US Preliminary Extended Weather thru Jan 6

Below Normal Temperatures Expected Across Much Of The United

By Day 4...The Ensemble Spread By Itself Would Suggest Anything
Goes Along The West Coast As Energy From The East Pac Migrates
Eastward Into North America.

However...The Forecast Philosophy Really Does Not Change Much... With The Ridge Rebuilding Along 120w On Day 7. The Reason For The Large Spread In The Day4 Time Frame Remains Tied To The Individual Models And Their Run-To-Run Variability In Handling The Split-Flow Pattern And Embedded Energy Moving Around The Ridge Through Southwest Canada And The Desert Southwest.

And More Importantly...How Will The Day4-5 System Interact With The Upper-Level Ridge And Where Will That System Reorganize Downstream.

The Medium Range Temperature/Precipitation Progs Suggest Very
Little Change And Not Much In The Way Of Appreciable Precipitation
Potential Except Along The Gulf Coast...Great Lakes And New
England. Aside From Some Downsloping (Adiabatic Warming) Across And Immediately Downstream Of The Northern Rockies... Mt/Wy/Co Mainly...The Sensible Weather Parameters Beneath The Upper Ridge Appear To Be 'Unphased' By The Day3-4 Pacific System And Its Attempt To Take The Northern Route Through Alberta And
Saskatchewan Before Entering The Confluent And Dry Northwest Flow Anchored Over Manitoba And The Upper Midwest.

Temperatures Should Remain Well Below Normal In The Great Basin And Desert Southwest/4 Corners Area.

The Baseline Guidance Used In This Morning Package (29/12z Cycle)
Did Have Some Interesting Outcomes. The Canadian Solution Appeared To Take Nearly All The Energy Butting Up Against The Upper-Level Ridge Northward...And Into Bc. This Has Been The Biggest Departure. Its 'New' Northward Rather Than The Aggressive Southern Track Through Much Of California Was To Be Expected... Given It Was In Serious Trouble Last Night (Its Very Slow 28/12z Cycle
Solution) In The Gulf Of Alaska.

The Recent Runs Of The Ecmwf Still Attempt The Migration Of A Cutoff Low Along The California Coast...But The 29/12z Offered A Curiously Improbable Track Through The Center Point (Or Heart Of The Ridge Axis) Invof 40n Latitude. Its The Gfs That Continues To Be The Fast Outlier. However...Early Day 4 It Does Start Out Like The Ecmwf Track...Then Turns The System Northeastward. Curiously...By Day 6...It (The Gfs) Sides With The Ecmwf And The New Cutoff Solution Along 140w And Generally Fits Within Reason Alongside The Ecmwf Over The Aleutians And Gulf Of Alaska. That Said...

The Key For Any Appreciable Change In The Medium Range Across The Conus...Is Apparently 'Anchored' Downstream In Eastern Canada. And From What I Can Decipher This Morning...There Is Not Going To Be Much Change Through Day 7 East Of The Mississippi... Including The Great Lakes... Northeast... Midwest... Ohio Valley... Central Appalachians And Mid Atlantic States. In Fact...Hudson Bay And Its Broad Vortex Is Quasi-Stationary Through The Period...With A
Deep/Cold Trough Anchored In Place Across The Northeast And Great Lakes And A Confluent Transition Zone For The Cold Canadian
Airmass Running Wnw To Ese From Roughly Western Iowa/Eastern
Nebraska To The Outer Banks As Split-Flow Energy Upstream Exits
The Rockies.

Rainfall In The Medium Range Period Should Be Confined To The
Zonal Southern Stream...With The Gulf Coast States Receiving The
Bulk Of The Moisture And Brief Over Running Episodes In The
Southern High Plains/Rio Grande Valley.

The Higher Probabilities Of Measurable Snowfall Should Set Up In The Drier...Northern Stream And Mainly Impact The Great Lakes Region And Northeast...Upper Ohio Valley And Northern Mid Atlantic. As Mentioned Above...The Greatest Uncertainty For P-Type...Is Within
The Oscillating Transition Zone Between 35-40n Latitude... Generally East Of 100w Longitude In The Expected Flow Regime Across North America Through Day 7.

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