US Extended Forecast thru Oct 20

Overview And Preferences...

Latest Guidance Is In Some Ways Trending Toward Better Agreement
With Aspects Of The Fcst Mid-Late Week As A Deepening Mean Trough Settles Toward E-Cntrl Noam In Response To A Strong Ern Pac/West Coast Into Nwrn Noam Ridge... And Leading Low Pressure Tracks Newd From The Grtlks Early In The Period.

There Is Still Some Question As To The Evolution Of Energy Descending Swd Along/Inland From The West Coast And Timing Of A Shrtwv Ejecting From The Cntrl Rockies.

By Next Weekend Previously Advertised Spread With Flow Upstream
From The Ridge Persists With Increasing Impact On Wrn Noam Flow.

An Even Blend Of The 00z Gefs/Ecmwf Means With Minor Adjustments
Provides The Best Account For Trends That Have Some Confidence As Well As Current Guidance Spread Early-Mid Period... Then Holds
Onto A More Stable Upstream Nwrn Noam Ridge Compared To Some Other Solns By Next Sat-Sun.

Guidance Evaluation...

For The System Tracking Newd From The Grtlks Early In The Period ...Recent Ecmwf/Ukmet/Cmc Runs Had Generally Been On The
Slower Half Of The Spread But Have Overall Trended Faster Recently
In Response To A More Phased Evolution Aloft. The Resulting
Consensus Is Faster Than Continuity But Has Enough Support To
Incorporate Into The Latest Fcst. The Initial Ensmean Blend Is
Similar To A General Operational Model Consensus. Note However
That There Is Still Enough Sensitivity In Flow Details During The
Latter Part Of The Short Range Time Frame That Further Adjustments
Are Psbl.

Shrtwv Energy Initially Ejecting From Near The Cntrl Rockies May
Support Weak Waviness Along Leading Cold Front Crossing The Sern States. The 00z Gefs/Ecmwf Ensemble Means Show A Good
Intermediate Soln With Shearing Of This Energy As Upstream Hgt
Falls Approach.

Meanwhile There Is Steady Improvement In Guidance Clustering For
How Short Range Wrn Canada Energy Settles Into The Mean Trough
Over The Conus. The Past Couple Days Of Ecmwf/Ukmet/Cmc Runs Have Generally Trended Away From Having Some Of The Energy Amplify Rather Sharply Over The West... Instead Forming A Broader/Ewd Trough That Appears More Reasonable Based On Teleconnections Relative To The Upstream Ridge. Support Still Exists For A Modest Degree Of Elongated Troughing Reaching The Swrn Conus. Gfs Runs In Particular Have Been Random In The Evolution/Track Of This Energy... Favoring The Ensemble Means Until Operational Runs Become More Stable.

By The Latter Half Of The Fcst Ensembles And Operational Models
Display Increased Spread With Evolution Of The West Coast/Nwrn
Noam Ridge Due To Diffs With Upstream Flow That Have Existed For
At Least The Past Couple Days. Although Ecmwf Means Have Trended A Little Ewd With The Ridge Axis Over Recent Runs... Tendency For Guidance To Often Weaken Potent Ridges Too Quickly Supports Giving At Least Half Weight To The More Resilient 00z Gefs Mean That Is Quite A Bit Stronger Than The 00z Ecmwf Mean.

Sensible Weather Highlights...

Low Pressure Departing From The Grtlks And Cold Front Trailing
Swwd Will Be Accompanied By Areas Of Rnfl Over The Srn/Ern States.

Locations From Tx Into The Lwr Ms Vly/Cntrl Gulf Coast Have The
Best Potential For Enhanced Rnfl Due To Ongoing Flow Of Deep Mstr
From The Tropical Ern Pacific.

Shrtwv Energy Ejecting From The Rockies May Locally Improve Organization Of Rnfl Elsewhere Along The Front. Energy On The Swrn Periphery Of The Evolving Conus Mean Trough Aloft May Support Areas Of Pcpn From The Rockies Into The Plains But Spread In Precise Flow Details Lowers Confidence In Pinpointing Coverage/ Intensity.

Pcpn In Hier Elevs Of The Rockies May Be In The Form Of Snow.

As The Deepening Mean Trough Aloft And Cool Cyclonic Low Lvl Flow Settle Over The E-Cntrl Conus Expect Pcpn To Increase Over The Grtlks With Some Lake Enhancement Psbl... Though Temps Should Be Warm Enough To Support Mostly Rain.

Greatest Negative Anomalies For Daytime Highs Should Be Over The
Rockies/Plains Early In The Period And More Toward The E-Cntrl
Conus With Less Extreme Values Late.

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