US Final Extended Forecast thru Jun 22

...Overview And Preferences...

Models/Ensembles Generally Agree Upon Mean Troughing Over Ern Noam And Near 120w Longitude With A Ridge Over The Plains.

By The Latter Half Of The Period Both Troughs Are Expected To Relax
Somewhat While The Ridge Builds Into The Ms Valley.

Two Prominent Areas Of Uncertainty Continue From Prior Days. During The First Half Of The Period Guidance Remains Varied With Shrtwv/Sfc Details Over The East... While The Latter Half Of The Period Features Meaningful Spread For Some Aspects Of Flow From The Pacific Through Canada With Potential Influence On Nrn Latitudes Of The Conus.

From Day 3 Tue Into Early Day 5 Thu A Compromise Among The 06z
Gfs/06z Gefs Mean/00z Ecmwf Offers The Most Reasonable Soln For
Resolving Diffs Over The Ern Conus/Canadian Maritimes And Is Close To Consensus For The Mid Lvl Closed Low Moving Into The Nwrn States. By The Latter Half Of The Fcst There Are Enough Question Marks About The Ewd Extent And/Or Closed Nature Of Ridging That Evolves Over The Wrn Half Of Canada In The 00z Ecmwf/Ecmwf Mean Or 12/14 Ecmwf To Favor Leaning More To The 12z/14 Ecmwf Ensemble Mean With Minority Input From The 00z Naefs Mean.

...Guidance Evaluation...

During The First Half Of The Fcst The Most Prominent Issue Involves A Potential Wave From The Oh Vly Through Mid Atlc And Off The East Coast... With Diffs Beginning To Arise Late In The Short Range.

The 00z Gfs Is A Prominent Outlier With Its Depth Sfc/Aloft And Thus Is Discounted. However There Is Fair Agreement On The The Existence Of A Weaker/More Suppressed Wave As Reflected By The Preferred Compromise Among The 06z Gfs/06z Gefs Mean/00z Ecmwf. The 00z Ukmet/Cmc Are Reasonably Close To This Idea.

A Stronger Core Of Dynamics Farther Nwd Should Favor Deeper Low
Pressure From Just N Of Maine Into The Canadian Maritimes.

Farther Wwd... There Is Still Decent Agreement For The Closed Low
Moving Into The Northwest Though The 00z Ukmet/Cmc May Be A Tad
Fast By Early Thu.

From Late Thu Into Sat... Multi-Day Means By D+8 Reflect The Diffs
In Exactly How Ridging Over Nwrn Noam Will Evolve By That Time.

Fortunately Teleconnections Indicate That The Conus Should See
Modest Mean Troughs Near The West Coast/120w And Over The East
Regardless Of Whether The Core Of Positive Hgt Anomalies End Up
Near The Nrn Coast Of Alaska Or Wrn Canada. Nearly Zonal Mean
Flow Would Be Favored Over The Mid-Latitudes Of The Pacific.

Current Prefs Are Toward A Somewhat Slower Ewd Shift Of Initial
Alaska Ridging Than Indicated The 00z/12z Ecmwf And 00z Ecmwf
Mean... By Way Of A 12z/14 Ecmwf Mean-00z Naefs Mean Blend 2/3
Toward The 12z Ecmwf Mean. Over The Conus The Inclusion Of Some Naefs Guidance Tones Down The Wrn Trough Amplitude A Little Given Expected Flat Flow Upstream While Accounting For Indications That A Modest Shrtwv Ridge Could Briefly Reach Into The Ern Noam Mean Trough.

...Sensible Weather Highlights...

One Emphasis For Rnfl Should Be From The Mid Atlc Into The
Southeast With A Wavy Front Sagging Swd Into The Srn States.

Note That The 00z Gfs Is Likely Too Far Nwd With Its Axis Of Heaviest
Amts. Although The Front Will Gradually Weaken After Stalling Over The Southeast... Expect Diurnally Enhanced Convection To Persist Over That Region For Most Of The Period.

The Trailing Part Of This Front May Also Serve To Focus Convection Over Portions Of The Plains Tue Into Thu.

Meanwhile The Vigorous System Moving Into The West Will Spread Mstr From The Pac Nw Ewd With Time. Some Locally Hvy Convection Is Possible From The Nrn Tier States Into The Grtlks From Late This Week Into Next Weekend.

Expect The Coolest Daytime Temps Relative To Normal... By 10-20
F... From The Northwest Into The Nrn High Plains In Assoc With The
Closed Low Aloft Crossing The Region. The Cntrl-Srn High Plains
Will Be The Focus For Warmest Temps Relative To Normal Thu-Sat
With Some Locations Reaching 10-15 F Above Normal One Or More Of Those Days.


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