Severe Weather Threat thru Sep 4

Thu Aug 28 Convective Outlook
Storm Prediction Center Norman Ok
No Svr Tstm Areas Forecast...

Scattered Strong Thunderstorms Are Possible Today From The Mid-Missouri Valley Southward Into The Southern High Plains. Additional But More Widely Scattered Strong Storms May Occur From The Mid-Mississippi And Lower Ohio Valleys Into North Carolina.

Slowly Progressive Split Flow Will Once Again Prevail Over The Lwr 48...With The Main Belt Of The Wlys Remaining Confined To Srn Canada And Cntrl/Nrn New England...And Ridge Persisting Across The Lwr Ms Vly/Southeast. In The Srn Branch...Gradual Weakening Of Co Low/Trough Continues As The System Moves Into Wrn Ks/Neb Later Today...And Into Ern Neb/Cntrl Ks Tngt/Early Fri.

At Lwr Lvls...Elongated Low/Trough Now Extending From Cntrl Neb Ssw Into W Tx Will Edge Slowly Ewd Through The Period. Front Extending Ese From Srn Neb To Cntrl Mo Should Advance Slowly Newd...While The Ern Extent Of The Same Boundary Moves Farther S Across The Tn Vly And Carolinas In Response To A Shortwave Impulse Crossing Ny/New England.

Mid-Mo Vly Ssw Into W Tx This Aftn/Eve...

Tstms Now Over Cntrl Ks/Ern Neb And Sw Ia Are Associated With Lead Impulse Ejecting Nne Ahead Of Co Upr Low/Trough. This Activity Should Continue Moving/Developing Generally Newd Through The Day...Affecting The Remainder Of Ia And Parts Of Mo...Mn...And Il. With Most Of The Storms Becoming Increasingly Elevated Atop Weak Warm/Stnry Front...And With Upr Impulse Moving Beyond Zone Of Greatest Low-Lvl Instability...Likelihood For Sustained Svr Weather Will Be Low. A Cell Or Two Could...However...Yield Locally Dmgg Wind In Addition To Very Heavy Rain Given High Pw /Approaching 2 Inches/ Over Region.

Later Today...Sfc Heating Should Result In A Band Of Stronger Instability /Sbcape Of 1500 To 2500 J Per Kg/ Along Lee Trough From W Tx Nne To Vicinity Of Front Over Cntrl/Ern Neb. Coupled With The
Simultaneous Arrival Of Forcing For Ascent Associated With Main Portion Of Co Upr System...Expect Fairly Vigorous Aftn Storm Development Along The Trough. Mid-Lvl Lapse Rates And Deep Shear Will Remain Modest Given Meridional/Unidirectional Mid/Upr-Lvl Flow.

Overall Setup Likely Will Be Sufficient For Some Degree Of Storm Organization And Sustenance. The Stronger Updrafts Could Yield Svr Hail And Locally Dmgg Wind As They Organize Into Slowly-Moving Bands/Clusters Through Early Tngt.

Mid-Ms/Lwr Oh Vlys Ese Into Nc This Aftn...

Deep Shear And Mid-Lvl Lapse Rates Will Be Weak Along Cold Front Settling S/Sw Across The Carolinas...The Tn Vly...And The Lwr Oh/ Mid-Ms Vlys Today Given Proximity Of Upr Ridge.

However...Appreciable Moisture Will Persist...Especially Over The Lwr Oh And Mid-Ms Vlys...Where Pw Will Be Around 2 Inches. Sfc Heating Should Promote Development Of Wdly Sctd Diurnal Tstms...A Few Of Which Could Yield Locally Dmgg Wind As They Merge Into Small Clusters.


Fri Aug 29 Convective Outlook
Storm Prediction Center Norman Ok
No Svr Tstm Areas Forecast...

Widespread Showers And Thunderstorms Are Forecast To Spread Gradually Eastward Across The Central United States On Friday... Most Numerous Within A Zone From The Upper Great Lakes South-Southwestward To The Southern Plains. Isolated Severe Risk Will Be Possible With Stronger Storms ...Mainly Over The Northern Half Of This Area -- From Roughly Eastern Kansas And Missouri To The
Upper Great Lakes Area.

Continued Advance Of A Weakening Trough Across The Central U.S. Is Expected This Period...While A Much Stronger/Upstream Trough Moves Into The Wrn States. While The Progression Of The Wrn Trough Will Suppress A Swrn U.S. Ridge With Time...The Ern U.S. Ridge Will Persist Through The Period.

At The Surface...A Weak Cool Front Will Drift Ewd/Sewd Across The Central Plains Through The Day...While A Second Surge Of Cooler Air Spreads Swd Across The N Central U.S. With Time. Meanwhile...A Much Stronger Cold Front Will Push Across The Nwrn U.S. In Conjunction With The Advancing Wrn Upper Trough.

Ern Ks/Mo Vicinity Newd Into Sern Mn/Srn Wi/Wrn Lower Mi...

Showers And Thunderstorms Are Forecast To Be Ongoing At The Start Of The Period From Portions Of Tx/Ok Newd To The Upper Great Lakes Region...And Should Increase In Coverage Through The Afternoon And Evening While Shifting Gradually Ewd.

Given The Ongoing/Relatively Widespread Nature Of The Convection And Associated Cloud Cover...Airmass Destabilization Should Remain Somewhat Hindered Across Large Portions Of The Area. In Addition...With Relatively Modest Mid-Level Swlys Ahead Of The Trough...Overall Flow Field Should Remain Only Marginally Supportive Of Organized Severe Storms.

The Most Favorable Area For A Few Stronger Cells Appears To Exist From Roughly Ia Into Sern Mn/Wi...But Attm Confidence That Risk Warrants Slight Risk Upgrade Remains Low. Thus...Will Maintain A Broader 5% Risk Area This Forecast.


Sat Aug 30 Convective Outlook
Storm Prediction Center Norman Ok
Slgt Risk Svr Tstms for parts of Nrn Plains...

Showers And Thunderstorms Are Forecast Across A Large Portion Of The Eastern United States On Saturday...While Other Showers And Thunderstorms Affect The Pacific Northwest And Northern
Intermountain Region...And Then Into The Northern And Central Plains From Saturday Afternoon Through Early Sunday. Some Severe Risk Is Evident Over The Northern Plains Vicinity Where Most Vigorous Afternoon Storm Development Is Expected.

As A Weakening Short-Wave Trough Continues Moving Enewd Into/ Across The Upper Great Lakes Region...A Much Stronger/Larger Trough Will Continue Advancing Across The Intermountain West.

Though Relatively Widespread Convection Is Forecast Across The Ern U.S. In Association With The Lead Feature...More Substantial Storm Development Is Forecast Over The Nrn Plains By Late Afternoon ...Near A Sharp Cold Front Associated With The Wrn Upper System...And Progged To Move Into The Plains Through The Second Half Of The Period.

Portions Of Far Ern Mt/Wrn And Central Nd/Nwrn Sd...

Late Afternoon Thunderstorm Development Is Forecast Across The Nrn High Plains Vicinity...Near The Surface Cold Front As It Shifts Across Ern Mt/Wy Toward The Dakotas. Though Relatively Modest Low-Level Moisture /Dewpoints Near 60/ Should Limit The Degree Of Destabilization Potential...A Few Robust/Locally Severe Storms Are Nonetheless Anticipated Given Roughly 40 Kt Mid-Level Flow Spreading Into/Across The Dakotas Beginning Late Afternoon.

With Shear Sufficient For Organized/Rotating Updrafts...Large Hail Will Be Possible Initially...With Wind Damage Potential Possibly Increasing During The Early Evening As Some Potential For Upscale Growth In A Linear Fashion May Occur Along/Ahead Of The Cold Front. Risk Should Diminish Some Later In The Evening In Conjunction With Overnight Airmass Stabilization.


Aug 31-Sep 4 Convective Outlook
Storm Prediction Center Norman Ok

The Gfs And Ecmwf Appear To Be In Fairly Good Agreement Through Roughly Day 6 /Tue 9-2/ With Respect To The Evolution Of The Large-Scale Pattern.

Both Models Depict The Advance Of A Fairly Strong Upper Trough Into The Central U.S. Day 4 /Sun 8-31/...Along With An Associated/Sharp Cold Frontal Progression.

On Day 5...The Main Punch Of Short-Wave Energy Within The Larger-Scale Trough Is Progged To Shift Quickly Newd Across The Great Lakes And Into/Across Ontario...Leaving A Much-Less-Amplified Cyclonic Flow Field In Its Wake.

By Day 6...A Nearly Zonal Upper Pattern Is Forecast Across The U.S. -- Though A Trough Shifting Sewd Out Of The Gulf Of Ak/Wrn Canada Will Begin Affecting The Pac Nw Late.

Model Differences With Respect To The Handling Of This Trough Through Become Increasingly Apparent Day 7 And Beyond.

The Most Substantial Severe Risk This Period Remains Apparent Day 4 From The Central Plains Newd To The Upper Ms Valley...As The Upper Trough Shifts Into/Across This Area.

As The Associated Cold Front Advances Into A Moist/Destabilizing Afternoon Airmass...Vigorous Thunderstorm Development Is Expected To Occur. With A Belt Of 40 To 50 Kt Swly Flow Progged To Spread Across The Mid Mo Valley Vicinity Through The Day Atop Low-Level Warm-Sector Sselys...Shear Will Become Favorable For Rotating Storms.

As A Result...A Risk For Large Hail And Locally Damaging Winds -- And Possibly A Few Tornadoes -- Seems Likely To Materialize... Particularly Within A Zone From Nrn Ks Nnewd Into Mn/Wrn Wi During The Afternoon And Early Evening Hours...And Then Into Ia/Nwrn Mo Through The Evening Hours.

Widespread Convection Is Forecast At The Start Of Day 5 Across The Mid And Upper Ms Valley/Upper Great Lakes Area...As The Strongest Uvv Spreads Newd Into Ontario With Time. Widespread Clouds / Precipitation And Thus Limited Destabilization Potential Would Appear To Be A Limiting Factor For Significant Severe Weather.

By Day 6...A Belt Of Fast Wly Flow Aloft Should Reside Across The Nrn Half Of The Conus...But With A Weakening/Increasingly W-E Oriented Front Extending Across The Midwest And Into The Plains... Location And Degree Of Severe Potential Appear Too Uncertain To Warrant Any Areal Highlights.

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