US Final Extended Forecast thru Aug 25

...Overview And Preferences...

Latest Models/Ensembles Continue To Advertise A Gradual
Amplification Of The Pattern During The Medium Range Period...
With Troughs Settling Over The Ern Pacific And Canadian
Maritimes/Extreme Wrn Atlc.

At The Same Time A Mean Ridge Should Drift Slowly Ewd From The Plains/Srn Rockies While Another Ridge Should Remain Cntrd Off The Sern Coast To The N Of The Bahamas.

Although There Is Good Agreement/Continuity With The Fcst For
Large Scale Flow... Spread With The Timing And Amplitude Of
Individual Shrtwvs Within The Flow From The Ern Pac Across Srn
Canada/Nrn Tier Conus Presents Problems For Determining The Exact Posn Of The Mean Sfc Bndry Expected To Set Up From The Nrn Plains Into The Mid Atlc. Such Details Are Typically Not Easily Resolved In The Medr Time Frame So Prefer A Blend Of The 06z Gefs/00z Ecmwf Means With Minor Detail Enhancements. This Soln Provides Better Continuity Than Most Operational Models At This Time.

...Guidance Evaluation...

With Leading Hgt Falls Crossing The Ern Half Of Srn Canada During
The First Half Of The Period The 00z Ecmwf Starts Leaning Toward
The Faster/Amplified Side Of The Spread By Late Thu-Fri... While
In Varying Ways The 00z Gfs/Cmc Become Fairly Amplified With Their
Ern Noam Trough Albeit Within The Ensemble Spread. The Preferred
Ensemble Means Tone Down Trough Amplitude And Sewd Progression Of The Leading Cold Front Slightly.

Upstream Diffs At The Sfc Become Pronounced By Day 5 Fri As Recent Ecmwf Runs Have Been Trying To Bring A Wave Into The Upr Ms Vly/Upr Grtlks While Gfs Runs Keep Much Higher Pressures In Place Over The Region.

The 00z Ukmet Hints At An Ecmwf-Type Wave But The 00z Cmc As Well As Latest Gefs/Ecmwf/Cmc Means Are Not Very Enthusiastic About Such A Wave. Especially Given The Relatively Flat Nature Of The Mean Flow Along The Us-Canadian Border At That Time... Would Prefer To See More Agreement From Guidance Before Trending Toward The Ecmwf Scenario. Behind This Area Of Enhanced Spread The 06z Gfs Compares Less Favorably To Consensus Than Most
Other Solns By Day 7 Sun With Its Stg Srn Canada Low Pres That
Pulls The Mean Frontal Bndry Farther Nwd Over The Nrn Plains.

Elsewhere... There Is Now Decent Agreement With The Closed Low
Ejecting From Near The Ca Coast With The 00z Cmc A Little Slower
Than The Majority Cluster. With Minimal Sfc Impact... Solns Are
Quite Diverse With The Ultimate Strength/Path Of Weak Energy
Initially Over The E-Cntrl Conus. Some Or All Of The Energy May
Progress Slowly Ewd Psbly Reaching The Wrn Atlc With A Minority
Option Being Some Swwd Shearing As Per The 00z Gfs. The 00z Ecmwf Is Stronger Than Most Other Solns With Energy Lifting Nwd Over The Plains Fri-Sun.

...Sensible Weather Highlights...

Convection Over The Sern Third Of The Conus Should Gradually
Become Less Organized With Time... Trending Toward A Focus Along
Localized Boundaries... As The Front Over The Gulf/Sern Coasts

Uncertain Evolution Of Initial E-Cntrl Conus Energy Aloft Lowers Confidence In Determining Placement Of Heavier Rnfl Totals. The Combination Of The Mean Frontal Bndry Stretching E/Se From The Nrn Plains... And Shrtwvs Embedded In The Mean Flow Aloft... Will Likely Support One Or More Episodes Of Convection Across Nrn Areas. One Of These Shrtwvs Will Include The Remains Of The Initial Ca Closed Low That May Enhance Convection From Nrn Ca Into The Nrn Rockies Wed-Thu. Also Expect A Continuation Of Monsoonal Convection Over The Cntrl/Srn Rockies.

The Midwest Should See The Most Consistently Above Normal High Temps During The Fcst Period... With Other Locations In The Nrn Half Of The Conus E Of The Rockies Also Above Normal When On The Warm Side Of The Mean Frontal Bndry. Uncertain Details Of Waviness Along This Front Lead To Potential For Greater Than Avg Fcst Errors With Temps At Some Locations Especially From The Nrn Plains Into The Grtlks.

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