000
FXUS64 KHUN 171528 AAB
AFDHUN

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HUNTSVILLE AL
1028 AM CDT MON JUN 17 2013

.UPDATE...
MORNING FORECAST UPDATE. MODEST ADJUSTMENTS MADE TO POPS AND TEMPS.

&&

.DISCUSSION...
LATEST WATER VAPOR IMAGERY SUGGESTS THE PRESENCE OF A WEAK SHORTWAVE
RIPPLING ACROSS MIDDLE TN/EXTREME NORTHEAST AL, WHICH HAS BEEN
RESPONSIBLE FOR SCATTERED-NUMEROUS STORMS TO THE NORTH AND EAST OF
HSV. THERE ARE CLEARLY SOME BOUNDARY INTERACTIONS AT WORK AS WELL,
GIVEN THE TRAINING ECHOES NOTED OVER EXTREME NORTHERN MOORE AND
FRANKLIN COUNTIES OVER THE LAST 1-2 HOURS. ROUND 2 OF STORMS IS NOTED
OVER NORTHERN/CENTRAL MS, ALSO ASSOCIATED WITH ANOTHER WEAK SHORTWAVE
TROUGH. A THIRD, MORE ROBUST SHORTWAVE IS LOCATED OVER EASTERN OK,
AND WILL AFFECT THE REGION TONIGHT.

IT IS STILL UNCERTAIN WHETHER THE SHOWERS AND STORMS OVER NORTHERN MS
WILL COMPLETELY HOLD TOGETHER AS THEY MOVE INTO AL. THE FORCING IS
ROBUST ENOUGH TO CONTINUE WITH HIGHER POPS WEST OF I-65,
PARTICULARLY SINCE THAT AREA IS LIKELY WARMER AND MORE UNSTABLE GIVEN
CURRENT TEMPS AND DEWPOINTS. WE WILL MAKE A FEW TWEAKS TO POPS BASED
UPON CURRENT TRENDS, BUT THE ORIENTATION WILL REMAIN THE SAME. WE
WILL ALSO INTRODUCE A MENTION OF HEAVY RAIN IN THE GRIDS AND ZFP IN
LIGHT OF HOW MUCH RAIN HAS FALLEN IN SOME AREAS, HOW MOIST THE
ENVIRONMENT IS (BLENDED TPW IMAGERY INDICATES ABOUT 1.9 INCHES PW, OR
ALMOST 150% OF NORMAL), AND HOW QUICKLY MINOR FLOODING DEVELOPED IN
LYNCHBURG. THE EXISTING HWO MENTIONS THIS POSSIBILITY, AND WE WILL
CERTAINLY CONTINUE MONITORING FOR LOCALIZED FLOODING.

TEMPERATURES WILL BE NUDGED DOWN JUST A DEGREE OR SO, ANTICIPATING
THAT WESTERN AREAS ARE NEAR THEIR DAYTIME HIGHS, AND THAT EASTERN
AREAS WILL WARM UP AS THEY DAY GOES ON BEFORE MORE SHOWERS DEVELOP.

BCC

&&

.AVIATION...
/ISSUED 645 AM CDT MON JUN 17 2013/
FOR 12Z TAFS...MULTIPLE ROUNDS OF SHRA/TSRA ARE XPCTED LATER TODAY
AND TONIGHT...AS A SERIES OF UPPER WAVES CONTINUE TO MOVE EWD ACROSS
THE AREA. CONDS MAY LOWER INTO THE MVFR CAT IN AND NEAR SOME OF THE
HEAVIER PRECIP...BUT CONFIDENCE IS LOW AS FAR AS THE EXACT
PLACEMENT/TIMING OF ANY CONVECTIVE DEVELOPMENT. AS SUCH...WILL
MAINTAIN VFR CONDS FOR MOST OF THE TAF PERIOD...WITH A PERSISTENT
MID/UPPER CLOUD DECK. WILL ALSO MAINTAIN A CB LAYER AFTER 18Z...AS
SLIGHTLY HIGHER CONCENTRATIONS OF SHRA/TSRA APPROACH FROM THE W.

09

&&

.PREV DISCUSSION...
/ISSUED 509 AM CDT MON JUN 17 2013/
WATER VAPOR SATELLITE ANIMATION AND ANALYSIS OF UPPER-AIR DATA
INDICATE THAT A MODERATELY STRONG WEST-NORTHWEST FLOW REGIME ALOFT
HAS BECOME ESTABLISHED ACROSS THE TENNESSEE VALLEY...TO THE NORTH OF
A ZONALLY ORIENTED SUBTROPICAL RIDGE POSITIONED ALONG 25N LATITUDE.
THE FIRST IN A SERIES OF MID-LEVEL WAVES...WHICH AIDED IN THE
DEVELOPMENT OF CONVECTION YESTERDAY AFTERNOON...HAS NOW PUSHED TO THE
EAST OF THE SOUTHERN APPALACHIANS...WITH ANOTHER WEAK DISTURBANCE
CURRENTLY INITIATING NEW CONVECTIVE DEVELOPMENT IN THE WARM/MOIST AND
UNSTABLE AIRMASS ACROSS THE LOCAL AREA. ALTHOUGH MESOSCALE DETAILS
ARE DIFFICULT TO PINPOINT EVEN WITHIN THE NEXT 6-12 HOURS...ALL
PARAMETERS SUGGEST THAT THE AREAL COVERAGE OF CONVECTION TODAY WILL
BE SIMILAR TO WHAT WAS EXPERIENCED YESTERDAY AND WILL HOLD POPS IN
THE 50-60 PERCENT RANGE. THIS IS SUPPORTED BY RECENT GUIDANCE FROM
THE NSSL WRF/WRF-NMM AND HRRR. GUIDANCE FROM GLOBAL MODELS...
INCLUDING THE GFS/GEM/UKMET/ECMWF...ALL INDICATE THAT ENVIRONMENTAL
CONDITIONS WILL BECOME MUCH MORE FAVORABLE FOR A WIDESPREAD
CONVECTIVE EVENT BEGINNING EARLY TUESDAY MORNING IN NORTHWEST AND
NORTH CENTRAL ALABAMA...AND LINGERING OVER THE ENTIRE REGION FOR MOST
OF TUESDAY MORNING -- BEFORE DIMINISHING FROM WEST-TO-EAST DURING THE
AFTERNOON. ESSENTIALLY...WE ARE EXPECTING ONE OR MORE ORGANIZED
CONVECTIVE COMPLEXES TO DEVELOP LATER THIS EVENING ALONG A WEAK COLD
FRONT DRIFTING SOUTHWARD INTO THE OZARKS/SOUTHERN PLAINS. THIS
ACTIVITY IS EXPECTED TO SHIFT EAST-SOUTHEASTWARD INTO THE REGION
EARLY TUESDAY MORNING...WITH WIDESPREAD SHOWERS AND STORMS CONTINUING
THROUGH THE MORNING AS A SLIGHTLY STRONGER MID-LEVEL WAVE INDUCES THE
DEVELOPMENT OF A WEAK SURFACE LOW ALONG THE FRONT. ALTHOUGH A MODEST
INCREASE IN MID-LEVEL FLOW MAY RESULT IN A GREATER THREAT FOR STRONG
STORMS FROM LATE TONIGHT THROUGH TUESDAY MORNING...DEEP-LAYER
VERTICAL WIND SHEAR DOES NOT APPEAR TO BE FAVORABLE FOR SEVERE
THUNDERSTORMS. HOWEVER...MULTIPLE EPISODES OF RAIN/THUNDERSTORMS MAY
LEAD TO A HEIGHTENED RISK OF FLASH FLOODING DURING THIS PERIOD.

THE SYNOPTIC PATTERN WILL BEGIN TO CHANGE BY TUESDAY NIGHT AND
WEDNESDAY...AS THE MID-LEVEL WAVE RESPONSIBLE FOR OUR CONVECTION
SHIFTS EASTWARD INTO THE CAROLINAS/GEORGIA. A STRONGER VORT MAX --
PROGGED TO DIG SOUTHEASTWARD ACROSS THE UPPER MIDWEST ON TUESDAY AND
LOWER GREAT LAKES/UPPER OHIO VALLEY ON TUESDAY NIGHT -- WILL COMBINE
WITH PRONOUNCED HEIGHT RISES ACROSS THE SOUTHERN PLAINS TO INDUCE
MORE OF A NORTHWEST FLOW REGIME ACROSS THE LOCAL REGION...AND THIS
WILL EFFECTIVELY ALLOW THE SURFACE COLD FRONT TO DRIFT SOUTHWARD. THE
ADVECTION OF A DRIER AIRMASS FROM THE NORTHEAST AND WEAK DEEP-LAYER
FORCING FOR UVM WILL LIMIT RAIN CHANCES FROM TUESDAY NIGHT INTO
WEDNESDAY.

THE PATTERN IN PLACE AT THE END OF THE SHORT TERM PERIOD WILL
CONTINUE IN THE EXTENDED...ALTHOUGH OUR LOCAL WEATHER REGIME WILL
BECOME INCREASINGLY INFLUENCED BY A STRONG MID-TROPOSPHERIC
ANTICYCLONE BECOMING ESTABLISHED ACROSS THE SOUTHERN PLAINS. A COUPLE
OF WEAK DISTURBANCES WILL TRANSLATE SOUTH-SOUTHEASTWARD ON FRIDAY AND
SATURDAY...PERHAPS BRINGING ISOLATED SHOWERS AND STORMS TO THE
REGION. HOWEVER...WE STILL ANTICIPATE MORE OF A DIURNAL CONVECTIVE
CYCLE TO EVOLVE EARLY NEXT WEEK...AS THE SOUTHERN PLAINS RIDGE BEGINS
TO EXPAND EASTWARD INTO THE REGION.

70/DD

&&

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

$$

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