US Extended Forecast thru May 11

Overview And Preferences...

During The First Half Of The Period... The Past 24 Hrs Or So Of
Guidance Has Trended Toward A More Concentrated Depiction Of
Ejecting Wrn Conus Trough Energy Through Late In The Week To Yield Somewhat Slower/Deeper Low Pressure Reaching The Vicinity Of Lake Superior By Early Fri.

Trailing This System Some Residual Troughing Is Fcst From The Srn Rockies Into Nwrn Mexico.

By Mid-Late Period... Guidance Clustering Has Improved With Larger
Scale Pacific Features But Solns Still Diverge Farther To The N As
Well As With The Upr Low Drifting Over Srn Canada... Contributing
To The Spread That Persists From The Ern Pac/West Coast As Of Fri
And Extending Downstream Thereafter.

Guidance Evaluation...

Guidance Is Continuing To Exhibit A Divergence Of Solns Over The
Ern Pac/Wrn Conus By Late In The Week/Weekend.

Ecmwf/Ecmwf Mean Runs Still Bring The Lowest Hgts Aloft Into The West With Operational Ecmwf Runs In Particular Showing The Farthest Swd Track Of Nern Pac Closed Low Energy Into The Nwrn Conus... Ultimately Leading To Broad Wrn Conus Troughing By Day 7 Sun.

Gfs/Gefs Trends Over The Past 36 Hrs Seem To Be Pointing Toward
Lower Hgts Over The West Late In The Fcst As They Have Adjusted
The Posn Of The Ridge Axis From The Wrn States Into The Ern Pac.

An Offshore Ridge Is Also Not Unreasonable Given The Fairly Well
Agreed Upon Trough Upstream Over 145-155w Longitude.

However Teleconnections Relative To Positive Hgt Anomaly Centers Over The Ern Aleutians And Nrn Canada In The Multi-Day Means By The D+7/D+8 Time Frame Still Keep Flow Rather Flat With The Only Hint Of Psbl Mean Ridging Over The Interior West.

These Offsetting Considerations Recommend A Soln Between The 06z Gefs/00z Naefs Means And 00z Ecmwf Mean With Slight Majority Weighting Toward The Former Means In Deference To Continuity.

00z/06z Guidance Has Continued The Ideas From 12z Yday Toward A
More Concentrated Handling Of Ejecting Wrn Energy So Latest Solns
Are Generally A Little Slower/Deeper With Low Pressure Tracking
Newd From The Cntrl Plains Through Lake Superior.

Strength Of The Downstream Ridge Aloft Lends Some Skepticism To The 00z Ecmwf/Ecmwf Mean Which Bring Leading Hgt Falls Aloft And Assoc Cold Front Farther Ewd Than The Majority Of Solns By Fri-Sat...

So Less Than Half Weighting Of Ecmwf-Based Guidance Is Reasonable.

Also On Fri The 06z Gfs/00z Cmc Trail The Center Of Model/Ensemble
Spread With The Sfc Low And Already On Thu The 06z Gfs Strays From Consensus With The Upr Low Over Canada.

Trailing This System... The Uncertainty With Upstream Flow Leads To Significant Implications For The Ultimate Amplitude/Timing Of
Residual Troughing Over The Srn Rockies/Nwrn Mexico As Of Fri.

The 00z/06z Gfs And 00z Ecmwf All Indicate Rather Quick Progression Into The East By Sun.

The Ensemble Means Are All Slower But With Considerable Spread Among Individual Members.

It Would Not Be Surprising For A Scenario Somewhere Between The
Models And Means To Occur... But Continuity And Long Term
Verification Favor The Means While Awaiting Better Guidance
Agreement.

Sensible Weather Highlights...

System Tracking From The West/Plains Newd Will Generate A Broad
Area Of Active Weather During Mid-Late Week With One Area Of
Highest Pcpn Totals Likely From The N-Cntrl Rockies/High Plains...
Where Low Lvl Upslope Flow May Enhance Activity At Some
Locations... Into The Upr Ms Vly/Upr Grtlks.

Expect At Least Some Pcpn To Fall As Snow In The Higher Elevs Of The Rockies.

From Wed Night Or Thu Onward Expect Some Locally Hvy Convection Along/Ahead Of The Sfc Front With Areas From The Srn Plains Into The Mid-Lwr Ms Vly Seeing The Best Potential For Hvy Rnfl.

Ongoing Feed Of Gulf Mstr/Stalling Of The Sfc Front May Support Some Hvy Rnfl Into The Weekend But Uncertainty With Details Aloft By That Time Leads To Lower Confidence In Existence/Location Of Enhanced Activity.

Consult Spc Outlooks For Further Info Regarding The Potential For
Severe Weather In Assoc With This System.

Expect Daytime Highs Up To 10-20f Below Normal Over Parts Of The Nrn Tier While A Broad Area In The Warm Sector To The E/Se Should Experience Above To Well Above Normal Temps.

Behind This System Pacific Flow Should Bring One Or More Periods
Of Pcpn To Locations From The Pac Nw Into The Nrn Rockies From
Late Thu Onward.

Ongoing Spread In Guidance For Details Of Flow Aloft Over The Region Lowers Confidence In Determining Swd Extent And Intensity Of This Pcpn.


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