US Final Extended Weather thru Mar 17

...Overview And Preferences...

From Day 3 Wed Into Early Day 5 Fri There Is Reasonable Agreement
With The Large Scale Flow... Consisting Of An Ern Pac Mean Trough/ Wrn Conus Ridge And An Ern Conus Trough That Broadens As It
Moves Steadily Ewd. Within The Large Scale Consensus There Are
Typical Diffs With Some Smaller Scale Details. The Operational
00z Ecmwf Run And 00z Gefs/Ecmwf Ensemble Means Offer The Most Appealing Overall Solns For This Part Of The Fcst.

By The Latter Half Of The Period Model/Ensemble Solns Show Rapidly Increasing Divergence And Poor Run To Run Continuity Due To Combined Difficulty In Resolving Complex Flow Over Nrn Noam And Ern Half Of The Pacific.

By Day 7 Sun The Mean Trough/Psbl Embedded Closed Low Over Ern Canada And Ridging Over/Near Greenland Are The Only Features That Ensembles Suggest Have Above Avg Predictability.

Low Confidence In The Overall Fcst And Some Support From Teleconnections Favor Starting With A 00z Gefs/Ecmwf Mean Blend For Days 6-7 Sat-Sun.

...Guidance Evaluation...

During The First Half Of The Period When There Is Good Large Scale
Consensus With Significant Features... The 00z/06z Gfs Runs Differ
From Most Other Solns In Being Slower With Sfc Low Pres Reaching
Swrn Canada By Wed And Continuing Ewd Thereafter.

In The Short Range The 06z Gfs Looks Particularly Questionable With Its Handling Of The Compact Closed Low Off The Ak Panhandle With This Issue Translating Downstream Across Canada In The Medr Time Frame. Interestingly The 06z Gfs Gradually Conforms Better To The Ensemble Means Once This Flow Reaches The Nrn New Eng/Canadian Maritimes Closed Low Next Weekend.

By Next Weekend Individual Models And Ensemble Solns Become Quite Diverse From The Ern Pac Thru An Increasingly Large Portion Of The Conus And Vicinity... Related To Diffs That Originate Across The Higher Latitudes Of Noam And Nern/E-Cntrl Pac.

Highlighting The Diffs That Develop... By Day 7 Sun Individual Models/00z Ensemble Members Show A Potential Range Between A Ridge Or A Trough Aloft Everywhere From The West Coast Into The Plains. Individual Gfs/Ecmwf Runs Illustrate This Conflict As Well.

The 12z/9 Gfs Brought Much Sharper/Amplified Energy To The West Coast Than The 00z/10 Run... And The 00z/10 Ecmwf Has A Stg Ridge Over The West In Contrast To A Vigorous Trough In The 00z/9 Run.

Given This Model/Ens Spread And Poor Model Continuity... Confidence In Any Particular Operational Soln For Mid Lvl Features
And Assoc Sfc Evolution Is Quite Low.

The Most Similar Signal Seen In The Multi-Day Means By D+8 Is An Elongated Core Of Positive Hgt Anomalies Aloft Extending From Near Greenland/Davis Strait Nwd Toward The North Pole.

Regardless Of Which Part Of This Positive Core Is Strongest There Is Reasonable Teleconnection Support For Modest Broadly Cyclonic Flow With Below Normal Hgts Over The Ern Conus/Wrn Atlc.

Emphasis On A North Pole Anomaly Center For Teleconnecting Leads To Flat Flow Over The Ern Pac/Wrn Noam While The Davis Strait/Greenland Center Might Eventually Support A Little More Wrn Troughing... Perhaps After Day 7.

Based On These Considerations The 00z Ensemble Means Provide The Most Acceptable Guidance For The Low Confidence Days 6-7 Fcst. The 00z Canadian Mean Is Closer To The Gefs Mean Aloft Over The Ern Pac Into Noam And Closer To The Ecmwf Mean Over/Near The Canadian Maritimes.

...Sensible Weather Highlights...

The Large Scale Pattern Will Favor Above To Well Above Normal
Temps On Avg From The West Into Portions Of The Plains... While
The Nern Quadrant Of The Conus Should Be On The Chilly Side
Relative To Normal.

Between These Two Relative Extremes Will Be A Mean Frontal Boundary Containing One Or More Waves. Uncertainty Aloft Esp By Next Weekend Leads To Low Confidence In Determining Exact Frontal Posn From The Cntrl-Srn Plains Ewd And Thus With Temps At Some Locations Over This Area.

As An Illustration... For Day 7 Sun The 00z Ecmwf Ensemble 1 Pct Or Greater Probability Of Max Temps Less Than 32f Extends Nearly As Far Swd Over The Red River Vly As The Nwd Extent Of The 1 Pct Or Greater Prob Of Max Temps Reaching At Least 90f.

The Pac Nw... Especially Nrn Areas... Will Have The Greatest
Potential For Periods Of Mdt-Hvy Pcpn During The Period. Also
Expect One Or More Areas Of Pcpn To Slide Sewd Mostly To The N Of
The Wavy Mean Sfc Frontal Bndry Over The Cntrl/Ern Conus...
Affecting Areas From The Nrn Plains And Psbly Grtlks Through The
Cntrl East Coast. Expect More Snow In The Nrn Part Of The Overall
Pcpn Shield And A Mix Or Rain Farther Swd. The Northeast May Also
See Some Lgt Activity In Assoc With The Cold Trough Aloft Mid-Late

Any Gulf Inflow Is Expected To Be Limited Thru Most Of The Week But Could Start To Increase A Little During The Weekend.

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