The Gulf Coast And Should Persist Across The Southeast Into The Afternoon/Evening.

Despite Modest Midlevel Lapse Rates...Rich Boundary Layer Moisture Will Yield Mlcape Values Around 500 J/Kg Over Cntrl/Ern Gulf Coast States...Decreasing With Nwd Extent.

This Should Be Sufficient To Maintain Some Semblance Of A Convective Line Ewd Throughout The Day...Including Parts Of Al/Ga And The Appalachians/Carolinas.

Low-Level Shear Will Likely Be Sufficient For Strong-Svr Wind Gusts And Perhaps An Isolated Tornado Threat...Primarily Over Al/Ga And Perhaps Parts Of Middle/Ern Tn.

A Lower-End Wind Threat Could Extend N Of This Area As Well.

Mid-/Upper-Level Forcing For Ascent Will Be Quite Weak In The Wake
Of The Lead Upper Trough Moving Across The Great Lakes...And Well
Downstream From A Positive-Tilt Trough Over The Great Plains.

With The Lack Of Focused Synoptic-Scale Lift And The Likelihood Of Only A Marginally Unstable Air Mass...A 30 Percent Probabilistic Area Will Not Be Delineated Attm.

Immediate Coastal Areas Of The Sern Atlantic And Mid-Atlantic...

Showers/Tstms Could Persist Along/Ahead Of The Cold Front Through Late Morning...Primarily Along Coastal Areas Extending From Nrn Fl Into The Carolinas.

A Slight Strong Wind Gust Threat May Exist With This Activity With Moderately Strong Swly Deep-Layer Flow Persisting.

The Cold Front Is Expected To Mostly Be Offshore By Afternoon...With Exception To The Segment Farther S Over The Fl Peninsula.

Tue/D6 Through Thu/D8...

High Pressure Returns To Most Of The Nation Tue/D6 And Wed/D7.

Another Shortwave Upper Trough May Move Across Central Portions Of The Conus Thu/D8...But Moisture Return Ahead Of This System Is
Likely To Be Limited.

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