Wet and Stormy Christmas

| December 23, 2012 @ 8:32 am

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As we have been discussing for the last several days, it is shaping up to be a wet and stormy Christmas for Central Alabama and portions of the Southeast US. To get the most out of the discussion, you need to view the video which has all of the details and graphics.

The first storm system will be moving by tonight and Monday bringing us a shot at rain and perhaps a few claps of thunder. Patches of rain were shoing up on radar this morning, however, the atmosphere is very dry aloft, so it will have to moisten up before any of that rain reaches the ground. The frontal system is expected to stall probably over South Alabama Monday evening as the upper short wave moves by taking with it the southward push to the front. That opens us up for the big short wave coming out of the southern Rockies as it moves into the Red River Valley area of Texas. As that strong short wave approaches, a surface low will form over Texas. While the models are in good agreement on the general position of the surface low, even small variations as to its exact track will have impacts on our weather. This is why it is important to stay current on the latest weather developments.

Both the ECMWF and the GFS project the surface low to move from Southwest Louisiana across the northeast corner of Mississippi to near Nashville, TN, by midday on Wednesday. Based on this track, which looks pretty good, we will come into the warm sector on Christmas afternoon and evening opening us up to the potential for severe thunderstorms and isolated tornadoes. See the video for details, but CAPE values are projected to be much better than we’ve seen in the last two systems. While not spectacular values, they are sufficient for severe storms with values in the 300 to 500 j/kg range. As with previous systems, the shear is excellent with Bulk Shear values way over 40. So this is shaping up to be a dangerous situation for Christmas afternoon and evening for us.

Following the passage of the front and the surface low on Wednesday morning, there is the potential for the precipitation to change over to a rain/snow mixture or perhaps snow flurries before ending. 850 millibar temperatures are supportive of the cold air arriving and precipitable water forecasts suggest that some moisture sticks around as the cold air arrives. This is not, I repeat, not a set up for a major snow event. The major snow with 2 to 4 inches possible will be from Central Arkansas northeastward into Ohio. Again, the video has graphics depicting this.

Rainfall amounts for the next five days are likely to reach 1.5″ to 2.5″ for totals. The first round will probably be less than a half inch while the second round will bring higher rainfall totals. Flash flooding may be an issue, but my focus has been on evaluating the severe weather risk.

Thursday and Friday should be dry but moisture increases Friday into Saturday bringing us another shot at some rain on Saturday.

Looking into voodoo, the New Year starts warm with a trough over the Four Corners area putting us under a nice mild and moist southwesterly flow aloft. But by January 7th there is another major trough coming into the Central Plains that promises us another round of wet weather.

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Sorry to be a little late on the posting. Lots to analyze this morning. Enjoy the day and Godspeed.


Category: Alabama's Weather

About the Author ()

Brian Peters is one of the television meteorologists at ABC3340 in Birmingham and a retired NWS Warning Coordination Meteorologist. He handles the weekend Weather Xtreme Videos and forecast discussion and is the Webmaster for the popular WeatherBrains podcast.

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