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US Extended Forecast thru Jan 25

Extended Forecast Discussion
Nws Weather Prediction Center College Park Md
119 Am Est Sat Jan 18 2014
Valid 12z Tue Jan 21 2014 - 12z Sat Jan 25 2014

...Overview And Preferences...

Medium Range Forecast Period Remains Under The Influence Of
Highly-Amplified Flow Over North America...With Strong Upper-Level
Ridging Along Its West Coast And Deep/Cold Long Wave Troughing
Over The Eastern Third Of The Continent.

In General Terms...Very Cold In The East...Unusually Warm In The
West. And For The Plains States...A Little Of Both.

Not A Bunch Of Changes Were Implemented This Morning...As The
17/18z Gefs And 17/12z Ecens Means Reasonably Handle The Complex Pattern (Aloft And At The Surface).

Their Deterministic Runs Intend To Deliver Two Significant And Progressively Colder Shots Of Arctic Air Across The Great Lakes... Northeast And The East Central Conus and Are In Good Agreement For A Rather Organized Surface Cyclone Over The Eastern Lakes Region On Day 4.

An Unusual Day 6-7 Storm Track Originating In Northern Manitoba-Northwest Ontario Offers A Unique Twist To What Has Been An Interesting Start To The 2013-2014 Winter Season.

Day 3-4...The Initial Arctic Surge Will Be Spreading From The Upper Midwest To The Ohio Valley And By Day 5...Works Its Way Through The Northeast And Mid Atlantic Region.

This Airmass Will Easily Take Temperatures Down To 10-20f Below Normal Values Behind The Front.

Mid-Level Warm Advection Pattern With This System Suggests At Least A 6-9 Hour Window Of Banded Snows Fanning Out Across Its Eastern Quadrant.

The Aforementioned Deterministic Gfs/Ecmwf Runs Take The Leading Edge Of This Airmass Into The Southeastern States And Its I-20 Corridor. The Cooler Airmass Eventually Migrates Into Florida And The Entire Gulf Coast.

Moisture Is Very Limited And The Front Is Very Progressive...Which
Does Not Support Organized Precipitation As It Tracks Through The
South.

By Mid Day 7...An Airmass Rivaling The Early January Arctic Blast Will Be Poised To Invade The Upper Midwest States Of North Dakota... Minnesota...Wisconsin And Michigan.

The Surface Low Actually Originates Over Central Canada And Migrates Southeastward...Which Is Not The Usual Storm Track In Winter...But Given The Highly-Amplified Flow Over North America... The Result Is...A Secondary Shot Of A High-Arctic Airmass--From Of All Places---Originating In Nunavut (The Eastern Portion Of The 'Old
Northwest Territories).

Not To Ignore The West...But A Rather Large Cluster Of The Ec
Ensemble Members Migrate A Cold Core Cutoff Low Along The Western Flanks Of The Upper-Level Ridge And Attempt To Brush The Coast Of California And Southwest Oregon With Mid-Level Moisture... And Some Precipitation (Around Day 4).

The Gfs Deterministic Runs Support The Notion That A Feature Does Migrate Eastward...But There Really Is No Consensus...And The Naefs...Ec...Gefs Means Do Not Support A Significant...Or Prolonged Period Of Precipitation.

This Would Go Against The "Persistence" Forecast From Yesterday. But Overall...The Event May Not Get Enough Low-Level Inflow (More Of
An "Offshore" Flow Looks More Likely).

So...Support For Significant Precipitation Over Coastal Waters... Versus...Where Its Needed Most...Over Land Looks Like A Middle-Ground Solution.

As A Side Note...What Has Been a Temperature Forecasting Challenge In The West Has Been How Efficient The Ridge Has Been In Producing An Intense Subsidence Inversion Over Portions Of
Oregon/Washington...Where The Fog/Stratus Layer Has Persisted And Has Not Led To Any Of The Warm Weather Experienced Elsewhere.

Hopefully This Inversion Breaks Up As The Cold Core Low Edges
Towards The Coast On Days 3-5.

...Sensible Weather Highlights...

No Adjustments Made...Though It Is Of Note That The 18/00z Gfs Mos
Probably Has Not Captured The Mid-Day 7 Arctic Blast Just Yet Over
The Upper Midwest.

That Said...There Remains Some Room For Timing Errors...So Will Let The 70-30 Blend Of The Ecens-Gefs Start The Process.

Am Sure Wpc Will Likely Make The Correct Adjustment In The Next Couple Of Cycles (If They Are Needed).

That Said...

The Trough In The East Favors The Great Lakes...Upslope Regions Of The Appalachians And Northeast With Higher Probabilities Of Wintry Precipitation...With The Lake-Effect Machine In Play.

From A Synoptic-Scale Viewpoint...Light Mid-Level Warm Advection
Processes And Precipitation Will Be Limited To A Storm Track
Originating In The Northern Plains...Through The Midwest And
Reaching The Ohio Valley.

The More Organized Systems (e.g., The Gfs/Ecmwf Day 4 And A Storm Track Invof The Upper Great Lakes...(Day 7) Will Attempt To Exit The Continent In A Favorable Environment For Periods Of Snow And Snow Showers Across The Northeast.


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