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Archive for December 23rd, 2012

Update on Christmas Weather

| 9:13 pm December 23, 2012

Some new model data is rolling in tonight, and quite frankly I don’t see any reason to change our thinking for the weather in Alabama for Christmas. Still, unfortunately, a significant severe weather threat. If there is any shift in thinking, the event might be a tad later in getting here. But, not by much.

Below is the new NAM output valid at midnight Tuesday night…

NAM_221_2012122400_F54_PLI_30_0_MB_ABOVE_GROUND

The green on the above map shows where there will be surface based instability (lifted index below zero).

A very high amount of shear will be available…

NAM_221_2012122400_F54_SHRM_850_MB

And, the STP (significant tornado parameter) values remain high…

CONUS_ETA212_ATMOS_STP_54HR

Bottom line is that a major severe weather threat is building for the Deep South. In Alabama, the primary risk will be along and south of U.S. 278 (Hamilton to Cullman to Gadsden) from about 3:00 p.m. Tuesday through 3:00 a.m. Thursday. All modes of severe weather will be possible, including even the potential for a few strong tornadoes.

For those of you in the Tennessee Valley of extreme North Alabama, you will have a chance of severe storms as well, but the big question there is the amount of instability. New guidance tonight hints that there will indeed be enough buoyancy for severe weather to the Tennessee border.

This is a very difficult time for a severe weather event, needless to say, since so many people are traveling and “out of pocket”. Please be sure your friends, neighbors, and family members understand the risk, and are able to receive severe weather warnings Christmas afternoon into the nighttime hours.

I will have a full briefing here very early tomorrow morning…

Evening Update: A Few Light Showers For Now

| 7:03 pm December 23, 2012

2012-12-23_19-02-45

Scattered light rain showers are occurring across mainly the northwestern third of Alabama this evening, generally northwest of a line from Butler to Rockford to Huntsviile.

They are moving east northeast at about 40 mph.

The showers are in response to a moist airmass that is being lifted as it moves from west southwest to east northeast in the flow over the Deep South. The atmosphere has been too dry for much of the day for more than sprinkles to reach the ground, but that is beginning to change.

Light rain was being reported at Hamilton and Huntsvlle. Light drizzle was falling at Cullman. Light rain has been reported within the hour at Tuscaloosa.

Temperatures were in the 50s south of US-78, with 40s over the northwestern, northern and eastern sections of the state. A few breaks in the clouds allowed readings at Anniston to fall back to 45F.

Highs today included 55F at Birmingham and Anniston, 56F at Calera and 57F at Tuscaloosa.

Lows tonight will fall back into the lower 40s in the east and north and upper 40s elsewhere.

We continue to headline a significant threat of severe weather across Alabama for Christmas Day as a rapidly strengthening low pressure system passes just to our northwest tomorrow night. Damaging winds and tornadoes look to be a good possibility, so please dust off those severe weather safety plans and pay close attention to the weather, especially Tuesday afternoon and Tuesday night.

We also want to point out that a significant winter storm will develop Christmas Day across Oklahoma and spread east and northeast across much of Arkansas, southeastern Missouri then into Illinois and Indiana. Winter storm watches are posted for these areas. Significant snowfall accumulations are expected in this region, which will cause travel problems for folks trying to return home.

Amounts in the winter storm watch areas will generally be 2-6 inches, with locally higher amounts over the Ozarks of Arkansas and Missouri.

Lesser accumulations will occur from western Kentucky back through western Tennessee, southern Arkansas and northeastern Texas. Light snow accumulations (generally one inch or less are expected in western Tennessee and northern Mississippi.

Leftover rain will change to a few snowflakes Wednesday morning over the Tnessee Valley of North Alabama as well, but no accumulations are expected. Central Alabama shouldn’t see any snowflakes. Darn!

On This Date: 1F at Birmingham

| 3:00 pm December 23, 2012

On this date in 1989, an epic cold wave was diving south to the Gulf Coast.  On the left side of this image, you can see the upper air chart:

2012-12-23_13-37-41

Over one hundred and twenty cities across the central and eastern United States reported record low temperatures for the date.  Forty one of the cities also record lows for the month of December, some which had only been set the day before. 

The temperature fell to 11 degrees at New Orleans and Lake Charles LA, 4 below zero at San Angelo TX and 26 below zero at Topeka KS, all establishing all-time record lows for those locations. 

Here in Birmingham, the coldest morning was the 23rd, when it was 1F at the Airport.  The 1F on the 23rd was sandwiched between twin readings of 4F on the 22nd and 24th. 

The pressure at the center of the anticyclone reached an amazing 1061 millibars.  Here is the weather map from 6 a.m. that morning.

2012-12-23_13-36-22

Meanwhile, a strong storm moving across the Florida peninsula produced heavy snows along the Carolina coast.  Fifteen inches of snow fell at Wilmington NC and 13.3 inches at Cape Hatteras NC.  It was the first white Christmas of record from Florida to North Carolina.

Follow my weather history tweets on Twitter.  I am @wxhistorian at Twitter.com.

A Cloudy Sunday

| 2:14 pm December 23, 2012

2012-12-23_14-13-09

Clouds started gathering overnight and have been thickening all day across Central Alabama. Temperatures are in the 50s. Showers started breaking out over Mississippi this morning and spread into parts of West Central Alabama this morning. Much of the precipitation was not reaching the ground early on, but that will change as the atmosphere moistens.

Rain chances will go up overnight as a warm front comes northward in response to a developing surface low over Northeast Texas. There could be a little thunder involved toward sunrise, but no real storminess is expected with this first system. Rainfall amounts should average around one half inch by mid morning tomorrow. Overnight lows will drop into the upper 40s.

Showers and some embedded thunder will be ongoing in the morning ahead of the cold front. The showers should be southeast of I-59 by mid-morning and out of East Alabama by earlier afternoon, although there could be a few lingering showers for a few hours behind the front. There should be a few peeks of sunshine during the late afternoon, especially over western sections. The clearing will be brief, however, as clouds will re-thicken again overnight. Temperatures will be mild for Christmas Eve, dropping only to 50F-52F.

SEVERE WEATHER THREAT: By Tuesday morning, a very strong upper level disturbance will be swinging across Texas. This upper trough will become oriented in a northwest to southeast manner, which is not a good thing. We call it negatively tilted, and it can really enhance the energy available for severe weather.

The trough will power up a rapidly deepening surface low over the Piney Woods of eastern Texas Tuesday morning. The surface low will move quickly northeast to a position near Columbus, Mississippi by Tuesday evening. A warm front will lift across Southwest and into Central Alabama late Tuesday afternoon and evening in response to this vortex.

This may be the focus for severe weather Tuesday afternoon and evening as it lifts northward. With strong wind fields aloft and the convergence at the ground, these storms could produce damaging winds and even tornadoes. The only question mark is meager instability. But up to 750 joules of CAPE is expected across much of the southern three quarters of Alabama Tuesday afternoon and evening. This is plenty sufficient to produce significant severe weather.

The SPC maintains a 30% chance of severe weather within 25 miles of points south of the Tennessee Valley. This is on the high end of the slight risk category and wouldn’t take much to get into the moderate risk category. They SPC warns that supercell thunderstorms could develop in the warm sector over southern Mississippi into South Central and Southwest Alabama late Tuesday. They even mention the possibility of strong tornadoes if this situation comes together.

LATE MODEL NOTE: Brian was commenting on the amazing consistency between our two favorite long range models in their handling of this system. The European is now in, and is on the same track as previous runs. It might be a little slower and a little further north with the warm front. This continues to lend more and more credence to the severe weather threat.

PAY ATTENTION TO LATER FORECASTS: Since many folks will be pre-occupied with holiday plans and away from the weather grid, it is important to remind friends and family to keep an eye on the weather situation. It will be important to have your source of weather alerts close at hand and to review your severe weather safety plan for Tuesday and Tuesday night.

HAVING SAID ALL THAT: Many people are asking if this will be like April 27th. We certainly don’t think so. This is a winter event with low instability and high shear, unlike the generational outbreak of April 27, 2011 that generally only comes along every 40 years in Alabama. But all it takes is one tornado coming down your street for it to be YOUR April 27th. Take the situation seriously, but don’t panic. Just be prepared.

Agony of the Wait

| 12:06 pm December 23, 2012

If you are reading this Blog today, it’s probably because you have been reading our posts or you have heard about the potential for severe storms on Christmas afternoon and evening. And you probably have a big interest in the weather.

As a meteorologist, I have a big interest in the weather, but sometimes I can become immensely aggravated at how slow things happen. Take today as a good example. I wrote/videoed the Weather Xtreme Video using data from the 06Z model runs, 00Z for the European since it only runs twice a day. Here we are approaching noon and I want more data – morning soundings and the latest model runs. And I’m getting some of that! But SPC won’t be posting an update to Day 3 until about 2:30 am tomorrow, and I do appreciate their take on these developing severe weather scenarios.

So here I sit wanting desperately to provide new information but there isn’t a whole lot new to tell yet!

The GFS is coming in so we’re seeing some data and from what I’ve been able to see, the discussion from this morning is still on track.

The morning soundings are in! They confirm that the atmosphere over Central Alabama is very, very dry. So no matter what radar echoes you see for much of the afternoon, little if any of that rain will reach the surface because the atmosphere will have to moisten up before anything can get to the ground. So the risk for any rain through early evening is very small.

The European model is not in yet! So I can’t compare the two models yet to see how they are doing. I must say, though, that I cannot remember a time when those two models have been in such close agreement on a weather system for so many days. I think I started looking seriously at the Christmas Day storm last Thursday, and the two models have been in close agreement since then. Close agreement does not mean identical, but when the low positions and low tracks are as close as they have been, confidence is high on that solution. This is pretty amazing considering that most of the time the models don’t typically agree closely that far out. Close agreement means confidence goes up, but we all know BOTH models can be wrong!!

Speaking of wrong, I’m still hopeful that the storm system might take a more southerly track or not be as intense. It doesn’t seem likely, but such a track or lesser intensity would reduce the area exposed to severe weather. And I can’t think of anyone who wants to see severe weather on this particular day of the year!

And while I’m rambling and ranting a bit, let me wish everyone who reads the Blog a Merry Christmas and Happy New Year. Please be weather safe and keep up with the latest information. Godspeed.

-Brian-

Wet and Stormy Christmas

| 8:32 am December 23, 2012

An all new edition of the ABC 33/40 Weather Xtreme video is available in the player on the right sidebar of the blog. You can subscribe to the Weather Xtreme video on iTunes by clicking here.

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.

And you can follow news and weather updates from ABC 33/40 on Twitter here. Stay in the know by following the whole gang – here’s the list…

James Spann Charles Daniel Ashley Brand
J. B. Elliott Bill Murray Brian Peters
E-Warn (AL wx watches/warnings)

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

-Brian-

Significant Severe Weather Risk Christmas Afternoon/Night

| 7:09 am December 23, 2012

Brian will be along in a bit with his discussion and a new Weather Xtreme video.

Unfortunately parameters are still in place for the potential for a major severe weather threat for the Deep South Tuesday into Tuesday night. If you are reading this, I am not worried about you and your family being aware of the threat, but be sure and pass this on to your friends, neighbors, and relatives. We have a much harder time reaching the masses at Christmas time, but this is something everybody needs know. This isn’t to alarm anyone, but simply to let you know you need to be close to a source of severe weather information.

THE SETUP: A deep surface low will run from near Shreveport to Nashville Christmas Day. This keeps Alabama in the warm sector of the storm system, and all models show sufficient instability and shear/helicity for severe weather… below is the projected instability at 6pm CST Tuesday. The green is where lifted index goes below zero, or where there is surface based instability.

NAM_221_2012122306_F66_PLI_30_0_MB_ABOVE_GROUND

Bulk shear values remain impressive southeast of the surface low…

NAM_221_2012122306_F66_SHRM_850_MB

Below is the SPC “Day Three” convective outlook…

day3otlk_0830

The “hatched area” below is where significant severe weather is possible, roughly from Tuscaloosa southwest to near Lake Charles. SPC defines significant severe weather as F2 or greater tornadoes, damaging winds with speeds greater than 65 knots, or large hail 2″ or greater in diameter.

day3prob_0830

THREATS: We will have the dual threat of severe storms with damaging winds, and tornadoes with this system. If discrete cells can form ahead of the main squall line, some of them could rotate and produce a tornado. A strong tornado is possible considering the dynamics.

PLACEMENT: The greatest risk of severe weather in Alabama will be along and south of U.S. 278… Hamilton to Cullman to Gadsden… but the latest model data suggests a few strong to severe storms are possible up to the Tennessee border, but the limited instability there suggests the risk could be smaller. Bottom line is that all of Alabama will need to be ready for this.

TIMING: Keep in mind showers are possible as early as tonight as moisture begins to return and a warm front organizes to the south. We will have potential for showers tomorrow and tomorrow night as well, but as the warm front lifts north of here and we get into the unstable air, the primary risk of severe weather will come from 2:00 p.m. Tuesday through 2:00 a.m. Wednesday.

CALL TO ACTION: This is a very challenging event due to so many people traveling. Bottom line is this… everybody in Alabama needs to be sure they have a good way of hearing severe weather and tornado warnings, and that should NEVER be an outdoor siren. Those things are good only for reaching a handful of people outdoors. Have a good, working NOAA Weather Radio receiver in your home, properly programmed, with fresh batteries in case power goes out. On top of that, if you have a smart phone, have a good warning app installed and running, and of course, properly programmed.

For iPhone, a great choice is MyWarn. For Android phones, iMap WeatherRadio is fantastic; there is also an iPhone version. You can watch our live streaming coverage on both, and you receive the warnings only if you are in a tornado warning polygon (remember, warnings are polygon based, not county based).

And, be sure you review your plan of action. If you live in a mobile home and you are in a tornado warning polygon, you have to leave and go to shelter. In site built homes, be in a small room (hall, closet, bathroom) on the lowest floor (basement if you have one), away from windows, and near the center of the house. Be sure everybody in your home, including visitors, understands this plan.

SNOW TO THE NORTHWEST: For those of you traveling, a big snow is likely in the cold sector of this storm in the broad area from Fort Smith, Arkansas to Indianapolis…

nam_3hr_snow_acc_east_29 (1)

Here in Alabama Wednesday will be cold and raw; we probably won’t get out of the 30s and snow flurries are possible over the northern third of the state, but accumulation isn’t expected.

Let’s hope we escape with no major problems, but we must be prepared. I hope you and your family have a very merry and meaningful Christmas this year, but we must be safe. Stay tuned to the blog for updates as the event gets closer.