US Final Extended Forecast thru Sep 14

...Guidance Evaluation...

There Is Reasonable Mid-Larger Scale Guidance Agreement And
Predictability Into Midweek For Much Of Noam...But Hard To Diagnose Smaller Scale Differences With Locally Heavy Pcpn Focusing Energy Lifting Over The Wrn Us Around The Periphery Of A S-Central Us Centered Ridge Remain. From Day 5 Thu Onward Individual Solns Continue To Diverge Widely With Respect To Flow Details From The Ern Pac Into Noam And This Enhanced Uncertainty Influences The Ern Noam Trough Fcst Heading Into Next Weekend.

Accordingly...Overall Prefer A 00z Gefs/00z Ecmwf Ensemble Mean
Blend Days 3-7 To Maintain Reasonable Continuity From Previous Wpc Fcsts...While Awaiting Sufficiently Strong Signals From Guidance
Before Committing To A Significantly Different Scenario.

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 Few Gfs Runs Have Tended To Bring Some Hgt Falls Into Parts Of The West As A Trough Or Barely Closed Low Or Hold More
Offshore...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. 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 Seems A Reasonable Compromise Between The Two Soln Envelope Extremes And In Line With A 00 Utc Gfs/Ecmwf Ensemble Mean Blend.

With The Mid-Upper Level Trough Amplifying Into Ern Noam By
Mid-Period And Beginning To Weaken By Day 7 Next Sat...The
Deterministic Models And Especially The Ecmwf Have Offered Poor
Run To Run Consistency Recently. Accordingly Prefer Instead An
Ensemble Mean Approach And Associated And Lingering Trough
Amplitude Seems Reasonable Considering Lead-In Upstream Ridge
Amplitude.

...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. Mstr Will Be Enhanced From Weakening Ern Pac Tropical Depression 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 Calendar 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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