US Extended Forecast thru Jan 18

Extended Forecast Discussion
Nws Weather Prediction Center College Park Md
Valid 12z Tue Jan 14 2014 - 12z Sat Jan 18 2014

...Potential Heavy Precipitation Across The Mid-Atlantic / New
England On Tuesday...

The Mid-Level Pattern During The Medium Range Period Will Remain
Of A High Amplitude With A Ridge Anchoring The Western U.S. While Negative Heights Continue To Affect The Central/Eastern States.

With The Exception Of The Initial System Crossing The Eastern
Seaboard On Tuesday...The Period Should Relatively Dry Across The
Conus.

This Strong Shortwave Has The Potential To Spread Heavy Rainfall Along The East Coast With Wintry Precipitation Possible Over More Interior/Elevated Locations.

Thus Far...Only The 12z Ecmwf/Ecmwf Ensemble Mean Are Depicting This Solution While Other Guidance Keeps The Heaviest Precipitation Offshore.

This Has Actually Been A Theme During The Early Part Of The Medium Range With The Ecmwf Suite Insisting On A Solution That Is More Amplified And Slower Than The Flatter/More Progressive Gefs
Members.

With The 12z Ecmwf...Its 500-Mb Output Is Actually One Of The Least Amplified Among The 50 Ensemble Members.

The Scenario The 12z Ecmwf Forecasts Allows The Southern Stream To Dominate Leading To Quite The Pronounced Surface Low Lifting Into The Upper Mid-Atlantic By Midday Tuesday.

Other Guidance Allows The Northern Stream To Dominate The Synoptic Pattern Which Leads To A Much Weaker Low Center With Precipitation Primarily Relegated To Offshore Locales.

Did Not Want To Go All In On The Ecmwf Idea Although Still Gave It A Lot Of Credit In The Blend Given How Consistent It Has Been With This Scenario Evolving.

The Wpc Preference Went Approximately 3/4 Toward The 12z Ecmwf With The Remaining Amount Given To The 18z Gfs With This Blend Extending Through Day 5/January 16.

One Of The Other Big Question Marks In The Forecast Is With Upstream Energy Initially Over The Northern Plains Early Tuesday
And How It Positions Itself While Moving Into The Lower Tn Valley
By Wednesday Morning.

As Expected...The Ecmwf And Gefs Members Diverge In The Same Way As The Initial Shortwave Crossing The Eastern U.S. Midday Tuesday.

The Models Across The Board Do Depict A Coastal Low Developing Sometime Wednesday Along The Coastal Atlantic. The 12z Cmc Is Furthest Offshore While The 18z Gfs/12z Ecmwf Are Closer To The Coast And For The Most Part Agree With One Another.

The Ensemble Surface Low Plots Show Quite A Bit Of Scatter With Some Solutions Straddling The Coastline While Others Are Offshore.

Will Need To Keep An Eye On This Surface Low Development Given The Potential For Wintry Precipitation Over The Northeastern U.S On Wednesday/Thursday.

Regardless...The Deep Upper Trof Crossing The Eastern U.S. Will Allow Below Normal Temperatures To Settle In With The Anomalies Most Pronounced Across The Deep South And Southeastern U.S. Readings May Be Up To 10 To 15 Degrees Below Normal With The Next Onslaught Of Cold Air.

For The Remainder Of The Period...Days 6/7...January 17/18... Leaned Much More Heavily On The 12z Ecmwf Ensemble/18z Gefs Means To Handle The Larger Scale Synoptic Pattern.

These Means Including The 12z Naefs/Cmc Ensemble Mean Are In Reasonable Agreement With This Setup Which Will Continue To Favor Above Normal Temperatures And Dry Conditions Across The Western U.S.

This Is Reflected In The Grids With 10 To 15 Degree Positive
Anomalies Anchoring The Western Half Of The Nation On Day
7/January 18.

Elsewhere...Broad Cyclonic Flow Over The Northeastern Sector Of The Country Will Continue To Favor Below Normal Temperatures And Increased Chances For Lake Effect Snows Next Weekend.


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