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US Preliminary Extended Weather thru Dec 19

Large Scale Overview...

The Medium Range Period Over The Conus Will Be Driven By Two
Mid-Level Positive Height Anomalies... The First A Mainly Stationary Center Over The North Central Pacific Near 40n/170w And The Other A More Mobile Center Moving Out Of The Great Lakes Northward Through Hudson Bay. These Two Areas Support One Another In Teleconnections And Both Favor Broad Troughing From The West
Coast Of The Conus Eastward. This Should Drive A Series Of Pacific-Born Systems Through The Pac Nw And Rockies/Sw Into The
Plains And Then Toward The East Coast. The Northern Tier Will Be
Relatively Quiet.

Model Guidance...

The 12z-18z/11 Guidance Largely Agree On The Synoptic Setup But
Have Struggled In Recent Days As To The Timing/Amplitude Of
Pacific Energy Streaming Eastward Just South Of The Aleutians.
With The Jet Progged At 150-180kts... It's No Wonder The Models
Have Had Trouble.

On The Flip Side... The Gefs And Ecmwf Ensemble Means Showed Better Agreement Today Than 24 Hrs Ago With The System Progression And Did Not Want To Stray Too Far From Their Good Agreement.

As Is Fairly Typical... The Gefs Slightly Outpaces The Ecens And The Ecmwf Trails The Ensembles. While Model Trends Verifying In Recent Days May Have Been Toward A Quicker Solution... The Forecast Trend Into A More Blocky Pattern /Or At Least Less Progressive/ Suggests Leaning Toward The Slower Side Of The Guidance. As Such... Based The Forecast On The 12z/11 Ecmwf
Ensemble Mean And Its Nearest Deterministic Solution... Which Was
The 12z/11 Ecmwf Days 3-6 Before It Became A Slower Outlier.
Incorporated The 12z/11 Gfs By Next Wed/D7 As It Offered A
Reasonable Solution In Light Of The Ensembles.

Sensible Weather Impacts...

Over The Upcoming Weekend... A System In The Central Plains Will
Move Northeastward And Spread Warm Advection Precip Through The
Great Lakes And Into The Northeast With Gulf-Fed Moisture Through
The Southeast. Expect A Brief Warmup Ahead Of The Cold Front With
A Cooldown Back To Just Normal Behind It.

Back Over The West... With The Flow Generally Into Washington/ Oregon Initially... Precipitation Should Focus Along The Coast And Into The Terrain Before Lessening Through The Great Basin And Southwest.

As The Energy Progresses Through The Southern Plains By The Start Of Next Week... The Models Really Diverge In Its Track... Preventing Much Specificity To The Forecast. However... Based On The Ecmwf Ensemble Probability... Sfc Low Pressure Is Forecast To Track Through The Southeast And Then Exit The East Coast Somewhere In The Mid-Atlantic. The Potential Exists For Heavy Comma Head Precipitation To The Nw Of The Sfc Low And Also Along And Ahead Of The Cold Front. Again... This Is Dependent On Its Track And Intensity... Which Will Ebb And Flow Over The Next Several Days.


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