Severe Weather Threat thru Mar 22

Sat Mar 15 Convective Outlook
Storm Prediction Center Norman Ok
Slgt Risk Of Svr Tstms For E Tx/Arklatex To La & Ms Coast...

Upper-Air Pattern Will Be Dominated This Period By High-Amplitude
But Progressive Ridging...Moving Ewd From W Coast...And Large
Cyclonic Gyre Covering Much Of Ern Canada And Centered Over Hudson Bay.

E Of That Ridge--Two Shortwave Troughs Will Serve As Primary Mid-Upper Influences On Convective Potential Day-1...

1. Srn-Stream Perturbation Now Evident In Moisture-Channel Imagery
Over Ern Nm...Far W Tx And Chihuahua.

This Trough Will Lose Amplitude As Embedded 500-Mb Vorticity Max/Weak Circulation Ejects Enewd Across N-Central Tx/Extreme S-Central Ok Around 00z...Reaching Sern Ok/Swrn Ar/Ne Tx By End Of Period.

2. Nrn-Stream Trough Currently Moving Sewd Across Portions Srn Mt ...Wrn Wy And Ern Ut.

This Feature Will Turn Ssewd Across Srn Rockies And Intensify Considerably By 12z...Reaching Lower-Middle Pecos Valley And Portions N-Central Mex.

Cyclonic Flow Associated With These Features Will Broaden Across Srn Plains And Nrn Mex...With Height Falls Intensifying And Shifting
Slowly Ewd Across These Regions And Nwrn Gulf By End Of Period.

At Sfc...11z Analysis Showed Wavy/Quasistationary Frontal Zone From
Mo Bootheel Region Wswwd Across Ern/Swrn Ok...Nw Tx...Between
Lbb-Maf...And Over Sern Nm.

Warm Frontogenesis Was Evident From Between Dys-Cds Ewd Across Txk Area And Srn Ar.

Both Of These Boundaries Are Expected To Become Ill-Defined Today As Return Flow Occurs Ahead Of Separate Cold Front Moving Sewd Across Central High Plains...And Perhaps More Importantly...Growing Areas Of Clouds...Precip And Tstms Over Tx And Ok Reconfigure Boundary-Layer Baroclinicity Considerably On Mesoscale.

Srn Plains...Morning Through Evening...

Messy Scenario Evident With Scattered-Numerous Showers And Tstms Expected To Develop Through Remainder Morning/Early-Aftn Hours Across Portions W-Central/Nw/N-Central Tx And Much Of Ok...Offering Mrgl Wind/Hail Risk.

Additional Tstms Should Form Through Aftn Over Central Tx And Move/Spread Enewd....These Having Better-Organized Svr Threat.

This Process Will Occur As Large-Scale Ascent Aloft...Immediately Preceding Mid-Upper Trough...Becomes Increasingly Juxtaposed With Favorable Low-Level Thetae Advection.

Moisture Transport/Advection Already Underway Above Sfc Will Be
Manifest In Preconvective Sfc Environment By Nwd Spread Of 60s F Sfc Dew Points Now In Central/S Tx Toward Red River...And 50s That Have Reached Srn Ok.

Thick Middle-High Clouds Will Preclude Stg Sfc Diabatic Heating Across Much Of This Area...However...Combination Of Diffuse Insolation And Waa Will Boost Mlcape And Reduce Mlcinh Through Midday Into Aftn In Preconvective Air Mass.

Tstm Coverage Should Extend And Shift Ewd Across Nrn/Central Tx Through Aftn And Into Eve...As Inflow-Layer Air Mass Moistens.

Buoyancy Will Depend Strongly On Availability Of Localized Pockets
Of Enhanced/Sustained Insolation Over Central Tx...And Absence Of
Precip/Outflow Farther N...Near And N Of I-20.

Although Low-Level Winds Will Remain Weak Through Much Of Aftn...Limiting Hodograph Size...Wrn Rim Of Llj Will Enlarge Hodographs Around 00z And Thereafter For Any Sfc-Based Tstms Developing And Moving Ewd/Enewd From Central To E-Central/Ne Tx.

This Corridor Represents Most Probable Juxtaposition Of Favorable Buoyancy/Shear From Late Aftn Into Evening.

Farther S Into S Tx...Though Cape Will Be Greater...So Will Cinh...And Foci For Convective-Scale Lift Become More Unclear.

Se Tx To Ms Delta/Coast Regions...Tonight...

Attm It Still Is Uncertain Whether Tx Convective Regime Will

1. Run Continuously Into La/Ms. Some Swd Backbuilding Is Psbl Into
Se Tx And Swrn La...Though Deamplification Of Upper Wave Farther N
And Related Lack Of Large-Scale Ascent Extending Swd Across Sabine River Area May Disfavor That Idea.

2. As Most Convection-Permitting High-Res Models Suggest... Develop As Separate Area Of Tstms And Become Sfc-Based Closer To Gulf Coast Over La/Ms.

Fcst Soundings Suggest Accompanying/Weakly Capped Low-Level Waa Zone That Will Be Accompanied By Large...Supercell-Favoring Low-Level Hodographs And Strengthening Deep Shear--E.G. Effective Srh Exceeding 400 J/Kg And Effective Shear Magnitudes 45-60 Kt.

Though Mid-60s Dew Points Are Fcst...Lapse Rates Will Be Weaker Than Farther W...Keeping Mlcape/Mucape Around 1000 J/Kg Or Less.

Weak Low-Level Lapse Rates During Overnight Hours May Limit Vigor Of Many Updrafts...Despite Technically Sfc-Based Character Of Effective-Inflow Parcels In Fcst Soundings.

Nrn Ok/Extreme Srn Ks...

Some Moist Advection Also May Extend Out From Beneath Cloud Shield And Into Better-Heated Areas Across Portions Nrn Ok/Srn Ks...Ahead Of High-Plains Cold Front.

This Could Foster Conditional/Short-Lived Potential For A Few Stg-Mrgl Svr Tstms In That Area.

Mid-Upper Support Will Diminish With Nwd Extent...Low-Level Flow/Shear Will Be Weak...And Low-Level Lift Is In Question Given Lack Of Boundaries Other Than Differential-Heating Zones And Decaying/Diffuse Front.

Still...Steep Deep-Layer Lapse Rates...Mlcape 1000-1500 J/Kg...And Enough Heating To Remove Cinh Are Anticipated...Suggesting Isolated Gusts/Hail Near Svr Limits May Occur.

Mrgl Svr Probabilities Accordingly Have Been Extended Nwd Into This Region.

Isolated Tstms Near Svr Levels Also May Form Along Cold Front After Dark As It Encounters Residual/Mrglly Favorable Low-Level Moisture/Instability.

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Sun Mar 16 Convective Outlook
Storm Prediction Center Norman Ok
Slgt Risk Of Svr Tstms For Se La...Srn Ms...Srn Al & Fl Panhandle...

Cntrl To Ern Gulf Coast...

An Upper-Level Trough Will Move Across The Srn Plains On Sunday.

At The Sfc...A Low Is Forecast To Move From The Ozarks Ewd Into The Tn Valley As A Trailing Cold Front Advances Sewd Into The Lower Ms
Valley.

Numerous Thunderstorms Should Be Ongoing At The Start Of The
Period In A Region Of Strong Warm Advection Across The Cntrl Gulf
Coast States.

This Activity Should Organize Into A Line By Late Morning On The Wrn Edge Of The Low-Level Jet As Boundary-Layer Convergence Becomes Enhanced Across The Warm Sector.

This Should Enable The Line To Continue Ewd Across The Fl Panhandle Sunday Afternoon.

The Warm-Sector Environment From Se La Ewd To The Fl Panhandle On Sunday Will Be Moist With Sfc Dewpoints In The Mid To Upper 60s F.

This Should Allow For Moderate Instability To Develop By Midday Along The Immediate Coast In Areas That Are Not Affected By Thunderstorm Activity.

Nam Forecast Soundings At Pensacola Fl At 18z To 19z Show Sbcape Near 1500 J/Kg With 0-6 Km Shear Around 45 Kt.

This Combined With Unidirectional Wind Profiles May Be Enough For A Wind Damage Threat With The Better-Organized Segments Of The Line.

A Marginal Tornado Threat May Also Develop Along The Immediate Coast Of Al And The Fl Panhandle Around Midday Due To The Presence Of A 40 To 50 Kt Low-Level Jet.

The Ecmwf Forecasts The Low-Level Jet To Move Newd Away From The Fl Panhandle From Late Sunday Afternoon Into The Early Evening.

This Seems Reasonable As The Upper-Level Trough In The Mid Ms Valley Approaches.

For This Reason...The Severe Threat May Become Marginal By Early Evening In The Ern Gulf Coast Region.

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Mon Mar 17 Convective Outlook
Storm Prediction Center Norman Ok
No Svr Tstm Areas Forecast...

Florida...

An Upper-Level Low Near The Sabine River At 12z Monday Is Forecast
To Move Into The Lower Ms Valley Monday Afternoon.

At The Sfc...A Low Is Forecast To Move Across The Ern Gulf Of Mexico Monday Morning With A Cold Front Approaching The West Coast Of Fl By Afternoon.

A Line Of Thunderstorms Should Be Ongoing Ahead Of The Front Along A Corridor Of Enhanced Low-Level Convergence.

Although Some Uncertainty Exists Concerning Timing...The Current Thinking Is That The Line Will Move Onto The West Coast Of Fl During The Afternoon.

A Very Moist Airmass Should Be In Place Ahead Of The Front With Sfc
Dewpoints Expected To Be In The 65 To 70 F Range.

This Combined With Sfc Heating...Should Allow Moderate Instability To Develop By Midday On The Fl West Coast.

The Nam Forecast Sounding For Tampa Bay At 21z Shows Mlcape Around 1000 J/Kg With 60 Kt Of 0-6 Km Shear.

This Environment Along With 50 Kt Of Flow Just Above The Sfc Should
Support Isolated Damaging Wind Gusts Associated With The Line.

At This Point...The Magnitude Of The Severe Threat Is The Main
Question.

The Ecmwf...Nam And Gfs Solutions Keep The Strongest Large-Scale Ascent Well To The West Of The Front Suggesting The Main Driving Factor Will Be Warm Advection And Low-Level Convergence.

For This Reason...Will Keep The Severe Probabilities At 5 Percent For
Now.

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Mar 18-22 Convective Outlook
Storm Prediction Center Norman Ok

The Ecmwf And Gfs Models Begin The Day 4 To 8 Period With An
Upper-Level Trough Over The Cntrl Rockies And Four Corners Region.

These Models Move The Upper-Level Trough Ewd Across The Great Plains On Tuesday/Day 4 With The Gfs The Faster Of The Two Solutions.

By Wednesday/Day 5...The Ecmwf And Gfs Solutions Move The Upper-Level Trough Into The Great Lakes Region.

By Thursday/Day 6...The Model Solutions Move The System To The Atlantic Seaboard With The Gfs Again The Faster Solution.

In Response To The Upper-Level System Crossing The Cntrl And Ern U.S...A Cold Front Is Forecast To Move Across The Scntrl States.

Cold Sfc High Pressure Should Limit Moisture Return Making Thunderstorm Activity Sparse During The Early To Mid Week.

Beyond Thursday...Confidence Is Low Concerning The Weather Pattern Across The Conus.


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