US Extended Forecast Updated thru Nov 23

Short Range Forecast Discussion
Valid 00Z Sun Nov 17 2013 - 00Z Tue Nov 19 2013

***Wintry weather expected for the Rockies and Cascades***

***Severe weather possible on Sunday ahead of cold front***

***Warmer in the East and colder in the West***

An active weather pattern is expected to continue through Sunday for the Pacific Northwest and Central/Northern Rockies. A very strong upper level jet stream oriented along the west coast of Canada, along with mid-level shortwave energy, will help develop an upper level trough over the Western U.S. Colder temperatures and plenty of mountain snow can be expected, and winter storm warnings are in effect for some of these mountainous areas.

A strong cold front developing over the Plains is forecast to move
eastward towards the East Coast by Monday morning, and this will likely result in the development of strong and severe thunderstorms from the Deep South to the Lower Great Lakes region. Increasing dewpoints and a strong low level jet will interact with increasing shear in the atmosphere, and these are favorable conditions for severe weather. A band of showers and embedded thunderstorms is also expected for the East Coast states, however these storms are expected to weaken.

In the temperature department, expect colder than average conditions from the Rockies westward, and warmer conditions east of the Mississippi River. The mild weather should last through Monday, before the cold front brings another round of below-average temperatures.


Extended Forecast Discussion
Valid 12z Tue Nov 19 2013 - 12z Sat Nov 23 2013

...Overview And Guidance Preferences...

Individual Model And Ensemble Solutions Continue To Display
Significant Spread And Run-Run Differences For Details Within A
Large Scale Evolution That Should Trend From Low Amplitude Flow
Early Next Week Toward An Ern Pac/West Coast Ridge And Downstream Troughing By The End Of Next Week.

Much Guidance Run To Run Variance Over The Lower 48 Including System Emphasis/Timing And Stream Separtation Issues Seem To Stem Significantly From Varied Handling Of Alaskan Based Energies Down Into The Nern Pacific...With Latest Trends Holding More Troffing Aloft Farther Wwd That Plausibly Better Fitting Upstream Ridging.

In General Latest Operational Model Runs Differ Enough From Each Other And Ensemble Means To Favor Emphasizing The Ensemble Means. While Mean Run-Run Continuity Has Also Been Quite Adversly Effected In This Pattern Recently...The Latest 06 Utc Gfs Ensemble Mean And Yesterdays 12 Utc Ecmwf Ensemble Mean Both Offer Some Plausible And Compatable Ideas Over Canada And The Lower 48 That Maintained Reasonable Wpc Continuity. A Blend Of These Means Was Primarily Used To Derive The Wpc Medium Range Guidance Suite.

...Sensible Weather Highlights...

Low Amplitude Flow Early In The Period Will Favor Enhanced Pcpn
From The Cntrl-Nrn West Coast Into The Nrn Rockies...With Lesser
Amounts Pushing Sewd Across The Region Through The Rest Of The
Week Along With Cooling.

As Evolving Conus Troughing And Leading Sfc Cold Front Head Across The Central/East-Central States Expect Rainfall Of Varying Intensity To Develop From The Srn Plains Newd. There Is Sufficient Spread In Guidance Sfc/Aloft To Keep Confidence Fairly Low With Determining Coverage/Amounts.

Ely Low Level Flow At Lower Latitudes Will Likely Also Support Periods Of Rainfall Over The Fl Peninsula And Wrn Gulf Coast And A Question Remains Whether Enough Srn Stream Separation Can Hold Any Heavier Qpf Near The Srn Portion Of The Main Frontal Push Back Across The Gulf Coast/Sern Us Into Next Weekend.

In Fact...The 00 Utc Ecmwf And To A Lesser Extent The 00 Utc Ecmwf Ensemble Mean Certainly Hold More Closed Low Energy Way Back Over The Swrn Us In A Massive Change From Prior Runs Than Most Other Guidance...With The 06 Utc Gfs Less Potent But Also Less Eastwardly Progressive By Then Across The Us Srn Tier States Than The 00 Utc Gfs.

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