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US Extended Forecast thru Feb 23

...Overview And Preferences...

Expect Large Scale Mean Flow To Trend From A Flat/Progressive
Regime To An Amplified Ern Pac Ridge And Downstream Trough.

As This Evolution Takes Place Guidance Is Finally Appearing To
Converge Somewhat With Details Of A Leading Wrn Conus Shrtwv That Will Influence Sfc Evolution From The Plains Toward James Bay
Wed-Fri.

While Uncertainty With This Part Of The Fcst Has Decreased... Much Greater Spread/Run To Run Continuity Changes Exist With Trailing Energy Reaching The West Thu-Fri And Continuing Downstream Thereafter With Significant Influence On Exact Sfc Details Over The Ern Half Of The Conus.

For Days 3-5 Wed-Fri A Compromise Among The 06z Gfs/00z Ecmwf/00z Ecmwf Mean Provides A Good Intermediate Soln For Primary Features Of Interest.

Prefer To Adjust Toward The 00z Ecmwf Mean By Day 7 Sun By Way Of An 80/20 Blend Of The Ecmwf Mean/Ecmwf On Day 6 As The Best Way To Maintain As Much Continuity As Possible Over The Conus
While Maintaining A Stronger Ern Pac Ridge Than Recent Gfs Runs.

...Guidance Evaluation...

The Preferred Blend Helps To Resolve Lingering Minor Detail Diffs
With The System Fcst To Cross The Northeast At The Start Of The
Period On Wed.

Model/Ensemble Guidance Is Trying To Converge For The Wed
Night-Thu Night Plains/Grtlks/Srn Canada Evolution That Has
Displayed Considerable Spread In Recent Days.

Both Gfs/Ecmwf-Based Model/Ensemble Solns Have Shown Some Adjustments Toward Each Other In Some Respects... With A Srn Canada Sfc Low Expected To Merge With A Plains Through Grtlks Wave Somewhere Between The Grtlks And James Bay.

As Of Early Thu The 00z Gfs/Gefs Mean Are Nwd Of Consensus With The Srn Canada Sfc Low As Of Early Thu While The 00z Ecmwf Could Be A Tad Fast With The Plains-Grtlks Wave.

The Next Feature Of Interest Will Be A Shrtwv Reaching The Pac Nw
On Thu And Rockies/High Plains On Fri.

During The Latter Half Of The Period... Over The Past Day Or So The Gfs/Ecmwf And Gefs Means Have Trended Toward More Of A Positive Tilt For The Overall Mean Trough From A Neutral Tilt While The Ecmwf Mean Has Displayed This Positive Tilt For A Longer Time.

This Mean Trough Orientation Could Allow For A Fairly Progressive Ejection Of The System Reaching The Rockies/High Plains Fri... And If Dynamics Are Sharp Enough Support A Well Defined System Reaching The Nern Conus Or Sern Canada Late In The Period As Indicated By The 00z-06z Gfs/00z Ecmwf.

Lack Of Shrtwv Details In The Means Keeps Their Sfc Reflection More Subdued With The Ecmwf Mean Providing The Best Compromise Between The Faster Gefs Mean And Slower Cmc Mean.

Prefer Such A Conservative Approach For Now Until Operational Runs
Establish Better Continuity And Spread Of Individual Ensemble Sfc
Lows Decreases.

Over The Ern Pac Gfs-Based Guidance Continues To Bring More
Upstream Energy Into The Amplifying Ridge Aloft Than Other Solns.
Until Trends Recommend Otherwise... Biases Favor Leaning Away From The Gfs Scenario.

...Sensible Weather Highlights...

Rnfl And Higher Elev Snow Over The Nrn Half Of The West... And
Heaviest Near The Coast And Wwd-Facing Slopes Of The Cascades ... Should Taper Off From West To East Late This Week Into The Weekend As The Axis Of The Amplifying Ern Pac Ridge Aloft Approaches The West Coast.

Nrn Areas Of The West Should See Below Normal Temps.

Farther Swd There Should Be A Cooling Trend Early But With Temps
Remaining Near To Above Normal... And Psbly Some Warming Again
Over Ca.

System Crossing The Northeast At The Start Of The Period Wed
Should Be Accompanied By Only Lgt Pcpn.

Expect More Active Weather Upstream With Pcpn Developing Over The Ern Plains/Ms Vly Around Wed Night And Expanding Ewd/Newd With Time.

Potential Still Exists For The Front Trailing From The Plains/Ms Vly System To Stall Over The South Late This Week Into The Weekend As Flow Aloft Becomes More Parallel To The Front And Then Another Shrtwv Aloft Psbly Approaching And Passing By To The N... While Low Lvl Flow Brings In Gulf Mstr From The S.

Highest Probability Of Hvy Rnfl Is Currently Expected From The Lower Ms Vly Through The Carolinas.

Nrn Half Of The Plains Ewd May See Another Round Of More Modest Pcpn During The Latter Half Of The Period.

From Wed Into Fri Very Warm Air Will Progress Ewd From The Plains ... With Anomalies Reaching Plus 10-20f For Highs And Locally Plus 20-30f For Lows.

Colder Air Will Spread Into The Nrn Plains Late This Week.

By Next Sun Below Normal Temps Should Extend From Most Of The Plains Into The Ms Vly And Wrn Oh Vly/Grtlks.

Thus Expect Wintry Pcpn To Be Confined To Very Nrn Areas During The First Half Of The Period... Trending Farther Sewd By Fri-Sun.


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