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US Final Extended Forecast thru May 19

...Overview And Preferences...

Medium Range Guidance Shows A Relatively Low Amplitude Pattern
From The Multi-Day Mean Perspective... With A Transition Toward
Split Flow Over Wrn-Cntrl Noam By The Latter Half Of The Period As
A Trough Moves Into/Through The Wrn States Toward The Plains And A Ridge Builds Over W-Cntrl Canada.

Meanwhile A Broad Mean Trough Over Ern Canada Should Extend Into The Nern States For Most Of The Period While A Srn Stream Shrtwv Over The Plains On Wed Is Fcst To Progress Steadily Ewd. Operational Model Solns Differ Sufficiently From Each Other And Ensemble Means For Some Details That A Blend Of The 00z Ecmwf/Gefs Means Provides The Most Reasonable Overall Starting Point For The Days 3-7 Wed-Sun Fcst. Localized Enhancements Were Made To The Initial Blend Where Appropriate.

...Guidance Evaluation...

Ensemble Means Have Generally Been More Agreeable And/Or
Consistent Than Operational Solns With E-Cntrl Canada Low Pressure Which Should Bring A Trailing Frontal System Through The
Grtlks/Nern Part Of The Conus... And Operational Solns Still Display Some Degree Of Spread With Track Of The Sfc Low And Trailing Front Over The Conus. However An Avg Of Operational Models Should Provide A Fcst Fairly Close To The Favored Ensemble Means.

Behind This System Gfs/Gefs Mean Runs Have Trended Toward
The Less Amplified Ecmwf Means With The Modest Nern Conus Trough Aloft While The Past Couple Ecmwf Runs Show More Troughing Than Earlier Runs That Had Hgts On The High Side Of The Guidance Spread.

Farther Swd There Is Decent Clustering With The Trough Progressing Ewd From The Srn Plains.

There Is Reasonable Agreement In Principle Upon A Trough Entering
The West By Fri And Reaching The Rockies Or Plains By Sun...
Leading To Sfc Low Development Over The Plains Late In The Period.

Some 00z Ecmwf Details Are Out Of Phase Relative To Consensus
Over The Ern Pac/West Coast During The First Half Of The Period But Compare Better To Other Guidance Thereafter. The 00z Gfs Becomes Rather Deep With The Core Of Its Mid Lvl System By Late
Sat-Sun. Still It Compares Better To Ensemble Consensus In
Principle Than The 06z Gfs Which Becomes More Amplified Than Other Solns With Upstream Energy... Fast With The Trough Reaching The Plains... And Pushes The Downstream Ridge Into The Northeast.

Thus The 06z Gfs Is Quite Fast To Bring Low Pres Into The Ms
Vly/Grtlks. As Per Its Occasional Bias The Cmc Leans Toward The
Amplified Side Of The Envelope With The Trough Of Interest. Over
The Past 1-2 Days The Ecmwf/Cmc Means Have Trended Somewhat
Stronger With The Trough Toward The Gefs Means. This Trend Along
With Timing Diffs Between The Gefs Means And Slower 00z Ecmwf Mean That Are Well Within Typical Day 6-7 Errors Favor Inclusion Of
Both Solns Within The Favored Blend.

...Sensible Weather Highlights...

Frontal System Crossing The Northeast Around Midweek And Extending Into The N-Cntrl Plains Will Be Accompanied By Rnfl Of Varying Intensity... With The Midwest Still Seeing The Best Potential For Highest Totals Due To Psbl Training Of Some Activity As The Sfc
Front Decelerates Over That Region. Scattered Convection Is Psbl
In Assoc With The Srn Stream Trough Moving Ewd From The Plains.

Expect Mstr To Spread Across The Northwest By Thu-Fri And Ewd
Thereafter. Focus Over The Nw Will Be Over Typically Favored
Terrain.

By The Latter Half Of The Fcst Period Interaction Of This Mstr With The Sfc Bndry Near 40n Latitude... And Psbl Added Input Of Some Gulf Mstr... Will Support A Threat Of Locally Hvy Rnfl Within An Area From The Nrn Half Of The Plains Into Portions Of The Grtlks/Oh Valley. Trough Aloft Moving Into/Through The West Will Bring A Cooling Trend To The Region.

Near To Above Normal Temps Should Prevail Over Most Of The Cntrl/Ern States... Aside From Fl Tending To Be Slightly Below Normal Most Days And Highs Trending Below Normal Over The Nrn Tier By Next Sun.


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