US Final Extended Weather thru Dec 31

Possible Coastal System To Impact The Nern Conus On Dec 29/30...

The Medium Range Period Will Essentially Cover The Remainder Of
2012 With A Very Active Pattern In Store.

The Mid-Level Flow Is Fcst To Consist Of A High Amplitude Pattern As Trof Energy Loads Up In The Swrn Conus Before Ejecting Ewrd Toward The Srn Plains/Lwr Ms Valley.

Such A Pattern Appears To Be Locked In Place As The System Over The Coastal Mid-Atlc Early D3/Thu Should Follow This Particular Track During The Short Range.

As This Disturbance Lifts Up Toward Nova Scotia...Broad Swrly Flow Aloft Will Be Featured Acrs The Ern U.S. As A Trof Begins Digging Over The Four Corners Region.

Thru D4...The Model Guidance Is In Relatively Good Agreement But Spread Evolves Thereafter. Much Of The Uncertainty Exists In How Amplified This Swrn Trof Becomes As It Crosses Into The Plains/Ms Valley.

Early D5/Sat...The 00z Ukmet Is Most Aggressive/Progressive With The Shrtwv Reaching The Lwr Tn Valley While The Gfs Suite Of Solns Continues To Be More Suppressed.

Looking Upstream...The Past Few Runs Of The Gfs Continues To
Insist On Energy Splitting Off From The Nrn Stream Into The Pac Nw
Which Is Not Supported By Any Of The Global Ens Means. This Gfs
Idea Leads To A Lower Amplitude Upstream Ridge Resulting A
Flatter/Quicker Soln In The Nern U.S. On The Other Hand...The 00z
Ecmwf Shows Much More Amplification Leading To A Stronger Coastal System Along The Mid-Atlc/New England Coast By Sat Night/Sun Morning. While The Ens Means Are Not Quite As Developed As The Deterministic Ecmwf...A Large Amt Of The 540-Dm Spaghetti Plot 00z Ecmwf Ens Members Depict Large Amplification In The East. The Gefs Members Are Definitely In Stark Contrast Being More Progressive With Less Amplitude.

Looking Back Toward The Wrn U.S...An Anomalous Upper Low Is Fcst To Peel Off The Belt Of Westerlies And Sink Swrd To Near 30n Well Offshore Of Baja Ca By 31/1200z. At That Pt...It Appears This System Should Keep A Large Enough Distance Away From The Polar Jet To Remain Cut-Off For The Foreseeable Future. All Guidance Agrees On Such An Evolution Although The Recent Gfs Solns Have Been Farther S Relative To The Ens Means. The 00z Ecmwf Agrees On The Posn But Is Much More Intense Aloft.

The Primary Impacts During This Period Will Begin With The
Lingering Heavy Pcpn With The Coastal Storm Affecting New England
On D3...Thu.

Later On...The Threat Shifts To The Cntrl/Ern Gulf Coast Where Heavy Rainfall Will Be Possible On Fri Into Sat.

As This Same System Lifts Toward The Nern Conus...A Coastal Storm Is Fcst To Develop Along The Ern Seaboard With Impacts Varying Depending On The Model.

A Soln Closer To The Coast Could Bring A Significant Pcpn Event Over The Nern States On Sat/Sun. Given The Cold Air Mass Settling Into Place...Much Of The Pcpn Would Be Snow Or Some Sort Of Mixture Of Pcpn Types. Given How Far This System Is Into The Medium Range...It Is Difficult To Speculate On Any Details At This Time.

Hpc Favored A Nearly Equal Blend Of The 06z Gfs And 00z
Ecmwf/Ukmet On Days 3/4 Given The General Agreement In The
Guidance. Thereafter...The 00z Ukmet Was Removed Given It Became
Too Progressive With The Lead Shrtwv In The Tn Valley.

For The Final Two Days Of The Period/Year...Global Ens Means Were Used More Heavily With Equal Contributions Of The 06z Gefs/00z Ecmwf Ens Mean Given The Uncertainty. However...A Small Amt Of 00z Ecmwf Was Added During This Period To Introduce Additional Isobars Given The Threat Of A Strong System Being In Play.


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