US Final Extended Weather thru Apr 17

...Overview And Preferences...

A Trough/Embedded Closed Low Over Sern Canada And E-Cntrl Conus As Of Early Day 3 Sat Will Progress Steadily Ewd With Time. Upstream A Leading Core Of Energy And Assoc Sfc System Will Track Ewd Along The Wrn/Cntrl Us-Canadian Border While Nern Pac Flow Will Amplify Into A Fairly Significant Wrn-Cntrl Conus Trough.

Meaningful Spread Develops With The System Along The Us-Canadian Border By Late In The Weekend... And There Is Wide Spread In Model/Ensemble Solns For Exactly How The Mid-Late Period Trough Will Evolve With Resulting Spread For Downstream Flow As Well.

Thus Confidence In Specific Details Is Below Average By The Days 5-7 Mon-Wed Time Frame. Given The Fcst Uncertainty Prefer To Maintain Elements Of Continuity Where Feasible. A Blend Of The 00z Ecmwf/Ecmwf Mean Best Reflects Continuity And Majority Clustering Of Guidance Days 3-5 Sat-Mon. The 00z Ecmwf Compares Less Favorably To Other Solns Thereafter So Day 6 Follows The 00z Ecmwf Mean Exclusively. Day 7 Wed Starts With A Blend Of The 06z Gefs/00z Ecmwf Means As The Latter Departs Somewhat From Continuity With Ern Canada Evolution While The Gefs Mean Trends Toward A Plausible Soln Over Ern Noam At That Time.

...Guidance Evaluation...

For The System Departing The Grtlks/Northeast After Early Day 3
Sat... Gefs Mean Trends Lead Toward The Ecmwf/Ecmwf Mean Idea Of Separate Sfc Lows To The Ne Of The Grtlks And Offshore New
England. Gfs/Ukmet/Cmc Runs Suggest The Gefs Means May Be A
Little Slow With Both Lows.

Guidance Diffs With Upstream Evolution Become Pronounced By Late
Day 4 Into Day 5 Sun-Mon. The 00z Ecmwf/Ecmwf Mean... Which Show A Fairly Strong Sfc Low Tracking Over/Near Nrn Mn By Early Mon... Currently Have Support From The 00z Ukmet/Cmc As Well As Good Continuity In Earlier Runs. 00z/06z Gfs And Gefs Mean Runs Are More Suppressed But Multiple Earlier Runs Had An Evolution More Similar To The Ecmwf Cluster. Also By Early Mon The 00z/06z Gfs Bring Lower Hgts Through The Northeast... Resulting In A Much
Farther Swd Frontal Posn Over The East. Preference Is To Maintain
A Soln Closer To The 00z Ecmwf/Ecmwf Mean In Light Of Guidance
Majority And Continuity At This Time... As Well As A Reasonable
Tendency Toward Hgts Rising Over The East In Response To Wrn Conus Troughing By Mon. The 00z Ecmwf Becomes Faster Than Consensus With Its Wave Tracking Over Sern Canada After Day 5 So That Piece Of Guidance Is Excluded From Consideration After Mon.

Models/Ensembles Develop A Broad Range Of Potential Solns For The Posn/Amplitude Of The Wrn-Cntrl Conus Trough As Well As For
Surrounding Flow By The Latter Half Of The Period. While Not
Quite An Outlier The 00z Ecmwf Leans To The Extreme Side Of The
Envelope With The Swwd Extent Of Its Trough And Wwd Longitude Of
The Downstream Ridge. The 06z Gfs Shows Some 00z Ecmwf Traits
With The Trough But By Day 7 Wed Has Higher Hgts Off The West
Coast Than Most Other Guidance. On The Other Hand The 00z Brings A Closed Low Near Vancouver Island... Swd Of Most Other Solns.. And A Closed Low Tracking From Mn Across Lake Superior In The 00z Gfs Next Wed Has Low Confidence Given Comparisons To Other Guidance.

Over Ern Canada/Nern Quadrant Of The Conus... The 00z Ecmwf Mean Rapidly Weakens Ern Canada Low Pres That Previous Runs Had Kept Better Defined And Remains So In Gefs Means. At The Same Time The 00z Ecmwf Mean Develops Day 7 Wed Lower Grtlks Low Pres Which Is Not Reflected In Other Ensemble Means But Cannot Be Discounted Given The Upstream Mean Trough. A Blend Of The 00z Ecmwf/06z Gefs Means Is Currently Favored To Resolve These Diffs.

...Sensible Weather Highlights...

System Tracking Near The Wrn/Cntrl Us-Canadian Border And Assoc
Flow Aloft Will Support Pcpn From The Pac Nw Into The Nrn-Cntrl
Rockies And Eventually The Grtlks.

At Least Some Of This Activity Should Be In The Form Of Snow Over Higher Elevs As Well As Nrn Tier Locations Near The Canadian Border. Based On Preferred Evolution Of This System... Expect Highest Pcpn Totals From The Nrn Nd Border Into Mn/Wi.

Amplifying Trough Aloft Over The West And Eventually Moving Into The Plains Will Support Further Pcpn Over The Nrn Half To 2/3 Of The West.

Ahead Of Both Systems... Expect Low Lvl Gulf Inflow To Support One Or More Areas Of Locally Hvy Rnfl Over The Ern Half Of The Conus.

One Area Currently Favored Is Near The Gulf Coast Into Extreme Southeast Around Sun-Mon.

Sfc Front Heading Into The E-Cntrl Conus May Also Serve As A Focus By Tue-Wed.

The Greatest Anomalies For Daytime High Temps Should Be From The Nrn Rockies Into Upr Ms Vly With Readings Consistently 10-25 F Below Normal. The Srn Half Of The West Will Trend Cooler Due To The Amplifying Trough Aloft... While The East Will Trend Above Normal After A Cool Start To The Period On Sat.

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