Severe Weather Threat thru Nov 23

Sat Nov 16 Convective Outlook
Slgt Risk Of Svr Tstms For Parts Of Lwr Mo And Mid Ms Vlys...

Fast Cyclonic Flow Will Prevail Across The Lwr 48 Through Early Sun
As Strong Jet Streaks Now Over The Gulf Of Ak And Wa/Id Progress
Rapidly Ese To Amplify Existing Broad Trough Over Cntrl North
America.

This Pattern Will Maintain And...Later In The Period...Strengthen Strong Low Lvl Jet Stream Now In Place From The Srn Plns To The Upr Grt Lks.

At The Sfc...Loosely-Organized Low Pressure Now Covering The Cntrl / Nrn Plns Should Consolidate Over Ne Ks/Se Neb Late Tngt... And Move Into Ia Early Sun...As Wa Upr Impulse Reaches The Cntrl High Plns.

Persistent Waa/Moisture Transport Along The Low-Lvl Jet Stream... And Ascent Associated With Lead Upr Impulse Now Entering The Cntrl/Srn High Plns...Should Foster A Gradual Increase In Shower/ Tstm Coverage Through The Period Over A Broad Swath From The Srn Plns To The Upr Grt Lks.

Some Of This Activity Could Become Svr...Especially Late Tngt And Early Sun...Over Parts Of The Lwr Mo And Mid Ms Vlys.

Lwr Mo To Mid Ms Vlys Today Through Early Sun...

Lead Shortwave Impulse/Elongated Band Of Ascent Now Extending From Wrn Ks Ssw Into Ern Nm Should Shear Ene Across The Cntrl/Srn Plns Today Before Weakening Over The Mid/Upr Ms Vly Tngt.

A Gradual Increase In Elevated Convection Should Occur To Its E During The Period...From Parts Of Ok Newd Into Il. While Elevated Buoyancy Will Slowly Increase With Time...Degree Of Instability Should Remain Weak...With Any Associated Svr Risk Limited To Marginally Svr Hail...Despite Strengthening Wind Field.

Farther Nw...A Window Of Opportunity Will Exist For A Few Sfc-Based
Storms Late This Aftn Into Early Tngt As The Band Of Ascent
Overtakes Nw Fringe Of Low-Lvl Moisture Return Over Nrn Mo/Srn Ia.

Relatively Cool Mid-Lvl Temps And 60+ Kt Wswly Deep Shear Atop Zone Of Low-Lvl Confluence Marking Wrn Edge Of The Sswly Llj Could Support A Supercell Or Two With A Risk For Svr Hail/Wind...And
Possibly A Tornado. This Activity Should Weaken By Mid Eve As Upr
Impulse Continues Ene Away From Region And Diurnal Cooling Occurs.

A New Round Of Strong To Potentially Svr Tstms May Arise Later Tngt
Or...More Likely...Early Sun Over Srn/Cntrl Ia And Perhaps Adjacent
Parts Of Mo And Nw Il As Stronger Ascent And Mid-Lvl Cooling
Associated With The Jet Streak Now Over Wa/Id Approach The Region.

Combination Of Strengthening Winds /With 500 Mb Speeds Increasing To Around 75 Kts/...Moistening Low-Lvl Environment /With Sfc Dewpoints Increasing To Around 60 F/...And Convergent Low-Lvl Flow Invof Deepening Sfc Low Together Suggest A Conditional Potential For Supercells With Svr Hail...Wind...And A Couple Tornadoes.

Arklatex To Lwr Oh Vly Later Today Through Early Sun...

Increasing Moisture Within Confluence Zone On Ern Side Of Persistent Low-Lvl Jet Stream Expected To Support The Eventual Development Of An Extensive Band Of Loosely-Organized Showers/Tstms From Ne Tx/Sw Ar Newd Into Se Mo And The Lwr Oh Vly Later Today And...Especially...Tngt/Early Sun.

While Much Of This Activity Will Remain Somewhat Elevated... Especially With Newd Extent...By Late Tngt/Early Sun Some Of The Storms Could Become Nearly Sfc-Based Across Ern Ar/Far Se Mo Into Far Srn Il...Sw Ind...Wrn Ky...And Wrn Tn.

Large-Scale Forcing For Ascent/Dcva Will Remain Minimal. Nevertheless...Given Strengthening Wind Field On Se Fringe Of Upr
Trough Amplifying Across The Cntrl Plns/Mid Ms Vly...Some Risk May
Develop For Embedded Circulations/Lewps. Such Activity Could Pose A Conditional Risk For A Tornado And/Or Locally Dmgg Wind...Especially Late In The Period.

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Sun Nov 17 Convective Outlook
Mdt Risk Of Svr Tstms for Extreme Ern Il to Ind...Oh...Srn Mi & Nrn Ky...
Slgt Risk Of Svr Tstms for Great Lakes..Oh & Tn Valley..Nern & S Ctrl States...

A Strong Upper Jet Now Evident In Satellite Imagery Dropping Sewd
Into The Pacific Nw Will Continue Through Base Of Synoptic Scale
Trough.

Attendant Shortwave Trough Will Eject Negatively Tilted Through The Mid Ms...Oh Valleys And Great Lakes Sunday...Reaching Wrn Portions Of The Nern U.S. Toward The End Of This Period.

This Feature Will Induce A Sfc Cyclone That Is Forecast To Undergo
Significant Deepening As It Moves From The Upper Ms Valley Into The
Great Lakes By Sunday Afternoon.

Cold Front Trailing From The Low Will Sweep Through The Mid Ms...Oh And Tn Valleys...While A Warm Front Lifts Nwd Through The Great Lakes.

Oh And Tn Valleys And Great Lakes Regions...

Potential Exists For A Widespread Damaging Wind Event And A Few
Tornadoes Sunday Afternoon And Night...Especially In And Near The
Moderate Risk Area Across Parts Of The Oh Valley And Great Lakes.

Current Observations Show Dewpoints Rising Into The Mid 60s Along
Coastal Tx With 70 Not Far Offshore.

A Strong 50+ Kt Sswly Llj Will Advect Partially Modified Gulf Air With Low 60s Dewpoints As Far North As The Oh Valley With Mid 60s Farther South Across The Tn Valley. However...The Moisture Return Will Be Accompanied By Widespread Clouds That Will Limit Diabatic Warming In Much Of The Pre-Frontal Warm Sector.

It Still Appears Probable That Areas Of Showers And A Few Thunderstorms Will Be Ongoing Along Warm Conveyor Belt Sunday Morning. Thus...The Primary Destabilization Mechanism Will Be Low-Level Theta-E Advection Beneath A Plume Of Ewd Developing 7-7.5 Mid-Level Lapse Rates. In Wake Of Warm Advection Storms... An Axis Of Mlcape From 500-1500 J/Kg Will Likely Develop In Pre-Frontal Warm Sector.

The Deepening Cyclone Will Be Accompanied By An Increase In
Frontogenetic Forcing Along The Cold Front Sweeping Ewd Through The Great Lakes And Oh Valley.

Storms May Redevelop By Afternoon Along Pre-Frontal Warm Conveyor Belt Beneath Diffluent Upper Jet Exit Region As The Atmosphere Destabilizes.

Should Sfc Based Warm Sector Initiation Occur...80+ Kt Mid-Level Wswly Winds Will Promote Fast Moving Storms That Should Remain Ahead Of Advancing Cold Front.

These Storms Will Likely Be Discrete Where Large Hodographs And 50+ Kt Effective Bulk Shear Will Promote Supercells Capable Of Producing Large Hail And Tornadoes. However...Degree Of The Tornado Threat /Should These Storms Develop/ Will Depend On Magnitude Of Destabilization Within The Warm Sector Boundary Layer.

Otherwise...Storms Should Initiate Along Strengthening Cold Front
From The Great Lakes Swwd Into The Mid Ms And Tn Valleys And
Subsequently Develop Ewd.

Given Strength Of Vertical Shear...These Storms Will Likely Evolve Into An Organized Linear Mcs With Lewp And Bow Echo Structures Capable Of Producing Widespread Damaging Wind. Isolated Tornadoes Associated With Embedded Meso-Vortices Also Will Be Possible With The Squall Line.

Nern U.S....

Storms Will Eventually Outpace The Axis Of Richer Low Level Moisture
Later Sunday Night And Encounter Much Weaker Instability As They
Approach The Nern States. However...Some Threat For Damaging Wind May Persist With Remaining Low Topped Convection Late This Period.

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Mon Nov 18 Convective Outlook
No Svr Tstm Areas Forecast...

Negative Tilt Shortwave Trough Will Continue Newd Through The Nern States And Sern Canada Monday.

By 12z Monday The Attendant Occluded Sfc Low Will Reside Over Sern Canada. Trailing Cold Front Extending Swwd Through The Nern U.S. Into The Gulf Coast States And Srn Tx Will Move Off The Atlantic Seaboard Monday Morning While Swrn Extension Of This Boundary Continues Swd Into The Gulf.

Srn New England...

A Forced Low Topped Line Of Convection With Little To No Lightning
Will Likely Be In Progress Along The Cold Front Across New England.
This Convection Will Be Embedded Within Meager Cape But A Very
Strong Kinematic Environment Along A 60+ Kt Llj. At Least A Low End
Threat For Damaging Wind Will Persist With This Activity As It
Continues Ewd And Offshore...Especially Over Srn New England Where Instability Will Be Slightly Greater.

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Nov 19-23 Convective Outlook

A Large Area Of Cp High Pressure Will Move Through The Ern Half Of
The U.S. Days 4 Into Day 5 Maintaining Stable Conditions Inland.

By Late Day 5 Into Day 6...Moisture Will Begin Returning Nwd Through
Tx As A Lee Trough Becomes Established Over The Plains In Wake Of Retreating High Pressure. However...Models Become Dispersive With Evolving Split Flow Pattern And Especially With The Handling Of A Srn Stream Upper Trough.

In Contrast To The Gfs's More Progressive Srn Stream...Ecmwf And Several Ensemble Members Cutoff A Srn Stream Upper Low Over The Swrn U.S. While Maintaining A Progressive Nrn Stream Trough.

This Would Allow A Polar Front To Advance Into The Srn Plains Late Day 6 Into Day 7.

While Thunderstorms May Develop As This Boundary Interacts With The Moistening Boundary Layer Over The Srn Plains...Upper Pattern Would Not Be Favorable For An Organized Severe Event If Srn Stream Upper Low Cuts Off Over The Swrn States.


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