Archive for December 22nd, 2012
Looking at the latest snow cover analysis, this week’s winter storm covered much of the Plains, Midwest and Great Lakes of the U.S. with a blanket of snow. Many areas had been lacking snow cover and the system dumped heavy amounts snow in many of those areas. No snow cover in Alabama, but the mountains of Northeast Tennessee did pick up some accumulations. That is as close as the snow has gotten to us so far this year. We will have to see how this analysis changes through the week. No white Christmas in Alabama this year, but portions of Oklahoma and Arkansas are actually forecasted to have a White Christmas this year.
A look at the weather map this afternoon, we can see the storm system that impacted us earlier in the week with severe weather in the Southeast and blizzard conditions from the Plains into the Great Lakes, is pushing off the Northeast coast of the U.S. Still causing some lake effect snows in Pennsylvania and Upstate New York. That system swung a strong cold front across the eastern half of the U.S. Behind the front an area of high pressure, currently centered on the Northern Gulf Coast has become the dominant feature affecting our weather. The high brought colder air and a brisk northwest wind. As it is nearly centered over us, the winds have gone nearly calm over us, but with all the subsidence associated with it, no rain and hardly a cloud in the sky across the Southeast. Despite the cool air, it is a very beautiful day across the southern tier of states.
For the rest of today, the high will slide off to the east and will allow for a southerly flow to return across our part of the South. More moisture and warmer temperatures will be noticed as soon as tonight, with many areas in central Alabama only settling into the mid 30s. Low pressure in West Texas will also help pump in additional moisture from the Gulf. Unsettled weather will settle in across the Southeast the next few days.
Across the rest of the country, another strong Pacific system is moving onshore causing flooding rains and mountain snows from Central California all the way north along the Interstate 5 corridor to Southern Canada. Most of that moisture will be squeezed out of the atmosphere as it lifts over the mountains. For the central and U.S., cold air has settled in. The air is cold enough where the recent snow should only melt slowly.
With so many people traveling and being out of pocket at Christmas, we encourage you to “stay in the loop” with weather information as we get closer since we have a potential high impact weather event for much of the Deep South. A deep surface low will move from near Jackson, MS to Knoxville, TN, with potential for severe weather southeast of the low, and with snow to the northwest over the colder air.
SEVERE WEATHER: Below is the SPC “Day Four” convective outlook, which is for Tuesday and Tuesday night…
There will be sufficient instability and shear in the warm sector of the storm for severe weather as you can see from the maps below…
At this early stage of the game, it looks like the primary risk of severe weather in Alabama will come from about 6:00 p.m. Tuesday until 3:00 a.m. Wednesday, with the main risk in Alabama south of I-59. As usual in winter, the primary limiting factor will be the amount of available surface based instability, but we can’t rule out a few isolated tornadoes based on the projected helicity values. Damaging straight line winds will be possible as well with the stronger storms.
Understand the placement of the severe weather risk can, and probably will change as we get closer. Stay tuned.
SNOW: A nice snow event is setting up Christmas Day for parts of Arkansas, Southeast Missouri, Northwest Tennessee, and parts of Kentucky in the cold sector northwest of the surface low track. Below is the GFS snow depth projection for the system…
Wednesday in Alabama promises to be a windy and sharply colder day with falling temperatures. No doubt there could be a little light snow in the back side of the departing storm system over the Tennessee Valley of extreme North Alabama, but for now we figure the best chance of accumulating snow will be north of our state.
So… some fun days ahead in the weather office… our greatest concern here is the severe weather threat, especially for the southern half of Alabama. Scroll down for Brian’s Saturday morning discussion and take a look at the Weather Xtreme video for more details…
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It’s shaping up for a busy period of weather from now through the Christmas week as a series of upper level troughs move across the eastern half of the country. But for today we stay dry and coolish, but thankfully the wind should die down somewhat so it won’t feel quite as cold. But we still stay coolish with highs only in the lower 50s.
A short wave moves across north of us on Sunday afternoon, but I think the rain chances are minimal since the lower portion of the atmosphere will be dry. But it should moisten up fairly quickly with rain and perhaps some thunder late Sunday night into Monday morning. Clouds and rain should help to keep temperatures in check with highs in the upper 50s.
Rain chances continue on Monday, but I think the potential for rain diminishes during the day with a high climbing to around 60s. We start the day out on Christmas Day with cloudy skies, but we’ll probably be dry as the next and biggest system ejects out of the southern Rockies coming our way Christmas afternoon and into the day after Christmas. This is where the forecast gets a bit dicey with two significant weather elements to deal with – the first being severe weather threat and the second being the potential for some snow flurries or brief light snow.
The two primary medium range models are in good agreement with a surface low forming in the vicinity of Lake Charles and moving northeastward into Northwest Alabama by midnight on Christmas night. This storm track should put Central Alabama into the warm sector late on Christmas Day which would mean a fairly warm day with highs reaching the lower 60s. This should bring us some potential for severe thunderstorms. However, the greatest instability remains along the Gulf Coast in a fashion similar to what we’ve seen with the last couple of storm systems. Perhaps my greatest worry is that the GFS is under forecasting the northward surge of instability because the surface low on both the ECMWF and the GFS is pretty strong. And the two primary models are in good agreement on the positions and strength of the low. Definitely wise to keep an eye on this.
The surface low is forecast to move by into the eastern Ohio River Valley and Central Appalachians by midday on the 26th. This then throws the age old problem of whether or not the cold air will arrive BEFORE the moisture departs. Right now both models show conditions that appear likely for the occurrence of some snow flurries or brief light snow before the moisture leaves completely. So, again, this will be a watch and see scenario as to how the actual mesoscale conditions shape up. If you are looking for snow, the GFS places the greatest snow potential along the Ohio River Valley with 2 to 4 inches possible. For us in Central Alabama, temperatures will change little or fall during the day with readings mainly in the 40s.
We come under a ridge on the 27th giving us a break in the weather with a somewhat chilly day with highs reaching the upper 40s. And we should warm up a bit more on Friday with a cold morning. Friday into Saturday is interesting on the GFS with rain returning. I don’t buy that scenario right now as the whole placement of rain looks a bit out of whack.
Looking further out, we start 2013 on a mild note with a substantial trough moving across the Great Lakes while leaving a trough over the southern Rockies. That lacking trough brings some wet weather around the 2nd and by the 6th of January we see the development of a deep trough over the western US which puts the Southeast US under strong southwesterly flow. This would be a warm and moist flow if it pans out.
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We’ll be on a one-a-day Weather Xtreme Video schedule from now through January 30th with James Spann off on some well deserved vacation time. So you are stuck with me until he returns. Remember that you can catch my forecast each evening for the next nine days on ABC 3340 newscast. Enjoy this dry but cool day before the weather turns active again. Godspeed.