US Extended Forecast thru Sep 14

...Overview And Preferences...

For About The First Half Of The Period There Is Reasonable
Agreement Aside From Mild Scatter With Specifics Of Sfc Evolution
From The Upr Grtlks Into Canada... Assoc With A Cntrl Canada/Nrn
Tier Trough Aloft Poised To Amplify Into Ern Noam.

Elsewhere A Rather Fast Moving Ridge Will Cross The Northwest And Merge With Another Ridge Retrograding From The Sern Conus While A Nrn Pac Trough Heads Into The Ern Pac.

Through Day 4 Wed A Consensus Blend Among The 12z-18z Gfs/12z Ecmwf And 18z Gefs/12z Ecmwf Means Resolves Track/Timing Issues At The Sfc From The Grtlks Into Canada And Reflects The Good Clustering Elsewhere.

From Day 5 Thu Onward Individual Solns Continue To Diverge Widely
With Respect To Flow Details From The Ern Pac Into Noam. This
Area Of Enhanced Uncertainty Will Likely Begin To Influence The
Fcst For The Ern Noam Trough To Some Degree By Late In The Period. Prefer The 18z Gefs/12z Ecmwf Ensemble Means To Maintain
Reasonable Continuity From Previous Fcsts... While Awaiting
Sufficiently Strong Signals From Guidance Before Committing To A
Significantly Different Scenario.

...Guidance Evaluation...

There Is Still A Wide Variety Of Potential Solns For The Ultimate
Evolution Of Energy Contained Within A Trough Reaching The Ern Pac
By Wed-Thu. There Is Loose Agreement That Some Separation May
Occur With Nrn Energy Progressing Into Cntrl Canada And The
Remainder Either Closing Off An Upr Low Offshore The West Coast Or Coming Inland Over The West As A Trough/Closed Low. Over The Past 1-2 Days Gfs Runs Have Tended To Bring Some Hgt Falls Into Parts Of The West As A Trough Or Barely Closed Low... While Ecmwf Runs Have Been Closing Off A Low But With Much Variability In
Longitude. Not Surprisingly Individual Ensemble Members Include
These Scenarios And More. Spread Persists In The New 00z Guidance With The Ukmet/Cmc Both Similar To The 12z Ecmwf Closed Low Offshore Versus The Gfs That Brings The Closed Low Into The West.

It Would Not Be Surprising To See Flow Separate More Than Depicted
In The Ensemble Means... But Having Just Modest Hgt Falls Coming
Into The Nw Late In The Period Is A Reasonable Compromise Between The Two Extremes Of The Current Soln Envelope.

With The Trough Amplifying Into Ern Noam By Mid-Period And
Beginning To Weaken By Day 7 Sat... Latest Gfs Runs Have Trended
Slower Toward Established Consensus So An Avg Of Their Solns Could Be Included As Part Of A Favored Blend For More Of The Period Than Over Ern Pac/Wrn Conus Areas.

Although The Past Couple Ecmwf Runs Have Trended Closer To Consensus Than Prior Versions... They Continue To Generate Solns Worthy Of Some Skepticism With The 12z/6 Version Closing Off A Compact Low Over New England By Sat. Such A Soln Is Somewhat Extreme But Not An Outlier Relative To The Full Ensemble Spread. However 00z Guidance Thus Far Does Not Offer Much More Support For That Idea. The 00z Gfs Becomes A Little Faster Than Consensus With The Trough Axis By Next Sat. The Only Trend Noted In The Ensemble Means Is Slightly More Depth With The Trough Around Late Week.

...Sensible Weather Highlights...

Continue To Expect Periods Of Locally Hvy Convection Over The
Southwest/Four Corners Region Eventually Extending Nwd To Some
Extent As Supporting Mid Lvl Energy Over The Swrn Conus/Nrn Baja
Calif Progresses Nwd Under The Influence Of The Ridge To The E And Hgt Falls Reaching The Ern Pac. Some Mstr May Originate From
Weakening Ern Pac Tropical Storm Lorena.

The Northwest Should Be Very Warm With Highest Daytime Temps Around Wed-Thu... Up To At Least 10-15f Above Normal. After That Time The Fcst For Temps Over Parts Of The West Becomes More Uncertain Given The Spread In Solns Aloft.

Over The Cntrl-Ern States The Primary Focus For Rnfl Will Be The Cold Front Dropping Sewd From The Grtlks/Plains Toward The East Coast... As Well As Over The Fl Peninsula And Wrn Gulf Coast Under The Influence Of Deep Layer Easterly Flow.

Ahead Of The Front... Some Locations In The Midwest May See Highs 10-20f Above Normal And Psbly Approaching Day Records On Tue.

The Ern Half Of The Conus As A Whole Will See A Cooling Trend
Thereafter As The Front Pushes Sewd.

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