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Severe Weather Threat thru Apr 19

Sat Apr 12 Convective Outlook
Storm Prediction Center Norman Ok
Slgt Risk Of Svr Tstms for Central Ks To Ia And Srn Wi/Nw Il...

A Nrn Stream Trough Will Amplify Over The Nrn Rockies...As A Separate Srn Stream Wave Translates Ewd From Srn Ca To Nm.

Other Subtle Speed Maxima Will Move Newd From The Srn/Central High Plains Toward Lake Mi Through The Period.

At The Surface...An Initial Low In Se Sd Will Weaken As A Lee Cyclone Deepens By This Afternoon Across Sw Ks...Which Will Maintain A Sly/Sswly Llj From E Tx To Mo.

A Pre-Existing Front Across Ern Neb And Mn/Ia Border Will Drift Sewd
Through This Afternoon As The Warm Sector Destabilizes From The
S/Sw.

Meanwhile...An Upstream Surge Of Cold Air From Ab/Sk/Mt Will
Consolidate Into A Sharpening Frontal Zone From Nrn Ks To Ia By The
End Of The Period.

The Initial Frontal Zone Will Serve As A Focus For Severe Thunderstorm Development By Late Afternoon Across Ia...With Lesser Risks Both Newd Toward Lower Mi And Swwd Into Central Ks.

Upper Midwest To Central Plains This Afternoon Into Tonight...

Elevated Convection Will Spread Ewd From Ia/Mn To Wi This Morning In The Zone Of Stronger Low-Level Waa And Increasing Moisture Above The Surface.

In The Wake Of This Morning Convection... Steep Lapse Rates Observed Over The Plateau/Rockies The Past Two Days Will Spread Newd Above The Returning Moist Layer Across The Central Plains.

The Combination Of Boundary Layer Dewpoints Rising To The Upper 50s F Beneath Midlevel Lapse Rates Of 8.5-9 C/Km...And Afternoon Temperatures Of 78-80 F In The Moist Sector...Will Drive Mlcape Values To Near 2500 J/Kg.

Convective Inhibition Will Weaken First Across Ia Along The Slow-Moving Front /Farther Removed From The Eml Source Region/...And Then Gradually Wswwd Into Central Ks Ne Of The Triple Point.

Vertical Shear Will Not Be Particularly Strong...But Will Be Sufficient For Some Supercell Structures Initially...When Isolated Very Large Hail Will Be Possible.

Thereafter... Upscale Growth Will Likely Occur Into One Or More
Clusters Across Ia By Evening...With A Continuing Risk For Large
Hail And Damaging Gusts Into Tonight.

Storm Coverage Is More Uncertain Into Central Ks Where The Warmer Eml Will Reside.

However...Strong Surface Heating/Deep Mixing To The Dryline-Cold Front Intersection Could Support Isolated Development Of Somewhat High-Based Storms By This Evening...With A Conditional Large Hail/Damaging Wind Risk.

Convection Will Likely Become More Widespread And Should Persist Overnight From Nrn Ks To Se Neb...In A Zone Of Low-Level Ascent Along And Just N Of The Surface Front...Downstream From The Srn Stream Shortwave Trough Expected To Emerge Over The High Plains Sunday Morning.

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Sun Apr 13 Convective Outlook
Storm Prediction Center Norman Ok
Mdt Risk Of Svr Tstms for Eastern Ok...
Slgt Risk Of Svr Tstms for S Plains/Ozarks to Mid/Low Ms River Valley...

Longwave Trough Amplification With Strengthening/Increasingly
Prevalent Cyclonic Upper Flow Is Expected Sunday Over The Central
Conus...With Multiple Shortwave Impulses Overspreading The Southern Plains/Midwest.

At The Surface...A Frontal Boundary Extending Southwest-Northeastward From Ks To The Midwest Will Begin To Accelerate Southeastward Across Much Of The South-Central Plains And Lower Mo Valley/Ozarks Through Sunday Night...While A Preceding Dryline Will Reside/Move Slightly Eastward As It Extends From Central Ok Into North-Central/West-Central Tx.

Southern Plains/Ozarks To Middle/Lower Ms River Valley...

Given The Large-Scale Evolution As Previously Described...A Lead / Southern Stream Impulse And Associated Speed Max Will Spread East-Northeastward Over The Southern Plains/Ozarks...Reaching The Middle Ms River Valley Late Sunday Night.

The Main Southern Plains Surface Low/Associated Triple Point Will Exist Across West-Central/Southern Ok Sunday Afternoon/Early
Evening.

East-Southeast Of This Surface Low And Cold Front / Dryline... Persistently Strong Southwesterly Low-Level Winds Will Transport Moisture North-Northeastward Within An Increasingly Broad Warm / Moist Sector From East-Central Parts Of Ok/Tx And Ozarks Into The Middle/Lower Ms River Valley.

As The Air Mass Destabilizes Through Afternoon...Ample Forcing For
Ascent Tied To The Aforementioned Shortwave Trough And Cold Front
Should Influence Increasing Near-Surface-Based Tstm Development ... Potentially Relatively Early In The Afternoon Especially Northeast Of The Surface Triple Point/Near The Cold Front...Including A Corridor Across Southeast Ks And East-Central/Northeast Ok Into Adjacent Mo.

A Bit Later In The Afternoon...Discrete Strong/Severe Storms Including Supercells Will Be Possible Across Additional Parts Of Eastern Ok And North-Central/East Tx And Arklatex Within The Warm Sector And / Or Near The Dryline Extending Southward Across South-Central Ok Into North-Central/Central Tx.

Relative Early Afternoon Timing Of The Parent Mid-Level Shortwave Trough And Modest Mass Convergence In Vicinity Of The Dryline Account For Some Uncertainties Related To Severe Tstm Coverage Progressively Southward Of The Surface Triple Point /Namely Across Tx/.

Overall...Favorable Wind Profiles /45-50 Kt Effective Shear / Will
Support Initial Supercells...Although Increasingly Unidirectional
Winds And The Influence Of The Cold Front Suggest That Multicells / Line Segments Should Evolve By Evening In Most Areas With Near-Cold Frontal Storms Steadily Being Undercut By The Cold Front /From Northwest To Southeast/.

Large Hail Is Expected To Be The Dominant Hazard Overall...Although Damaging Winds And Some Tornadoes Will Also Be Possible Sunday Afternoon/Early Evening In Areas Near/East Of The Surface Triple Point Including Eastern Ok And Adjacent Parts Of Mo/Ar/North Tx.

Middle Ms Valley/Midwest...

Farther East...Additional Severe Tstms Will Be Possible Into The Middle Ms Valley/Midwest Near The Advancing Cold Front/Developing
Surface Wave.

Low-Level Moisture/Destabilization Will Be Comparatively Weaker... But Very Strong Shear/Srh Will Allow For The Development Of Line Segments/Some Supercells Capable Of Damaging Winds/Some Hail And Potentially A Tornado Or Two Provided Some Development Immediately Preceding The Cold Front.

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Mon Apr 14 Convective Outlook
Storm Prediction Center Norman Ok
Slgt Risk Of Svr Tstms for Central Gulf Coast States/Tn Valley...

Gulf Coast States/Tn Valley...

Although Some Guidance Variability Exists Among 00z Nam/Gfs/Ecmwf Regarding Timing/Amplitude...The General Scenario Will Be For A Continued Amplification Of A Longwave Trough Over The Arklatex And Middle/Lower Ms River Valley On Monday.

Scattered To Potentially Numerous Clusters Of Tstms...Some Strong...Should Be Ongoing Monday Morning Across Much Of The Ms River Valley/Arklamiss Ahead Of A Strong Southeastward-Moving Cold Front.

This Convection/Associated Cloud Cover Provides Some Uncertainty ... But The Front-Preceding Air Mass Should Continue To Moisten / Destabilize Through The Afternoon Ahead Of The Front And An
Anticipated Surface Frontal Wave /Likely Somewhere Across Ms-Al-Tn/.

Although Low-Level Winds May Gradually Weaken By Afternoon / Evening In Most Areas /Especially Away From The Surface Low/...Strengthening Winds Aloft And Residually Strong Low-Level Shear/Srh May Support Sustained Line Segments/Embedded Supercells Capable Of Damaging Winds...Some Hail...And Possibly A Couple Of Tornadoes Into The Evening Hours.

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Apr 15-19 Convective Outlook
Storm Prediction Center Norman Ok

A Southern Stream Shortwave Trough Should Continue East-Northeastward Across The Southeast States On Day 4/Tuesday.

A Relatively Moist Air Mass Will Exist Across The Region Ahead Of A
Weak Surface Low/Eastward-Moving Cold Front. While Destabilization
May Remain Modest...Especially Given The Likelihood Of Early Day
Convection/Cloud Cover...Some Strong/Possibly Severe Tstms Could
Occur Across Fl And/Or The Coastal Southeast States On Tuesday.

30 Percent Severe Probabilities Are Not Warranted.

Thereafter...Guidance Variability Exists Regarding The Gradual
Amplification Of An Upper Trough Over The Rockies And Plains Around Days 5-6 Wednesday/Thursday.

As Far As Deterministic Models...The 00z-Based Ecmwf Offers A Less Amplified Solution As Compared To The 00z Gfs/Ukmet...Which Are More Suggestive Of Some Severe Potential Across The South-Central Conus Around Thursday Vs The Nil Potential Of The Ecmwf.

Regardless...In The Absence Of Meaningful Moisture...A Relatively Quiet Pattern Should Result In A Fairly Limited/Below-Average Severe Potential Next Week.


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