US Final Extended Weather thru Mar 9

...Overview And Preferences...

The Medium Range Fcst Will Feature Two Dominant Systems Of
Interest.

The Wrn System Is A Fairly Vigorous Trough Progressing From The Ern Pacific Into/Thru The West With Some Separation Of Flow Likely By The Latter Half Of The Period.

Farther Ewd Deepening Low Pressure Is Fcst To Track From Near The S-Cntrl Ms Vly/Tn Vly Ewd Into The Atlc.

Some Aspects Of Individual Operational Models Could Merit Inclusion Within A Deterministic Blend For Some Locations... But Ensemble Guidance Raises Enough Question Marks About Model Details To Favor Leaning Toward The 00z Gefs/Ecmwf Ensemble Means As The Starting Point For The Days 3-7 Tue-Sat Fcst.

This Soln Offers Reasonably Good Continuity Given The Recent And Current Variability And Spread Of Operational Models.

...Guidance Evaluation...

Solns Agree Upon A Closed Low Being Positioned Off The Pac Nw
Coast As Of Early Day 3 Tue... But Then Steadily Diverge With The
Combined Handling Of Leading Energy Crossing The West/Ejecting
Thru The Nrn Plains And Trailing Flow Which Is Expected To
Separate From The Main Band Of Westerlies To Some Degree.

Compared To The Full Ensemble Spread The Operational 00z/06z Gfs Runs Appear Somewhat Extreme With The Swwd Amplitude Of The Trailing Energy Leading To A Closed Low That Tracks Just Off The Srn Ca Coast By Late Fri. Operational Ecmwf Runs Have Generally Favored A Late Week Closed Low Path That Is Slightly Inland...Though Some Runs Over Recent Days Have Reached Their Solns By Way Of Some Extreme Details Over The Ern Pac.

Given The Potentially Stg Upstream System Tracking S Of The Aleutians... It Would Not Be Surprising For Wrn Troughing To Be Amplified Enough To Allow Formation Of A Closed Low By Fri-Sat. This Leads To Favoring Some Inclusion Of The 00z Gefs Mean With The More Open 00z Ecmwf Ensemble Mean. Interestingly The 06z Gefs Mean Adjusted Somewhat Toward The Ecmwf Mean But Again There Is Enough Operational Model Support For A Closed Low... Even If Not As Far Swwd As The Gfs Runs... To Favor The 00z Run For The Gefs Mean Component Of The Blend.

Along Nrn Latitudes... The 00z Ecmwf Is A Little S Of The Primary Guidance Cluster With The Sfc Low Off The Pac Nw Coast Early Wed. As Energy Ejects Across The Nrn Tier Late In The Week The Ensemble Means Have Been Fairly Consistent With Timing Over
The Past Couple Days. 00z Gfs/Ecmwf Runs Are Agreeable With The
Means With This Energy And Assoc Sfc Front. However The 06z Gfs
Appears To Become Excessively Fast By Mid-Late Period... Bringing
A Shrtwv Into Nrn New Eng By Early Sat While Other Solns Display A
Ridge Aloft.

Over Recent Days Operational Models Have Displayed Significant
Spread And Run To Run Variability With Deepening Low Pressure
Tracking Ewd Across The Ern Conus/Wrn Atlc. Multiple Sources Of
Uncertainty Have Contributed To This Behavior... Timing/Latitude
Issues With The Initial Closed Low Crossing The Plains As Well As
Varying Degrees Of Interaction With Mid Lvl Energy That May Be
Lingering Over/Near The Grtlks As Well As Another Bundle Of Energy
Over/Near New England.

At The Moment The Most Notable Trend Seen In Operational Models Is Toward Showing Less Influence From The Extraneous Pieces Of Energy And Emphasizing Steady Ewd Progression Of The Initial Plains Closed Low. The 00z Cmc Is The One Model Still Showing Some External Influence Causing Its Wrn Atlc Closed Low To Wobble Farther Nwd. From The Multi-Day Perspective An Avg Of The Latest 00z Gefs/Ecmwf Means Provide The Most Stable Soln From The Ern Conus Thru The Wrn Atlc. Note That The 00z Gfs/Ecmwf Are On The Swrn Side Of The 00z Gefs/Ec/Cmc Ensemble Sfc Low Clustering During Wed-Thu. The 06z Gefs Shows A Favorable Trend Toward The Ensemble Means.

...Sensible Weather Highlights...

The Ern Pac System Tracking Into/Thru The West Will Spread A Broad
Area Of Pcpn Across The West During The Period... Extending Into
Portions Of The Cntrl-Srn Plains By Day 7 Sat As Gulf Inflow Begins To Interact With The Sfc Front Over The Plains By That Time.

Expect Heaviest Activity Along The Cntrl West Coast Tue-Wed With Some Of This Mstr Streaming Newd Into The Nrn Rockies Thereafter.

Later In The Period Expect Mstr To Reach The Southwest/Grtbasin. As Pcpn Develops And Intensifies Over The Cntrl High Plains And Areas E/Se

By Sat... Temps May Get Cold Enough For Wintry Pcpn In The Nwrn Part Of This Area.

System Tracking Ewd From Near The Tn/Ms Vly Into The Wrn Atlc
Should Generate Some Snowfall To The Nw/N Of The Sfc Low Track.
What Snow Occurs Should Be Rather Wet Given Low Lvl Temps Expected To Be Near Or Above Freezing At Least During The Daytime Hours.

With Greater Confidence Than The Snow Fcst... Expect Some
Locations To See Fairly Strong Winds Especially Late Wed Into Thu
Along The East Coast As Low Pressure Deepens Over The Wrn Atlc.

Daytime Temps Will Be Below Normal Over The Ern Half Of The Conus In The Wake Of This System... Moderating By Late Week Into The Weekend.


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