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Dynamic Storm System On The Way

| 1:54 pm December 19, 2012

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THIS AFTERNOON: What a beautiful day. Lots of sunshine with streaks of cirrus clouds overhead; temperatures are headed toward the upper 60s. But, to the west, a major storm system is stirring up a huge fuss over the nation’s mid-sections.

Blizzard warnings are in effect for parts of Colorado, Kansas, Nebraska, Iowa, and Wisconsin… in the broad area from Denver to Milwaukee. And, in the warm sector of the developing storm system, strong to severe storms are expected to form tonight west of Alabama; SPC maintains the standard “slight risk” of severe weather for much of Mississippi, Louisiana, and Arkansas. The convective initiation should begin in the 5-7 p.m. time frame, and those storms will blow into Alabama after midnight.

STORMY THURSDAY MORNING: Not much change in our thinking for tomorrow’s event. The main window for storms in Alabama will come from 3:00 a.m. until 12:00 noon (for our part of the state), and the severe weather threat is somewhat marginal due to the lack of buoyancy/instability.

The 12Z model runs show a little surface based instability over the southern half of Alabama, and SPC maintains the standard “slight risk” of severe weather for Alabama generally south of I-20. It is your classic cold season high shear, low instability event. Very high shear values will be in place, so we will have to watch for any small, brief spin-up tornadoes along the low topped squall line that will move through, but the main threat will come from strong straight line winds in the 40-60 mph range. This would be enough to knock down a few trees and power lines.

We should mention that tomorrow will be a very windy day, even away from storms. West winds will average 15-30 mph, with gusts to 40 mph… meaning we might even see some trees toppled by the gradient wind away from thunderstorms.

Take a few minutes to watch the Weather Xtreme video for all of the maps, graphics, and details.

COLD SHOT TOMORROW NIGHT: The weather turns windy and sharply colder. Temperatures will reach the upper 20s by Friday morning, with a gusty northwest wind wind chill index values should reach the teens. Friday will be sunny, but windy and cold with a high in the upper 40s.

PRE-CHRISTMAS WEEKEND: Expect a low in the 20s early Saturday, with low 30s at daybreak Sunday. The high Saturday will be in the mid 50s, with a high closer to 60 by Sunday. The weekend will be rain-free.

CHRISTMAS WEEK: We won’t be able to give you a high confidence forecast for next week until we get past tomorrow’s storms.

A few showers should break out Monday, and now the GFS (the 12z run) develops a deep surface low northwest of Alabama Christmas Day, meaning Tuesday would be breezy with occasional showers and storms. A few strong to severe storms would be possible Tuesday night into Wednesday morning with this setup.

On the other hand, the ECMWF (12Z run) shows a batch of showers Monday, then generally dry conditions on Christmas Day, followed by a big storm system with potential for strong to severe storms on Wednesday.

However the rain/storm event unfolds early in the week, we should turn much, much colder over the latter half of the week. But we simply don’t have enough skill in forecasting weather 4-8 days in advance to be very specific. Again, I encourage you to watch the Weather Xtreme video for details, thoughts, maps, and graphics.

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Look for the next Weather Xtreme video here by 7:00 a.m. tomorrow… and stay tuned for updates on storms to the west of Alabama as they develop tonight.

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