US Extended Forecast thru Nov 21

Short Range Forecast Discussion
Valid 00Z Fri Nov 15 2013 - 00Z Sun Nov 17 2013

...Heavy snow likely over the Western U.S...

...Mild temperatures return for the weekend across the East Coast...

The upper pattern across the nation for the middle of the November will feature an expansive trof nearly extending from coast to coast. Initially, very little precipitation is expected across the Continental U.S. early in the period given the scant moisture content available.

The weather will become much more active by Friday afternoon onward over much of the Western U.S. in response to a strengthening upper trof from British Columbia. As this system noses southward, Pacific moisture is forecast to ramp up with upslope precipitation commencing across much of the northwestern states. Snow levels will gradually begin to drop as cold air surges southward from western Canada. This should eventually bring wintry precipitation to some of the valley locales of the Intermountain West.

The latest WPC winter weather desk forecast suggests the heaviest snowfall amounts over the Washington/Oregon Cascades and Bitterroots where roughly 12 to 18 inches of snow will be possible through Saturday afternoon. Elsewhere, amounts closer to 6 to 12 inches are expected over the Tetons, Wasatch, and Colorado Rockies.

An arctic frontal zone which sunk well into the southern extent of the
Gulf of Mexico is forecast to rise back toward the north as a warm front. This will ultimately advect a moisture rich air mass back toward the Gulf coast which will increase the threat for showers and thunderstorms.

At this point, the heaviest rainfall amounts are expected to straddle the
coast although this activity could remain just offshore. Regardless,
milder temperatures combined with a threat for showers and thunderstorms will be the norm for the Central/Eastern Gulf Coast from Friday morning into Saturday.

After a bout with well below normal temperatures the past couple of days, the eastern third of the country will gradually begin to rebound. This is in response to a surface ridge which will shift eastward into the coastal Atlantic. The clockwise flow around the anticyclone will allow the flow to come more out of the Gulf of Mexico which should moderate temperatures. This should bring readings closer to normal or just above climatology.

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Extended Forecast Discussion
Valid 12z Sun Nov 17 2013 - 12z Thu Nov 21 2013

...Pattern Overview...Guidance/Uncertainty Assessment...Sensible
Weather Highlights...

Models And Ensembles Continue To Bring Ample Short Range Mid-Upper Level Trough Energies Out From The Wrn Us This Weekend And Out Through The Central States To The Ern Us Next Week.

This Still Includes Significant Canadian Cold Airmass Surges Down Through The Central Then Ern Us In A Winterlike Pattern Prior Now To
Development Of A Increasingly More Zonal Flow Pattern. Continuity
Inland From The Nern Pacific And Alaska Over The Past Few Days Has Been Less Than Stellar And These Differences Has Now Led To A Trend Toward A Less Amplified And More Progressive Downstream
Pattern With Next Week Across The Lower 48.

Even Though Comparison Of The Latest Models And Ensembles Offers Decent Overall Pattern Evolution Agreement...This Was Also The Case Yesterday And Now The Latest Solutions Show These Pronounced Aforementioned Trends. This Lends Less Credance To Deterministic Details. Decided To Address This With Primary Usage Of The 00 Utc Ecmwf Ensembles...Whose Mean Seems Most In Step With Latest Deterministic Guidance Versus The Gefs/Naefs Means.

In This Transitional Pattern...The West Will Cool And Become
Increasingly Unsettled Into The Weekend With Digging Impulses
Spreading Qpf Including Some Locally Heavier Terrain Enhanced
Snows With Approach/Passage.

The Downstream Timing Of Main Frontal Pushes Next Week And Post-Frontal High Pressure Will Likely Continue To Fluxuate Within Guidance.

This Will Effect Timing Of Associated Periods Of Post-Frontal Upslope Fetch As Well As The Lead Focus For Quite Of Swath Of Heavier Rains With Some Severe Potential Into Sun/Mon As Per Spc And Some Wrap-Back North-Central Us/Great Lake Effect/ Nrn New England Snows On The Nw Periphery Of The Main Pcpn Shield/Post-Frontal After Deeper Moisture Feeds Ever Inland From The Gulf Of Mexico And Further Downstream Into The Srn/Sern Us From The Atlantic Where There Should Be A Defined Local Coastal Focus Of Qpf.

Increasingly Zonal And Energetic Flow Setup Over The Nwrn Us Next Week Also Points To A Prolonged Pattern Of A Favored Terrain Enhanced Heavy Snow Threat.


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