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Archive for March 17th, 2013

Monday’s Severe Weather Threat

| 4:58 pm March 17, 2013

The most recent Day 2 Convective Outlook shows much of Alabama has been outlined in the threat for severe weather for Monday. An intensifying area of low pressure over Texas this afternoon will continue to move across the Mississippi River Valley tonight and will be in the Ohio River Valley by tomorrow morning. The low will be tracking into Indiana and Ohio through the day tomorrow. The low will be swinging a cold front across the Southeast during the time and will be the focal for strong to severe thunderstorms tomorrow.

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For widespread, organized severe weather events that impact many locations, our best set up is for a low pressure to be in Arkansas or Northern Mississippi. When this happens, veering winds will usually enhance the atmosphere and increase the threat for tornadoes. This low pressure will be much farther north, either in northern Kentucky or southern Illinois. Low pressures tend to move along gradients and there is a significant temperature gradient in the Ohio River Valley. Temperatures in the 70s and 80s in the Southeast today verses temperatures in the 30s and 40s north of the stalled frontal boundary. So with this in mind, that means the greater dynamics will be to our north. However, the very warm air and increasing dew points/moisture across the region, mean the greater instabilities will be in place over us. The front will be providing uplift and thunderstorms will develop. Some will be strong and severe weather is possible in some locations tomorrow. The main threats will be damaging winds and some hail will be possible as well.

Here is what we can expect across Central Alabama tomorrow. Starting the day off, don’t be surprise if there are ongoing showers and thunderstorms across Northern Mississippi and Alabama. Some of the storms could be strong to severe with the greatest threat being damaging winds, as dynamics will be interacting with the unstable atmosphere in place. As the low pressure continues to lift northeastward, the main forcing dynamics will begin moving away from the state. The low will send a front through the area and this is what we will have to watch heading into the afternoon and evening.

As we head into the afternoon and evening. The front will be moving in allowing for additional thunderstorms to develop. Daytime heating will allow for the atmosphere to destabilize and instabilities should increase in much of the area throughout the day. This additional convection could include more widespread strong to severe thunderstorms. Damaging winds and large hail will be the main threat from these storms. Very large hail could be possible with hail stones greater than two inches in diameter possible. There could be a chance for some isolated tornadoes tomorrow as well. The best shear and dynamics across the state later in the day should be across our southern counties. No matter what the case, tomorrow looks to be a fairly active weather day across the state. Make sure you pay carful attention to the changing weather conditions tomorrow.

Clouds with a Few Peeks of Sun

| 3:34 pm March 17, 2013

Clouds increasing in coverage today. More moisture and warm air continues to move into our area from the Gulf of Mexico. This will provide the instability needed for some strong to severe storms that will develop later today in the ARKLATEX and will be impacting much of the Southeast tomorrow. Most areas are seeing a few peeks of sunshine this afternoon with most area reporting a broken cloud deck. Despite the clouds most area have warmed to near 70 this afternoon. No chance of rain the afternoon and much of the evening. Rain chances increasing late tonight. Great weather for any and all St. Patrick’s Day festivities you may have planned.

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The Elba Floods

| 9:30 am March 17, 2013
From the NWS Birmingham

From the NWS Birmingham

Elba is the county seat of Coffee County, in South Alabama. It started out as a ferry on the Pea River, at the confluence with Whitewater Creek in the 1830s. Its first name was Bridgeville. The name was changed to Elba in 1851. The winning name was chosen in a contest. The winning entry was submitted by a man who had just read a biography of Napoleon.

The Pea River has always been an important part of life in Elba. Originally named Talakatchee River by the Creeks, settlers renamed it the Pea. Floods have also been an integral part of the river’s role on history. The town was destroyed in 1865 by a major flood.

Another flood threatened to destroy the town in 1929. On Thursday morning, March 14, 1929, townspeople were warned to evacuate as the river started to rise. The downtown was flooded by lunchtime. The flood of Elba was the worst in the history of Alabama until that time. After that, levees were built around the town. More floods followed, one about every twenty years.

But the worst cane in 1990 when a week of heavy rains and flooding swamped parts of South Alabama. The Pea River crested at nearly 48 feet during the event on March 17th. But it was Whitewater Creek that breached the levees in the 1990 flood. About 7 a.m. on the 17th, the levee failed and water rushed into the town. It would flood the entire town, nearly destroying it completely. Damage across South Alabama totaled $100 million.

In 1994, Tropical Storm Alberto brought extremely heavy rains to South Alabama. This time, the river didn’t flood the town, it was heavy rainfall that could not drain properly from inside the town’s ring levees. After that event, town officials asked for help. A stormwater drainage system was designed and built in 1997 using FEMA money.

In addition, a program was implemented to convince homeowners to give up their homes in the floodplain. Fifty four homes were sold to FEMA in a successful mitigation project.

The river would rise again in 1998 when as much as twelve inches of rain fell across the area from overnight storms on March 8th. A levee on the Pea failed as the River crested at nine feet above flood stage. The entire downtown was inundated again. Two people died, and 2,000 people had to be evacuated because of the floodwaters.

Nice Today, Stormy Monday

| 7:16 am March 17, 2013

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.

Look for another gorgeous day across Central Alabama, much like yesterday, but with a few more clouds. Fog across Southeast Alabama has prompted a dense fog advisory for places like Montgomery, Dothan, and Eufaula, but the for should burn off by 9 am or so. I still expect to see the mercury climb nicely into the mid 70s across our area even with a few more clouds. But while we are enjoying a very nice day, a weather system is shaping up that could bring some severe thunderstorms with damaging wind and large hail to the area on Monday.

Aloft, a trough is coming out of the northern Rockies and will become negatively tilted as it reaches Minnesota. A fairly deep surface low will be situated near the western tip of Lake Superior with a secondary low in the Ohio Valley while a cold front trails southwestward into the Lower Mississippi River Valley. Ahead of the front from about mid afternoon, say 2 pm or so, until roughly about midnight, severe thunderstorms and large hail will be possible in an area from about Meridian, MS, to Jackson, KY, including places like Birmingham, Chattanooga, Nashville, and Knoxville. As I noted yesterday, the environment appears to be characterized by strong instability but low shear. This means that the threats will be primarily damaging wind and large hail. Details on the instability and shear are in the video.

The atmosphere will stabilize after sunset, so the threat of severe weather should diminish rapidly shortly after the sun sets. One small fly in the pattern is a weak inversion just below 700 millibars, but as long as it is not stronger than the GFS is suggesting, it should be easily broken.

The front moves by late Monday evening pushing the rain and storms eastward away from Alabama. We should see a return to sunshine on Tuesday, but as the trough slowly deepens over the East Coast, look for a cooling trend with Tuesday nice with highs in the mid 60s but Wednesday a tad chillier with highs around 60 degrees. Morning lows will dip into the upper 30s on Wednesday and Thursday morning, so look for patchy frost in those typically colder locations.

Thursday promises a return of clouds and perhaps some rain. We’ve got some model differences from Thursday into the weekend, primarily in the position and timing of the system. But we should be somewhat wet as we head into the weekend with fast moving disturbances in the upper flow that will generate a surface low along the Gulf Coast. In spite of the model differences, both longer range models do show the system moving east of us with improving weather on Sunday.

Week 2, also known affectionately as voodoo country, promises some interesting changes. If the GFS is correct, and we always have our doubts this far out, we are in for a substantial freeze around March 26th. That will be followed by a warmup as we reach April 1st along with a return of rain.

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)

I hope you will be able to enjoy the taste of Spring today by getting out into the warm day. James Spann will be back with the next edition of the Weather Xtreme Video first thing on Monday morning. Have a wonderful day and Godspeed.

-Brian-

Early Sunday Morning Notes

| 6:29 am March 17, 2013

Some interesting times are ahead in the weather office… Brian Peters will be along with a full discussion and a few Weather Xtreme video shortly.

SEVERE WEATHER THREAT TOMORROW: SPC has much of North and Central Alabama in the standard “slight risk” of severe weather tomorrow…

day2otlk_0600

Below is the projected instability (lifted index) at 3:00 tomorrow afternoon from the NAM model…

NAM_221_2013031706_F39_PLI_30_0_MB_ABOVE_GROUND

As you can see, the air will be very unstable, but below is the forecast bulk shear between the surface and 850 mb, and the higher shear values are well to the north, away from the best instability…

NAM_221_2013031706_F39_SHRM_850_MB

Bottom line is that the primary risk tomorrow will come in the form of hail and strong, perhaps damaging straight line winds. While we can’t totally rule out an isolated tornado, the threat seems pretty low at this point with the best upper support so far north.

While storms are possible tomorrow morning, the best chance of a severe storm will come from about 12:00 noon until 7:00 p.m.

COLD RAIN LATE IN THE WEEK; SOME SNOW? A strong impulse will impact Alabama late in the week, and the GFS has been hinting at some snow over parts of North Alabama at times. The latest run (06Z) just shows a dusting over the northwest corner of the state.

gfs_snow_depth_east_43

While snow in late March is NOT that unusual for Alabama, the last few deterministic runs of the GFS and the ECMWF have hinted at just a cold rain for this part of the state, and we will keep that going in the forecast. But, the NAO/AO (North Atlantic Oscillation/Arctic Oscillation) are going strongly negative, and that suggests the door will be open for much colder air in the 5-10 day period from now.

COLD MARCH 24-28: The Euro is hinting at a cold pattern for this period, with some potential for flurries or light snow along the way. Below is the output for Monday evening March 25 at 7pm local time…

ecmwf_apcp_f216_us

Long time growers know this, but you never plant something that will be hurt by a frost or a freeze in March in Alabama. Best to wait until after April 10…

Again, Brian will be along with a new video shortly. Enjoy your Sunday…