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Severe Weather Threat thru Nov 21

Thu Nov 14 Convective Outlook
No Tstm Areas Forecast...

Srn Plains...

Convection That Developed Over Nm Within A Relative Cold Pocket
Aloft...Associated With A Mid/Upper Vort Max...Has Weakened With The
Loss Of Diurnal Heating.

Farther E...Scattered Shower Development Has Occurred Within A Weak Low-Level Waa Regime Across Ok And N Tx. 00z Oun Sounding Sampled Midlevel Lapse Rates Around 6 C/Km...And As Low-Levels Continue To Moisten...Narrow Cape Profiles /With Less Than 100 J/Kg/ May Evolve.

While A Few Lightning Strikes Will Be Possible Overnight Across Parts Of Central And Ern Ok...Coverage Is Expected To Remain Below 10 Percent...Precluding Inclusion In A General Thunder Area.

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Fri Nov 15 Convective Outlook
No Svr Tstm Areas Forecast...

Extensive Cyclonic Upper Flow Will Prevail Over The Conus On Friday.

This Will Be Highlighted By An Eastward-Moving Shortwave Trough From The Great Basin To The Central High Plains By Friday Night... While An Additional Trough Digs Southeastward Over The Pacific Northwest.

A Cold Front Will Spread East-Southeastward Across The Eastern Great Basin/Four Corners Area...While Cyclogenesis/Moist Advection
Otherwise Increases Across The Central/Southern Plains Into Friday
Night.

Four Corners Area...

Weak Diurnally-Maximized Destabilization Is Expected In Conjunction
With Mid-Level Cooling/Forcing For Ascent Associated With A Lead
Shortwave Trough. This Scenario Should Allow For At Least A Few
Tstms Mainly Friday Afternoon/Evening.

Southern Plains To Middle Mo Valley Friday Night...

While Continental Trajectories And The Influences Of A Lingering
Surface High Will Be Slow To Abate...Moist Advection Is Expected To
Occur Near/Above The Surface Friday Night With Aid Of A
Strengthening Low Level Jet.

The Degree Of Elevated Moistening Aloft Relative To Lingering Capping Provides A Measure Of Uncertainty Regarding The Likelihood/Coverage Of Tstms Friday Night. But Even So...A Low Probability Of Tstms /Highly Elevated/ Will Exist Late Friday Night/ Early Saturday Across Parts Of The Region.

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Sat Nov 16 Convective Outlook
No Svr Tstm Areas Forecast...

The Vigorous Short Wave Impulse Expected To Dig Into The Pacific
Northwest By Late Friday Night Appears Likely To Remain Progressive During This Forecast Period.

Considerable Variability Exists Among The Models Concerning The Speed Of This Feature Into And Through The Central U.S...With The Gfs Remaining Significantly Faster Than The Ecmwf East Of The Rockies And Through The Central Plains.

The 14/00z Operational Ecmwf And The Ecmwf Ensemble Mean Have Trended A Bit Faster...And Appear In Relatively Good Agreement With The 14/03z Ncep Sref...Which Is Faster The 14/00z Operational Nam.

It Currently Seems Most Probable That Strong Mid-Level Height Falls Associated With The Short Wave Trough Will Shift East Of The Rockies Into The Central Plains Saturday Night...Supporting A Deepening Surface Cyclone Across The Central Plains Through The Mid Missouri Valley By 12z Sunday.

In Advance Of The Primary Short Wave Impulse...And Associated
Surface Cyclone...Another Significant Short Wave Impulse And
Associated Surface Frontal Wave Are Expected To Rapidly Progress
Northeast Of The Central Plains...Into The Upper Great Lakes
Region...During The Day Saturday...Before Continuing North
Northeastward Through Northern/Eastern Ontario.

Although Low-Level Moistening Will Already Be Underway In Association With A Developing Return Flow Across The Western Gulf Coast...Toward The Upper Mississippi Valley/Upper Great Lakes Region...Deeper Boundary Layer Moisture Return Will Be Slower To Occur...And May Not Begin Increasing Substantively Across Eastern Portions Of The Central Plains/Ozark Plateau And Middle Mississippi Valley Until Saturday Evening.

Destabilization Probably Will Be Sufficient To Support Increasing Thunderstorm Activity East Of The Mid Missouri Valley Through The Upper Mississippi Valley/Upper Great Lakes Region During The Day Saturday...But Any Severe Thunderstorm Potential Still Appears Likely To Await Better Moisture Return...And Mid-Level Forcing Associated With The Strong Upstream Impulse.

Lower Central Plains Into Upper Mississippi Valley...

Models Are Becoming More Suggestive Of Increasing Severe Storm
Potential Across The Central U.S. During The Latter Half Of This
Forecast Period.

Due To Considerable Lingering Uncertainties... Only Sub-Slight Risk Severe Probabilities Are Being Introduced For Now...But These Could Be Increased In Later Outlooks For This Time Period.

The Areal Delineation Of The 5 Percent Severe Probabilities Was Heavily Influence By The Aforementioned Ecmwf/Ecmwf Ensemble And Ncep Sref Ensemble Depiction Of Developments. Increasing Low-Level Moisture/Cape And Vertical Shear Along The Western Edge Of The Strengthening Low-Level Jet /50-60+ Kt At 850 Mb/ May Provide The Focus For Severe Storm Development...As The Leading Edge Of Stronger Mid-Level Forcing For Upward Vertical Motion Shifts Into The Plains.

This Could Be As Early As Late Saturday Evening...Before Potential
Increases And Slowly Develops Eastward Overnight. The Environment May Become Conducive To The Development Of Supercells...And The Evolution Of A Squall Line.

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Nov 17-21 Convective Outlook

Some Uncertainty Lingers...But Trends In The Medium Range Forecast Guidance Are Increasingly Suggestive Of The Development Of An Environment Supportive Of An Outbreak Of Severe Thunderstorms Across Parts Of The Middle Mississippi Valley Eastward Through Much Of The Ohio Valley On Sunday.

Most Guidance Now Appears Generally Faster With The Continued Eastward Progression Of A Strong Short Wave Trough...From The Central Plains Early Sunday To The Lower Great Lakes/Upper Ohio Valley/Central Appalachians Region By Late Sunday Night.

Most Models Are Now Suggestive That This Will Be Accompanied By Strong Surface Cyclogenesis...With Most Rapid Surface Pressure Falls Across Parts Of The Great Lakes Region And Ohio Valley Late
Sunday Afternoon Into Sunday Night.

A 90+ Kt 500 Mb Jet Streak Nosing Through The Ohio Valley...Coupled
With Strengthening Southerly Warm Sector 850 Mb Flow...Perhaps In
Excess Of 70 Kts Across Parts Of The Ohio Valley Into The Lower
Great Lakes...Will Contribute To Very Strong Deep Layer Wind Fields
And Shear. It Also Appears Increasingly Probable That This Will
Coincide With An Influx Of Seasonably High Moisture Content At Least
As Far North And East As The Lower Ohio Valley...Contributing To
Sufficient Cape For Vigorous Storm Development.

Supercells With A Risk For Tornadoes Will Be Possible...Particularly In Early Stages Of Convective Development...Perhaps As Early As Mid Day Across Parts Of The Middle Mississippi Into Lower Ohio Valley Valley.

Eventually...Though...Activity Probably Will Evolve Into A Squall Line With Damaging Straight-Line Winds Becoming The Most Prominent
Severe Threat.

It May Not Be Out Of The Question That This Could Progress Into Parts Of The Mid Atlantic Seaboard And Northeast Late Sunday Night Into Monday...But This Is Still Too Uncertain To Delineate A Regional Severe Risk Area East Of That Currently Depicted.

Thereafter...Convective Potential Through The Remainder Of The Period Appears Low.


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