Severe Weather Threat thru Jun 3

Tue May 27 Convective Outlook
Storm Prediction Center Norman Ok
Slgt Risk Svr Tstms for parts of Tx and Southwest La...

Severe Thunderstorms Will Be Possible Especially This Afternoon And Early Evening Across Portions Of Central And Eastern Texas To
Southern Louisiana.

Other More Isolated Strong To Severe Thunderstorms Will Be Possible In Areas Such As The Northeast United States...Mississippi River Valley...The Dakotas...And Montana This Afternoon And Evening.

A Split Longwave Regime Will Continue Over The Conus And Canada Into Early Wednesday.

A Slow-Moving Southern-Stream Upper Low Will Continue An East-Southeastward Progression From The Southern Plains To The Lower Ms River Valley.

Meanwhile...Some Amplification Of The Northern-Stream Westerlies Will Occur Over Southern Canada And The Conus Northern Tier Ahead Of An Amplifying Upper Trough Over The Pacific Northwest.


The Upper Low Will Continue To Move Slowly East-Southeastward Today Toward The Arklatex...With A Cyclonic Ribbon Of Moderately Strong /30-40 Kt At 500 Mb/ Of Mid-Level Winds Overspreading Much Of Western/Central Tx To Southeast Tx/Southern La.

Early Day Thinking Is That A Squall Line Will Persist East-Southeastward This Morning Across East Tx/Upper Tx Coast And La.

Vertical Shear Will Tend To Weaken With Eastward Extent And The Exact Degree Of Pre-Squall Line Destabilization Is Uncertain Owing To Cloud Cover/Outflow Influences.

Regardless...Some Re-Intensification Could Occur With The Squall Line And/Or Along Residual Outflow With A Severe Risk Into The Afternoon Amid A Moist Low-Level Environment.

Farther West/Northwest...Near And Immediately West/Southwest Of The Upper Low...The Air Mass Should Steadily Destabilize And Become Weakly Capped This Afternoon Across The Rio Grande Vicinity Into Much Of Central/North-Central Tx.

Around 1500-2000 J/Kg Mlcape Appears Possible Across Central / North-Central Tx...With As Much As 2500-3000 J/Kg Of Mlcape Possible Near The Rio Grande.

Mass Convergence Will Be Modest In These Areas...But Sufficient
Heating/Possible Residual Outflows Should Influence At Least
Isolated/Widely Scattered Deep Convective Development This
Afternoon/Early Evening In The Presence Of Weak Inhibition.

Deep Convective Development Should Also Occur In Vicinity Of The Mexican Mountains/Higher Terrain And Will Potentially Cross The Rio Grande This Evening.

Associated With Relatively Strong Mid/High-Level Northwesterly Winds...40+ Kt Of Effective Shear Coincident With Moderate Instability Would Support South-Southeastward Moving Severe Tstms / Supercells Capable Of Large Hail And Perhaps A Tornado Or Two.

Organized Forward-Propagating Clusters May Evolve By Evening And
Pose A South/Southeastward Transitioning Damaging Wind Threat Across Areas Such As The Tx Hill Country And South-Central/East-Central Tx.

Northeast/Mid-Atlantic States And Upper Oh Valley...

A Low-Amplitude Shortwave Trough/Speed Max And Cold Front Moving
Southeastward Out Of Northern Ontario And Quebec Will Likely
Influence Tstm Development Across Parts Of The Region.

In Particular...A Relatively Favorable Combination Of Vertical Shear / Instability Will Likely Exist Across Parts Of The Northeast States Including Areas Such As Northern/Eastern Ny And Western New

In These Areas...This Will At Least Support A Conditional Potential For Isolated Supercell Development With Large Hail And Damaging Winds Possible Particularly This Afternoon And Early Evening.

Within A Weaker Vertical Shear Environment...Pulse-Type Severe Tstms Capable Of Locally Damaging Winds/Possibly Marginal Hail Will Be Possible Across The Upper Oh River Valley/Central Appalachians Ahead Of A Cold Front And/Or Across The Mid-Atlantic States/Carolinas Near A Weak Surface Trough.

Upper Midwest...

Near A Residual Weak Upper Low And Near/South Of A Frontal
Boundary...Isolated/Very Episodic Instances Of Pulse-Type Marginally
Severe Wind And/Or Hail May Be Possible Across The Region This
Afternoon/Early Evening.

Dakotas And North-Central High Plains...

Stronger Westerlies/Forcing For Ascent Will Generally Remain North
Of The International Border...But The Air Mass Will Become Weakly
Capped/Moderately Unstable Across The Dakotas This Afternoon
Near/Ahead Of An Eastward Moving Front.

Isolated/Widely Scattered Tstms Should Develop Across East-Central Nd And Sd...And Potentially As Far West-Southwest As The Black Hills/Eastern Wy Coincident With A Stalling Portion Of The Front And A Developing Upslope Regime.

Most Storms Should Be Multicellular In Nature With Isolated Severe
Hail/Wind Possible This Afternoon/Evening.


In Advance Of The Amplifying Pacific Northwest Upper Trough...The
Northern Rockies Will Be Increasingly Influenced By The Leading Edge Of Height Falls/Forcing For Ascent By Tonight.

At Least Isolated Strong/Severe Tstms Should Develop By Late Afternoon/Early Evening...Initially Across West/Southwest Mt In Vicinity Of The Higher Terrain.

Isolated Severe Hail/Locally Damaging Winds May Be Possible Across Mt Through The Evening Hours.


Wed May 28 Convective Outlook
Storm Prediction Center Norman Ok
Slgt Risk Svr Tstms for parts of Ne Mt And Nw Nd...

Severe Thunderstorms With Large Hail...Wind Damage And Possibly A Tornado Or Two...Are Expected To Develop Across Parts Of
Northeastern Montana And Far Northwestern North Dakota From Late
Wednesday Afternoon Into The Evening.

Other Marginally Severe Thunderstorms With Strong Gusty Winds May Develop Across The Texas Coastal Plain And Far Southwest Louisiana.

Ne Mt/Far Nw Nd...

An Upper-Level Ridge Will Build Nwd Across The Nrn Plains As
Southwest Mid-Level Flow Remains In Place Across The Nrn High

At The Sfc...A Low Should Deepen Across Ern Mt As A Cold Front Advances Ewd Across Ecntrl Mt.

The Cold Front Should Be A Focus For Convective Development Along With A Warm Front Extending Newd From The Sfc Low.

As Storms Initiate During The Late Afternoon...A Small Cluster Of Strong To Severe Thunderstorms May Develop Across The Region.

Adjusted Nam Forecast Sounding At Glasgow Mt For 00z/Thu Shows An Impressive Thermodynamic And Shear Environment With Mlcape Above 2500 J/Kg And 0-6 Km Shear Of 50 To 55 Kt.

As A Capping Inversion Weakens During The Late Afternoon...This Environment Along With Very Steep Mid-Level Lapse Rates Should Support The Development Of Supercells With Large Hail.

Hail Greater Than 2 Inches In Diameter Will Be Possible If The Most Intense Cells Can Remain South Of The U.S.-Canada Border.

As The Low-Level Jet Strengthens During The Early Evening...A Tornado Or Two Will Also Be Possible With Supercells That Interact With The Wrn Edge Of The Low-Level Jet.

Further To The East Across Much Of Nd And Nrn Mn...The Models
Suggest Moderate Instability Will Develop By Late Wednesday

Although Large-Scale Ascent Will Be Weak...Isolated Thunderstorm Development Can Not Be Ruled Out Along Any Mesoscale Zone Of Enhanced Low-Level Convergence.

Moderate Deep-Layer Shear And Steep Lapse Rates May Be Enough For Marginally Severe Wind Gusts And Hail.

Tx Coastal Plain/Sw La...

An Upper-Level Low Is Forecast To Move Slowly Toward The Lower Ms
Valley On Wednesday.

At The Sfc...Sly Winds Should Be In Place From The Middle Tx Coast Newd To The Coast Of Sw La Where Dewpoints Are Forecast To Be In The Upper 60s And Lower 70 F.

This Should Result In The Development Of Moderate Instability By Wednesday Afternoon.

Although Deep-Layer Shear Is Forecast To Be Relatively Weak...Steep
Low-Level Lapse Rates May Be Enough For Marginally Severe Wind Gusts With Any Cells That Can Initiate Wednesday Afternoon.


Thu May 29 Convective Outlook
Storm Prediction Center Norman Ok
No Svr Tstm Areas Forecast...

Marginally Severe Thunderstorms With Gusty Winds And Hail May
Develop Across Parts Of The Northern Plains Thursday Afternoon.

Other Marginally Severe Storms With Strong Gusty Winds May Develop
Across Parts Of Carolinas.

Nrn Plains...

An Upper-Level Ridge Will Remain In Place Across The Nrn Plains On

At The Sfc...A Cold Front Is Forecast To Advance Ewd Across The Cntrl Nd And Wrn Sd.

Large-Scale Ascent Will Be Limited But Isolated Convective Initiation May Still Occur Along The Boundary In The Late Afternoon Due To Enhanced Low-Level Convergence.

Although Deep-Layer Shear Should Be Relatively Weak...Lapse Rates Are Forecast To Be Steep Along The Boundary Suggesting Any Cell That Can Initiate Near Peak Heating...Could Have Strong Wind Gusts And Hail.


Height Falls Are Forecast Across The Cntrl And Srn Appalachian Mtns
On Thursday.

At The Sfc...A West-To-East Zone Of Low-Level Convergence Is Forecast Across The Carolinas...Along Which Sfc Dewpoints Should Be In The Mid T0 Upper 60s F.

This Combined With Strong Sfc Heating Should Allow For Scattered Thunderstorm Development Along A Corridor Of Moderate Instability By Afternoon.

Steep Low-Level Lapse Rates And Precipitation Loading May Result In A Marginal Wind-Damage Threat Near Peak Heating.


May 30-Jun 3 Convective Outlook
Storm Prediction Center Norman Ok

The Ecmwf And Gfs Solutions Begin The Day 4 To 8 Period With An
Upper-Level Ridge Over The Mid To Upper Ms Valley And Move This
Feature Slowly Ewd On Friday/Day 4.

Strong To Severe Thunderstorms Will Be Possible Along A Cold Front In The Nrn Plains On The Back Side Of The Upper-Level Ridge.

Heights Fall Across The Nrn And Cntrl Plains On Saturday/Day 5 As Southwest Mid-Level Flow Becomes More Firmly Established Across The Region.

Isolated Strong To Severe Thunderstorms Will Be Possible From Mt Ewd Across The Dakotas Where The Models Forecast Low-Level Moisture And Deep-Layer Shear Sufficient For Severe Storms.

Further To The East Across The Upper Ms Valley On Saturday...The Gfs And Ecmwf Differ With The Ecmwf Developing Numerous Storms Along A Tongue Of Low-Level Moisture Across Much Of Mn.

If This Solution Were To Verify...Then A Substantial Severe Threat Could Develop Across The Upper Ms Valley Saturday Afternoon With Supercells And Possibly Tornadoes.

However...The Gfs Is Less Aggressive On Saturday Suggesting This
Potential Is Uncertain.

On Sunday/Day 6...The Models Move An Upper-Level Trough Into The Intermountain West With Southwest Mid-Level Flow Remaining Over The Cntrl And Nrn Plains.

Severe Thunderstorms Could Again Develop In The Nrn Plains Sunday Afternoon.

On Monday/Day 7...Considerable Differences Exist In The Ecmwf And Gfs Solutions.

This Makes Predictability Low For The Severe Threat Potential On Monday.

Attm...Will Not Add A Severe Threat Area In The Upper Ms Valley For Saturday/Day 5 Due To Differences In The Model Solutions.

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