US Final Extended Weather thru Jan 5

...2013 To Start Off 'Cold' Across Much Of The United States...

This Upcoming Week...Much Of The U.S. Will See A Steady Supply Of
Dry Continental Air...With Modified Arctic Air Reaching The Southern Tier...And True Arctic Air Locked In Over The Great Lakes/Midwest Toward New England And Parts Of The Mid Atlantic.

High And Low Temperatures Are Forecast About 5 To 12 Degrees Below Average For Much Of The Nation.

It Will Remain Milder In Peninsular Florida...As The Primary Frontal Zone And Storm Track Stalls Parallel To The Upper Flow...Stretching From An Anchoring Upper Low In Central Mexico Across The Northern Gulf Of Mexico...To The Atlantic Offshore Of Southeast Georgia. The Frontal Zone Will Support A Swath Of Moderate Precipitation. Much Of This Will Be Rain...Although Some Light Wintry Precipitation Is Possible At The Northern Edge...Toward The Interstate 40 Corridor.

Hpc Continues To Take A Conservative Approach To The Coverage And Accumulation Of Precipitation Within This Pattern. The Model Qpf Has Tended To Look Too Widespread North Of The Surface Front...Where Deep Northerly Flow Should Dry Out The Low Levels. Much Of The Forcing Will Also Be In The Form Of Relatively Narrow Frontogenetical Bands...With Some Southward Propagation Away From The Mid Level Forcing Due To Convection. The Models Do Appear To Have Trimmed Back On The Northward Extent Of Precipitation During The 00z Cycle.

One Place We Will Emphasize The Potential For Heavier Rain Is In The Northern Florida Peninsula...Possibly Southeast Georgia By Day 5/6...As A Northern Stream Wave Is Showing More Amplitude... Capable Of Tightening The Jet Circulation Along The Southeast U.S. Coast.

Model Choice...

The 00z Gfs Was Usable To Day 4...But Then Continued To Display A
Bias Toward Flatter Flow And Faster Progression Than The Other
Models All The Way From The Pacific Across North America. The Gefs
Has Been Displaying The Same Bias To A Lesser Extent. The Ecmwf
Ensemble Mean...And At Times The Naefs...Has Provided A Good
Starting Point The Past Several Cycles.

One Of The Stronger Synoptic Features Is A Large 588 Decameter Ridge Growing Over The Caribbean Islands. Teleconnections Based On A Ridge Center Just East Of Puerto Rico Gives Us Results That Match Remarkably Well To The Ecmwf Ensemble Mean...Including The Widespread Sub-Average Temperatures Over The Conus And Tendency For Increased Rainfall In Southeast Georgia And Northern Florida. Therefore...We Continued With The Ecmwf Ensemble Mean...But Were Also Able To Use The 00z Operational Ecmwf And Ukmet.

The Feature Of Greatest Model Spread Has Been The Trough Or Closed Low Approaching California On Days 6/7. Some Of The Solutions...Including The 00z Ecmwf...Have The Low Cutting Too Directly Into The Northwestern U.S. Ridge. We Maintained Continuity By Taking A Weaker Feature Farther South Along The Coast...Which Is Supported By A Few Ecmwf Ensemble Members.


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