US Short Term and Extended Forecast thru Oct 31

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
233 AM EDT Thu Oct 24 2013
Valid 12Z Thu Oct 24 2013 - 12Z Sat Oct 26 2013

***Unseasonably cool over the eastern half of the U.S.***

***Lake-effect rain and snow showers near the Great Lakes***

***Nice weather for the West Coast and Inter-Mountain West***

The main story making weather headlines through the end of the work week will be the much cooler temperatures east of the Mississippi River.

A pronounced trough has developed over the Eastern U.S., and this will allow for a series of disturbances to move southeastward from the Upper Midwest and into the Southeast states. Each of these systems will help to reinforce the unseasonably cool weather that is expected to continue through Friday.

Many locations in the Ohio Valley and Mid-Atlantic region have frost and freeze advisories/warnings for expected overnight lows in the upper 20s to mid 30s, which is at least 10 degrees below normal for
late October.

The trough pattern is creating enough wind flow over the Great Lakes to produce some of the first lake-effect precipitation of the season.

Temperatures will be marginal concerning snowfall potential, and the
chance of snow will be highest during the overnight hours and for any
higher elevations in Michigan and Upstate New York, and also the highest elevations of West Virginia. Elsewhere, cold showers can be expected from time to time.

Scattered showers and storms are also likely for South Florida as the cold front advances through the state.

Over the Western U.S., very pleasant conditions can be expected through Friday as upper level ridging governs the weather pattern. Sunny to partly cloudy conditions along with seasonal to above average temperatures are expected. The exception will be parts of New Mexico and Colorado where a few showers will be possible.

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Extended Forecast Discussion
Nws Weather Prediction Center College Park Md
147 Am Edt Thu Oct 24 2013
Valid 12z Sun Oct 27 2013 - 12z Thu Oct 31 2013

...Overview And Model Preferences...

The Rather Extended Period Of Amplified Flow May Reach A Turning
Point Late Next Week... But Until Then The Strong Ridging In The
Ne Pacific And Se Alaska Should Persist/Dominate.

500mb Height Standardized Anomaly Near +3 To +3.5 Is Forecast To Linger Near The Panhandle And Allow Troughing To Plunge Southward Through The Interior West Closing Off A Mid-Level Center Over Id/Ut Into Co.

The Simultaneous Extratropical Transition Of Typhoons Francisco
And Lekima Should Maintain The Strong Ridging Ahead Of Deep
Troughing Along 175w... Into Which The Systems Should Gravitate.

The Ensembles Continue To Show A Large Amount Of Spread In Both
Depth/Path/Speed Of The Western Troughing. In-House Ensemble
Clustering Method Shows A Nearly Even Split Among A Majority Of
The 70 Gefs/Ecens Members That End Up More Than 1000 Miles Apart By Tue/D5... Leaving Especially The Ecens Mean To A Bimodal
Pattern.

Preference Remains For A Slower Solution That The Several Recent Deterministic Runs Of The Gfs/Ecmwf Have Shown. A Varying Blend Between Them And The 18z Gefs Mean... Which Was Overall Slower Than The Ecmwf Ensemble Mean... Was Used For The Base Of The Forecast.

The Ec Mean Has Trended Toward Lower Heights In The West From Its Run 24 Hrs Ago... Again Lending Credence Toward The Gefs Mean Solution. As The Energy Exits The Rockies... It Is Quite Unclear As To What Speed And Whether Or Not It Will Open Up. Opted To Rely On The Gefs Mean But Ensemble Differences By Thu/D7 Exceed 2000 Miles... So Almost Anything Is Possible.

...Sensible Weather Highlights...

Despite The Southward Plunge Of 500mb Heights... Coldest Air And
Bulk Of Rain/Snow Should Focus Along/East Of The Divide... Though
The Entire West Should Experience A Cool Down.

Tight Pressure Gradient Over Mt/Wy/Co Should Develop A Robust Upslope Event With A Brisk East Wind.

Not To Be Left Out... The Northeastern Third Of The Conus Should See Some Precip As A Couple Systems Swing Trough... With Much More Uncertainty By Wed-Thu/D6-7 Tied To The Western Trough Evolution.


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