US Extended Forecast thru Mar 30

Overview And Preferences...

With The Very Deep Storm Off The Nern Coast And Trailing Ern Conus
Cold Air Leaving The Picture Early In The Period... Most Of The Lower 48 Should Experience More Typical Spring Weather With The
Establishment Of Moderately Amplified But Progressive Pacific
Flow.

There Is Still A Moderate Amount Of Spread With The Details Of Individual Features As Guidance Essentially Diverges Into Two
Clusters Over The Pacific And Eventually Into Wrn Noam Days 4-7
Thu-Sat While These Issues Along With Smaller Scale Detail
Uncertainties Influence The Fcst For The Leading Trough Aloft
Crossing The Conus And Sfc System Tracking Newd From The Cntrl
Plains.

Overall An Avg Of Latest Solns Provides The Best Account For Lingering Spread Days 3-4 Wed-Thu.

Ongoing Spread And Continuity For The Plains-Grtlks System Favor A Soln Closest To The 00z Ecmwf Mean/06z Gefs Mean Days 5-7 Fri-Sat While Somewhat Greater Support Remains For The More Progressive 00z Ecmwf Mean Versus Gfs/Gefs Mean Runs From The Pac Into Wrn Noam.

Combining These Considerations Yields A 70/30 Weighting Of The 00z Ecmwf Mean/06z Gefs Mean Fri And Exclusive Use Of The 00z Ecmwf Mean Sat-Sun.

Guidance Evaluation...

The Spread With Mid-Late Period Pacific/Wrn Noam Flow Originates
Over The Wrn-Cntrl Pac Days 4-5 Thu-Fri As Gefs/Gefs Guidance And
Ecmwf/Ecmwf Mean-Cmc/Cmc Mean Solns Develop Two Separate Clusters With Respect To Two Well Defined Shrtwvs.

The Result By Day 6 Sat Is That These Two Groups Are Essentially 180 Degs Out Of Phase Near 165w Longitude.

Downstream Impact Is For The Trough Off The West Coast At The Start Of Next Weekend To Become Flatter And More Progressive In The Ecmwf Cluster As A Shrtwv Immediately Upstream Begins To Feed Into The Longer Term Ern Pac Mean Trough Depicted In The D+8 Multi-Day Mean Charts.

Distribution Of Solns Has Changed Little Over The Past Day Or So While Teleconnections Relative To The Best Defined Hgt Anomaly Centers By D+8 Seem To Be Arguing For Fairly Progressive Flow.

Therefore Will Maintain Continuity With The Faster Ecmwf Mean Which Helps To Downplay Less Confident Details Of Operational Ecmwf/Cmc Runs.

Farther Ewd There Is Decent Agreement With An Elongated Area Of
Sfc Low Pressure From The Cntrl Plains Into Upr Ms Vly As Of Early
Thu But Spread And Run To Run Discontinuities Increase Fairly
Rapidly Thereafter With Diffs In Timing And Exactly How Energy
Within The Mid Lvl Trough Evolves.

Thus Far Ensemble Means Have Been The Most Stable With This System And At The Moment Provide A Good Compromise Between The Slower 00z Ecmwf And Faster 00z/06z Gfs.

Note That The 06z Gfs Becomes Quite Extreme With The Progression Of Its Mid Lvl Shrtwv Trough Thus Clearing Mstr From
The Ern States Well Ahead Of Consensus.

In Spite Of Upstream Issues The 06z Gefs Mean Has Trended Better Defined And A Little Faster Toward The 00z Ecmwf Mean During The Latter Half Of The Period.

This Adds Some Increment Of Confidence To The Preferred Scenario But Overall Confidence Remains Avg Or Below Based On Spread / Model Variability Thus Far.

Some Modest Though Potentially Locally Significant Detail Diffs
Remain For The Very Deep System Off The Nern Coast As Of Early
Wed.

Sensible Weather Highlights...

Establishment Of Pacific Flow Will Bring Moderate Temps... With Only Smaller Regions Seeing Temps More Than 10f Either Side Of
Normal On Any Particular Day.

This Flow Will Bring A Quick End To The Very Chilly Temps Reaching 10-25f Below Normal Over Ern Areas During Wed Lingering To A Lesser Degree Into Early Thu.

Initial Trough Aloft Reaching The West Will Spread Mstr Across At Least The Nrn 2/3 Of The Region Wed-Thu With Some Uncertainty Over Swd Extent Beyond That.

As This Trough Moves Ewd Pcpn Will Increase In Coverage/Intensity From West To East Over The Cntrl-Ern States Mid-Late Week.

Potential Still Exists For A Band Of Snow To The Nw Of Sfc Low Pressure Tracking Newd From The Plains... And Psbly At The Start Of The Event Over The Northeast In Leading Warm Advection.

Meanwhile Pockets Of Hvy Rnfl Are Psbl In The Warm Sector Due To A Period Of Enhanced Gulf Inflow Around Thu-Fri.

Departure Of The Trough From The West Will Lead To A Drying Trend
Over The Srn Half Of The Region But Upstream Flow/Mstr Will Support Continued Pcpn Through The Weekend From The Cntrl-Nrn West Coast Into The Nrn Rockies And Psbly Somewhat Inland.

Locally Mdt-Hvy Activity Is Psbl Along Favored Terrain Near The Pac Nw Coast/Nrn Ca.


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