Severe Thunderstorm Warning 173, NWS Huntsville, AL

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HUNTSVILLE AL
633 PM CDT THU JUL 19 2012

.UPDATE...
FOR 00Z TAFS.

&&

.DISCUSSION...
/ISSUED 329 PM CDT THU JUL 19 2012/
LATEST WATER VAPOR IMAGERY AND H5 RUC ANALYSIS INDICATE A
TROUGH-RIDGE-TROUGH PATTERN PREVAILS ACROSS THE CONUS...WITH SMALL
VORTICES RETROGRADING AROUND THE SOUTHERN EXTENT OF THE RIDGE. ONE
OF THE SHORTWAVES MOVING THROUGH THE GENERALLY CYCLONIC FLOW IN THE
NORTHEAST US IS DRAGGING WITH IT A SURFACE LOW AND ATTENDANT COLD
FRONT. THIS FRONT IS CURRENTLY DRAPED FROM LOWER MICHIGAN TO
KANSAS...WITH A PREFRONTAL TROUGH EVIDENT THROUGH SURFACE ANALYSIS
AHEAD OF THIS FRONT. AFTER A VERY OVERCAST START TO THE DAY FOR MUCH
OF THE TENNESSEE VALLEY...IT IS FINALLY HEATING ACROSS THE CWFA...AND
TEMPERATURES ARE GENERALLY RUNNING NEAR NORMAL. MUSCLE
SHOALS...WHICH WAS THE FIRST TO CLEAR OUT THIS MORNING...IS RUNNING
SEVERAL DEGREES ABOVE OTHER LOCATIONS...IN THE MIDDLE 90S. DESPITE
THE WARM CONDITIONS ACROSS NORTHWEST ALABAMA...THE CU FIELD IS JUST
NOW STARTING TO DEVELOP...SUGGESTING THAT AFTERNOON PRECIPITATION
WILL BE LIMITED.

THE MAIN QUESTION FOR THIS FORECAST PACKAGE CENTERS AROUND THE
APPROACHING COLD FRONT. MOST OF THE GLOBAL MODELS HAVE A CONSISTENT
HANDLE ON THE TIMING AND LOCATION OF THE COLD FRONT/SURFACE
LOW...WITH THE REQUISITE SUBTLE DIFFERENCES IN LOW LEVEL JET STRENGTH
AND INSTABILITY.

FOR TONIGHT...THE FRONT WILL CONTINUE TO SLIDE SOUTHEAST...PROBABLY
NEARING A LOUISVILLE TO MEMPHIS LINE BY 12Z FRIDAY. AHEAD OF THE
FRONT...EXPECT WARM AND MUGGY CONDITIONS. DESPITE THE LACK OF
APPRECIABLE PRECIPITATION TODAY...THERE HAS BEEN PLENTY AS OF
LATE...SO LOOK FOR PATCHY FOG DEVELOPMENT BY MIDNIGHT AS SOUNDINGS
SHOW LOW LEVEL SATURATION. FOR PRECIPITATION CHANCES...OPTED TO SHOW
A CHANCE OF THUNDERSTORMS...AND THIS WILL ACCOUNT FOR BOTH
PRECIPITATION THAT POSSIBLY DEVELOPS EARLY THIS EVENING AS WELL AS
ANYTHING ELEVATED THAT DEVELOPS TONIGHT WELL AHEAD OF THE FRONTAL
BOUNDARY.

FOR TOMORROW...EXPECT DAYTIME HEATING TO QUICKLY WARM TEMPERATURES
INTO THE LOWER 90S. WITH THE APPROACHING COLD FRONT...IN ADDITION TO
A MID/UPPER LEVEL JET ASSOCIATED WITH THE SHORTWAVE CROSSING THE
OHIO RIVER VALLEY...MODERATE TO STRONG INSTABILITY WILL DEVELOP
ACROSS MUCH OF THE CWFA. SHEAR VALUES WILL BE RELATIVELY HIGH FOR A
SUMMERTIME EVENT...SO THIS COMBINED WITH DRY AIR IN THE MIDLEVELS
AND STEEP LOW LEVEL LAPSE RATES SUGGESTS THAT STORMS TOMORROW WILL
CARRY AN ENHANCED SEVERE WEATHER THREAT...WITH DAMAGING WINDS AND
HAIL POSSIBLE. STORM MOTION WILL BE ABOUT 10 KNOTS...WHICH IS A
LITTLE FASTER THAN THE STORMS WE HAVE SEEN IN THE PAST WEEK...BUT
GIVEN HOW SOME SOILS ARE SATURATED FROM RECENT STORM
ACTIVITY...LOCALIZED FLASH FLOODING WILL BE A CONCERN.

STORM ACTIVITY SHOULD WANE FRIDAY EVENING...WITH A
NORTHWEST-SOUTHEAST POP GRADIENT IN THE EVENING. NOT EXPECTING ANY
SORT OF COOL-DOWN FOR TEMPERATURES BEHIND THE FRONT...AND LOWS ON
FRIDAY NIGHT WILL STILL BE IN THE LOW 70S.

THUNDERSTORM CHANCES WILL TRANSITION TO A DIURNALLY ENHANCED REGIME
BY THE WEEKEND...WITH POPS GREATEST IN THE SOUTH ASSOCIATED WITH THE
REMNANT STALLED FRONT. THIS GRADIENT WILL BECOME MORE DIFFUSE THROUGH
THE EARLY PART OF THE WORK WEEK...BEFORE ANOTHER WEAK FRONT
APPROACHES THE SOUTHEAST BY THE MIDDLE OF THE WEEK. TEMPERATURES
THROUGH THE PERIOD WILL BE IN THE LOW/MIDDLE 90S FOR HIGHS...AND IN
THE 70S FOR LOWS.

JLL

&&

.AVIATION...
FOR 00Z TAFS...A FEW THUNDERSTORMS HAVE DEVELOPED JUST EAST OF KMSL
AND THIS WILL CREATE A BRIEF PERIOD OF OUTFLOW WIND GUSTS PERHAPS AS
HIGH AS 20KTS. A STORM COULD BACKBUILD OVER THE AIRPORT WHICH WOULD
BRIEFLY REDUCE VSBY AS LOW AS IFR IN +RA. AFTER SUNSET...THIS
CONVECTION SHOULD DIMINISH AND MUCH OF THE NIGHT WILL BE QUIET/VFR
CONDITIONS AT BOTH TERMINALS. LATE TONIGHT INTO EARLY FRIDAY...WILL
BE WATCHING TSTMS NOW OVER SE MO/WRN TN AND KY AS THEY DRIFT
SOUTHEAST AHEAD OF A COLD FRONT.

DJN.83

&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...NONE.
TN...NONE.
&&

FOR MORE INFORMATION PLEASE VISIT OUR WEBSITE
AT WEATHER.GOV/HUNTSVILLE.

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE HUNTSVILLE AL
530 PM CDT THU JUL 19 2012

ALZ001>010-016-TNZ076-096-097-201000-
LAUDERDALE-COLBERT-FRANKLIN AL-LAWRENCE-LIMESTONE-MADISON-MORGAN-
MARSHALL-JACKSON-DEKALB-CULLMAN-MOORE-LINCOLN-FRANKLIN TN-
530 PM CDT THU JUL 19 2012

THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTH ALABAMA AND PORTIONS
OF SOUTHERN MIDDLE TENNESSEE.

.DAY ONE...THIS AFTERNOON AND TONIGHT...

ISOLATED TO WIDELY SCATTERED THUNDERSTORMS ARE EXPECTED FROM LATE
AFTERNOON INTO THE EVENING HOURS. SOME STORMS COULD BE STRONG AND
PRODUCE GUSTY WINDS...FREQUENT LIGHTNING AND LOCALLY HEAVY RAINFALL.

ADDITIONAL SCATTERED THUNDERSTORMS ARE POSSIBLE OVERNIGHT AS A SLOW
MOVING FRONT APPROACHES THE REGION FROM THE NORTH. A FEW STRONG TO
SEVERE STORMS ARE POSSIBLE OVERNIGHT WITH THE PRIMARY THREAT BEING
DAMAGING WIND GUSTS.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY...

THUNDERSTORM COVERAGE IS EXPECTED TO BECOME MORE NUMEROUS LATE FRIDAY
MORNING...AND CONTINUING INTO THE AFTERNOON PERIOD AS A WEAK COLD
FRONT APPROACHES THE AREA FROM THE NORTHWEST. SOME STORMS ARE
EXPECTED TO APPROACH OR EXCEED SEVERE THRESHOLDS...WITH DAMAGING WIND
GUSTS THE PRIMARY WEATHER THREAT. OTHERWISE...GUSTY WINDS...FREQUENT
LIGHTNING AND LOCALLY HEAVY DOWNPOURS ARE POSSIBLE WITH ANY
THUNDERSTORMS. LOCALIZED FLASH FLOODING WILL ALSO BE POSSIBLE GIVEN
THE EXCESSIVE RAINFALL OVER THE PAST SEVERAL DAYS. THE THUNDERSTORM
THREAT IS EXPECTED TO WEAKEN DURING THE EVENING HOURS.

THIS FRONT IS EXPECTED TO STALL NEAR THE TENNESSEE VALLEY HEADING
INTO THE WEEKEND PERIOD...CONTINUING A LOW CHANCE FOR MAINLY
AFTERNOON AND EARLY EVENING THUNDERSTORMS THROUGH THE MIDDLE PART OF
NEXT WEEK.

.SPOTTER CALL TO ACTION STATEMENT...

ACTIVATION OF STORM SPOTTERS AND EMERGENCY MANAGEMENT PERSONNEL IS
NOT ANTICIPATED TODAY. HOWEVER...FORMAL ACTIVATION MAY BE NEEDED
STARTING LATE FRIDAY MORNING...AND CONTINUING THROUGH THE AFTERNOON
PERIOD.

15

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE HUNTSVILLE AL
640 PM CDT THU JUL 19 2012

ALZ002-004-200030-
COLBERT-LAWRENCE-
640 PM CDT THU JUL 19 2012

...SIGNIFICANT WEATHER ADVISORY FOR COLBERT AND LAWRENCE COUNTIES
UNTIL 730 PM CDT...

AT 639 PM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING A
STRONG THUNDERSTORM NEAR WHITEOAK...OR 8 MILES SOUTHEAST OF MUSCLE
SHOALS...MOVING SOUTH AT 5 MPH.

PEA SIZE HAIL...WIND GUSTS UP TO 50 MPH...FREQUENT CLOUD TO GROUND
LIGHTNING...AND HEAVY DOWNPOURS ARE EXPECTED WITH THIS STORM.

* LOCATIONS IN OR NEAR THE PATH INCLUDE...
  WHITEOAK.
  SPRING VALLEY.
  NE SMITH.
  LA GRANGE...LITTLEVILLE.

REMEMBER...IF YOU CAN HEAR THUNDER...YOU ARE CLOSE ENOUGH TO THE
STORM TO BE STRUCK BY LIGHTNING. SEEK SAFE SHELTER IMMEDIATELY.

&&

LAT...LON 3475 8743 3455 8742 3456 8753 3457 8753
      3457 8770 3476 8765
TIME...MOT...LOC 2340Z 004DEG 5KT 3467 8755