Severe Weather Threat thru Apr 27

Sun Apr 20 Convective Outlook
Storm Prediction Center Norman Ok
Slgt Risk Of Svr Tstms for parts of Wrn/Nwrn Tx and Swrn Ok...

Scattered Thunderstorms -- A Few With Potential To Produce Hail And
Damaging Gusts -- Will Continue To Evolve Across Portions Of The
Western Half Of Texas And Far Southwest Oklahoma This Afternoon And Early Evening.

Showers And Scattered Thunderstorms Continue To Develop Over The Wrn Half Of The Srn Plains This Afternoon.

One Cluster Of Weak Convection -- Associated With A Subtle Upper
Circulation Center -- Is Moving Enewd Across N Tx Attm.

Meanwhile Behind This Feature And Associated Cloud Cover... Airmass Heating/Destabilization Are Ongoing Ahead Of A Weak Trough / Dryline E Of The Tx/Nm Border.

Aided By Ascent Associated With The Main Upper Feature Now Centered Over Far Nwrn Portions Of The Tx Panhandle...Isolated Storm Development Is Ongoing From The Tx/Ok Panhandle Vicinity Swd Into The Davis Mtns.

With Flow Aloft Relatively Weak Invof The Upper Circulation Center...Marginal Hail Will Likely Be The Main Severe Risk.

Farther S...Where Mid-Level Flow Is A Bit More Robust... Multicell / Weak Supercell Storms Can Be Expected... With Attendant Risk For Locally Damaging Winds And Hail.

Later This Evening...Convective Intensity/Severe Risk Will Diminish
In Conjunction With Diurnal Boundary-Layer Stabilization.


Mon Apr 21 Convective Outlook
Storm Prediction Center Norman Ok
Slgt Risk Of Svr Tstms for parts of Central And Nern Tx...

Scattered Strong Storms...A Few Possibly Severe...Are Expected To
Develop From The Hill Country Of Central Texas Into Northeastern
Texas During The Day Monday.

Phasing Of Nrn And Srn Stream Vorticity Maxima Over The Central U.S. Will Continue Through The Day 2 Period...With An Increasingly
Consolidated Trough Progged To Shift Ewd Into The Ern Half Of The

As This Occurs...A Weak Cool Front Will Progress Ewd Across The Midwest And Sewd Across The Mid Ms/Lower Mo/Red River Valleys Into Ar/Tx Into The Evening Hours.

This Front Will Focus An Area Of Shower/Storm Development Centered Over Tx During The Afternoon.

Elsewhere...A Much Stronger Upper Trough Crossing The Ern Pacific
Will Approach The W Coast Late...With A Cold Front Crossing Ca And
The Great Basin Through The Period.

Tx Hill Country Enewd Into Nern Tx...

Diurnal Destabilization Is Forecast Across A Large Portion Of E Tx
Day 2...As Afternoon Heating Of A Modest Boundary Layer Moisture
/Upper 50s To Low 60s Dewpoints/ Commences Beneath Steep Mid-Level Lapse Rates Spreading Into Central Tx.

With 1500 To 2000 J/Kg Mixed-Layer Cape Expected To Evolve Through The Afternoon Above A Deepening/Well-Mixed Boundary Layer...Isolated Storms Are Forecast To Develop Near And Ahead Of The Weak/Sewd-Moving Cool Front.

With Relatively Modest Mid-Level Wlys /Around 25 To 30 Kt At H5/ --
Particularly Across Central Tx Where The Most Unstable Environment
Is Forecast...Organized/Sustained Updrafts Are Expected.

Cool Mid-Level Temperatures/Steep Lapse Rates Support A Hail Risk With Stronger Storms Given The Kinematic Environment...While The Deep Mixed Layer Also Suggests Potential For Locally Damaging Winds.

Storms May Locally Grow Upscale Into Multicell Clusters Into Late
Afternoon...Possibly Enhancing The Risk For Damaging Winds Locally.

With Time However...The Loss Of Daytime Heating Will Yield A Fairly
Rapid Stabilization Of The Boundary Layer...And A Subsequent
Decrease In Convective Intensity/Coverage.


Tue Apr 22 Convective Outlook
Storm Prediction Center Norman Ok
No Svr Tstm Areas Forecast...

A Few Strong Storms May Form Across The High Plains From Northwest Kansas Into Southeast Montana During The Afternoon And Early Evening Hours.

Nrn/Cntrl High Plains...

A Notable Change Within The Large-Scale Pattern Should Lead To
Strengthening Lee Trough Across The Nrn And Cntrl High Plains

Latest Short-Range Model Guidance Is In Fairly Good Agreement Regarding The Evolution Of Upper Trough As It Moves Inland Across The Interior Nwrn U.S.

By The End Of The Period A Substantial Speed Max Will Round The Base Of The Progressive Trough And Begin To Eject Newd Across Co/Wy.

While This Feature Will Not Time Particularly Well For High Plains Convection During The Afternoon Hours...It Appears Sufficient Low-Level Convergence Will Develop Along The Lee Trough For At Least Isolated Tstms During Peak Heating On Day3.

Moisture Will Initially Be Somewhat Marginal Across The High Plains
But Strengthening Llj Should Aid Modified Boundary Layer Moisture To
Advect Nnwwd Across Wrn Ks Into Sern Mt Where Sfc Dew Points Are
Expected To Rise Into The 40s.

Strong Heating Along This Corridor Should Prove Instrumental In Convective Initiation Where Sfc Temperatures Rise Into The 70s... Yielding Sbcape Values Of 500-1000 J/Kg.

While Absolute Moisture Content Is Expected To Remain Marginal ... Strengthening Wind Fields Will Become Increasingly Favorable For Sustained Rotating Updrafts.

For This Reason...Along With Steep Lapse Rates...Have Opted To Introduce 5 Percent Severe Probs To Account For Hail/Gusty Winds With High-Based Convection.

Ern U.S...

Weak Positive-Tilt Long-Wave Trough Should Migrate Across The Ern
U.S. During The Day3 Period.

Modest Moisture And Sufficient Instability Should Exist Ahead Of Weak Sfc Front For Isolated-Sct Tstms Within A Broad Corridor From The Lower Sabine River Valley Of The Upper Tx Coast...Newd Into The Nrn Middle Atlantic.

Shear/Instability Appear Inadequate For Organized Severe Thunderstorms.


Apr 23-27 Convective Outlook
Storm Prediction Center Norman Ok

Models Are In Somewhat Better Agreement Regarding The Evolution Of Long-Wave Trough As It Progresses Across The Rockies Into The Plains Wednesday.

However...Considerable Uncertainty Exists Beyond Day4 As Gfs Is Quite A Bit Stronger With Ejecting Short-Wave Trough/Speed Max Across The Mid Ms Valley Than The Ecwmf.

Additionally...Moisture/Instability May Not Initially Be Of Quality That Will Support Significant Organized Severe Downstream Of The Plains.

However...There Is Growing Confidence That Robust Convection Will
Develop During The Day4 Period Across The Cntrl/Srn High Plains.

Lee Trough Will Be Well Established By Tuesday Across The High
Plains And A Narrow Corridor Of Boundary Layer Moisture Should
Advance Nwd Across West Tx Into Neb.

There Is Reason To Believe Near 60f Sfc Dew Points Will Reside Just East Of The Dryline By Peak Heating along with Sbcape On The Order Of 1500-2000 J/Kg Appears Possible Along Wrn Fringe Of Thicker Low Clouds Within Return Flow.

With 40-50kt 500mb Swly Flow Expected To Overspread The Dryline ...Environmental Shear Will Support Organized Rotating Updrafts.

Will Maintain 30 Percent Severe Probs For Expected Supercell Development.

Although Significant Organized Severe Is Not Currently Forecast
Beyond Day4...Latest Medium-Range Guidance Would Seem To Favor Several Bouts Of Severe During The Day4-8 Time Period.

Model Discrepancies Will Prevent A More Accurate Depiction Of This
Threat...Thus Probabilities Will Remain Too Low To Justify An
Outlook Day 5-8.

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