US Preliminary Extended Weather Update thru Dec 22

A Very Active Mid-December Weather Pattern Next Week...

Significant Sensible Weather Changes And Winter Weather Potential
Gradually Shifts Focus Next Week From The West...Great Basin And
Rockies To The Plains...Midwest And Northeast.

Very Little Change Adjustment Needed East Of The Continental
Divide With The 15/00z Ecmwf And Gefs Ensemble Packages In Very
Good Longwave Agreement Through Next Week.

A System In The Central Rockies Ejects East-Northeastward Out The Central Rockies Next Wednesday And Thursday...Then Tracks The System Through The Midwest...Ohio Valley And The Northeast.

Sprawling Canadian High Pressure Spreads Across The Majority Of The Continental US Behind This System...With Another Cold Frontal Passage For The South And A Coastal Storm For The Northeast.

A Building Surface And Upper-Level Ridge With The Key Being...A Quasi-Stationary Ridge...In The Western Half Of The Nation Spells A Cold And Blustery Trough Pattern East Of 90w Longitude From The Canadian Border To The Central Gulf Of Mexico And Eastern Seaboard For Day 6-7.

In The West...A Persistent Ridge Of Very Cold High Pressure Locks
Into Place Behind The Tuesday Pacific Front...And By Friday...This
Ridge Builds Slowly Westward To The Coastline. The Resultant
Stagnation Of The Flow Pattern In The West Is Handled Reasonably
Well By The Gefs/Ecmwf Means...Allowing For A Cutoff Low To
Meander Offshore Invof 130w-135w Longitude With No Appreciably Tap Of Moisture/Dynamics From The Gulf Of Alaska. The Operational
Ecmwf/Gfs Are Somewhat Different In Handling The Weak Shortwaves Rotating Around The Cutoff...But Both Essentially Keep The Cyclonic Flow Over Open Water And Maintain A Split-Flow Pattern
Aloft.


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