US Final Extended Weather thru Dec 9

Day 1...


Changes Made Btwn The Prelim And Final Day1 Were Based On
Latest Observational Data. Changes Made Elsewhere Based On The
12z Ecmwf Or 18z Nam/Gfs Were Minor.

Concerning The Shrtwv Trof Moving Inland Over The Wrn U.S....

Model Mass Fields From The 12z Runs Remained In Vry Good Agreement Handling This System. The Model Qpf Was Also Very Similar.

Main Focus For Pcpn Will Be Shifting South Across Parts Of Ca As
The Mid/Upper Level Flow Becomes Northwest Following The Passage Of The Upper Trof And Broad Cyclonic Flow Is Temporarily Replaced By Mid Level Shortwave Ridging.

Moderate To Locally Heavy Pcpn Rates As Of Late Sunday Morning Across The Central Sierra Nevada Ranges Is Expected To Taper Off Quickly And Much Of Ca/Nv And Southern Ore Dries Out As High Pressure Noses In From The Pacific Ocean And Broad Cyclonic Flow In The Low/Mid Levels Is Replaced By Mid Level Shortwave Ridging.

Meanwhile..The Strength Of The Synoptic Scale Forcing And
Available Moisture Will Be Enough To Continue Supporting Areas Of
Snow From The Northern Rockies And Great Basin Into Parts Of Co/Wy As The Main Wave Propagates Eastward. The Widespread Mdt To Hvy Pcpn There As An Evolving Sfc Low And Contribution Of A Stg Wly Upslope Component Help To Enhance The Lifting Processes. Generally Light Pcpn Should Linger In Parts Of The Pac Nw Where Onshore Flow Persists...But Rafl Rates Should Generally Be Light.

In Both Areas...The 12z Nam/Ukmet And 00z Ecmwf Coverage/Pcpn
Totals Were Similar And Were Given Most Weight In Preparing The
Hpc Pcpn Forecast.

Shrtwv Trof Now Advancing Ewd Fm The Eastern Great Lakes...

Lgt To Mdt Pcpn Totals Are Expected Along And Ahead Of This
Feature And Its Asoctd Front As It Progresses Ewd Thru The Pd.
Increased The Amounts A Bit Along The Oh River Where The Lightning Detection Network Has Been Showing Activity Throughout Much Of The Morning. Dont Expect To See Too Much Pcpn Making It Very Far East Of The Appalachians. Model Qpfs Are Similar...And We Tended To Place The Axis Of Heaviest Pcpn Ahead Of The Shortwave Which Also Was In The Right Entrance Region Of A Weak H25 Jet Streak.

Upper Midwest To Western Great Lakes...

Shortwave Energy Kicking East Of The Rockies Should Stay North Of
The Border...But A Vort Lobe Extending South From That System Will
Graze The Upper Midwest To Wrn Great Lakes. Moisture Availability
Is Limited For More Than A Tenth Of An Inch Of Pcpn. Gave Most
Weight To The Nam/Ukmet Since The Gfs/Ecmwf Looked A Little
Aggressive With Light Pcpn Amounts Extending Back To The Central
Ms Valley.

Days 2/3...

Western U.S...

Another Amplified Shortwave Trough Will Dig Toward The Coast On
Tue...Once Again Focusing A Plume Of Deep Moisture Across Western Wa/Ore Into Northern Ca. 850-700 Mb Moisture Flux Anomalies Are Forecast By The Gfs/Nam To Once Again Well Exceed 2 Standard Deviations And Reach As High 4 Across The Region With Pws Climbing Above An Inch Along The Coast.

A Weak Wave Along The Associated Front With A Favorable Upper Jet Couplet Will Help To Focus The Heaviest Amounts Of The Period Along The Southern Ore Coast Into The Northwestern Corner Of Ca Where An Additional 1-3 Inches With Locally Heavier Amounts Are Expected...Once Again Raising Runoff Concerns.

As The Shortwave Continues Inland...Moisture Spilling Eastward Across The Northern Intermountain Region Will Fuel A Secondary Max In The Upslope Regions Of The Northern Rockies...Particularly In The Vicinity Of The Bitterroot And Sawtooth Ranges. Refer To The Hpc Winter Weather Suite For Details Concerning The Heavy Snow And Icing Threats Across The Region.

Great Lakes/Ms Valley To The Eastern U.S....

The Frontal System And Associated Shortwave Currently Impacting
The West Is Forecast To Reach The Midwest States By Monday Night
And Tuesday.

As A Developing Surface Low Develops And Becomes Occluded Over Ontario A Trailing Cold Front Extending Southeastward Through The Great Lakes Into The Mid Ms Valley Early Tue Will Have Enough Moisture Convergence Along It To Generate Mainly Light To Locally Moderate Qpf Amounts.

As The Front Continues South And East On Tue...Deepening Moisture Along With Enhanced Divergence Along The Right-Entrance Region Of The Upper Jet Could Help To Produce Some Heavier Precipitation From The Lower Ms Valley Northeastward Into The Tn And Oh Valleys.

Front Is Expected To Push Through The Lower Great Lakes Region/ Oh And Tn Valleys Into The Eastern U.S. Tue Night Into Wed.

While Diminishing Moisture Along The Boundary Will Limit The
Potential...Strong Upper Forcing May Still Help To Produce Moderate To Locally Heavy Amounts. With A Well-Defined Vort Digging Through The Base Of The Trough As It Moves Across The Northeast...The Latest Models Are Trending More Amplified And Slower Aloft With A Wave Developing Along The Frontal Boundary As It Moves Offshore... Resulting In A More Prolonged Period Of Precipitation And Heavier Amounts Along The Northern New England Coast Late In The Period.

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