Severe Weather Threat thru Jun 5

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

Isolated Severe Thunderstorms Will Be Possible Over The Northern
Plains...The Carolinas...And The Central Gulf Coast During The
Afternoon Into The Evening.

Mid-Level Cyclonic Flow Will Trail Swwd Into The Nwrn States In The
Wake Of A Shortwave Impulse Progressing Newd Across The Canadian Prairies.

Downstream Ridging Will Cover The Nrn Plains To The Great Lakes ...While A Shortwave Trough Covers The Nern States.

A Cut-Off Cyclone Will Remain Centered Over The Lower Sabine River Valley.

At The Sfc...A Cold Front Will Shift Ewd/Sewd Across Parts Of The
N-Cntrl States While A Residual Boundary Remains Draped Across The Mid-Ms Valley To Coastal Sections Of The Carolinas.

Broadly Cyclonic Flow And Rich Moisture Will Exist At The Sfc Across Parts Of The Deep South Beneath The Cut-Off Cyclone.

Wrn Dakotas...

Capping Associated With H7 Temperatures Of 10-12c Near The Base Of An Eml Being Drawn Newd Atop The N-Cntrl-States Frontal Zone Should Largely Limit Diurnal Convective Development.

This Will Occur Despite The Development Of Strong Conditional Instability On The Warm Side Of This Boundary...Where Diurnal Sfc-Layer Heating Of Lower 60s Dewpoints Occurs.

The Bulk Of Strong Mid-Level Flow And Ascent Accompanying The Aforementioned Shortwave Impulse Will Reside On The Cool Side Of The Front...Further Diminishing Confidence In Robust Diurnal Storm Development.

By Mid-Evening...Minor Height Falls May Glance The Frontal Zone And Support Some Increase In Near-Sfc-Based Convection Which Could Produce Isolated Svr Wind/Hail.

However...Given The Front-Parallel Orientation To The Mid-Level Flow...And Given The Poor Phasing Between The Modest Boost Of Ascent And The Peak Of The Diurnal Heating Cycle...Confidence In
A More Robust Svr Event Is Currently Limited.

However...Should More Adequate Phasing Occur To Support A Greater Svr Risk...Categorical Upgrade To Slight Risk May Be Needed In Subsequent Outlooks.

Carolinas...

The Combination Of Frontal Ascent And Diurnally Bolstered Orographic Circulations Over The Srn Appalachians Will Foster Thunderstorm Development During The Afternoon.

Middle/Upper 60s Sfc Dewpoints S Of The Residual Boundary Will Support Moderate To Locally Strong Instability To Enhance Updraft / Downdraft Strength.

Sporadic Instances Of Dmgg Winds And Marginally Svr Hail Could Occur.

However...The Presence Of Weak Mid-Level Flow -- E.G. H5 Wind Speeds Aob 15 Kt -- Will Offer Too Little Shear For Any Substantial
Convective Organization.

Cntrl Gulf Coast...

Convection Will Linger Into The Morning Hours While Additional
Convection Develops Through The Day...As Diurnal Heating Occurs
Amidst Weak Capping Beneath The Mid-Level Cyclone.

Moist-Neutral Thermodynamic Profiles Through The Low/Mid Levels Will Be Associated With Only Marginal Buoyancy.

However...Rich Deep Moisture -- E.G. Pw Around 1.75-2.00 Inches Per Gps Data -- Could Support A Few Wet Microbursts With Dmgg Wind Gusts.

Sufficient Low-Level Shear Beneath A 20-25-Kt Llj May Also Support A Few Storm-Scale Circulations...And A Weak Tornado Cannot Be Ruled Out In This Low-Lcl Environment.

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Fri May 30 Convective Outlook
Storm Prediction Center Norman Ok
No Svr Tstm Areas Forecast...

Marginally Severe Thunderstorms With Hail And Strong Gusty Winds
Will Be Possible From The Northern Plains Southwestward To The
Central Rockies Including Parts Of The Central And Northern High
Plains Friday Afternoon.

Cntrl And Nrn High Plains/Cntrl Rockies...

Southwest Mid-Level Flow Will Be In Place From The Nrn High Plains
Swd Into Cntrl Rockies On Friday.

At The Sfc...Upslope Flow Is Forecast With An Axis Of Low-Level Moisture Extending Wwd Across Cntrl And Nrn Wy.

As Instability Increases Friday Afternoon...Isolated To Scattered Thunderstorms Appear Likely To Initiate From Ncntrl Wy Sewd Into Nern Co.

Modified Forecast Soundings For Casper And Cheyenne Wy At 21z/Fri Show Mlcape Around 1000 J/Kg With 30 To 40 Kt Of 0-6 Km Shear.

In Addition...Lapse Rates Are Forecast To Be Quite Steep Across Cntrl And Ern Wy Suggesting A Threat For Hail And Strong Wind Gusts Will Be Possible.

Although A Supercell Threat Can Not Be Ruled Out...Uncertainties
Still Exist Upon The Amount Of Instability That Can Develop.

For This Reason...Will Not Upgrade To Slight Risk At This Time.

Nrn Plains...

An Upper-Level Ridge Is Forecast To The Move Slowly Ewd Into The Wrn Great Lakes Region Friday As Southwest Flow Becomes Established Across The Nrn High Plains.

At The Sfc...A Front Is Forecast To Become Quasi-Stationary From Nw Mn Extending Swwd Across Ern Nd Into Cntrl Sd.

As Sfc Temps Warm During The Day And Low-Level Convergence Increases...Thunderstorms Should Initiate Along The Boundary Friday
Afternoon.

Sfc Dewpoints Near The Boundary Should Be In The 60 To 65 F Range With Several Pockets Of Moderate Instability Developing.

In Addition...Nam Forecast Soundings At Fargo Nd And Aberdeen Sd At 21z/Fri Show 0-6 Km Shear Less Than 20 Kt.

In Spite Of The Weak Deep-Layer Shear...Low-Level Lapse Rates Are Forecast To Become Quite Steep Suggesting That A Potential May Still Exist For Marginally Severe Wind Gusts Near Peak Heating.

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Sat May 31 Convective Outlook
Storm Prediction Center Norman Ok
Slgt Risk Svr Tstms for parts of Nrn Plains and Cntrl Hi Plains...

Severe Thunderstorm Development Is Expected To Take Place Across
Parts Of The Northern Plains And Central High Plains On Saturday.

Other Marginally Severe Thunderstorms May Develop Southward Into The Southern High Plains And Across Parts Of The Upper Mississippi
Valley.

Nrn Plains And Cntrl High Plains...

Southwest Flow Is Forecast To Become Firmly Established On Saturday From The Nrn Plains Swwd Into The Cntrl Rockies.

At The Sfc...A Low Is Forecast To Deepen Near The Wy-Sd-Neb Intersection With A Lee Trough Extending Swd Across Ecntrl Co.

Sfc Dewpoints In The 55 To 60 F Range Along With Sfc Heating And Increased Low-Level Convergence...Will Likely Result In Scattered Thunderstorm Initiation Near The Sfc Low And Lee Trough.

The Storms Should Develop In The Higher Terrain Of Ern Wy And Ern Co And Move Ewd Across The Slight-Risk Area Late Saturday Afternoon.

Other Storms Should Develop Newd Along A Zone Of Low-Level Convergence Into Cntrl And Nrn Sd.

Nam Forecast Soundings Near The Sfc Low And Lee Trough At 00z/Sun For Rapid City Sd And Cheyenne Wy Show Mlcape In The 1500 To 2500 J/Kg Range With 0-6 Km Shear Of 35 To 40 Kt.

This Environment Along With Very Steep Lapse Rates Should Support The Development Of Supercells With Large Hail.

Hailstones Greater Than 2 Inches In Diameter Will Be Possible With Cells That Intensify The Most.

A Tornado Threat May Also Develop Across Nern Wy And Wrn Sd Early
Saturday Evening Due To The Strengthening Low-Level Shear.

The Severe Threat Could Persist Into The Late Evening As The Low-Level Jet Becomes Focused Across The Cntrl High Plains.

Upper Ms Valley...

Southwest Mid-Level Flow Is Forecasts To Be In Place Across The Nrn
Plains And Upper Ms Valley On Saturday.

At The Sfc...A Moist Axis Is Forecast To Extend From Ern Sd Newd Across Nrn Mt Where Sfc Dewpoints May Be In The Lower To Mid 60s F.

This Should Allow For The Development Of Moderate Instability Along This Corridor By Saturday Afternoon.

Forecast Soundings At 21z/Sat For Fargo Nd Suggest Deep-Layer Shear Will Be Relatively Weak But The Low-Level Lapse Rates Will Become Steep By Afternoon.

This May Support A Marginal Wind Damage Threat With The Stronger Multicells Near Peak Heating.

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Jun 1-5 Convective Outlook
Storm Prediction Center Norman Ok

The Ecmwf And Gfs Medium-Range Models Begin The Day 4 To 8 Period With An Upper-Level Ridge Over The Ern States...Southwest Flow In The Rockies And An Upper-Level Trough Over The Intermountain West.

A Broad Corridor Of Low-Level Moisture Is Forecast Across The Great
Plains And Ms Valley.

Severe Thunderstorms Will Be Possible In The Nrn And Cntrl Plains Sunday Afternoon As A Shortwave Trough Approaches The Region From The West. On Monday/Day 5.

The Gfs Develops Zonal Flow In The Ncntrl States While The Ecmwf Moves The Upper-Level Trough Across The Cntrl Plains.

Although The Models Differ...Both Solutions Would Result In A Potential For Severe Storms From The Upper Ms Valley Swwd Into The Mid Mo Valley On Monday Afternoon.

On Tuesday/Day 6...The Ecmwf And Gfs Solutions Are Markedly Different.

The Ecmwf Appears More Reasonable...Driving A Cold Front Sewd Into The Srn Great Lakes And Mid Ms Valley Where Isolated Severe Thunderstorms Could Occur On Tuesday Afternoon.

Beyond Day 6...Much Uncertainty Exists Due To Model Differences.

For The Day 4 To 8 Period...Severe Storms Will Be Possible Each Day
Across The Nrn And Cntrl States.

However...Predictability Remains Too Low To Warrant The Issuance Of An Outlook Area.


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