US Extended Forecast thru Mar 17

Overview...

Large Scale Flow Continues To Feature A Wrn Noam/Ern Pac Mean
Ridge With Troughing Farther To The E.

For Embedded Features The Model And Ensemble Guidance Is Fairly Agreeable For The First 2-3 Days Of The Period... But Then Diverges With The Ultimate Evolution Of Pac Energy Entering Wrn Noam Around Fri Night And Degree Of Separation With An Upstream Trough Farther Offshore.

As A Result By Days 6-7 Sun-Mon There Is Lower Confidence In Fcst
Specifics Over The Ern Half Of The Conus/Wrn Atlc And Along The
Nrn Half Of The West Coast.

Guidance Evaluation And Preferences...

With The Deep System Near The New England Coast As Of Early Day 3 Thu... The 06z Gfs/Gefs Mean Have Trended Toward The 00z
Ecmwf/Ecmwf Mean That Are Closer To The Coast Than The 00z
Gfs/Gefs Mean.

Behind This System Low Pressure Tracking Along/N Of The Us-Canadian Border Will Bring A Front From The Plains Through The Northeast.

Gfs/Gefs Mean And Ecmwf/Ecmwf Mean Runs Are Persistent With Their Respective Tracks... Gfs Farther Swd... While The Cmc/Ukmet Are Generally Between The Two.

Meanwhile A Modest Upr Low Over The West On Thu Will Open Up And Eject Ewd.

The 06z Gfs Is On The Fast Side Of The Guidance Spread With This Ejecting Energy And A Weak Sfc Reflection From The Srn Plains Ewd During Fri-Sat.

Finally As Of Early Sat Recent Gfs/Ecmwf Runs Are Within A Typical
Day 5 Error Range With Ern Pac Energy Reaching The Nrn Rockies And Vicinity.

For Days 3-5 Thu-Sat A Blend Of The 06z Gfs/Gefs Mean And 00z Ecmwf/Ecmwf Mean Provides A Reasonable Fcst For Consensus
Or A Desired Compromise... With 06z Gfs Weighting Sufficiently
Small Not To Have An Adverse Impact Over The South.

By The Latter Half Of The Period The Fcst Becomes Significantly More Complicated With Increased Potential For Significant Error.

First... Solns Differ Over The Extent To Which Flow Within An Ern
Pac Trough Will Separate By Sun-Mon.

This Evolution Will Then Determine The Shape Of The Ridge Over The Wrn Conus... Which In Turn Will Influence The Amplitude And Timing Of The Shrtwv Energy Near The Nrn Rockies As Of Early Sat.

Flow Around The Mean Upr Low Over The Ern Half Of Canada May Also Have A Part To Play By Early Next Week As Well.

The Past Two Ecmwf Runs And 00z/06z Gfs Runs On Their Own Suggest How Much Sensitivity There Is Between Energy Amplifying Into The Srn Plains Versus Progressing Through The Southeast... And Not Surprisingly The Ensemble Spread Widens Significantly In This Time Frame.

Some Input From Operational Models Appears Reasonable Over The Ern Pac As They Agree Fairly Well Upon An Upr Low Being Left Behind Near 30-35n 140-145w While Nrn Stream Energy Continues Into Wrn Noam... Versus The Ensemble Means That Maintain A More Phased Trough As Is Typically The Case Due To Combining Their Varied Members.

Gfs Runs Could Be A Little Fast With The Nrn Stream Energy.

Farther Ewd The 06z Gfs Provides A Less Appealing Soln Due To Its Hudson Bay Upr Low Straying W/Sw Of Consensus Around Sat-Early Mon Leading To A Neg Tilt Trough Over The Ern Conus.

Even If There Are Question Marks Over Ensemble Mean Details Near The West Coast Late In The Period... At Least The Ecmwf Means Have Been Fairly Stable In Showing Sfc Low Pressure Near The Sern Coast By Next Mon.

Gefs Means Have Been Waffling Between The Wrn Atlc And Closer To The Sern Coast.

The 06z Gefs Mean Is One Of The Runs Close To The Ecmwf Mean And Thus Preferred More Than The 00z Version.

Although Not The Most Elegant Blend... By Days 6-7 Sun-Mon Including The 00z And 12z/09 Ecmwf Runs Along With The 06z Gefs/00z Ecmwf Means Helps To Provide Reasonable Continuity With The Uncertain Ern Conus/Wrn Atlc Evolution While Incorporating Some Of The Operational Consensus Idea Of Flow Separation Over The Ern Pac.

Sensible Weather Highlights...

Most Of The West Should Be Warm And Dry During The Period.

Exceptions Include S-Cntrl Areas That May See A Period Of Lgt Pcpn
In Assoc With An Ejecting Upr Low Early In The Fcst... And The Pac
Nw/Nrn Rockies Which May See An Area Of Lgt-Mdt Pcpn Move Through Around Fri-Sat.

The Srn 3/4 Of The West Should See One Or More Days With Highs Of At Least 10-15f Above Normal.

Over The East The Period Will Start With A Very Wintry Feel On Thu
Behind A Departing Deep Sfc Low... With Windy Conds And Daytime
Highs 15-25f Below Normal.

Some Lingering Snow Is Psbl Over New England.

Record Cold High Temps For The Date Thu Are Also A Possibility At Some Locations In The Northeast.

Expect A Rapid Moderation Toward Normal Thereafter.

Cold Front Trailing From Low Pressure Along/N Of The Us-Canadian Border Thu-Sat Should Be Accompanied By Relatively Lgt Rnfl And Perhaps Snow Extreme N.

Expect The Pattern To Become More Active Over Cntrl-Ern Areas By
Sun-Mon But With Decreasing Confidence In Type/Coverage/Intensity
Of Pcpn At Any Specific Location.

Best Potential For Meaningful Pcpn At That Time Extends From The Srn Tier Into The Northeast.


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