US Preliminary Extended Weather thru May 4

...Overview And Model Preferences From The 12z-18z/26 Cycle...

Upper Pattern Over The Conus Is Forecast To Become Quite Amplified With A Cutoff System Developing In The Mid-Ms Valley Late In The Week.

The Roadblock In The Atmosphere Will Be Strong Upper Ridging As Part Of An Omega Block Over Labrador With Another Closed Low Or
Merging Closed Lows Near 40n/45w. Upstream Ridging Moving Into The Pac Nw Will Also Aide In Holding The Upper Low In Place.

The Models/Ensembles Show Good Agreement Tue-Wed/D3-4 As A Sfc Low Moves Through Southern Canada And Pushes Its Cold Front Through The Rockies/Plains.

From Thu/D5 Through Sat/D7... The Gfs/Gefs Members Outpace The Ecmwf Ensemble Members And Especially The Deterministic Ecmwf ... Which Has Generally Been The Case. Though The Trend In Both Ensemble Systems Has Been Toward A Deeper And Farther West Closed Low... The Increased Uncertainty With Closed Lows Warrants A Cautious Approach. Thus... Wpc Trended Toward A 70/30 Compromise Between The Slower 12z/26 Ecmwf Ensemble Mean And The Quicker 18z/26 Gefs Mean.

Another Feature In The Mix Will Be Southern Stream Energy Moving
Eastward Along The Gulf Coast Toward Florida... Which Is Forecast
To Induce Modest Cyclogenesis In The Northeast Gulf.

The Gfs Is Most Eager To Phase This Energy Into The Farther East Closed Low Than The Ecmwf /With Its Slower Solution/... While The Ensembles Generally Favor A More Separated Solution With The Low Moving Slowly Out To Sea Se Of The Carolinas. Due To The Uncertainty Upstream With The Closed Low... Again Favor The Ensembles At This Point.

...Sensible Weather Highlights...

Cold Front Will Bring A Brief Cool Down To The Great Basin And Four Corners Region But With The Upper Forcing Diving Southeastward... Expect A Much Bigger Drop In Temperatures For The Central And Southern Plains /30 Degrees Colder/ Behind The Front.

Temperatures Should Stay Well Below Average Thereafter East Of The Divide... With The Exception Northern New England Closer To The Upper High.

Precip Should Be On The Light To Moderate Side Through The West/Central States With The Bulk Of The Gulf Moisture Caught Up With The Southern Energy Moving Toward Florida.

Models Are Still All Over The Place With How Much Rain May Fall Over The Sunshine State Wed-Thu. Heavy Rain Remains A Potential Threat As The Ecmwf Ensemble Mean Produces About 3 Inches Of Rain Just Offshore.

By The End Of The Week The Deterministic Models Diverge So Much
That Details Are Difficult To Assess. Should The Quicker Gfs/Gefs
Pan Out Much More Moisture From The Southern Stream Energy Should Get Wrapped Back Into The Mid-Atlantic. But If The Ecmwf/Ecens Mean Verify Then The Heaviest Rain Would Be Confined Farther West And Also Over The Southeast Before The System Pushes Offshore. Split The Difference With The Qpf In Similar Fashion With The Sfc And Upper Pattern To Focus The Rain Axis Into The Carolinas And Virginia.

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