Monday Afternoon Forecast Discussion

The weather today has been much calmer for us and temperatures haven’t been too bad. Highs reached into the middle 50s and tonight we will have low temperatures just below freezing. It’s a totally different ballgame for portions of the Midwest. An arctic high dropping southward is lowering many cities into the negative digit temperature range. The core of this air will slide northeast of us; however, we will experience some chilly conditions in the days ahead. Tonight the lows will be just below freezing, but a westerly flow ahead of the leading edge of the cold air will allow us to reach the low to mid 60s for tomorrow. Tomorrow will be a mostly sunny day, with a breezy afternoon.

Temperatures will drop into the middle 30s tomorrow night, with a partly to mostly clear sky. The leading edge of the really cold air will settle into the northern portion of the state and this will set up a big temperature contrast over the state by Wednesday. The forecast for Wednesday in Decatur calls for a chance of sleet, with highs in the 40s. A southwest flow will begin overrunning this cooler air over the state and this will bring clouds and rain for our area late Wednesday and into the day on Thursday. There may be a lingering shower early on Friday, with some clearing for the weekend.

Hopefully the clouds will be scattered Wednesday night for the viewing of the lunar eclipse at 7:43 Wednesday night! We will have much more on this in the coming days…Be sure to join us tonight at five, six, and ten for more details!

Wes Wyatt
WVUA Chief Meteorologist

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Severe Weather Awareness Week-“Severe Thunderstorms”

Severe Weather Awareness Week is underway in Alabama and we’ve certainly had to consider many safety measures recently. Be sure to check out the survey results from the National Weather Service in the previous post. Major damage occurred throughout portions of central Alabama as severe thunderstorms produced tornadoes yesterday. An EF-3 was classified to have hit Autauga County where 200 homes and 40 businesses were damaged. There were 50 injuries in that particular county, but the blessing is that there were no fatalities. Severe thunderstorms are what produce tornadoes and they need to be taken seriously. In fact, a majority of wind related damage in Chilton County yesterday was a result of thunderstorm straight-line winds. Today’s severe weather topic is on the power of thunderstorms and I wanted to share some thoughts. All thunderstorms produce lightning because lightning is what creates thunder and it’s important to note that thunder is natures way of saying seek shelter from an approaching thunderstorm. Even though we have criteria for a severe thunderstorm, I consider all storms severe with regard to the threat of cloud to ground lightning.

Thunderstorms go through various stages of development and there are different types of storms, such as multicell clusters, squall lines, or supercell storms. Thunderstorms are created by forced mechanical lift or by simple convective heating, such as warming of the earth’s surface. As this air rises, vertical air motions lead to the development of cumulus clouds. This is referred to as the “cumulus stage” of thunderstorm development. Secondly, as the air rising into cumulus clouds lifts into the middle layers of the atmosphere and as the air condenses, dry air aloft leads to evaporation. The evaporation process cools the air and this cooler air pools towards earths surface, resulting in a downdraft. These downdrafts can sometime be quite violent and you may have heard the term “downburst” before. This term is used to describe a severe downdraft of wind that sinks and spreads below the cloud base, along earth’s surface. Damage from downbursts is often evident by objects or trees toppled in a uniform direction. Winds can exceed 100 mph, which is as strong as a small tornado.

When an updraft and downdraft are present within a thunderstorm it is then in the “mature stage” of growth. This is when large hail, heavy rain, and lightning can be observed. If upper air winds are weak, thunderstorms may tend to weaken quickly as the downdraft may cut off the warm inflow of air or updraft. This is quite common with summer time single-cell thunderstorms. This stage is known as the dissipating stage however, the cool air reaching the surface can act like a mini cold front and ignite more thunderstorm development. The Supercell Thunderstorm is more tilted with height and can sustain itself for a longer portion of time. This tilt is due to faster winds aloft and that’s why you may hear us talk about upper level support with regard to thunderstorms or severe weather development. This presence of fast upper air winds can be evident by the large anvil that extends from the upper portion of some classic storms.

Severe thunderstorm watches are issued by the Storm Prediction Center and this does not mean there is a storm approaching, but this means that conditions are favorable for severe thunderstorms. A severe thunderstorm warning is issued when a storm has been sighted or detected and it is approaching your community. With the addition of polygon warnings, communities in the direct path of the storm will be warned by local media and the National Weather Service.

(Image Source: NOAA)

Wes Wyatt
WVUA Chief Meteorologist

The Latest From the NWS-Damage Survey

000
 NOUS44 KBMX 182055
 PNSBMX
 ALZ011>015-017>050-190000-PUBLIC INFORMATION STATEMENT
 NATIONAL WEATHER SERVICE BIRMINGHAM AL
 300 PM CST MONDAY FEB 18 2008

...DAMAGE SURVEYS UNDERWAY ACROSS CENTRAL ALABAMA...

ON SUNDAY FEBRUARY 17, 2008 A STRONG UPPER LEVEL LOW EJECTED OUT OF
 THE SOUTHERN PLAINS TRACKING ACROSS THE TENNESSEE VALLEY.  STRONG
 SOUTHERLY WINDS IN CONJUNCTION WITH DEWPOINTS CLIMBING INTO THE
 LOWER 60S...A STRONG LOW LEVEL JET...AND TEMPERATURES IN THE IN
 EXCESS OF 70 DEGREES RESULTED THE DEVELOPMENT OF SEVERAL SUPERCELL
 THUNDERSTORMS.

BEFORE NOON A SQUALL LINE DEVELOPED ALONG THE ALABAMA MISSISSIPPI
 STATE LINE AND TRACKED EASTWARD ACROSS CENTRAL ALABAMA...
 INTENSIFYING DURING THE AFTERNOON HOURS.  BY SUNSET...DAMAGE WAS
 REPORTED AT NUMEROUS LOCATIONS...GENERALLY ALONG AND SOUTH OF A LINE
 FROM DEMOPOLIS TO WEDOWEE.

TORNADO WATCHES WERE IN EFFECT FOR PORTIONS OF CENTRAL ALABAMA
 BETWEEN 530 AM AND 8 PM.  A TOTAL OF 20 TORNADO WARNINGS AND 7
 SEVERE THUNDERSTORM WARNINGS WERE ISSUED BETWEEN 10:59 AM AND 5:05
 PM BY THE NATIONAL WEATHER SERVICE OFFICE IN BIRMINGHAM.

AUTAUGA COUNTY:
 A NATIONAL WEATHER SERVICE SURVEY TEAM IS IN THE PROCESS OF
 ACCESSING THE DAMAGE IN AUTAUGA COUNTY.  IT HAS BEEN DETERMINED THE
 DAMAGE WAS THE RESULT OF A TORNADO...RANKING EF-3 ON THE ENHANCED
 FUJITA SCALE.  A TOTAL PATH LENGTH IS YET TO BE DETERMINED...BUT THE
 DAMAGE PATH IS 450 YARDS WIDE AT ITS WIDEST POINT.  THE MOST DAMAGE
 OCCURRED ALONG EAST MAIN STREET NEAR MCQUEEN SMITH ROAD AND IN THE
 SILVER HILLS SUBDIVISION.  AN ESTIMATED 200 RESIDENTIAL HOMES AND 40
 BUSINESSES WERE DAMAGED OR DESTROYED. HUNDREDS OF TREES WERE EITHER
 SNAPPED OR UPROOTED.  IN ADDITION...50 INJURIES WERE REPORTED.  WIND
 SPEEDS ARE ESTIMATED TO BE UP TO 150 MILES PER HOUR.  THIS DAMAGE
 OCCURED AT APPROXIMATELY 305 PM.  A TORNADO WARNING WAS IN EFFECT
 FROM 2:31 PM UNTIL 3:30 PM.  THIS STORM ALSO PRODUCED DAMAGE IN
 LOWNDES COUNTY AND THIS STORM CONTINUED INTO ELMORE COUNTY.

CHILTON COUNTY:
 A NATIONAL WEATHER SERVICE SURVEY TEAM HAS ASSESSED THE DAMAGE NEAR
 EXIT 205 ALONG INTERSTATE 65 IN CHILTON COUNTY. IT WAS DETERMINED
 THAT THE MAJORITY OF THIS DAMAGE WAS THE RESULT OF STRAIGHT LINE
 WINDS. THIS DAMAGE ENCOMPASSED AN AREA NEARLY 2.75 MILES LONG BY 1.5
 MILES WIDE BETWEEN COUNTY ROAD 7 AND COUNTY ROAD 41. HOWEVER THE
 SURVEY ALSO INDICATED A LOCALIZED AREA EAST OF INTERSTATE 65 WAS THE
 RESULT OF A TORNADO RATED EF-1 ON THE ENHANCED FUJITA SCALE. WINDS
 ARE ESTIMATED TO BE UP TO 110 MPH.  THE DAMAGE PATH WAS 1.1 MILES
 LONG AND 0.25 MILES WIDE AT ITS WIDEST POINT. DAMAGE WAS PRIMARILY
 TO TREES...APPROXIMATELY 300 TREES WERE EITHER UPROOTED OR SNAPPED.
 IN ADDITION...AROUND 15 STRUCTURES WERE DAMAGED...THE WORST BEING A
 MOBILE HOME ALONG COUNTY ROAD 41 THAT HAD TWO LARGE OAK TREES FALL
 ON IT.  THIS DAMAGE OCCURRED AT APPROXIMATELY 1:05 PM. TWO TORNADO
 WARNINGS WERE ISSUED FOR THIS STORM.  THE FIRST WAS ISSUED AT 1208
 PM AND EXPIRED AT 1:00 PM. THE SECOND TORNADO WARNING WAS ISSUED AT
 12:53 PM AND EXPIRED AT 1:30 PM. IN ADDITION...A SEVERE THUNDERSTORM
 WARNING WAS ISSUED AT 12:28 PM AND EXPIRED AT 1:30 PM. NO INJURIES
 WERE REPORTED.

DALLAS COUNTY:
 A NATIONAL WEATHER SERVICE SURVEY TEAM HAS ASSESSED THE DAMAGE IN
 DALLAS COUNTY AND DETERMINED THE DAMAGE WAS THE RESULT OF A
 TORNADO...RANKING EF-2 ON THE ENHANCED FUJITA SCALE.  THE TORNADO
 PATH WAS APPROXIMATELY 7 MILES LONG AND 150 YARDS WIDE AT ITS WIDEST
 POINT.  SEVEN HOMES AND TWO BUSINESSES WERE TOTALLY DESTROYED IN
 ADDITION TWELVE TO FIFTEEN ADDITIONAL STRUCTURES WERE DAMAGED TO
 VARIOUS DEGREES. NUMEROUS TREES WERE SNAPPED AND OR UPROOTED AS
 WELL. WIND SPEEDS ARE ESTIMATED TO BE AS HIGH AS 120 MPH.  THIS
 TORNADO TOUCHED DOWN NEAR WARRIOR DRIVE...JUST SOUTHEAST OF THE
 PERRY COUNTY LINE...TRACKED ACROSS HIGHWAY 219 NEAR THE INTERSECTION
 OF COUNTY ROAD 230...AND ENDED JUST WEST OF THE INTERSECTION OF
 COUNTY ROAD 37 AND COUNTY ROAD 866.  THIS DAMAGE OCCURRED AROUND
 1229 PM.  A TORNADO WARNING WAS IN EFFECT FROM 12:08 PM UNTIL 1:00
 PM.  NO INJURIES WERE REPORTED.

PIKE COUNTY:
 A NATIONAL WEATHER SERVICE SURVEY TEAM HAS ASSESSED THE DAMAGE IN
 PIKE COUNTY AND DETERMINED THE DAMAGE WAS THE RESULT OF A
 TORNADO...RANKING EF-1 ON THE ENHANCED FUJITA SCALE. THE TORNADO
 PATH LENGTH WAS APPROXIMATELY 8.2 MILES LONG(IN PIKE COUNTY) AND 200
 YARDS WIDE AT ITS WIDEST POINT.  ONE HOME AND ONE CHURCH WERE
 DAMAGED AND NUMEROUS TREES WERE SNAPPED OR UPROOTED.  WINDS ARE
 ESTIMATED TO BE UP TO 100 MPH.  THE STORM ENTERED PIKE COUNTY FROM
 COFFEE COUNTY APPROXIMATELY 5 MILES SOUTHEAST OF HENDERSON...CROSSED
 STATE HIGHWAYS 87 AND 167 AND ENDED JUST NORTH OF THE INTERSECTION
 OF COUNTY ROADS 6 AND 57.  IT SHOULD BE NOTED THAT THIS STORM
 TRACKED ACROSS COUNTIES IN BOTH MOBILE AND TALLAHASSEE AREA OF
 RESPONSIBILITY.  THE FINAL EF RANKING AND PATH LENGTH/WIDTH WILL BE
 DETERMINED BY THE MAXIMUM RANKING FROM THE THREE OFFICES.  THIS
 DAMAGE OCCURED AT APPROXIMATELY 223 PM.  A TORNADO WARNING WAS IN
 EFFECT FROM 1:50 PM UNTIL 245 PM.

IF YOU ARE AWARE OF DAMAGE AT LOCATIONS OTHER THAN LISTED ABOVE...
 PLEASE CALL IN YOUR REPORT TO YOUR LOCAL LAW ENFORCEMENT OR YOUR
 COUNTY EMERGENCY MANAGEMENT OFFICE IF YOU HAVE NOT ALREADY DONE SO.

DAMAGE ASSESSMENT TAKES TIME AND IS A DYNAMIC PROCESS.  THIS PRODUCT
 WILL BE UPDATED MANY TIMES.  CHECK BACK FREQUENTLY FOR THE LATEST
 INFORMATION.

IF THERE ARE ANY QUESTIONS REGARDING SUNDAYS EVENTS OR OUR PLANS TO
 SURVEY ON MONDAY...PLEASE CONTACT THE POST EVENT COORDINATOR AT THE
 BIRMINGHAM NATIONAL WEATHER SERVICE OFFICE AT 205-664-3010.