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US Extended Forecast thru Feb 28

On The Large Scale The Medium Range Period Is Relatively Straight Forward...With The Dominant Characteristic Being High Amplitude In The Northern Stream...Causing Again A Displacement Of The Circumpolar Low Into Southeast Canada.

At The Surface Arctic High Pressure Will Persist Across The Northern Tier Of The U.S. While Expanding South And East...And By Days 6 And 7...Next Thu/Fri...The Gefs Mean Forecasts 850 Mb Temperature Anomalies Of 1 To 3 Standard Deviations Below Climatology Over The Eastern Two-Thirds Of The Nation.

The Coldest Air Will Slide Into The Great Lakes.

Along The Leading Edge Of The Cold Air One Weather System Will
Spin Up As It Heads Away From New England Monday Morning.

A Second Wave Is More Likely To Yield Widespread Precipitation Across The South And East On Wed/Thu...With Air Likely Cold Enough To Support Ice And Snow In A Stripe Centered From Around Northern Mississippi Toward The Western Carolinas And Toward The Mid Atlantic Coast.

As The Wed/Thu System Exits The East Coast A Wave Is Anticipated
Into The West Coast...Undercutting The Ridge Center That Will
Become Better Closed Off As It Slides Up Into Alaska/Yukon.

The Lead Wave Is Forecast To Be Of Short Wavelength...Tracking
Primarily Into California And Then The Central Rockies.

A Larger Scale Trough Will Move More Bodily Onto The West Coast On Days 7/8.

Model Preferences And Uncertainty Assessment...

During Recent Cycles The Ecmwf/Ecmwf Ensemble Mean Led The
Way...But With The Pattern Dominated By Large Scale Features... There Is Now Good Agreement Between The Ecmwf/Gfs And Their Respective Ensemble Means.

The Gfs Does Appear Somewhat Fast With The System Affecting The South And East Wed/Thu...And Is More Aggressive At Driving 850 Temps Below -20 C All The Way To The Mid Atlantic Coast By Thursday Morning.

The Ecmwf...On The Other Hand...May Be Too Suppressed And Out To Sea With Its Coastal Low Development Late Wednesday...Judging By The Ensembles And Other Global Models.

We Represented Our Thinking Here With A 50/40/10 Blend Of The Ecmwf/Gfs/Ec Mean. For Much Of The Rest Of The Forecast The Blend Was Roughly 70/20/10...Using No More Than 20 Percent Of The Ec Ensemble Mean Given The Conceptual Agreement Between The Operational Gfs/Ecmwf And The Mean.

Sensible Weather Highlights...

Much Of The South Central And Southeastern States Will Undergo A
Gradual Cooldown With The Northern Plains...Great Lakes...Midwest
And Northeast Noting The Apparent Return Of Winter-Like
Temperatures (Some 20-30 Degrees Below Normal).

In The Southern States...The 'Gradual Cooldown' Caused By The Rapid Surges Of Continental Polar And Arctic Air...Mean That The 70s-80s Of Recent Experience...Will Be More Like Low/Mid 60s On Day 4...And 40s-50s By Day 5-7.

Aside From The Immediate Gulf Coast And Southern Half Of Florida ...The Modified Canadian Airmass Will Bring A Noted Sensible Weather Change.

With The Colder Airmass...Expect Periods Of Wintry Precipitation For The Northern Plains...Great Lakes And Northeast.

The West Will Be Mainly Dry And Mild For Days 3/4...Until The Negative-Tilt Trough...Begins To Spread And Deepen The Pacific Moisture Inland To The Continental Divide.

The Negative-Tilt Trough Emerging Along The California Coast By Wednesday Focuses The Bulk Of The Precipitation Over Northern California...The Central Coast And The Sierra.

The Geographical Coverage And Mean Qpf Distributions Of The Gfs/Ecmwf And Gefs/Ecens Means Looked Good By Comparison
Across The Rockies And Northern High Plains With Respect To
Increase Chances For Measurable Precipitation Toward Thursday And Friday.


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