US Extended Forecast thru Dec 22

...Another Arctic Airmass Over The Northern Plains Thursday-Sunday...

...Heavy Rain Possible In Oh/Tn Valley & Southeast Next Weekend...

...Overview And Guidance Preferences...

Upper Pattern Forecast To Transition To A Ridge/Trough/Ridge
Orientation By The End Of The Week Over The Eastern Pacific/ Southern Rockies/Western Atlantic... Respectively.

Split-Flow Regime Can Wreak Havoc With Timing/Interaction But The
Models/Ensembles Have Handled The Forecast Evolution Fairly Well
Over The Past Several Runs.

Recent Gfs Runs Seem To Have Drifted Just Outside The Good Clustering Of The 06z Gefs And 00z Ecmwf/Ecens Mean Right From Wed/D3 Especially Over Sw Canada Into The High Plains As It Becomes Quicker Than Consensus.

By Fri-Sat/D5-6... The Gfs Lies On The Slower Side Of The Ensemble
Spread To Take The Southwestern Closed Low Eastward Which Has
Minimal Ensemble Support At This Time.

In The Northern Stream... Much Disagreement Exists Among The Guidance On How Quickly To Push Energy Eastward And How Far South To Push The Jet Into Southeastern Canada /Farther South In The The Gfs Vs The Other Models/.

This Coupled With Questions Over How Strong To Maintain The Ridge In The Bahamas /Stronger Seems To Be A Recent Trend The
Past Few Weeks/ Will Affect Where The Resultant Sfc Wave Along The
Cold Front Moves Through The East By Next Weekend.

Wpc Preference Leans Toward A Stronger Se Ridge And Thus A Much More Inland Track Of Any Sfc Wave... But With Guarded Confidence.

All Things Considered... The 06z Gefs And 00z Ecmwf/Ecens Mean Offered A Good Starting Point Wed-Fri/D3-5 Before Trending Toward A 70/30 Ecens/Gefs Blend Sat-Sun/D6-7.

...Sensible Weather Impacts...

Arctic Airmass Drifting Through The Northern Rockies Into The Plains And Upper Great Lakes Should Yield Another Round Of 15f To 25f Below Normal Temperatures With The 10f To 20f Above Normal
Temperatures Pushed Ahead Of The Cold Front From The Central
Plains Wed/D3 Into The Southeast By Next Weekend.

As The Southern Stream Upper Low Ejects Eastward... Strengthening Jet Coupled With Southerly Low Level Flow And Near-Record Monthly High Pw Values Should Set Up A Heavy Rain Potential In The Oh/Tn Valley Into The Southeast Next Weekend... Depending On The Exact Evolution.

Signal In The Ensembles Has Been Present For Three Days Now With Gefs/Ecens/Cmce Ensemble Mean Qpf Fairly High For A 7-Day Lead Time. Over-Running Precipitation Event For The Ohio Valley /Just Rain Along And To The East Of The Boundary/ With Winter P-Type Over-Running Moisture Near The Midwest/Eastern Lakes As Very Shallow Canadian Surface High Remains In Place Over Southeast Canada... Again Highly Dependent On The Speed Of The
Northern/Southern Stream With Embedded Energy.

Winter Weather Conditions Likely For The Northern Plains And Great Lakes North Of The Surface Cyclone Track.


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