#alwx Central: Saturday afternoon update on potential for sever - ABC 33/40 - Birmingham News, Weather, Sports

#alwx Central: Strong storms expected to weaken overnight, tornado watch still in effect for 8 counties (links, radar)

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Main threats from severe storms in Alabama between midnight and 4 a.m. Sunday, December 21, 2013. (NWS Birmingham) Main threats from severe storms in Alabama between midnight and 4 a.m. Sunday, December 21, 2013. (NWS Birmingham)
Severe weather threat levels in Alabama, Saturday, December 21, 2013 from the NWS in Birmingham. Severe weather threat levels in Alabama, Saturday, December 21, 2013 from the NWS in Birmingham.

With a strong line of storms expected in Alabama Saturday afternoon and into Sunday morning, be sure you are "Weather Aware" and have a severe weather plan of action.

You can get up-to-the-minute weather updates and storm alerts by downloading ABC 33/40's apps for your mobile devices: Click here for our News App; Click here for our Weather App; Click here for our Spann 24/7 App.

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The following is the latest updates via the National Weather Service and the ABC 33/40 Weather Blog:

11:14 p.m.

...SIGNIFICANT WEATHER ADVISORY FOR WESTERN WINSTON...NORTHWESTERN WALKER...EASTERN MARION...LAMAR AND FAYETTE COUNTIES UNTIL 1215 AM CST...

AT 1112 PM CST...THE NATIONAL WEATHER SERVICE WAS TRACKING STRONG THUNDERSTORMS ALONG A LINE EXTENDING FROM NEEDMORE TO 6 MILES WEST OF MILLPORT...AND MOVING EAST AT 20 MPH. WIND GUSTS UP TO 40 MPH ARE EXPECTED WITH THESE STORMS...ALONG WITH HEAVY RAIN AND FREQUENT DANGEROUS LIGHTNING.

LOCATIONS IN OR NEAR THE PATH OF THESE STORMS INCLUDE... WINFIELD... MILLPORT... LYNN... FAYETTE... CARBON HILL... TORRENTIAL RAIN...WHICH MAY FLOOD LOW LYING AREAS SUCH AS DITCHES AND UNDERPASSES...IS ALSO LIKELY. DO NOT DRIVE YOUR VEHICLE ON A FLOODED ROADWAY.

10:59 p.m.

TORNADO WATCH REMAINS VALID UNTIL 2 AM CST SUNDAY FOR THE FOLLOWING 8 COUNTIES IN ALABAMA:

CULLMAN, LIMESTONE, MADISON, MORGAN, DEKALB, JACKSON, MARSHALL AND LAWRENCE.

IN TENNESSEE THIS WATCH INCLUDES 3 COUNTIES IN SOUTHERN MIDDLE TENNESSEE FRANKLIN LINCOLN MOORE THIS INCLUDES THE CITIES OF...ATHENS...CULLMAN...DECATUR... FAYETTEVILLE...FORT PAYNE...GUNTERSVILLE...HUNTSVILLE... LYNCHBURG...MOULTON...SCOTTSBORO AND WINCHESTER.

10:33 p.m.

Storms weaken, but keep stay weather aware:

The line of thunderstorms over northwestern Alabama and eastern Mississippi has slowed its further progress and weakened tonight as the upper level dynamics associated with the system lift out across the Ohio Valley.

The line of storms is now over northwestern Marion County. It is about to enter northwestern Lamar County.

It is expected to continue slowly weakening across Central Alabama through the overnight hours. The storms may re-intensify Sunday afternoon over southeastern sections of the area.

Tornado watch continues until 2 a.m

We will continue to monitor the storms through the enter night and will have frequent updates and the latest from the affected areas.

Rain and storms may linger a good bit of the day across Middle Alabama. Putting the morning forecast together.

10:14 p.m.

SIGNIFICANT WEATHER ADVISORY FOR MARION COUNTY UNTIL 1115 PM:

AT 1010 PM CST...THE NATIONAL WEATHER SERVICE WAS TRACKING STRONG THUNDERSTORMS ALONG A LINE EXTENDING FROM 8 MILES NORTHWEST OF HACKLEBURG TO DETROIT...AND MOVING EAST AT 20 MPH. WIND GUSTS UP TO 50 MPH ARE EXPECTED WITH THESE STORMS...ALONG WITH HEAVY RAIN AND FREQUENT DANGEROUS LIGHTNING.

LOCATIONS IN OR NEAR THE PATH OF THESE STORMS INCLUDE... HAMILTON... WINFIELD... WESTON... HACKLEBURG... GUIN... TORRENTIAL RAIN...WHICH MAY FLOOD LOW LYING AREAS SUCH AS DITCHES AND UNDERPASSES...IS ALSO LIKELY. DO NOT DRIVE YOUR VEHICLE ON A FLOODED ROADWAY.

9:49 p.m.

Severe Thunderstorm Warning remains in effect in NW Alabama:

A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 1015 PM CST FOR CENTRAL LAUDERDALE...NORTHERN FRANKLIN AND SOUTHEASTERN COLBERT COUNTIES...

AT 947 PM CST...DOPPLER RADAR INDICATED A LINE OF SEVERE THUNDERSTORMS CAPABLE OF PRODUCING DESTRUCTIVE WINDS IN EXCESS OF 70 MPH. THESE STORMS WERE LOCATED ALONG A LINE EXTENDING FROM 9 MILES SOUTHEAST OF PULASKI TO 20 MILES WEST OF DECATUR...MOVING EAST AT 30 MPH.

LOCATIONS IMPACTED INCLUDE... FLORENCE...MUSCLE SHOALS...SHEFFIELD...RUSSELLVILLE...TUSCUMBIA... UNDERWOOD-PETERSVILLE...KILLEN...LITTLEVILLE...LEIGHTON...LEXINGTON AND SAINT FLORIAN.

9:29 p.m

Severe Thunderstorm Warning in NW Alabama:

THE NATIONAL WEATHER SERVICE IN HUNTSVILLE HAS ISSUED A SEVERE THUNDERSTORM WARNING FOR... COLBERT COUNTY IN NORTHWEST ALABAMA... FRANKLIN COUNTY IN NORTHWEST ALABAMA... CENTRAL LAUDERDALE COUNTY IN NORTHWEST ALABAMA... * UNTIL 1015 PM CST *

AT 923 PM CST...DOPPLER RADAR INDICATED A LINE OF SEVERE THUNDERSTORMS CAPABLE OF PRODUCING DESTRUCTIVE WINDS IN EXCESS OF 70 MPH. THESE STORMS WERE LOCATED ALONG A LINE EXTENDING FROM 10 MILES NORTHWEST OF FLORENCE TO 6 MILES SOUTHWEST OF RED BAY...AND MOVING EAST AT 30 MPH.

* LOCATIONS IMPACTED INCLUDE... FLORENCE...MUSCLE SHOALS...SHEFFIELD...RUSSELLVILLE...TUSCUMBIA... RED BAY...UNDERWOOD-PETERSVILLE...CHEROKEE...KILLEN... LITTLEVILLE...LEIGHTON...LEXINGTON...VINA...SAINT FLORIAN AND HODGES.

A TORNADO WATCH REMAINS IN EFFECT UNTIL 200 AM CST SUNDAY MORNING FOR NORTHERN ALABAMA AND CENTRAL TENNESSEE.

9:04 p.m.

Intense line of storms in NW Alabama:

Our line of intense storms is now into Northwest Alabama's Lauderdale County.

A severe thunderstorm warning is in effect for Colbert, Franklin and Lauderdale Counties.

The storms are now within 20 miles of western Marion County.

They have slowed a bit, now moving east at 20-25 mph. This will put them into northwestern Marion County just between 9:30 – 9:45.

Damage reports from northern and Mississippi have slowed down a bit. Radar indicates the storms might have weakened a tad.

A tornado watch is in effect for the northwestern third of Alabama until 2 a..m.

8:17 p.m.

Tornado Watch issued for 11 counties in Alabama

THE NATIONAL WEATHER SERVICE HAS ISSUED TORNADO WATCH 587 IN
EFFECT UNTIL 2 AM CST SUNDAY FOR THE FOLLOWING AREAS

IN ALABAMA THIS WATCH INCLUDES 11 COUNTIES

IN CENTRAL ALABAMA

BLOUNT JEFFERSON WALKER

IN NORTHWEST ALABAMA

MARION WINSTON

IN WEST CENTRAL ALABAMA

FAYETTE GREENE LAMAR
PICKENS SUMTER TUSCALOOSA

THIS INCLUDES THE CITIES OF…ALICEVILLE…BIRMINGHAM…
CARROLLTON…EUTAW…FAYETTE…HALEYVILLE…HAMILTON…HOOVER…
JASPER…LIVINGSTON…ONEONTA…SULLIGENT…TUSCALOOSA…
VERNON AND YORK.

7:42 p.m.

Saturday Storms:  By the Numbers

TEMPS/MOISTURE

Plenty of moisture in place with dewpoints in the 65F to 67F range in the I-20 corridor. Temperatures rage from 73F at Anniston and Birmingham to 76F at Tuscaloosa.

INSTABILITY
Surface based CAPE Value at BMX was 85 j/kg. We had thought it to be less than 500 j/kg. This gives the system a little more octane. Lifted Index was -4C which is moderate. Low level lapse rates are marginal, while mid level lapse rates are more robust.

CAP
There is a small remaining cap over Central Alabama, but that certainly won't cause any problems for the approaching squall line. Developing cells over eastern Mississippi indicate the cap is already broken there.

BULK SHEAR
0-6km speed shear is 57 knots. Plenty sufficient for organized updrafts.

STORM RELATIVE HELICITY
349 m2/s2 is plenty sufficient for supercells to develop. This number increases the further you go north.

STP (SIGNIFICANT TORNADO PARAMETER)
2.2 at Birmingham. This is concerning. While not off the scale, it is sufficient for a couple of significant tornadoes.

PRECIPITABLE WATER
1.68 inches: This is in the 99th percentile for late December and nearly a record. This means there will be plenty of heavy rain. Fortunately, the system is moving fairly quickly, so flooding will not be a major concern except in localized areas. Expect a few flash flood warnings though.

SUMMARY
Of course, instability values should slowly decrease, but the loss of heating could be offset by continued advection of warm, moist air. The wind fields will slowly decrease as the dynamics track further to the north overnight.

"We will watch those showers over eastern Mississippi to see if they can develop into thunderstorms. They would certainly rotate and could produce damaging winds and a couple of tornadoes. The main line will produce several reports of wind damage and could have embedded tornadoes as well."

7:13 p.m.

Tornado Watch Soon?

"Our solid line of intense thunderstorms now extends from near Jackson TN to just east of Holly Springs MS to Grenada to Greenwood to Yazoo City in Mississippi.

"It is moving east at 30 mph. At this rate of speed, it will reach western Alabama's Lauderdale, Colbert, Franklin and marion Counties around 9:15-9:30. It should reach Lamar and Pickens Counties before 10 p.m.

"Severe thunderstorm and tornado warnings are nearly solid along the line from southwestern Tennessee to near I-20 in Mississippi. One tornado warning is in effect north of Grenada MS and another east of Holly Springs. In Tennessee, another is in effect near and north of Jackson. Winds just gusted to 55 knots at Jackson TN (64 mph).

"In Tennessee, 65 mph winds were reported earlier in Germantown and one inch hail was reported in Collierville. A tornado was reported with some damage at Senatobia, MS.

"You can see additional showers have formed ahead of the main line. Any of these that manage to become thunderstorms concern us since they have the potential to be discrete cells ahead of the main squall. Those tend to have more potential to produce tornadoes.

"Ahead of the line, the airmass is moderately unstable, and the wind fields are intense. In these winter season events, it doesn't take much instability when you have these strong wind fields, so we continue a severe weather risk across much of Alabama west of a line from Wdowee to Montgomery to Brewton. There is an enhanced risk for areas west of a line Vernon to Haleyville to Athens.

"The NWS BMX sent up a special balloon at 6 p.m. The details will follow in another post.

"Look for a tornado watch to be issued soon for portions of West Central and Northwest Alabama."

5:53 p.m.

Severe storms crossing Mississippi River:

"The more intense storms are currently crossing the Mississippi River into Mississippi and western Tennessee. The storm are moving to the east rapidly and are producing very gusty winds, torrential rainfall and are bringing with them the threat of damaging winds, tornadoes, and flooding.

"Numerous severe thunderstorm warnings and flash flood warnings are accompanying these storms. Even some tornado warnings mixed in with the main line. Areas outlined in yellow are under a tornado watch, orange polygons severe thunderstorm warnings, red polygons are tornado warnings, and green and maroon are flooding and flash flooding.

Watches & Warnings

"Across Alabama currently, a few showers have developed and are currently east of Interstate 65. These showers are racing off to the north with the low-level jet. For the next few hours, we certainly could see showers develop at anytime. As the line of storms and better uplift begin to move closer to the state, we are likely to see some thunderstorm development ahead of the main line. We will have to watch these storms carefully if the do develop.

"The SPC maintain much of Alabama in a slight risk for severe weather tonight, with an area of northwestern Alabama in an enhanced moderate risk. Strong and severe storms will move into the the state over the next several hours. We are expecting the SPC to issue some sort of watch as these storms move closer to the state. Stay weather aware overnight as severe storms with damaging straight line winds and tornadoes will be possible."

4:35 p.m.

Strong, severe storms taking shape west of Alabama:

"The severe weather event is beginning to take shape to our west. A line of very strong and sever storms is marching east. Severe storms extend from Memphis, Tennessee south to Alexandria, Louisiana.

"Numerous severe thunderstorms warnings are in effect and we have started to see a few tornado warnings, and even reports of damage reported with one storm west of Memphis earlier.

Click image to enlarge.

"This line of storms will continue to head towards Alabama. Severe storms should persist through the overnight hours as strong dynamics will be moving closer. Out ahead of the line of storms, ample warm, moist and unstable air is in place as evident by the widespread upper 70s and 80s in place across the region.

"There are several showers developing along the Interstate 65 corridor and moving rapidly north. We still expect the line of storms to be approaching the western portions of the state between 8-9 PM. We will be watching areas out in front of the main line as there could be a few discrete supercells develop.

"For the Birmingham area, the bulk of the action should be impacting the area closer to the midnight time frame. Make sure you have a reliable source for severe weather alerts during the overnight hours."

3:39 p.m.

Tornado reported in Memphis:

"A thunderstorm that has a reported tornado with it is across the Mississippi River from Memphis.

"This storm is just to the west of Memphis and is impacting areas along Interstate 40 and will be impacting Interstate 55 as well."

12-21-2013 3-35-43 PM

2:17 p.m.

Afternoon update:

"The latest convective outlook from the SPC continues to keep most of Alabama in a risk for severe weather. Areas across northwestern portions of the state remained outlined in moderate risk for severe weather. This part of the state will have the most instability and dynamics and will be more likely to see severe weather. This moderate risk area includes areas from Pickens County, towards Fayette then up towards Hunstville.

"A slight risk has been issued for almost the rest of the entire state, with the exception being the extreme southeastern counties of the state. The slight risk includes Tuscaloosa, Birmingham, Anniston, Gadsden, Montgomery, Demopolis, Selma and Mobile.

"Tornado watches have been issued to our west and heading throughout the rest of the afternoon, we will be watching and waiting for these watches to be extended towards the east as the severe weather threat shifts east.

"Early this afternoon, the radar across Alabama remains mostly calm, with just a few very light showers racing north with the warm air advection that is ongoing. The main showers and storms remain well to our west across Arkansas, Louisiana, and Texas. As we head into the evening hours, we anticipate the radar to light up like a Christmas tree; first across Mississippi and then into Alabama.

12-21-2013 1-47-29 PM

"Timing: We still expect the main area of thunderstorms to be approaching our extreme northwestern counties by 8 or 9 PM this evening. There could be a few isolated discrete supercells ahead of the main band and those are certainly the storms we will have to keep an eye on as they are the most likely ones to be rotating.

"In addition to the supercells, a very strong line of thunderstorms with damaging winds will be heading across the state during the overnight hours. Within this line of storms, there certainly could be some tornadoes as well.

"With the worst of the weather expected overnight for much of Alabama, it is extremely important that you have a way to receive severe weather alerts overnight. Have a weather radio or a smart phone app like MyWARN to keep you notified of the severe weather threat."

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 12-21-2013 1-47-29 PM  

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