US Extended Forecast thru May 16

Guidance Agrees That A Rockies/Plains Trough Will Broaden As It
Moves Ewd With Time... Yielding A Mean Trough Covering Much Of The Ern Half Of The Conus/Canada By Late Next Week.

However Significant Diffs Exist For Some Details Within This Evolution.

The Most Pronounced Is A Faster Advance Of The Initial Trough In
Recent Gfs/Gefs Runs With Trends And Other Models Generally
Supporting Slower Timing.

The Amplified Nature Of The Overall Pattern Over Noam As Well As Ern Pac/Wrn Atlc Appears Supportive Of The Slower Half Of The Spread As Well.

Therefore The Latest Wpc Fcst Incorporates 70% Of The 00z Ecmwf Ensemble Mean Along With 30% Of The Now More Compatable 00z Naefs Mean Whose Gefs/Canadian Ensemble Components Have Taken Their Time To Trend Toward A More Amplified/Less Progressive Solution Over The Past 4 Days Worth Of Runs.

This Overall Solution Also Incorporates/Maintains Good Wpc Continuity.

Guidance Evaluation...

While The Trend Has Gradually Improved Over The Past Number Of
Days...Already Near The Start Of The Fcst Period Recent Gfs/Gefs
Runs Show Faster Progression Of The Cntrl Conus Trough Aloft And
Leading Sfc Low Pressure/Cold Front.

Even Among Remaining Solns There Is Still A Decent Amount Of Ensemble/Model Spread Regarding Exactly How Mid Lvl Energy And Sfc Low Pressure Will Evolve During The First Half Of The Week So Prefer To Stay Closest To The 00z Ecmwf Mean... With The Understanding That Operational Guidance Suggests Potential For A More Wrapped Up System.

At Least Trends Over The Past 1-2 Days In Gfs/Gefs Solns Toward A Sharper/Slower Trough Aloft Increase Confidence In A Soln That Leans More Toward The Slower Half Of The Spread.

This Tendency Toward Slower/Sharper Troughing Leads To Sharper / More Amplified Flow Downstream... And An Emerging Potential For Ern Canada High Pressure And Leading Backdoor Front To Push Farther Swd Along The East Coast Tue-Wed.

The Blend Consisting Mostly Of The 00z Ecmwf Mean Already Leads To A Meaningful Adjustment From Continuity From Yesterday And The
Latest Models Appear To Reinforce This Trend.

The 00z Gfs Is Still Lagging Consensus Here And Upstream But Along The East Coast Has Still Noticeably Trended Away From The 18z/12z Runs.

As The Broadening Trough Aloft Settles Over Ern Noam By Late Next
Week The Ecmwf/Gefs/Naefs Means Trend Toward Somewhat Better

Ahead Of This Trough A Notable Question By This Time Frame Is The Evolution/Track/Timing Of A Wave Which A Number Of Ensembles / Operational Runs Suggest May Develop E Of The Bahamas And Be Directed Toward The Sern Or Mid Atlc Coast.

Continuity Of Gfs/Ecmwf Runs Overall Indicates A Slower Trend To Develop Such A Wave Or Incorporate It Into The Frontal Zone Reaching The East Coast.

Confidence Is Below Average In Resolving Such A Detail At That Time Frame As A Look At All The Individual Ensemble Members
Shows Ample Strength/Track Forecast Spread.

Ridging Along The West Coast Should Strengthen Somewhat During The First Half Of The Period And Then Weaken Slightly As It Moves A
Bit To The E.

By Day 6 Thu Latest Guidance Thus Far Is Suggesting That The Upstream Trough May End Up Somewhat Farther Wwd Than The
00z Ecmwf Mean...A Plausible Scenario Given The Evolution

Sensible Weather Highlights...

Heavy Cntrl Rockies Snow Will Taper Off Early In The Week While The Emphasis Turns To Locally Hvy Rnfl Over Parts Of The Plains/Ms

Activity Reaching Ewd Beyond The Ms Vly By Midweek May Not Be As Hvy Due To Reduced Gulf Inflow...But Rnfl May Again Trend Heavier Near The East Coast Later In The Week In Response To Waviness / Slow Movement Along Portions Of The Sfc Front As Well As Potential Inclusion Of Some Mstr Originating From Lower Latitudes Off The Sern Coast.

Behind The Front Sct Rnfl Is Psbl In Assoc With One Or More Shrtwvs Embedded Within The Mean Trough Aloft... Including Along The Ern Slopes Of The Nrn Rockies.

The Ridge Aloft Near The West Coast Will Promote Warm/Dry Conds In Its Vicinity.

Expect The Greatest Anomalies For Daytime Highs To Be During Tue-Thu When Readings Should Reach 10-20f Above Normal And Psbly Higher At Isold Locations.

On The Other Hand Locations From The Cntrl Rockies Through The Nrn Tier Will Be Quite Chilly Early In The Week With Some Rockies / High Plains Anomalies Of Minus 20-30f For Highs On Mon.

Nrn Tier Areas Will Stay Cool For The Rest Of The Period As Troughing Aloft Settles Into The Ern Half Of Noam.

Summertime Ern Conus Warmth Under Ridging Aloft...Outside Of From An Northeast Based Backdoor Front/Trailing Sfc High...Will
Be Pushed Out After Midweek.

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