US Final Extended Weather thru Jan 6

...Below-Average Temperatures Expected Across Much Of The United

Changes Taking Place During The Short Range Period Bring Us To A
Split Flow Setup In The West By Day 3.

The Southern Stream Will Become Anchored By An Upper Low In Mexico Toward The Rio Grande Valley...Which Will Be Made A Quasi-Permanent Feature Via Occasional Releading Performed By Southern Stream Energy Off The Pacific.

Meanwhile Northern Stream Systems Will Skirt The Pacific Northwest ...Top The Ridge...And Then Dive Into The Midwest.

Rainfall In The Medium Range Period Should Be Confined To The
Zonal Southern Stream...With Really Only The Immediate Gulf Coast
And Southeast Coast Of The U.S. Remaining In Play For Rainfall On
Days 4/5.

Dry Continental Air Will Continue To Shove The Polar Front Farther Into The Gulf...Resulting In Mainly Dry And Cold Weather Over The Bulk Of The Nation By Days 5-7.

The Primary Areas Of Uncertainy In This Pattern Will Be The Depth
That The Northern Stream Waves Are Able To Achieve In The Midwest ...And The Handling Of Split Flow In The West. Though Cyclogenesis Will Be Absent Or Greatly Limited By A Steady Supply Of Cold And Stable Low Level Air...The Cold Mid/Upper Troughing Over The Midwest Should Produce Some Higher Probabilities Of Measurable Snowfall Mainly Impacting The Great Lakes Region And Northeast... Upper Ohio Valley And Northern Mid Atlantic.

Model Choice...

Although There Is Agreement Upon The Pattern Described Above... There Are Meaningful Differences With Respect To Shortwaves. All Of The Operational Models Fit Our Conceptual Model At One Time And Place Or Another...But Not One Run Does A Good Job Throughout The Medium Range Period.

The 00z Ecmwf Finally Trended A Little Less Agressive With A Closed Low Into California Day 3/4...But It Is Still Something Of An Outlier... Supported By Only A Handful Of Its Ensemble Members. We Prefer To Take A Lesser Amplified System Over The Top Of The Ridge As The Ukmet And Gfs Do.

Toward Day 6/7...The Ecmwf And Its Ensemble Are Slower In The
Eastern Pacific...With The Operational Being Particularly Strong / Deep / Slow. We Prefer The More Progressive Look Of The Gfs And Ec Ensemble Mean...With This Idea Also Having Support From The
00z Ukmet And Canadian.

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