US Extended Forecast thru Jul 27

Guidance Continues To Show A Stable Pattern Consisting Of A Southern Rockies Ridge And Eastern U.S. Trough While A Positively Tilted Longwave Trough Becomes Established Upstream In The Gulf Of Alaska. Teleconnections Relative To Both An Aleutians Ridge And A Less Pronounced Core Of Positive Height Anomalies Forecast Near Hudson Bay...Correspond Well To The Expected U.S. Pattern. This Lends Us Some Confidence In The Large Scale Flow...And The Model Spread Even For The Shortwave Details Is Less Than Usual... Certainly Less Than Seen 24 Hours Ago.

00z/06z Ensemble Means Show Agreement Through Day 7. The Gefs Mean Trends Toward Its Usual Bias...Being Flatter And More Progressive At Longer Lead Times...Especially Evident In The North Pacific This Cycle. Therefore...We Preferred A Near Equal Blend Of The Ecmwf Ensemble Mean And Naefs Mean...The Latter Incorporating More Sharply Defined Features And Slower Progression Seen In The Operational Canadian And Associated Ensemble Mean.

One Of The Desirable Traits Of The Gefs/Cmc Ensemble Was To Pull Back Just Slightly On The Forward Speed Of The Robust Shortwave Over The Northwest U.S./Southern Canada On Days 4/5. All Solutions Produce A Dynamic Trough That Is At Least 1.5-2.0 Standard Deviations Below Climatology Within The Mass Fields. These Numbers Increase To 3 Standard Deviations In The Gfs Solutions.

The Pacific Nw Will See A Combination Of Positive And Negative Changes In The Weather With Respect To Wildfire Issues...Increased Rainfall And Cooler Temps Versus Some Thunderstorms With Lightning And Gusty Winds. As This System Continues Eastward Expect Convection To Develop Over And Se Of The Northern Plains / Upper Ms Valley...With A Leading Warm Front Providing An Additional Focus For Locally Heavy Rainfall By Late Week. In Its Wake Expect A Cooling Trend Over The Northern Tier.

The Cold Front Reaching The East Coast By Thu Will Be Accompanied By Rain Followed By Cool High Pressure Tracking Into The Grtlks. Expect Diurnal Convection Over The Southeast With Some Locally Heavy Amounts Possible. A Stalled Surface Boundary And Weak Mid Level Circulation Over The Central Gulf Coast States Early In The Period Translates to Coverage Of Diurnally Enhanced Thunderstorms That are More Likely To Be Greater Than Climatology For That Region.

The Most Persistent Temperature Anomalies Should Be Of The Positive Variety Near The Four Corners Upper High...With Passage Of The Pac Nw System Allowing For Expansion Of Above Normal Readings Over Much Of The Interior West By Next Weekend.


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