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Area Forecast Discussion

354
FXUS64 KHUN 280000 AAA
AFDHUN

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HUNTSVILLE AL
700 PM CDT SUN JUL 27 2014

.UPDATE...
FOR 00Z TAFS

&&

.DISCUSSION...
/ISSUED 107 PM CDT SUN JUL 27 2014/
LATEST SURFACE ANALYSIS SHOWS A BROAD AREA OF LOW PRESSURE CENTERED
ACROSS THE LP OF MICHIGAN WITH A TRAILING COLD FRONT EXTENDING
THROUGH THE OHIO VALLEY ACROSS THE OZARKS AND INTO THE TX PANHANDLE.
REMNANTS FROM THE OVERNIGHT/EARLY MORNING MCS ACROSS THE OHIO VALLEY
HAS EVOLVED INTO A CELLULAR TYPE CONVECTIVE EVENT ACROSS CENTRAL/ERN
KY THIS AFTN WHERE THE COMBINATION OF SHEAR/INSTABILITY REMAINS
CONDUCIVE FOR SUPERCELL TYPE DEVELOPMENT.

CLOSER TO HOME...PROXIMITY SOUNDINGS SHOW A LID/CAP IN PLACE AROUND
AROUND 800 MB (WHICH IS SUPPORTED BY THE 12Z RAOBS AND U/A ANALYSIS).
THIS CAP HAS HELPED TO LIMIT THE VERTICAL EXTENT OF THE CUMULUS
DEVELOPMENT SO FAR TODAY DESPITE FAIRLY RICH LOW LEVEL MOISTURE
ACROSS THE REGION. AT 18Z...TEMPS WERE RUNNING IN THE UPPER 80S TO
LOWER 90S WITH DWPTS IN THE LOW/MID 70S. THIS TRANSLATES TO HEAT
INDICES AS HIGH 102...OR JUST BELOW ADVY CRITERIA.

THE FRONT WILL DRIFT SOUTHWARD WITH TIME THIS EVENING AND OVERNIGHT
TONIGHT TOWARD THE TENNESSEE VALLEY. GUIDANCE REMAINS SPLIT ON
CONVECTIVE POTENTIAL ALONG THE WESTERN END OF THE FRONT AND
MAINTENANCE OF CONVECTION AS IT PROGRESSES FURTHER SOUTH. WHILE
THERE IS MORE THAN SUFFICIENT CAPE IN PLACE TO SUPPORT ROBUST/STRONG
CONVECTION ...THE AFOREMENTIONED CAP MAY BE TOUGH TO ERODE ACROSS
THE DEEP SOUTH PER MODEL SOUNDINGS GIVEN THE LIMITED MECHANICAL
FORCING PROGGED BY THE MODELS. THE LATEST RAP/HRRR SHOW A RATHER
RAGGED SCT/BKN LINE MAKING ITS WAY INTO THE CWA AFT 04Z. CONVECTION
MAY BE SOMEWHAT ELEVATED BY THAT TIME PERIOD WHICH MAY LIMIT WIND
POTENTIAL. HOWEVER...MID LEVEL LAPSE RATES WOULD FAVOR ISOLATED
SEVERE HAIL POTENTIAL AND CERTAINLY FAIRLY EXTENSIVE LIGHTNING
PRODUCTION WITH ANY CONVECTIVE CORES.

EXPECT DRIER AIR WITH FRONT TO PRESS SOUTHWARD INTO THE REGION BEFORE
12Z AND HAVE REMOVED POPS FROM THE 2ND PERIOD IN ALL AREAS. THIS IS
SUPPORTED BY ALL THE LATEST MODEL GUIDANCE. DESPITE THE DRIER AIR AND
NORTHERLY WINDS...EXPECT TEMPS TO REACH NEAR CLIMO TEMPS AGAIN ON
MONDAY AS ANY "COOL" ADVECTION SHOULD NOT OFFSET THE RATHER WARM
START TO THE DAY. AS WE PROGRESS INTO THE WORK WEEK...THERE IS
OVERALL GOOD AGREEMENT IN THE MEDIUM RANGE GUIDANCE MAINTAINING A
RATHER HIGH AMPLITUDE PATTERN ACROSS THE LOWER 48 THROUGH MUCH OF THE
PERIOD. THE L/W TROUGH AXIS WILL MAINTAIN A GENERAL POSITION FROM
JAMES BAY THROUGH THE CENTRAL GREAT LAKES INTO THE MID ATLANTIC
THROUGH LATE WEEK.

THIS WILL PLACE THE TN VALLEY IN BROAD NORTHWESTERLY FLOW WHICH IS
TYPICALLY A FORECASTING NIGHTMARE AROUND HERE. IN TERMS OF THE
SENSIBLE WEATHER...THE GFS/ECMWF SHOW LITTLE SPREAD THROUGH EARLY/MID
WEEK BUT VARY SOMEWHAT WITH THE IMPULSES ROUNDING THE BASE OF THE
TROUGH LATE WEEK AND THE ASSOCIATED MOISTURE AVAILABILITY WITH THESE
FEATURES. THE ECMWF IS A BIT MORE ROBUST WITH PRECIPITATION POTENTIAL
IN THE THU-FRI TIME FRAME WHILE THE GFS HOLDS THE BETTER PRECIP
CHANCES UNTIL LATE FRI-SAT WITH A STRONGER S/W AND ASSOCIATED VORT
MAX. FOR THIS FORECAST PACKAGE WILL SPLIT THE DIFFERENCE BETWEEN THE
GFS/ECMWF IN THE LATTER PERIODS WHICH MATCHES WELL WITH NEIGHBORING
OFFICES. VERY LITTLE SPREAD IS NOTED IN TEMPERATURE GUIDANCE AND WILL
THUS LEAN TOWARD ENSEMBLE MEAN MAX/MIN TEMPS FOR THE 4-7 DAY PERIOD.

15

&&

.AVIATION...
FOR 00Z TAFS...VFR CONDS LIKELY TO CONTINUE THRU ~05-06Z AT
KHSV/KMSL UNTIL A BKN LINE OF SHRA/TSRA ARRIVE IN THE AREA. COVERAGE
OF SHRA IS EXPECTED TO BE SCTD WITH THE EXTENT OF TSRA PERHAPS ONLY
ISOLD. THUS...KEPT VFR PREVAILING CONDS AT TAF SITES FOR NOW. IF A
STRONG CELL IMPACTS A TAF SITE HOWEVER...EXPECT IFR/MVFR VIS IN HVY
RAIN CORES. TSRA WILL BE MORE LIKELY IN NERN AL...AND WAS INCLUDED
IN KHSV TAF. SW WINDS ~10-15KT WILL CONTINUE AT KHSV/KMSL UNTIL
~05-06Z...WITH WSHFT IN ASSOC/W CDFNT ~07-08Z.

KDW

&&

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

$$

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



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