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Severe Weather Threat thru Apr 26

Sat Apr 19 Convective Outlook
Storm Prediction Center Norman Ok
No Svr Tstm Areas Forecast...

Isolated Strong Storms Are Possible Today Along Florida And Georgia
Atlantic Coastal Areas...Across Parts Of Southwest Texas And
Adjacent Southeast New Mexico...And Across Parts Of North Central
Kansas Into Southern Nebraska. Some Of These Could Approach Or
Briefly Exceed Severe Limits.

Little Change To The Large-Scale Upper Pattern Is Expected Through
This Forecast Period. Mid-Latitude Westerlies Emerging From The
Pacific Will Remain Split Across The U.S...With One Zonal Branch
Across The Northern Tier States Remaining A Bit Stronger And More
Progressive Than The Slightly More Amplified But Weaker Branch
Across The Southern Tier.

In The Wake Of The First Of A Pair Of Prominent Perturbations Within
The Southern Branch...Considerable Drying Is Ongoing Across Much Of The Gulf Coast Region Into The Gulf Of Mexico.

However...Weak To Modest Moisture Return Is Underway In A Narrow Plume Across Parts Of The Rio Grande Valley...Ahead Of The Upstream Perturbation...Which Is Forecast To Gradually Migrate East Northeastward Across The Four Corner States And Northern Mexican Plateau Today And Tonight.

Some Moistening Also Is Expected To Continue In A Corridor Across The Central High Plains Into The Mid Missouri Valley...Ahead Of A Lee
Surface Trough...And A Weakening Cold Front Associated With One In A Series Of Vigorous Northern Stream Impulses.

Otherwise...Moisture Levels Across Much Of The Nation Will Remain
Seasonably Low...With Relatively Low Convective Potential For The
Time Of Year.

South Atlantic Coastal Areas...

Models Generally Suggest That A Band Of Enhanced Forcing For Upward Vertical Motion...And Associated Vigorous Thunderstorm
Activity...Will Be In The Process Of Spreading Off Southeast Florida
Atlantic Coastal Areas During The 12-15z Time Frame.

In Its Wake...Mid-Level Subsidence...Associated Lower/Mid Tropospheric Drying...And A Veering Of Low-Level Flow To A More Westerly Component Likely Will Diminish Convective Potential.

However...North Of The Miami Area...Between Palm Beach And
Melbourne...Mid-Level Cooling And Ascent On The Southern Fringe Of
The Upper Low Could Contribute To New Convective Development During The Afternoon.

Inland Advancement Of The Sea Breeze Still Appears Unlikely... Though...And Strong Convective Development May Be Limited To Areas East Of The Coastal Waters.

Meanwhile...In Closer Proximity To The Mid-Level Cold Core /With 500
Mb Temps Of -16 To -18c/...Residual Low-Level Moisture Near A Weak
Surface Low/Trough May Contribute To Thermodynamic Profiles
Supportive Of Strong Thunderstorms Capable Of Producing Hail And
Strong Wind Gusts.

Some Of This Could Approach Or Briefly Exceed Severe Limits Around Jacksonville Fl...Northward Into Southeast Georgia...During The Afternoon Hours.

Parts Of Southwest Texas And Adjacent Southeast New Mexico...

Models Suggest That Boundary Layer Warming And Moistening Will Only Support Weak To Modest Cape This Afternoon.

However...Veering Winds With Height Beneath 30-50 Kt Southwesterly 500 Mb Flow Ahead Of The Approaching Upper Trough Likely Will Contribute To Strong Deep Layer Shear Supportive Of Organized Convection...Potentially Including Supercells.

This Appears Enough To Support At Least Low Probabilities For Severe Hail And Wind Late This Afternoon And Evening.

North Central Kansas Into Southern Nebraska...

Models Suggest That Strong Surface Heating And A Focused Area Of
Large-Scale Ascent Supported By Low-Level Warm Advection May Provide The Support For Vigorous Convective Development Late This Afternoon And Evening.

Mid/Upper Flow May Be Relatively Weak Across The Region...But The Evolution Of At Least A Small Storm Cluster Appears Possible. And A Remnant 30 Kt Southerly 850 Mb Jet...Coupled With The Evolution Of A Relatively Deep Mixed Boundary Layer...May Contribute To The Risk For A Downburst Or Two...As Well As Vigorous Cold Pool Development Accompanied By Strong Surface Gusts.

Isolated Severe Hail May Also Not Be Out Of The Question...Before Activity Weakens By Mid To Late Evening.

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Sun Apr 20 Convective Outlook
Storm Prediction Center Norman Ok
Slgt Risk Of Svr Tstms Across West Tx...

Isolated Severe Thunderstorms Are Expected To Develop Along A
Dryline Across The Southern High Plains Of West Texas. A Few Strong Storms May Also Develop Across Portions Of Western Oklahoma Into Central Kansas.

Southern/Central Plains...

Slow-Moving Upper Low Is Drifting Ewd Across The Lower Co River
Valley. This Feature Is Expected To Gradually Deamplify And Eject
Into The Srn Rockies Early Sunday Morning With The Trough Axis
Likely Extending Across The Srn High Plains Of West Tx By 21/00z.

Strongest Belt Of Mid-High Level Flow Will Translate Over Nrn Mexico
With 30-40kt At 500mb Forecast To Extend Over West Tx Dryline By
Peak Heating. Deep-Layer Shear Should Increase Enough To Support Sustained Rotating Updrafts...Especially South Of I-20 Where Sfc-6km Values Should Exceed 40kt.

Latest Model Guidance Continues To Suggest 50s Sfc Dew Points Will Advance Nwwd Into Convergent Lee Trough/Dryline Such That Ample Instability Should Exist By Early-Mid Afternoon For Robust Updrafts.

In Fact...Cooling Profiles Aloft May Allow Inhibition To Weaken Enough For Tstm Initiation Fairly Early...Possibly By 18z.

However...Continued Boundary Layer Heating Could Result In Sbcape
Values Approaching 1500 J/Kg Within Strongly Sheared Environment.

Forecast Sounding At Maf At 21/00z Strongly Supports Supercell
Development.

Convection That Evolves Across The Srn High Plains Should Move Esewd Though Newd Development Along The Dryline Is Expected Across Ok Into Ks.

Tstms That Develop Across The Cntrl Plains Will Do So Within Considerably Weaker Shear And Forecast Instability Does Not Appears Strong Enough To Warrant More Than 5 Percent Severe Probs Despite Sct Coverage Expected.

Large Hail Is The Primary Severe Threat With Supercells Along With
Gusty Winds. While A Brief Tornado Can Not Be Ruled Out Over West
Tx Low Level Shear May Be Inadequate To Support More Significant
Tornado Threat.

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Mon Apr 21 Convective Outlook
Storm Prediction Center Norman Ok
Slgt Risk Of Svr Tstms Across Cntrl/Nern Tx...

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

Tx...

Slow-Moving Short-Wave Trough Will Eject Across The Tx South Plains During The Day2 Period To Near The I-35 Corridor By 21/12z.

Sfc Front Will Coincide With Mid-Level Trough Early But Lag Across Cntrl Tx As Weakly Subsident Nwly Flow Deepens During The Afternoon Hours.

Even So It Appears Strong Heating And A Convergent Low-Level Wind
Shift Should Encourage At Least Isolated Convection Along Sw-Ne
Oriented Boundary.

The Greatest Threat For More Widespread Convection Will Occur Across Nern Tx Where Favorable Uvv Ahead Of Short Wave Will Encourage Sct-Numerous Tstms...However Instability May Be Reduced Across This Region.

Latest Thinking Is Sct Convection Will Be Ongoing Early In The Period Across Ok Into The Red River Region Of Nrn Tx.

Extensive Cloud Cover/Precip Should Maintain Weak Lapse Rates Across This Region Limiting More Significant Destabilization To Areas South Of Ok.

Strong Heating West Of I-35 Should Result In Deepening Boundary
Layer And Sfc-3km Lapse Rates Approaching/Exceeding 9 C/Km.

While Primary Region Of Ascent Will Spread Into The Arklatex Region
Early...Daytime Heating Should Contribute To Afternoon Convection
Shortly After 18z Along Advancing Sfc Boundary.

Modest Deep Layer Shear...On The Order Of 30kt...Should Contribute To Multi-Cell Updrafts...And Perhaps Even A Few Weak Supercells.

Primary Severe Threat Will Be Large Hail And Locally Damaging Winds With Slow-Moving Convection That Spreads Sewd During The Afternoon/Early Evening.

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Apr 22-26 Convective Outlook
Storm Prediction Center Norman Ok

Considerable Model Variability Exists Between The Gfs And Ecmwf As
Well As Single Model Run-To-Run Differences.

Even So There Appears To Be Support For A Well Established Lee Trough/Dryline By Mid Week As Substantial Swly Flow At Mid Levels Overspreads The High Plains.

Current Pattern Favors A Narrow Corridor Of Moisture/Instability
Across The High Plains From Nwrn Tx...Nwd Into Cntrl Neb.

While Details Of Short Wave Timing And Placement Of Speed Maximum Differ Among The Models...40kt+ Swly Flow Aloft Should Prove Adequate For Supercell Development Across This Region.

If A Broader And More Unstable Warm Sector Can Establish Itself Then A More Significant Severe Event...Possibly Over Multiple Days...Could Ensue.

However...Model Variability Will Preclude Delineating A Severe Threat Beyond Wednesday.


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