Archive for December 9th, 2012

Late Night Look

| December 9, 2012 @ 10:02 pm

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Not much change in the thinking late this evening.

The northern part of the line of storms is now into western Tennessee around Memphis. Recently saw a report of some dime sized hail at I-40. So the storms there are not severe.

This line weakens the further southwest you go.

But what appears to possibly be an MCV is over northern Louisiana near Monroe. This mesoscale convective vortex has the potential to produce damaging winds as it pushes northeast across Mississippi. It should reach Tupelo around 3 a.m. and the northwestern corner of Alabama around 5 a.m.

Just saw a report of tree and power line damage near Jonesboro LA. Makes sense.

The SPC just mentioned that they may extend the current severe thunderstorm watch into West Central Mississippi later. They put the odds at about 40% that they will issue a new severe thunderstorm watch into Mississippi before the current watch expires at midnight.

Otherwise, the trailing line of storms will push into western Alabama during the morning hours. While widespread severe weather is not expected with the main line, there will probably be a few severe thunderstorm warnings.

An Update on the Severe Weather Threat

| December 9, 2012 @ 7:08 pm

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A line of strong thunderstorms is pushing eastward across eastern Texas, northwestern Louisiana, eastern Araknsas, the Missouri Bootheel and western Kentucky.

Storms have formed ahead of the line over western Tennessee ahead of the main line.

Some of the storms have been severe this afternoon and a few severe thunderstorm warnings remain in effect this evening over eastern Texas, central Arkansas and western Tennessee.

A tornado watch is in effect until 9 p.m. for areas from southern Illinois to eastern Arkansas. A severe thunderstorm watch was issued recently for areas southwest of the tornado watch back into eastern Texas. It goes until midnight.

The Storm Prediction Center maintains a slight risk outlook through the overnight hours for areas from east of Austin TX to Evansville IN. It just touches the northwestern corner of Alabama.

That’s the bad news. The good news is that there have been few severe weather reports so far. There was a tornado in northern Arkansas around 3:30 p.m. There have been 13 reports through 6:45 p.m., mostly damaging winds.

The other good news is that the storms are weakening. The instability feeding the storms is weakening with the loss of the heating of the day. This means that the storms will continue to weaken through the overnight hours.

The storms will reach Memphis between 9-10 p.m. and the northwestern corner of Alabama around 2 a.m. We can’t rule out a few damaging wind reports with these storms.

The concern is that an approaching disturbance rounding the base of a trough over the Rockies this afternoon will help intensify the storms over Central Mississippi after midnight. These storms will push into Northwest Alabama around 2-3 a.m., pushing into the Huntsville area by 4:30 a.m.

By then though, the storms should start weakening as the disturbance weakens. As the storm rolls into the I-59 corridor around 7-8 a.m., the storms should be slowly weakening.

While significant severe weather is not expected, there will probably be a few warnings over western sections before sunrise, in the I-59 corridor between 7-11 a.m. and over northeastern Alabama through early afternoon. Damaging winds and hail will be the threats. The chance of any small tornadoes is low.

Temperatures will quickly drop into the 40s tomorrow morning behind the cold front. The front should reach I-59 by late morning, with temperatures falling from the 60s into the 50s during the early afternoon.

Rainfall amounts in the I-59 corridor will average between 0.75-1.25 inches, with higher amounts to the northwest.

Turn your Weatheradio to alert mode before retiring for the night tonight, or make sure that you have a reliable smartphone app or weather calling system available to wake you just in case warnings are required overnight or early tomorrow morning.

We will have frequent updates throughout the night here on the blog.

Afternoon Update

| December 9, 2012 @ 12:05 pm

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It has been a mixed bag of clouds and some sun across Central Alabama on this December Sunday. Patchy dense fog developed in areas that saw clear skies overnight, but visibilities were generally not too limited. Overnight lows looked more like the highs we would typically see in December, with morning temperatures in the middle and upper 50s.

A LITTLE MORE SUN TODAY: Parts of the area have seen more sunshine today as slightly drier low level air was working into Central Alabama this morning. That and mixing from increasing southerly winds should yield increasing sunshine. A little more solar insolation today should allow the mercury to reach the lower 70s, like we advertised yesterday in more locations. We note that Tuscaloosa was just at 60F at 11 a.m. The western Tennessee Valley was already in the 70s!

RADARS WILL BE HEATING UP: Numerous showers and thunderstorms were lined along a warm late this morning, from north of Nashville to north of Memphis to near Little Rock and Hot Springs, Arkansas. Surface low pressure was moving into western Arkansas early this afternoon. This low will intensify as it pushes northeast ahead of a trough that is digging southeastward. As the low tracks toward the Missouri Bootheel late this afternoon, its accompanying cold front will get its act together and will push toward the Memphis area. Showers and storms will spread into western Tennessee and northern Mississippi late today and this evening. The SPC does forecast severe weather for places like Jackson, TN, Memphis, Little Rock, Greenville, MS, Shreveport and Lufkin, TX.

WHAT ABOUT US? The SPC has the northern half of Alabama included in their standard slight risk severe weather outlook for Monday. Instability will be very limited, which makes the situation marginal. But there will be decent wind shear, and an approaching upper level disturbance could help trigger a few severe thunderstorms. The main threat will be damaging winds and some hail. We will have to watch for the development of one of those mesoscale convective vortexes that can produce organized damaging winds.

TIMING: Some showers and thunder will spread into Central Alabama this evening, generally after 8 p.m. as a surge of moisture enters the area. This activity won’t be severe. The main line of showers and storms will enter northwestern Alabama after midnight and will push slowly southeastward overnight. By sunrise, it still may be northwest of Birmingham, probably not reaching the I-59 corridor until 9-10 a.m. There may be a narrow window for that severe weather during the morning as the upper disturbance swings by. The activity should weaken during the afternoon as it pushes southeast and the upper level energy lifts out to the northeast.

RAINFALL AMOUNTS: The precipitation will end from the northwest during the late morning and early afternoon. Rainfall amounts, especially north of I-20, could approach one inch, with lessening amounts to the south.

SHARPLY COLDER: The cold front powering the rain and storms will be noticeable. Winds will shift to the northwest behind it and will become quite brisk, ushering in much colder air. Morning readings will fall behind the front over Northwest Alabama, and folks in the Gadsden, Birmingham and Tuscaloosa areas will also notice a falling thermometer by early afternoon. The mercury will be in the 40s by early evening, on its way to the lower and middle 30s by Tuesday morning.

Warm Today but Turning Colder

| December 9, 2012 @ 8:11 am

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.

It appears certain that the mild weather of the last week or so will be coming to an end after today with Monday a transition day and much colder air coming into the area on Tuesday and Wednesday. And there is a marginal risk for severe storms on Monday with damaging wind the main threat.

Today we will be mild to warm with highs around the 70-degree mark. But the upper air trough brings a system out of the Rockies tonight and Monday with a strong cold front moving through Alabama. This will make Monday a transition day with the high Monday coming during the early morning hours with temperatures steady or falling during much of the rest of the day. As temperatures fall Monday evening we should see lows by Tuesday morning down close to freezing. And Tuesday should be a rather bitter day with clouds holding tough, a strong north to northwest wind, and highs struggling to reach the 50-degree mark.

As to severe weather, SPC has placed much of the northern half of Alabama and Georgia in a slight risk area for Monday. They note that the system is marginal with the greatest threat coming from damaging wind. Instability values as represented by the CAPE values are generally at or below about 700 with the lifted index values around -2 to -3. So there is some instability, just not a lot. And as James noted below, helicity values are low so we don’t think there is a tornado threat. But just like we saw last night with the isolated severe thunderstorm in northern Mississippi, we have just enough instability that could generate a few severe storms in what is likely to be a squall line configuration Monday.

We are certainly in need of some rain after the eight driest November on record for Central Alabama. It appears that we will see rainfall amounts in the three-quarters to one and a quarter range (0.75″ to 1.25″) for most locations.

While the main energy with this system zips by, a small piece of it holds back which will help to keep Wednesday chilly too. We probably will not clear out completely on Tuesday but should see some sun on Wednesday.

By Thursday we come under a ridge and the 540 thickness line zips back to the north all the way to the Great Lakes so we should see out highs bounce back to around 60 by Thursday and Friday. Another system coming out of the Rockies on Friday promises to bring some showers to the area on Saturday, but the showers should be ending early Sunday.

And looking out into the long range, also known as voodoo country, we see that the GFS has flipped again going from what appeared to be a fairly chilly pattern to a more zonal pattern which would be mild. Not sure that I truly buy the flip with the GFS this time. There appears to be enough evidence that we should be into a somewhat colder pattern, so this flip in the long range GFS projections just does not seem to fit. But perhaps we’ll see it flip back in the next run or two.

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
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Thanks for tuning into the Weather Xtreme Video. James Spann should be back with the next edition first thing Monday morning. Be sure to catch the latest forecast on ABC 3340 at 5 and 10 pm today. Have a great Sunday and Godspeed.


Severe Weather Tomorrow?

| December 9, 2012 @ 7:04 am

Brian will be along shortly with a full discussion and fresh Weather Xtreme video…

I note SPC has put North Alabama in the standard “slight risk” of severe weather tomorrow…

I am not overly impressed with the threat. Looks like a typical cold season high shear low CAPE type event. Yes, those can be problematic at times, and it certainly needs to be watched, but the overall parameters are pretty marginal.

Below is the projected surface based CAPE (convective available potential energy) at 10:00 a.m. tomorrow ahead of the cold front…

CAPE values remain under 500 j/kg, meaning very limited instability, or ability of the air to rise freely and form deep convection.

The low level helicity values remain high (veering of the wind with altitude in relation to storm motion)>..

But, the EHI values are low (less than 1)…

Bottom line is that strong storms are possible in the QLSC (quasi linear convective system) ahead of the cold front with gusty winds, but a major severe weather issue is not likely. The main issue will be straight line winds that could gust at times to 40-60 mph.

One thing is a certainty… it will be turning MUCH colder following the front. At midday Monday, northwest communities will be in the 40s behind the front, while South Alabama will be in the 70s. All of Alabama turns cold Monday night, and Tuesday will be a raw, cold day with most places around here not getting out of the 40s.