US Extended Forecast thru Aug 15

Within The Consensus Expectation Of A Mean Pattern Consisting Of A Bering Sea-Aleutians Upr Low And Nrn Pac Trough/Interior Wrn Noam Ridge/Ern Noam Trough... The Most Troublesome Part Of The Fcst Continues To Involve The Handling Of Energy Approaching The West Coast Around Next Tue Leading To Widening Model/Ensemble Spread For Details Of Flow Aloft From The West Coast Into Cntrl Noam By Wed-Fri.

Overall Clustering Is Better Than Avg For An Ern Conus Evolution More Typically Seen In The Cool Season.

Over The Past 24-36 Hrs The Ecmwf And Ukmet Have Been Most Consistent In Pulling Energy From The Srn Part Of The Approaching Ern Pac Trough Into A West Coast Closed Low But With Significant Run To Run Variation In Longitude.

The 00z Cmc Has Trended Away From This Idea And The Navgem Does Not Show It Either... So Operational Guidance Essentially Shows A 50/50 Probability At This Time. However The Past Two Ecmwf Means Have Settled On A Soln That Brings A Decent Amount Of Energy To The Cntrl West Coast But Not To The Extent Of The Operational Runs And Other Ensmeans Are Maintaining A Weakness Near The West Coast.

Teleconnections Relative To The Persistent Troughing Sw Of The Alaska Mainland And Ridging To The N Near 80n Have Favored A Modest Weakness Near The West. In Contrast The 00z Gfs May Have Too Much West Coast Ridging While The 06z Gfs/Gefs Mean May Bring The Overall Trough Too Far Inland.

Downstream The 00z Gfs Becomes More Amplified Than All But A Small Minority Of 00z Ensemble Members With The Trough Reaching The Nrn Half Of The Plains/Srn Part Of Cntrl Canada Late In The Period. Amplitude Of This Shrtwv Along With Timing Of The Leading Sfc Front Will Depend On How Energy Aloft Separates Near The West Coast Tue-Wed.

Ern Conus Evolution Is Showing Much Better Clustering Especially Aloft... With Lingering Spread For Sfc Wave Details Along/Offshore The East Coast. 12z/07 Model/Ensemble Guidance Started A Trend
Toward A Slower And More Separated System Aloft... Earlier Suggested By The 00z/07z Gfs... And Latest 00z/06z Solns Maintain This Scenario So The Updated Fcst Shows Little Change Aside From
Slightly Better Definition For A Separate Grtlks/Sern Canada Sfc Low And Then The Consolidated System Late In The Period.

Sensible Weather Highlights...

Over The West... A Compact Upr Low Ejecting Newd From The Nrn Ca Coast Should Support An Episode Of Organized Convection During The First Half Of The Week.

There Is Still Some Track / Timing Uncertainty Due To Issues With Approaching Upstream Flow. Otherwise The Spread In Guidance For Details Of Flow Aloft Makes It Difficult To Pinpoint Favored Areas For Convection Aside From Diurnal Activity In Assoc With Monsoonal Mstr From The Srn Half Of The Rockies Into The Southwest.

Expect The Most Pronounced Temp Anomalies To Be Over The Interior Northwest And Extending Into Wrn-Cntrl Montana Early In The Period With Some Highs At Least 10-15f Above Normal.

A Large Portion Of The East Should See One Or More Days Of Unsettled Weather With Some Areas Of Enhanced Rnfl With The Combination Of One Sfc Wave Tracking Near The East Coast And Another From The Grtlks Newd... Likely Consolidating Over/Near The Northeast... Along With Their Assoc Fronts.

Currently Expect Best Potential For Highest Rnfl Totals During The Medr Period To Be Over The Southeast With The Best Deep Mstr And One Frontal Bndry Ultimately Being Replaced By A Second... And Over The Northeast In Assoc With Strongest Dynamics And A Period Of Onshore Flow.

Farther Wwd Mid Lvl Energy Reaching The Plains And A Late Period Cold Front Reaching The Nrn Tier May Also Support Convection Of Varying Intensity. Except For The Srn Tier Expect Mostly Below Normal Temps And On Some Days Decent Coverage Of Minus 5-10f Anomalies.


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