US Final Extended Weather thru Mar 10

...Overview And Preferences...

Some Track And Timing Diffs Remain With The Storm System Fcst To
Affect Areas Near The East Coast Day 3 Wed With Breezy Conds
Continuing Into Thu Regardless Of Exact Evolution.

Once This System Departs The Focus Will Shift To A Trough/ Embedded Closed Low Moving Into/Through The West And Emerging Into The Plains Late In The Period... With Assoc Meaningful Weather Impacts Likewise Extending From The West Coast Into The Plains.

By The Latter Half Of The Period Amplitude/Phase Diffs With Nrn Stream Flow Lead To Some Spread For This System As Well As Frontal Progression Over The Nern Quadrant Of The Nation.

On Any Particular Fcst Day In The Wed-Sun Period Very Few Pieces
Of Guidance Offer An Ideal Soln For Every Feature Of Interest...
Leading To A Preferred Blend That Gradually Evolves Over The
Period. As A Whole The 00z Gefs/Ecmwf Ensemble Means Are The Most Common Elements Of The Favored Blend. Minority Weighting Of The 00z Gfs Is Included Wed Into Early Thu... 00z Ecmwf Wed Into Early Sat... And 06z Gfs Sat Onward.

...Guidance Evaluation...

For The First Half Of The Period Model/Ensemble Solns Have Made
Considerable Progress In Decreasing The Spread For The System
Moving Into The West.

Consensus Evolution Has A Closed Low Just Off The Pac Nw Coast Early Wed Briefly Opening Up Before Energy On The Wrn Side Of The Trough Forms Another Closed Low That Tracks Sewd Over Ca By Fri.

Through Fri The Dominant Clustering Is Most Similar To A Lagged Avg Of The Last Few Operational Ecmwf Runs... With 00z/06z Gfs Runs Representing A More Onshore Trend Versus Some Earlier Gfs Runs And Ensemble Means Trending More Amplified/Separated With Their Trough. A General Blend Of Operational Gfs/Ecmwf Runs With Some Ensemble Mean Input Appears Reasonable Over The West Days 3-5 Wed-Fri. However Note That Already By Mid-Late Thu The 00z Gfs Appears Too Aggressive In Bringing Leading Hgt Falls Across The Nrn Tier Conus/Srn Canada.

By Days 6-7 Sat-Sun The 00z Ecmwf Appears Too Eager To Break Down The Wrn Canadian Part Of The Upstream Ridge Aloft... Leading To Downstream Srn Canada/Nrn Conus Flow That Strays Faster Than Consensus. Although The 00z Gfs Does Not Have This Problem It Still Lowers Ern Conus Hgts More Than The Guidance Avg Albeit Not To The Point Of Being An Outlier. Individual Ensembles From The 00z Gefs/Ecmwf/Cmc Run Show Rapidly Increasing Spread With Srn Canada/Nrn Stream Flow... Complicating The Fcst For The Wrn Conus Closed Low Which Should Track From The Swrn States Into The Plains Next Weekend.

Currently The 00z Ecmwf Is On The Nwrn Fringe Of The Model/ Ensemble Spread With The Low Sfc/Aloft. Among Remaining Solns ... Tendency For The Fast Side Of The Spread Not To Verify Too Well With Swrn Closed Lows... And Slower Ensemble Mean Trends Over The Past 1-2 Days... Favor Leaning Away From The Faster Side Of The Spread.

Greatest Emphasis Is Placed On A Compromise Of The 00z Gefs Mean/06z Gfs By Late In The Period Given Slower Timing Than The 06z Gefs Mean/00z Ecmwf Mean For The System Tracking Into The Plains And Best Consensus With Flow Across The Nrn Conus/Srn
Canada. The 00z Gfs That Is A Little Slower With The Closed Low
May Well Have Some Merit But Issues With Flow Farther E/Ne
Preclude Its Us In The Overall Fcst Blend.

Meanwhile Ensemble Clustering With The East Coast/Wrn Atlc Storm
Has Slowed A Little From Previous Days.

An Avg Of The 00z Gfs/Ecmwf And Corresponding Ensemble Means Offers A Good Intermediate Soln Given Persistent Spread In Sfc Low Track/Timing. The 06z Gfs/Gefs Mean Are Faster Than This Consensus On Wed And Then Trend To The Nrn Side Of The Guidance Spread Once Over The Wrn Atlc. The 06z Gfs Is Weaker Than Consensus With The Ern Canada Ridge Aloft On Wed So Its Soln Appears Questionable At This Time.

...Sensible Weather Highlights...

Expect A Broad Area Of Rnfl And Higher Elev Snow To Progress
Across The West In Assoc With The Mid Lvl Trough/Embedded Closed Low Fcst To Drop Into The Southwest By Fri-Sat.

Track Of The Closed Low Should Ultimately Focus The Majority Of Pcpn Over The Cntrl-Srn Portions Of The West By Late This Week Into The Weekend.

Combination Of Dynamics Aloft Approaching/ Reaching The Plains And Leading Low Lvl Flow From The Wrn Gulf Should Enhance Pcpn Over The Cntrl-Srn Plains By The Weekend With Potential For Some Mdt-Hvy Amts.

A Significant Low Lvl Upslope Component Is Psbl Over A Portion Of The High Plains... While Marginal Low Lvl Temps Lead To Uncertainty In Determining The Extent Of Any Snowfall Immediately E Of The Rockies.

Deepening Sfc Low Tracking Off The East Coast Into The Atlc Is Still Expected To Generate Windy Conds And Early In The Period With A Band Of Mdt-Hvy Pcpn Over The Mid Atlc. Low Lvl Temps Continue To Pose Fcst Challenges For Extent Of Pcpn Falling As Snow And How Much May Accumulate. Even With Daytime Temps Likely To Be Above Freezing There Will Likely Be At Least A Narrow Band Where Stg Dynamics Would Support Meaningful Snow Accumulation.

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