US Extended Forecast thru Jan 19

...Overview And Preferences...

Medium Range Guidance Is Consistent With The Large Scale West
Coast/Wrn Noam Mean Ridge And Ern Noam Mean Trough... But Some Detail Issues Remain For Features Within The Mean Trough And For Ern Pacific Energy Approaching The West Coast By Sat.

During Days 3-5 Wed-Fri A General Blend Of The 00z Gfs/Ecmwf And 06z Gefs/00z Ecmwf Means Provides A Good Consensus For Mid Lvl Flow And Compromise Sfc Evolution.

The Last Two Days Of The Fcst Emphasize The More Agreeable And Stable Ensemble Means As Operational Gfs/Ecmwf Runs Diverge With Mid Lvl Details Over The West And Sfc Evolution Over The Nern States.

...Guidance Evaluation...

Considerable Spread Develops For Ern Pac Energy That May Move Into Portions Of The West By Next Weekend.

In Varying Ways From Run To Run The Gfs Has Been Bringing Its Energy Across The Nrn Half Of The West With Strength Generally Greater Than The Ensemble Means.

Thus Far Ecmwf Runs Have Been Inconsistent. The 00z/12 And 12z/11 Runs Keep Hgts Fairly High Over The Nwrn States But Close Off An Upr Low Well Swd. On The Other Hand The Ecmwf Run Prior To Those Brought A Trough Through Much Of The West And The One Before That None At All.

Teleconnections Relative To The Fcst D+8 Hgt Anomalies Nearby... A Positive Center In The Nwrn Conus Or Just N Of Mt And A Negative Center Near 160w... Do Not Appear To Support Undercutting Flow As Strong/Concentrated As Depicted In The Last Two Ecmwf Runs.

These Considerations Favor Maintaining An Ensemble Mean Approach Until There Is Enough Evidence To Support An Alternative Scenario.

Over The East There Is Still Some Spread With The Evolution Of
Shrtwv Energy Reaching The East Coast By Around Early Day 4 Thu...
Impacting Sfc Details Along/Offshore The East Coast.

As Of 12z Thu The 00z Gfs/Ecmwf/Cmc And 00z-06z Gefs/00z Ecmwf Means Are Fairly Close In Principle Aloft.

This Cluster Has Been Achieved By A Slower Trend In Gfs/Gefs Solns Compared To Yday So Less Consideration Would Be Given To The 06z Gfs That Has Adjusted Faster.

The Shrtwv Is Sharp Enough To Support A Wrn Atlc Sfc Wave As Of Early Thu But The Wave Should Then Weaken/Accelerate Due To
Shearing Out Ahead Of Rapidly Approaching Upstream Flow.

Scattering And Continuity Changes Are Fairly Modest For The System
Expected To Track Across The Upr Grtlks Into Ern Canada...
Favoring A General Consensus For This Feature.

However Sfc Details Across The Nern Conus/Sern Canada Diverge Late In The Period As Energy Contained Within Fast Flow Over/Near Nwrn Canada Feeds Into The Core Of The Ern Noam Mean Trough.

By Next Sun Solns Range Between A Fairly Vigorous Upr Grtlks/New England Sfc Low And Mere Maintenance Of Cyclonic Mean Flow.

Some Individual 00z Gefs/Ecmwf/Cmc Ensemble Members Depict A Defined Sfc Low But Not Enough For Respective Means To Have A Meaningful Feature.

For Now Will Maintain Ensemble Mean Continuity Of No Well Defined Day 7 System While Awaiting Better Agreement/Continuity From The
Operational Models.

...Sensible Weather Highlights...

The Mean Pattern Will Support Lower Than Avg Coverage Of Pcpn Over The Lower 48 During The Period.

Progression Of Systems Within The Ern Noam Mean Trough Will Bring Periods Of Snow From The Nrn Plains Into The Grtlks/ Northeast With Most Amts On The Lgt-Mdt Side.

Lake Effect Will Be Psbl At Times Downwind From Unfrozen Portions Of The Grtlks.

Some Mstr May Extend Into The Middle Third Of The Ern States With Varying Pcpn Type Depending On Local Thermal Profiles.

Meanwhile Lgt Pcpn May Reach The West Coast... Most Likely The Nrn Half... By Next Weekend.

Flow Around Ern Conus High Pressure Should Support Periods Of Lgt Rnfl Over Extreme Srn Tx.

Expect Temps Over The West To Be Above Normal Through The Period With Anomalies For Highs Reaching Up To Plus 15-20 F Over Parts Of Ca/Nv And Srn Or During Wed-Fri.

Cntrl-Ern Conus Temps Will Be More Variable.

It Will Be Quite Warm Relative To Normal Over The Nrn-Cntrl Plains Into Upr Ms Vly Wed-Thu... With Highs Up To 20-25 F Above Normal Over The Extreme Nrn Plains... But 5-15 F Below Normal From The Ms Vly Ewd Fri-Sat... Followed By Another Warming Trend Over The Plains Next Weekend.

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