Weather US Extended Outlook thru Oct 01

Preliminary Extended Forecast Discussion
Nws Hydrometeorological Prediction Center Camp Springs Md
829 Am Edt Fri Sep 24 2010

Valid 12z Tue Sep 28 2010 - 12z Fri Oct 01 2010

All Models Continue The Forecast Trend Of Cutting Off A Mid Level
Low In The Lower Ms Valley But Even At Day 3 Where Models Are
Usually In Good Agreement There Remains Locational Differences.
There Are Also Differences With A Following Shortwave In The
Westerly Flow Across Srn Canada Which May Drop Or May Not Drop
Sewd Into The Mean Trof And Closed Mid Level Low. These
Differences Between Models/Models Runs And Ensembles Lead Us To
Use A Lagged Average Forecast For Days 3-5 Which Is Most Like The
Ecmwf Ens Mean. Modesl Come Into Better Agreement After Days 5 As
Ridging Builds Over Wrn Conus And The Mean Downstream Trof Axis
Along 80w-85w Remains Fixed. Models And Ensembles Are In Much
Better Agreement Towards The End Of The Period Than The Beginning.

Closing Off The Mid Level Low In The Lower Ms To Tn Valley Will
Bring Very Wet Conditions Late Weekend Into Next Week From The
Applchns To The East Coast With Possibly Continued Very Wet
Conditions Along The Sern Seaboard Into Late Week Depending On The
Progress Of The Slow Moving Associated Frontal Boundary.

T.S. Matthew Expected To Move In The Yucatan Peninsula And Linger
Into Wednesday. See Nhc Advisories And Discussions. Global Models
Have Been Insistent But Somewhat Erratic On Another Area Of
Cyclogensis In The Western Caribbean And Continue To Do So With
Much Better Agreement. A Continued Westerly Phase Mjo Is Currently
And Forecast To Keep Up Anomalously Westerly H850 Mb Winds Over
The Tropical Epac And Into The Caribbean. This Creates Favorable
Broad Scale Cyclonic Flow And Along With Favorable Chi Vertical
Velocity Anomalies Sets The Stage For Some Form Of Cyclogensis In
This Region. All Global Models Gfs/Ecmwf/Ngps/Cmc/Ukmet And Their
Ensemble Means Indicate A Large Area Of Low Pressure With A Center
Roughly Near Wrn Cuba By Day 7 Fri. See Future Nhc/Tpc
Discussions. Hpc Preference At This Time Is Again The Depiction By
Ecmwf Ens Mean.

Hpc Prelim Prog Basis This Morning Is The 00z Ecmwf Ens Mean Thru
The Forecast Period.

Rosenstein


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