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360
FXUS64 KHUN 242345 AAA
AFDHUN

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HUNTSVILLE AL
645 PM CDT THU APR 24 2014

.UPDATE...
FOR 00Z TAFS

&&

.DISCUSSION...
/ISSUED 144 PM CDT THU APR 24 2014/
WHAT A SPLENDID DAY IN PROGRESS ACROSS THE TENNESSEE VALLEY.
THE EARLY AFTERNOON SURFACE PATTERN WAS A RATHER COMPLEX ONE
(IT IS SPRING AFTERALL). AT 18Z...A SURFACE LOW WAS POSITIONED
ACROSS EASTERN KANSAS WITH A WARM FRONT DRAPED FROM THE OZARKS
THROUGH THE MS DELTA TO JUST SOUTH OF I-20 IN ALABAMA. A TRAILING
"COOL" FRONT WAS SITUATED FROM EASTERN OKLAHOMA THROUGH THE METROPLEX
AND INTO THE HILL COUNTRY. A MODEST WEDGE PATTERN WAS NOTED ACROSS
THE SOUTHERN APPALACHIANS WHICH HAS HELPED TO KEEP DEWPOINTS ACROSS
CENTRL/NRN GA AND NRN ALABAMA DOWN INTO THE 40S THROUGH MUCH OF THE
DAY. HOWEVER...WINDS HAVE FINALLY VEERED AROUND TO THE SOUTHWEST
ACROSS MUCH OF THE TENNESSEE VALLEY OVER THE PAST COUPLE OF HOURS
WITH AFTN MIXING. THIS, ALONG WITH THE DEVELOPING LOW LEVEL JET EARLY
THIS EVENING, SHOULD AID IN QUICKLY LIFTING THE WARM FRONT NORTHWARD
ACROSS THE REGION.

THE AFOREMENTIONED SFC "COOL" FRONT, ALONG WITH ITS ASSOCIATED
UPPER SHORTWAVE TROUGH, WILL SWEEP QUICKLY EASTWARD AND ACROSS THE
TENNESSEE VALLEY BY EARLY FRIDAY. THE INITIAL FORECAST CONCERN IN
ASSOCIATION WITH THESE FEATURES IS THE EVOLUTION OF THE CONVECTION
DEVELOPING WEST OF THE MISSISSIPPI RIVER THIS AFTERNOON (AHEAD OF THE
FRONTAL BOUNDARY). THE 00Z NSSL WRF ALONG WITH THE MOST RECENT
RAP/HRRR RUNS SEEMS TO HAVE A PRETTY GOOD HANDLE ON THESE FEATURES
AND THE ASSOCIATED SENSIBLE WEATHER.

ALTHOUGH INSTABILITY WILL BE SOMEWHAT LIMITED (DUE TO THE CURRENT
DRY LOWER TROPOSPHERIC CONDITIONS), EXPECT A NARROW WINDOW OF
INSTABILITY TO FORM ALONG/JUST AHEAD OF THE LINE AS IT APPROACHES
NORTHERN MISSISIPPI BY MID EVENING. THERE IS SOME MODEST DIRECTIONAL
SHEAR WITH THIS FEATURE SO ANY INDIVIDUAL CELLS WITHIN THE LINE THAT
CAN MAINTAIN/SUSTAIN UPDRAFTS WILL HAVE TO BE MONITORED FOR BRIEF
ROTATIONAL POTENTIAL. HOWEVER, THE PRIMARY THREAT IS CERTAINLY
MARGINAL WIND GUSTS AS THE LINE TRACKS ACROSS THE AREA FROM WEST TO
EAST BETWEEN 05Z AND 10Z. A WEAK SFC HIGH WILL BUILD ACROSS THE
REGION ON FRIDAY IN ITS WAKE AS THE UPPER TROUGH AXIS IS SHUNTED
QUICKLY EASTWARD. THUS WOULD EXPECT FAIRLY QUICKLY CLEARING DURING
THE MID MORNING HOURS ON FRIDAY.

THE UPCOMING WEEKEND LOOKS TO BE WARM AND RATHER QUIET OVERALL
ACROSS THE TENNESSEE VALLEY AS THE AREA REMAINS SANDWICHED BETWEEN
THE UPPER TROUGH ACROSS THE WESTERN ATLANTIC AND THE SYSTEM TRACKING
THROUGH THE INTERMTN REGION (SATURDAY) AND EVENTUALLY INTO THE
PLAINS (SUNDAY). MADE VERY LITTLE MODIFICATIONS TO THE SATURDAY
THROUGH SUNDAY TIME PERIOD AS UPPER LEVEL RIDGING AND SOUTHERLY
WINDS WILL ALLOWS TEMPS TO WARM WELL INTO THE 80S BOTH DAYS. THE
12Z GFS AND 12Z ECMWF BOTH HINT AT A SMALL CHANCE FOR SHOWERS
AND THUNDERSTORMS LATE IN THE DAY ON SUNDAY AS THE ADVANCING WARM
FRONT LIFTS NORTHWARDS AND STRONG WARM AIR ADVECTION TAKES SHAPE TO
OUR WEST. WILL MAINTAIN LOW CHC POPS FOR THE AFTN/EVENING HOURS FOR
NOW BUT EXPECT MOST AREAS TO REMAIN DRY THROUGH SUNSET.

THE ACTION REALLY GETS GOING STARTING SUNDAY NIGHT THROUGH THE EARLY
WORK WEEK PERIOD. QUITE FRANKLY, THE MEDIUM RANGE MODELS HAVE BEEN
STRUGGLING FOR CONSISTENCY WITH THE STRONG SYSTEM PROGGED TO WRAP UP
ACROSS THE PLAINS AND IMPACT THE AREA. THE 12Z GFS HAS TRENDED BACK
TOWARD ITS OPNL 00Z SOLUTION OF LIFTING THE PRIMARY DYNAMICS
NORTHWARD WITH TIME. THIS SOLUTION HINTS AT A MULTI-PHASE SEVERE
WEATHER THREAT BEGINNING WITH A DYING MCS TYPE FEATURE LATE SUNDAY
NIGHT/MONDAY MORNING, REDEVELOPMENT IN THE WARM SECTOR/BOUNDARY
INTERACTION MONDAY EVENING, THEN ALONG THE PRE-FRONTAL TROUGH ON
TUESDAY. THE UPPER FLOW PATTERN BECOMES INCREASINGLY DIVERGENT WITH
TIME WHILE THE SHEAR DECREASES SOMEWHAT SO A TRANSITION FROM ROTATING
STORMS (EARLY IN THE EVENT) TO LINEAR TRAINING CELLS (TUESDAY) WOULD
SEEM TO BE FAVORABLE IN THE 12Z GFS SOLUTION.

HOWEVER, THE ECMWF/CMC SOLUTIONS INDICATE A MUCH MORE DYNAMIC SYSTEM
WITH A SLIGHTLY NEGATIVELY TILTED TROUGH AND ROBUST LOWER
TROPOSPHERIC SHEAR FOR ROTATING STORMS PRIMARILY WITH AN EVENT
MONDAY EVENING/MONDAY NIGHT. CAPE VALUES LOOKS TO BE QUITE FAVORABLE
WITH AFTN/EVENING CAPES REACHING 2-2.5 KJ/KG ACROSS A LARGE PORTIONS
OF THE MID SOUTH AND LOWER TENNESSEE VALLEY. ALTHOUGH IT`S WAY TOO
EARLY TO GLEAN ANY SPECIFICS, THIS IS CERTAINLY A SYSTEM THAT
REQUIRES VERY CLOSE MONITORING. GIVEN THE AFOREMENTIONED
UNCERTAINTIES, KEPT EXISTING POPS FOR MON-TUE TIME PERIOD IN TACT.
LOWER END POPS AND MOSTLY CLOUDY SKIES THROUGH THE MID WEEK PERIOD
SEEM REASONABLE AS THE UPPER TROUGH ROTATES SLOWLY EASTWARD WITH
TIME.

15

&&

.AVIATION...
FOR 00Z TAFS...
A LINE OF CONVECTION ORIENTED FROM EAST OF JACKSON TN TO OXFORD AND
GREENWOOD MS WILL REACH FAR NW ALABAMA AROUND 0130Z. THIS SHOULD
AFFECT KMSL TOWARD 02Z WITH VCTS...THEN MORE CERTAIN SHOWERS AND
STORMS BEFORE MIDNIGHT. TIMING FOR KHSV IS A COUPLE OF HOURS SLOWER.
BRIEF REDUCTIONS OF CIG/VIS VALUES INTO THE MVFR (POSSIBLY LOWER)
CATEGORIES ARE EXPECTED WITH THIS ACTIVITY...ALONG WITH ERRATIC/GUSTY
WIND. NEAR BREEZY CONDITIONS ARE FORECAST DURING THE OVERNIGHT...AS
SHOWER ACTIVITY MOVES EASTWARD ACROSS THE REGION. WEST WINDS AND VFR
CONDITIONS ARE EXPECTED A COUPLE HOURS AFTER DAYBREAK...WITH WINDS
BECOMING NW AFTER 25/1800Z.

RSB

&&

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

$$

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




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