Weather US Extended Outlook Through Sep 23

Extended Forecast Discussion
Nws Hydrometeorological Prediction Center Camp Springs Md
330 Pm Edt Thu Sep 16 2010

Valid 12z Sun Sep 19 2010 - 12z Thu Sep 23 2010

Final Progs Made No Changes To The Blend Used In The Earlier
Prelims -
The 500mb Longwave Pattern May Starting To Transition Around Tue
Day 5 As A Trof Off The Pacific Nw Coast Comes Ashore And
Flattens. The Pattern May Be Doing A Retrogressive-Re-Load Back
Around 150w At The End Of The Medium Range Period.
Meanwhile...Above Normal Heights Will Persist Over The Central And
Ern Portions Of The Country.

While Latest Ensemble Spaghetti Plots Underscore The High
Spread/Lower Confidence In The 500mb Height Forecasts Connected
With The Mean Trof Off The Pacific Nw Coast Flattening/ Moving
Onshore Days 6-7....The 12z/16 Deterministic Gfs/Ukmet/Canadian
Models Are In Surprisingly Good Agreement In Maintaining
Continuity From The Prelims With All The Main Weather Features
Across The Lower 48 Thru Day 6. The 12z/16 Ecmwf Is Still On The
Fast Side Of The Envelope Of Model And Ensemble Solutions Bringing
The Main Upper Trof Onshore Early Wed Day 6...While The More
Amplified Gfs Is In The Middle. Prefer A Slightly Diminished Gfs
Amplitude Here As It Has Support From The Slightly Faster Ukmet.

Models Agree On Showing A Cold Vort Max Digging Sw Into The Bc
Area Days 4-5 As The Last Shot Of Energy Into The Pacific Nw Coast
Trof Before It Flattens And Moves Downstream In Yielding To Strong
Upstream Flow. Phasing With Energy Farther S Is Not Expected.

Remnant Moisture From Hurcn Carl May Bring Periods Of Shra To Far
S Tx. The Mean Trof Off The Pacific Nw Coast May Contribute To
Significant Precip As Far S As Nrn Ca Sun-Mon Before The Main
Upper Energy Comes Inland. Lastly,... Under Above Normal
Heights...Pcpn Will Be Scanty Over The Central And Ern Conus
Before More Organized Precip Develops In The N Central States
Wed/Thu In Response To Height Falls Exiting The Nrn Rockies.


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