US Final Extended Weather thru Jan 25

...Bitter Cold Across The Upper Great Lakes And Northern New

...Arctic Chill Descends Upon The Eastern United States...

Medium Range Flow Pattern East Of 100w Will Be Dominated By A
Quasi-Stationary Upper-Level Trough Over Hudson Bay/Eastern

By The Day 5-6 Time Frame...The Prevailing Upper-Level Ridge In The West Erodes With A Strong Wave Migrating Through The Pacific Northwest...Northern Rockies And Northern Plains.

Good Continuity Was Maintained Along The West Coast...Using A Manual Blend Of The 18/00z Guidance...Including The Ecmwf Means And Aspects Of The Operational Ecmwf/Gfs Mass Field Forecasts.

Gfs/Ecmwf Operationals Were In Good Agreement To Day 4.5 (22/00z)
With The Core Of The Arctic Airmass Slowly Migrating East-Northeastward From The Upper Ms Valley To Maine And Northern New England. There Are Few Differences Between These 2 Pieces Of Guidance With This Overall Areal Spread Of This Modified Arctic Boundary Through Day 6 In The Midwest...East...Southeast...And
With A Gradual Warmup From West To East Across The Northern/ Central High Plains.

By Day 4...There Is Reasonable Evidence Of A Coastal Wave Developing Atop This Sloped Arctic Front...And Beneath A Complex 250mb Jet Structure East Of The Mississippi River. Enough Support/Evidence During The Last 48 Hours To Request A Series Of Noaa G4 Winter Recon Flights To Sample The North Central Pacific Between Hawaii And Alaska.

The 18/00z Gfs Was Not A Bad Piece Of Guidance On Day 6 In
Mt/Wy/Nd/Sd/Wrn Ne Generally Because The Operational Ecmwf Was Way Overdone With Lee Side Cyclogenesis (An Alberta Clipper)
Developing Along The Upper Front Associated With Pacific Flow
Invading From The West.

The Ecmwf's 990mb Surface Low On Day 6-7 Migrating Across Nd/Mn Looked Out Of Place Given The Lack Of Low-Level Moisture Return From The Western Gomex...A Pronounced Upper-Level Trough And Downstream Arctic Boundary Entrenched Across The Great Lakes And Eastern Conus. Manual Graphics Preferred A Manual Blend Of The Gfs/Ecmwf Mean At The Surface.

Aloft...Would Expect Some Sort Of Mid-Level Clipper-Type System To
Exit The Southern Canadian Rockies...But A Strengthening System
The Magnitude A Surface Wave/Clipper System Near 990 Mb Would Be An Extreme Example Of Merging Polar/Maritime Jet Stream

A 'Deep' Clipper Would Typically Bottom Out In The 998 Mb Ish Range At Best. I Started Out The Day 6-7 Graphics With A 'Weak' System Tracking Through The Great Lakes/Midwest.

The Surface Graphics Did Part Ways With Aspects Of The 18/00z Gfs
And Gefs Upstream...In Particular...Across The East And Central
Pacific After Day 5. The 18/00z Gefs/Gfs Are Unusually Slow With
The Progression Of A Deep Wave In The Northern Stream Westerlies
Along 45-50n Latitude. This Is The Time Frame We Broke Away From
The Previous Graphics And Sided With The Ecmwf Means.

This Does Not Change The Frontal Progression And Cold Advection Pattern Projected Days 5-7. If Anything...It Allows For Some Shortwave
Ridging (And Mid-Level Warm Advection) To Develop Downstream And Lee Of The Us Rockies Prior To The Clipper's Interaction With The Polar Jet Downstream Over Central North America And The Northern Plains.

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