US Extended Forecast thru May 17

Latest Guidance Continues The Theme Of High Amplitude And
Blocky/Slowly Evolving Flow Over Noam And Adjacent Oceans.

A Strong West Coast Ridge Will Support A Broad/Deep Trough Settling
Over The Ern Half Of The Continent While An Initial Ern Noam Ridge
Drifting Into The Wrn Atlc Will Encourage W-Cntrl Atlc Troughing
That Closes Off Into An Upr Low Near 35-40n Latitude.

An Amplified Trough Over The Pac Near 140-150w Longitude Is The One Feature Showing Signs Of Some Flattening/Progression By The Latter Half Of The Period But With Considerable Spread In How This
Occurs.

Trends Over Recent Days And Amplitude Of The Evolving Pattern Yield Good Continuity In Fcst Thinking/Guidance Choices.

70/30 Blend Of The 12z Ecmwf Mean/12z Naefs Mean Offers The Best
Option For Representing The Slower Half Of The Guidance Spread
With Progression Of Leading Hgt Falls/Sfc Front Over The Ern Half
Of The Conus While Downplaying Uncertain Details Of Individual
Models... And Resolving Less Confident Aspects Of Ern Pac/West
Coast Evolution Later In The Period.

...Guidance Evaluation...

While Gfs/Gefs Guidance Has Trended Somewhat Slower With The
Advance Of Leading Hgt Falls Aloft And Sfc Front Across The Ern Half Of The Conus... Even Ecmwf Mean Runs Have Been Trending A
Little Slower So Gfs/Gefs Runs Remain On The Leading Side Of The
Envelope Especially During The First Half Of The Fcst Period.

These Trends Along With The Amplified Nature Of The Pattern And
Occasional Bias Toward Too Much Progression In The Gfs Favor
Leaning More Toward The Slower Guidance.

Ahead Of The Conus Trough... An Ongoing Question Mark Is The
Handling Of A Lower Latitude Wave Which Most Operational Models
Suggest May Track From The Nrn Caribbean/Bahamas Into Florida
And/Or Farther Nwd Along The East Coast From Wed Onward.

The Fcst Along The West Coast Is Fairly Straightforward Through Day 5 Thu With A Strong Ridge Prevailing Over The Region.

Developing Diffs With Upstream Ern Pac Troughing And Flow Farther
To The W Lead To Rapidly Expanding Spread Among Solns By Fri-Sat.

While Not An Outlier... The 12z Ecmwf Is One Of The Strongest Pieces Of Guidance With Incoming Hgt Falls.

Amplitude Downstream Also Favors Leaning Away From The Faster Side Of The Spread Here.

...Sensible Weather Highlights...

The Strong Ridge Near The West Coast Will Provide Very Warm To Hot
Readings To Areas West Of The Rockies. Some Areas May See Highs 10-20f Above Normal... Psbly Approaching Or Reaching Record Values On One Or More Days.

Locations Away From The Southwest Should See A Cooling Trend By Next Sat.

Ahead Of The Cntrl Into Ern Conus Trough Aloft Expect A Wavy And Generally Slow Moving Frontal Bndry To Be The Focus For Locally Hvy Rnfl From The Sern Plains Ewd/Newd During The Period.

Potential Still Exists For Some Rnfl-Enhancing Lower Latitude Mstr To Be Drawn Into This System Near The East Coast By The Latter Half Of The Week... With More Precise Details Likely Not Becoming Resolved Until The Short Range.

On The Wrn Side Of The Trough A Persistent Band Of Mstr Will Support Periods Of Rain And Psbly Very High Elev Snow Over Parts Of The Nrn-Cntrl Rockies/High Plains.

Day 3 Tue Offers The Greatest Temperature Contrast With A Broad Area Of Highs 10-20f Below Normal Over The Cntrl States While Some Ern Locations... Away From A Nern Backdoor Front/Sfc High... Should Be 10-15f Above Normal.

Ewd Progression Of Cool Air Will Yield A Broad Area Of Near To Below Normal Readings Over The Cntrl-Ern States By Late Week With Most Extreme Negative Anomalies Tending To Be Over The Nrn Tier/Grtlks Region.


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