US Preliminary Extended Weather thru Mar 30

...Overview And Preferences...

Latest Medium Range Guidance Continues To Show Above Normal Hgts Aloft At Higher Latitudes Supporting Below Normal Hgts Especially Over The Ern Half Of The Conus... Though With A Modest Rise In Ern Conus Hgts By The Latter Half Of The Period.

Meanwhile A Couple Weak Bundles Of Mid Lvl Energy Will Impact The Northwest During Tue-Thu. Then In Varying Ways Models/Ensembles Begin To Develop A Split Flow Pattern Over The Ern Pac/West Coast Region. Exactly How This Split Evolves Will Ultimately Determine The Sfc Pattern Off The West Coast By Fri-Sat.

Farther Ewd Expect A Broadening Area Of Relatively Lower Sfc Pressures Over The Interior West... A Stnry Front Extending From The Nrn High Plains Into The S-Cntrl Plains... And High Pressure Drifting From The Plains Into The East.

During Days 3-4 Tue-Wed A Blend Primarily Composed Of The 18z
Gfs/12z Ecmwf Reflects The Most Agreeable Aspects Of Guidance For
The Sfc Low Off The Pac Nw Coast During That Time While Diffs Are
Relatively Subtle Elsewhere. Day 5 Thu Adds Increasing Weight Of
The 18z Gefs/12z Ecmwf Means On The Way To Days 6-7 Fri-Sat Which Side Exclusively With The Ensemble Means. This Soln Provides A Good Compromise With Respect To Timing/Degree Of Flow Separation Near The West Coast... While Downplaying Low Confidence Detail Diffs Aloft Farther Ewd.

...Guidance Evaluation...

For The Area Of Low Pressure Off The Pac Nw Coast Early In The
Period... The Majority Of Guidance Is Deeper Than The 18z Gefs Mean By Late Tue-Wed. A Compromise Of 18z Gfs/12z Ecmwf Runs
Reflects This Consensus. Detail Diffs Appear Minimal Farther Ewd.

With The Developing Split Flow Pattern Nearing The West Coast Late
In The Fcst... The 18z/12z Gfs And Gefs Mean Runs Along With The
12z Ukmet/Cmc Indicate That The Best Defined Bundle Of Energy Will
Trace A Wider/Wrn-Swrn Arc Before Approaching The West Coast
Compared To The 12z Ecmwf And Ecmwf Mean. The Past Couple Days Of Ecmwf Runs Have Been Quite Erratic Over The Ern Pac/Wrn Conus... So It Is Hard To Have Too Much Confidence In The 12z Ecmwf Run.

Also Some Previous Ecmwf Mean Runs Had Been Slower With The Trough Aloft... Favoring At Least Partial Weighting Of The Slower
Gfs/Gefs Mean Cluster. Within This Cluster The 18z Gfs/Gefs Mean
Are Slower Than The 12z Gfs And Similar To The 12z Cmc.

Preference For A Compromise Between The 18z Gefs And 12z Ecmwf
Means Yields A Moderately Defined Sfc System Off Ca Into Fri But
Dissipation To A Sfc Trough By Sat To Provide The Most Leeway In
Light Of Psbl Future Guidance Changes.

Over The Nrn Tier The Main Wild Card Is A Compact Closed Low Fcst
To Meander W Of Hudson Bay Around Midweek. The 18z Gfs And 12z
Ecmwf/Cmc Suggest This Feature Will Settle Far Enough Swd To Have Some Influence On Parts Of The Nrn Tier By Late In The Week While The 12z Gfs Carries It Ewd. Currently Suspect The Ensemble Means Mean Fill This Upr Low Too Quickly But With The Blocky Flow At Higher Latitudes Leaving The Eventual Path Of The Closed Low Quite Uncertain... Preference Is To Wait For Better Guidance Agreement Before Incorporating Psbl Impact On The Nrn Tier.

...Sensible Weather Highlights...

Over The West... Expect An Area Of Lgt To Locally Mdt Pcpn From
About The Nrn Half Of The West Coast Into The Nrn Rockies Tue-Thu
In Assoc With Leading Shrtwv Energy Reaching The Northwest. As
More Amplified Troughing Approaches The West Late In The Week
Anticipate The Pcpn Shield To Shift Swd By Fri-Sat. Daytime Temps
Should Be Above Normal At Most Locations During The Period.

Over The Cntrl/Ern States... Continue To Expect Consistently Below
To Well Below Normal Readings At Many Locations With Greatest
Anomalies Likely Tue-Wed.

Two Exceptions Will Be The Srn Plains Where Temps Should Rebound To Above Normal Late In The Week And Nrn New England Which Should See Near Normal Highs On Most Days.

Portions Of The East May See Lgt Pcpn Lingering Thru The Early
Part Of The Period After Passage Of The Short Range System Into
The Atlc... Followed By An Increase Of Mstr Over The Plains/Ms
Valley And Perhaps Extending Into The Oh/Tn Vlys Thu-Sat. The
Majority Of This Pcpn Should Be In The Form Of Lgt-Mdt Rnfl Though
Isold Heavier Pockets Of Rnfl And A Little Snow On The Nrn Side Of
The Pcpn Shield Cannot Be Ruled Out.


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