US Extended Forecast thru Feb 2

...Overview And Preferences...

Latest Guidance Continues To Advertise A Significant Pattern
Change As A Pacific Ridge Building Near 140w Longitude Encourages Wrn Conus Troughing By The Latter Half Of The Week.

Swly Flow Should Become Established Downstream With A Ridge Building Se Of Florida Further Aiding An Increase In Hgts Over The Ern Conus.

At The Same Time A Mean Frontal Bndry Should Set Up From The Nrn
Rockies Into The South-Central Plains And Newd To The E Coast.

Expect Greater Pcpn Coverage Over The Lower 48 Compared To The
Past Couple Weeks With Pcpn Types Dependent On Exact Frontal
Position. Wpc Depictions Are Shown In Our Graphics/Hpcguide Grids.

Models/Ensembles Are Sufficiently Agreeable To Suggest Near Or
Even Above Average Confidence In The Large Scale Evolution...But
There Remains A Lot Of Spread With Important Embedded Details So
These Sensible Weather Focusing Forecast Aspects Seem Subject To Considerable Error And Uncertainty.

Wpc Medium Range Guidance Was Primarily Derived From Continuity And A Blend Of The 06 Utc Gfs Ensemble Mean And Ecmwf Ensemble Mean That Seems To Represent The Most Consistent And Reasonable Considerations Where Meaningful
Differences Exist. Reservations Remain With Aspects And Run To
Run Variances Of Recent Models...Especially The 00 Utc Ecmwf.

...Guidance Evaluation...

One Significant Uncertainty Is Associated With Ern Pac Energy
Heading Toward The West Coast... With Possible Incorporation Of
Some Flow To The S Of The Upper High Worked Over Extreme Nwrn Noam Adding Complexity.

As Energy Nears The West Coast There Is Minimal Clustering Among Deterministic Models And Ensembles At The Surface With Recent Forecasts Ranging Between A Vigorous Low And A Weak Wave With A Variety Of Tracks And Timing.

Favor Leaning Toward A Slightly Slower/Amplified Solution Aloft Given The Initially Strong Ridge This Energy Is Heading Into.

By Mid-Late Week Recent Ecmwf Runs Become Rather Extreme Relative To The Full Ensemble Spread With The Amplitude Of The Overall Trough...Instead Recommending Greater Emphasis Of A More Composute Solution Blending The Gfs/Ecmwf Ensemble Means.

The Other Major Uncertainty Involves An Ern Pac Upr Low Now Off Ca
And Expected To Drop Toward Baja Calif In The Short Range.

Gfs Runs Have Tended To Be On The Faster Side In Ejecting This
Feature.

There Had Been Some Degree Of Agreement Toward Moderately Slow Ejection Based On The Idea Of The Upstream Ridge Being A Little Slower To Break Down Than Fcst Recent Gfs Runs...But The 00z Cmc Has Adjusted Toward Rapid Ejection As Well.

The 00z Ecmwf Also Shows A Significant Ewd Trend. The Quite
Uncertain Specific Of How This Feature Ejects Will Determine Which
Sfc Front Will Have Enhanced Waviness.

Fast Solns Generate A Wave On A Leading Front Over The Wrn Atlc While Slower Ejection Would Support A Wave Along The Mean Frontal Bndry Setting Up Over The Conus.

Even With Ensemble Means Losing The Upr Low Of Interest... There Is A Hint That Nrn Stream Flow May Also Support A Wave Near The Nern States Around Day 7 Sun. Its One Option.

...Sensible Weather Highlights...

Expect Much Below Normal Temps Over The South And East Wed Into
Thu...Possibly Reaching Daily Record Values For Min Or Coldest Max
Temps.

This Cold Air May Support A Band Of Wintry Pcpn Unusually Far S/Se Toward The Gulf/Sern Coasts.

Otherwise During Wed-Thu Pcpn Should Be Confined To The Great Lakes With Snow Downwind Of Unfrozen Portions Of The Lakes And A Frontal System Passing Through On Thu.

From The Plains Ewd The Developing Pattern Surface/Aloft Should Promote Pcpn Potential Over A Broadening Area Fri-Sun...With The Full Range Of Snow/Wintry Mix/Rain As One Travels From N To S.

This Pattern Tends To Yield Low Predictability Of Finer Details Due To Influence From Small Scale Impulses Embedded In Swly Flow Aloft.

By The End Of The Period The Nrn-Central Plains Into Great Lakes Should See Coolest Temps Versus Normal While The South Should Trend Above Normal.

Over The West...Temps Will Steadily Decline After Possible Record Warmth At Some Locations In The Srn Half Of The Region Wed-Thu.

N-Central Parts Of The West Should See The Best Organized Pcpn During The Period With Potential For Enhanced Amounts Depending On Currently Very Uncertain Details Of Mid Level/Surface Evolution Especially In The Wed-Fri Time Frame.

This Denotes Quite A Pattern Change.


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