Severe Weather Threat thru Aug 23

Sat Aug 16 Convective Outlook
Storm Prediction Center Norman Ok
No Svr Tstm Areas Forecast...

Marginal Risks For Severe Hail And Wind Will Exist Across Parts Of The Missouri Area...As Well As Eastern Montana And The Western Dakotas This Afternoon And Evening.

A Low-Amplitude Shortwave Trough Will Shift Slowly E/Ne From The Nrn Rockies To Srn Saskatchewan. An Associated Surface Trough Should Approach The Mt/Dakotas Border Area By Early Evening. A Weak Mid-Level Impulse Should Drift Se Across The Lower Mo To Mid-Ms Valleys. A Broad Upper Trough Will Persist From Se Canada Across The Ne States.

Mo Area...

Low-Level Waa Ahead Of The Weak Mid-Level Impulse Supports Early Saturday Morning Convective Cluster Across Nrn Portions Of Mo. This Convection Will Wane As The Llj Diminishes...With Destabilization More Prominent S/W Of Remnant Morning Activity.

This Should Give Rise To Redevelopment Of Isolated To Scattered Storms By Late Afternoon Centered Across Cntrl Mo... Immediately Ahead Of The Mid-Level Impulse. Middling Mid-Level Lapse Rates And Modest Effective Shear Should Favor Multicells Capable Of Marginally Severe Hail And Locally Damaging Winds.

Ern Mt And Wrn Dakotas...

Presence Of Upper 50s To Lower 60s Dew Points Ahead Of The Surface Trough Should Foster A Moderately Buoyant Air Mass With Mlcape Of Around 1000-1500 J/Kg. Convergence Along The Trough Should Aid In Isolated To Scattered Storms By Late Afternoon.

A Confluent Mid-Level Flow Regime Over The Nrn High Plains Should Aid In Sustaining 25-35 Kt Wlys At 500 Mb. Although Low-Level Winds Should Remain Light...Moderate Effective Shear Amidst Predominately Cellular Convection May Yield A Few Marginally Severe Hail Events And Locally Strong Winds.

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Sun Aug 17 Convective Outlook
Storm Prediction Center Norman Ok
No Svr Tstm Areas Forecast...

Strong Thunderstorms Will Be Possible Across Portions Of The Northern And Central Plains As Well As Over The Mid-Mississippi And Lower Ohio Valleys. Locally Strong Wind Gusts And Some Hail Will Be Possible With These Storms Sunday Afternoon And Evening.

Relatively Low Amplitude W/Nw Flow Will Encompass Much Of The U.S. From The Nrn Rockies Across The Nrn/Central Plains And Into The Midwest.

Two Embedded Shortwave Troughs Will Focus Strong To Severe Thunderstorm Potential Sunday Afternoon And Evening.

The First...Over The Mid-Ms Valley Moving Ewd Toward The Lower Oh Valley By Monday Morning...Will Lead To Enhanced Midlevel W/Nw Flow /30-40 Kt 700-500 Mb/ Over The Region. At The Sfc...A Weak Low Will Track Ewd Over Central/Srn Il Into Ind And A Trailing Cold Front Extending Swwd From The Low Will Push E/Se Toward The Ms River From Se Mo Into Nrn / Cntrl Ar By 00z Monday.

The Second Shortwave Impulse Will Drop Sewd From The Srn Canadian Prairie Provinces Across The Nrn And Cntrl Plains. A Sfc Trough Will Extent Swd Through The Wrn Dakotas And Wrn Neb...With A Dryline/Cold Front Surging Ewd During The Afternoon And Evening.

Mid-Ms And Lower Oh Valleys...

Showers And Thunderstorms May Be Ongoing Across Parts Of Il/Mo Sunday Morning And Associated Cloud Debris Adds Uncertainty To The Evolution Of The Severe Threat Sunday Afternoon From Se Mo/Nrn Ar Ewd Into Sw Indiana And Wrn Ky/Tn.

Depending On How Much Heating Can Occur... Dewpoints In The 70s Could Aid In Potentially Moderate To Strong Instability During The Afternoon.

Effective Shear Around 25-35 Kt Would Allow For Semi-Organized Storm Clusters Or Line Segments Capable Of Gusty/Locally Strong Winds And Some Hail. Deterministic Guidance Varies In The Degree Of Heating That Occurs And Also In How Much Deep Layer Shear Strengthens In Response To The Approaching Upper Shortwave Trough.

As Such...The Threat Appears Too Conditional At This Time To Introduce A Slight Risk...But One May Be Needed In Subsequent Outlooks Should Better Agreement Amongst Guidance Become Better Aligned.

Portions Of The Nrn And Central Plains...

Thunderstorms Are Expected To Develop Ahead Of A Sewd Advancing Cold Front Across The Wrn/Cntrl Dakotas During The Afternoon And Further South Into Wrn/Cntrl Nebraska Along A Sfc Dryline. S/Sely Low Level Flow Will Transport Upper 50s To Low 60s Dewpoints Across The Area And Moderate Instability Will Develop By Afternoon.

0-6 Km Shear Around 30-40 Kt In Conjunction With Steep Lapse Rates Will Be Sufficient For At Least Isolated Strong To Severe Thunderstorm Development With Some Hail And Wind Possible. The Better Thermodynamic Environment Will Be Over Neb...But Forcing For Ascent And Deep Layer Shear Will Be Weaker Here Further Removed From The Upper Impulse Over The Dakotas. This Should Preclude An Upgrade To Slight Risk.

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Mon Aug 18 Convective Outlook
Storm Prediction Center Norman Ok
No Svr Tstm Areas Forecast...

Isolated Strong To Severe Thunderstorms May Impact Portions Of The Central Plains And The Mid-Missouri Valley On Monday. Should These Storms Develop...Hail And Strong Winds Will Be Possible.

Low Amplitude Nwly Flow Will Be Maintained On Monday Across The Central And Ern Conus. A Shortwave Impulse Over The Lower Oh Valley Will Continue To Track Ewd Toward The Mid-Atlantic By 12z Tuesday.

The Associated Sfc Low Located In The Vicinity Of Srn Indiana Monday Morning Will Shift Ewd Across Ohio And The Central Appalachians And Chesapeake Bay By Tuesday Morning As A Weak Cold Front Sweeps Sewd Across The Oh Valley. Widespread Showers And Thunderstorms Are Expected From The Oh/Tn Valleys Into The Appalachians...But Severe Threat Appears Low At This Time Given Limited Instability And Poor Lapse Rates.

Further To The West...Another Shortwave Trough Over The Nrn / Central Plains Will Shift E/Se Through The Period Across The Upper Ms Valley Toward Lake Michigan. A Weak Sfc Low Will Shift Ewd Across The Upper Ms Valley And A Cold Front Will Slide E/Se From The Ern Dakotas/Central Nebraska Into Ks And Across Ia/Mo.

Portions Of The Central Plains And Mid-Mo Valley...

Potential For Organized Severe Storms Is Uncertain On Monday...As One Or More Thunderstorm Complexes May Be Ongoing/Approaching The Area During The Morning.

Forecast Guidance Is Varied In This Scenario With Some Depicting Ongoing Storms And Others Developing/Re-Intensifying Storms Later In The Afternoon Ahead Of The Cold Front. Depending On Morning Conditions...Strong To Severe Storms Capable Of Large Hail And Strong Winds Could Be Possible During The Afternoon Given Adequate Heating. Due To Uncertainty And Potentially Conditional Nature Of The Threat...Only Low Probabilities Will Be Introduced At This Time.

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Aug 19-23 Convective Outlook
Storm Prediction Center Norman Ok

Medium Range Guidance Indicates That A More Amplified Pattern May Try To Develop During The Extended Forecast Period...With An Upper Trough Over The Western U.S. And Along The East Coast...And An Upper Ridge Over The Plains Or The Mississippi Valley. Large Differences In The Exact Placement And Strength Of These Features Exist Amongst Various Guidance.

While This General Pattern Would Typically Favor Chances For Strong To Severe Storms Mainly From The Nrn/Cntrl Plains Into The Mid And Upper Ms Valley...Confidence In Organized Severe Storms Is Too Low To Warrant Any Highlights At This Time. Differences Among Guidance Leads To Difficulties Timing And Placing Shortwave Impulses Moving From The Western Trough Thru The Plains/Central U.S. Ridge.


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