Weather Sep 15 US Extended Outlook Through Sep 22

Nws Hydrometeorological Prediction Center Camp Springs Md
953 Am Edt Wed Sep 15 2010

Valid 12z Sun Sep 19 2010 - 12z Wed Sep 22 2010

Updated Prelim Progged Kept The Same Blend As The Early Prelim.
The 00z/15 Ecmwf Ensemble Mean And Ensemble Spaghetti Plots Show
Higher Uncertainty In The Stream Of Pacific Westerlies Spreading
Into The Wrn Conus Day 6 Underneath A Blocking Upper High Over Nrn
Alaska.

Most Guidance Is Fairly Well Clustered With The Evolution Of The
Ern Pac Mid Lvl Trof/Closed Low As It Ejects Inland And Supports A
Sfc Wave Fcst To Track Newd From The Plains. Some Deterministic
Model Detail Issues Remain As Expected. For Example The Ukmet Is
Slightly More Amplified With The Trof Versus Consensus... And The
Gfs Is Slower Than Consensus As The Trof Moves Inland By
Mid-Period. Also...The Canadian Leans To The Fast Edge Of
Guidance By The Latter Half Of The Fcst.

As Supported By Teleconnections Relative To The Core Of Positive
Hgt Anomalies Near Or To The N/Nw Of Extreme Nwrn Alaska...
Undercutting Pacific Flow Should Be Progressive With Fairly Low
Amplitude. Based On This Teleconnection-Favored Flow And The Full
Range Of Guidance... The Gfs Appears Somewhat More Amplified Than
Desired With Its Trof Entering The West By Day 7 Wed. Continuity
And More Recent Trends Seem To Favor Timing That Is In The Middle
To Faster Half Of The Current Spread With This Feature.

Over The Wrn Atlc Hurcn Igor Is Expected To Remain Well Off The
East Coast. The 12z Ecmwf/Ecmwf Ensemble Mean Bring The Track Of
Igor Well To The Left Of The Latest Tpc Track... So Those Solns
Were Not Acceptable Over The Wrn Atlc From Sun Onward. The 00z/15 Ecmwf Shows A Significant Ewd Trend To Igor's Track From Its
Previous Run For Early Next Week. Consult Latest Tpc
Advisories/Discussions For Further Info Regarding Igor.

The Days 3-5 Sat-Mon Fcst Started With A Blend Of 00z
Ecmwf/Canadian Global/Gefs Mean And 12z Ecmwf Ensemble Mean...
With Days 6-7 Tue-Wed Eliminating The Canadian Global Due To Its
Faster Sfc Wave Over The Plains/Grtlks. This Approach Provides
The Desired Compromise/Consensus Concerning The Pacific System
That Eventually Induces Plains To Wrn Grtlks Low Pressure. It Also
Reduces The Adverse Impact Of The 12z Ecmwf Mean Over The Wrn
Atlc.

Rausch/Flood


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