019
FXUS62 KCAE 042339
AFDCAE
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE COLUMBIA SC
739 PM EDT SAT JUL 4 2009
SYNOPSIS
A FRONTAL BOUNDARY AND INCREASING ATMOSPHERIC MOISTURE WILL LEAD TO
A CHANCE OF SHOWERS AND THUNDERSTORMS SUNDAY AND MONDAY. THE FRONT
WILL STALL NEAR OUR REGION...OR PUSH JUST TO OUR SOUTH TUESDAY.
NEAR TERM /UNTIL 6 AM SUNDAY MORNING/
UPPER HIGH CURRENTLY CENTERED OVER TX WITH UPPER TROUGH ALONG THE
EAST COAST. AN OLD FRONT REMAINS STALLED TO OUR SOUTH...WITH WEAK
SURFACE HIGH NEAR OUR REGION. LATEST LAPS SOUNDINGS CONTINUE TO
INDICATE A DRY AND CAPPED ATMOSPHERE OVER OUR FORECAST AREA
(FA)...PREVENTING ANY CONVECTIVE DEVELOPMENT. 12Z RAOBS INDICATED
DRY AIR OVER THE EASTERN CONUS WITH BETTER MOISTURE ACROSS THE
CENTRAL CONUS. HIGH LEVEL CLOUDINESS FROM UPSTREAM CONVECTION OVER
THE MID MISSISSIPPI VALLEY MAY BEGIN STREAMING SE TOWARDS OUR
REGION THROUGH TONIGHT.
SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY NIGHT/
UPPER HIGH WILL WEAKEN AND SHIFT WEST SOME...WHILE TROUGHINESS
DEEPENS OVER THE EASTERN CONUS...WITH A SERIES OF UPPER IMPULSES
MOVING ACROSS OUR REGION. FRONTAL BOUNDARY WILL SHIFT SE TOWARDS
OUR REGION BY LATE DAY SUNDAY...WHILE SURFACE LOW RIDES BY TO OUR
NORTH. MEAN ATMOSPHERIC FLOW WILL BECOME MORE SW TO W AND ALLOW
FOR A SIGNIFICANT INCREASE IN ATMOSPHERIC MOISTURE AND INCREASING
CLOUDINESS. UPPER LEVEL CLOUD COVER MAY WORK AGAINST DIURNAL
HEATING...BUT INCREASING MOISTURE AND INSTABILITY IS EXPECTED TO
PROVIDE A CHANCE OF SHOWERS AND THUNDERSTORMS BY LATE AFTERNOON. AN
INCREASE IN ATMOSPHERIC WIND SPEED TO PROVIDE FOR FAIRLY RAPID
MOVEMENT OF STORMS AND A CHANCE OF DAMAGING DOWNBURSTS. SPC
MAINTAINS NORTHERN AND CENTRAL FA IN A SLIGHT RISK OF SEVERE FOR
SUNDAY. BOTH NAM AND GFS INDICATE FRONT WILL BE SLOW TO MOVE THROUGH
MONDAY...WITH A SURFACE WAVE MOVING ACROSS. GENERALLY USED A
NAM/GFS MOS BLEND ON MOST ELEMENTS.
LONG TERM /TUESDAY THROUGH SATURDAY/
BOTH GFS AND ECMWF INDICATE UPPER RIDGE BUILDING BACK EASTWARD INTO
THE PLAINS...WITH ANOTHER UPPER HIGH BUILDS WELL TO OUR SE...WITH
WEAK TROUGHINESS IN BETWEEN ACROSS THE SE CONUS AND NORTHERN GULF.
FRONTAL POSITION AND MOISTURE WILL BECOME IMPORTANT. GFS INDICATES
THE FRONT AND THE BEST MOISTURE MAY REMAIN STALLED JUST TO OUR SOUTH
TUESDAY...WHILE NAM APPEARS TO HANG IT UP OVER OUR FA. SINCE FRONTAL
POSITION UNCERTAIN...THINK SLIGHT CHANCE POPS NORTH TO CHANCE SOUTH
IN ORDER. 00Z GFS/ECMWF GENERALLY MAINTAINED A STALLED FRONTAL
BOUNDARY AND BEST MOISTURE JUST TO OUR SOUTH FOR MOST OF THE
REMAINDER OF THE FORECAST PERIOD...WITH 00Z ECMWF SUGGESTING
DEEPENING EASTERN CONUS TROUGH WITH BACK DOOR FRONT MOVING DOWN INTO
OUR REGION LATE IN THE FORECAST PERIOD. 12Z GFS DIFFERS FROM
PREVIOUS RUN IN THAT IT DEVELOPS A LOW ALONG THE FRONT NEAR THE GULF
COAST WHICH TRACKS NE UP INTO OUR REGION THU/FRI. FOR NOW...ACCEPTED
BLEND OF HPC AND MOS GUIDANCE...WHICH ALLOWS FOR A CHANCE OF SHOWERS
AND THUNDERSTORMS WITH NEAR NORMAL TEMPS THROUGH THE REMAINDER OF
THE FORECAST PERIOD. HOWEVER...THIS WILL BE SUBJECT TO CHANGE GIVEN
WHAT APPEARS TO BE CONSIDERABLE UNCERTAINTY.
AVIATION /00Z SUNDAY THROUGH THURSDAY/
VFR CONDITIONS SHOULD OCCUR THROUGH THE TAF PERIOD. MODEL
SOUNDINGS STILL SHOWING AN INCREASE IN BOUNDARY LAYER WIND LATE
TONIGHT AHEAD OF THE NEXT APPROACHING FRONT. SHOULD BE ENOUGH LOW
LEVEL MIXING AND LINGERING DRY AIR TO HELP PREVENT FOG. INCREASING
MID LEVEL CLOUDS SUNDAY AFTERNOON AHEAD OF APPROACHING COLD FRONT.
CEILINGS LOWERING TOWARD END OF TAF PERIOD...BUT VFR EXPECTED.
A FRONTAL SYSTEM MOVING INTO THE REGION MAY RESULT IN PERIODS OF
WIDESPREAD IFR CONDITIONS IN THUNDERSTORMS FROM LATE SUNDAY
AFTERNOON INTO MONDAY.
CAE WATCHES/WARNINGS/ADVISORIES
SC...NONE.
GA...NONE.
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