997
FXUS62 KCAE 210245
AFDCAE
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE COLUMBIA SC
945 PM EST FRI NOV 20 2009
SYNOPSIS
HIGH PRESSURE CENTERED OVER THE LOWER OHIO VALLEY WILL DRIFT EAST
OVER THE NEXT 24 HOURS. SKIES WILL BE CLEAR OVERNIGHT WITH PATCHY
FOG DEVELOPING TOWARD SATURDAY MORNING. A LOW PRESSURE SYSTEM
DEVELOPING OVER THE WESTERN GULF OF MEXICO WILL MOVE NORTHEAST
ACROSS THE FLORIDA PANHANDLE BY SUNDAY NIGHT. THIS SYSTEM WILL
SPREAD RAIN NORTHEAST ACROSS THE AREA LATE SATURDAY NIGHT INTO
MONDAY MORNING. RAINFALL AMOUNTS WILL RANGE FROM A HALF TO THREE
QUARTERS OF AN INCH BEFORE ENDING MONDAY.
NEAR TERM /OVERNIGHT/
CLEAR SKIES...DRIER AIR...AND LIGHT WINDS HAVE ALLOW EVENING TEMPS
TO FALL A LITTLE FASTER THAT EARLIER FORECAST. HAVE TWEAKED
OVERNIGHT TEMP AND HOURLY GRIDS DOWNWARD ACROSS EASTERN COUNTIES A
LITTLE BIT. ONLY MINOR ADJUSTMENTS MADE TO DEWPOINTS AND WINDS.
HAVE INCREASED CLOUD COVER LATER TONIGHT TO ACCOUNT FOR INCREASE
IN HIGH LEVEL CLOUDINESS FROM THE WEST. UPDATES ALREADY OUT.
PREV DISC...SKIES WILL REMAIN MOSTLY CLEAR THROUGH THE NIGHT AS HIGH
PRESSURE SETTLES OVER THE AREA. RADIATING CONDITIONS WILL BE GOOD
AND TEMPERATURES WILL FALL INTO THE LOWER AND MID 40S 7 AM. PATCHY
DENSE FOG WILL ONCE AGAIN DEVELOP ESPECIALLY IN LOW LYING AREAS
AND AREAS NEAR MOISTURE SOURCES.
SHORT TERM /SATURDAY THROUGH SUNDAY/
ECMWF/NAM MOVE LOW PRESSURE FROM THE GULF OF MEXICO TO WESTERN
FLORIDA PANHANDLE BY SUNDAY EVENING. THE GFS WAS FASTER IN MOVING
THE SYSTEM. LEANED TO THE SLOWER NAM/ECMWF SOLUTION...SO REMOVED
THE CHANCE OF RAIN SATURDAY...REDUCING POPS SATURDAY NIGHT TO HIGH
CHANCE AND INCREASING THE CHANCE TO 100 PERCENT SUNDAY. HIGH
PRESSURE TO THE NORTH WILL PREVENT ANY WARMER AIR FROM REACHING
THE SURFACE SO EXPECT HIGHS ONLY IN THE 50S SUNDAY.
MODEL GUIDANCE RANGES FROM AROUND A QUARTER OF AN INCH FROM BUFKIT
GRIDS FROM THE NAM TO OVER 1.75 INCHES FROM THE GFS. USED HPC
GUIDANCE FOR THE RAINFALL AMOUNT FORECAST WHICH KEPT AMOUNTS
GENERALLY LESS THAN AN INCH. THERE IS A POTENTIAL FOR HEAVY RAIN
ESPECIALLY IF THE GFS VERIFIES...BUT ALL MODELS GUIDANCE WEAKENS
THE SYSTEM AS IT MOVES NORTHEAST. THEREFORE DID NOT MENTION HEAVY
RAIN IN THE FORECAST AT THIS TIME.
LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/
THE 12Z GFS AND ECMWF RUN SHOW A DIVERGENCE WITH THE GFS FASTER IN
MOVING SYSTEMS THAN THE ECMWF. TEMPERATURES WILL RISE BACK INTO
THE UPPER 60S TO THE LOWER 70S TUESDAY AS A PACIFIC ORIGIN HIGH PRESSURE
MOVES ACROSS THE MID ATLANTIC STATES. A STRONG SYSTEM DEVELOPS
OVER THE MIDWEST TUESDAY AND SWINGS A COLD FRONT THROUGH THE
REGION WEDNESDAY. WITH FORCING WELL TO THE NORTH...IT LOOKS TO BE
A DRY FRONTAL PASSAGE AND THAT IS REFLECTED IN THE FORECAST. THE
FRONT WILL BE FOLLOWED BY A COLD AIR MASS FROM SOUTHERN CANADA.
THIS WILL DROP LOWS INTO THE A COLD AIR MASS FROM CANADA THEN
CROSSES THE MOUNTAINS DROPPING LOW TEMPERATURES INTO THE UPPER 30S
TO LOWER 40S BY FRIDAY MORNING. LEANED TOWARD THE GFS IN THE
EXTENDED FORECAST.
AVIATION /03Z SATURDAY THROUGH WEDNESDAY/
FOR CAE...CUB AND DNL ...VFR CONDITIONS EXPECTED THROUGH 10Z. VIS
WILL DETERIORATE TO MVFR IN FOG FROM 10Z-14Z AS GOOD RADIATING
CONDITIONS WILL PREVAIL OVERNIGHT. DEWPOINTS ARE A LITTLE LOWER
TONIGHT THAN THEY WERE LAST NIGHT SO AT THIS TIME EXPECT VIS TO
STAY ABOVE IFR.
AT AGS AND OGB...DEWPOINTS ARE HIGHER SO EXPECT VIS TO GO MVFR
AFTER 06Z TO 08Z WITH TEMPO IFR VIS FROM 10Z TO 13Z. CONDITIONS
SHOULD RETURN TO VFR ALL SITES AFTER 14Z WITH ONLY THICKENING
HIGH TO MID LEVEL CLOUDS FOR THE REMAINDER OF THE DAY IN ADVANCE
OF AN APPROACHING LOW PRESSURE SYSTEM.
EXTENDED AVIATION OUTLOOK...WIDESPREAD MVFR OR IFR CONDITIONS
WILL LIKELY OCCUR LATE SATURDAY NIGHT AND SUNDAY ASSOCIATED WITH
AN AREA OF LOW PRESSURE EXPECTED TO MOVE NORTHEASTWARD FROM THE
GULF OF MEXICO.
CAE WATCHES/WARNINGS/ADVISORIES
SC...NONE.
GA...NONE.
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