978
FXUS62 KCAE 130641
AFDCAE
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE COLUMBIA SC
241 AM EDT TUE AUG 13 2013
.SYNOPSIS...
THE THUNDERSTORM CHANCE WILL INCREASE TUESDAY AS THE RIDGE
WEAKENS AHEAD OF AN APPROACHING COLD FRONT. THIS FRONT WILL STALL
NEAR THE FORECAST AREA WEDNESDAY.
&&
.NEAR TERM /UNTIL 8 AM THIS MORNING/...
SHORT WAVE CROSSING EASTERN GA HELPING TO PRODUCE SCATTERED
CONVECTION ACROSS THE CSRA AND SOUTHERN MIDLANDS. HAVE INCREASED
POPS FOR THIS AREA THROUGH THE PREDAWN HOURS. HEAVY RAIN POSSIBLE
GIVEN PWAT JUST OVER 2 INCHES. STILL EXPECT LOWS IN THE MID 70S.
&&
.SHORT TERM /8 AM THIS MORNING THROUGH WEDNESDAY NIGHT/...
TUESDAY AND TUESDAY NIGHT...WEAK COLD FRONTAL BOUNDARY BEGINS TO
SAG SOUTHWARD TOWARD THE FORECAST AREA AS EASTERN CONUS UPPER
TROUGH BEGINS TO INTENSIFY BRINGING SHORT WAVE ENERGY TO THE
REGION. MOISTURE FLUX INCREASING AND WILL INCLUDE 20-30 PERCENT
POPS EXCEPT FOR 40-50 PERCENT TUESDAY AFTERNOON ON INTO THE
EVENING HOURS. COLD FRONT STILL TO THE NORTH DURING THE DAY
TUESDAY. SO...WENT HIGHS STILL WARM IN THE LOWER 90S. MODELS DROP
COLD FRONT INTO THE REGION LATE TUESDAY NIGHT AFTER MIDNIGHT.
SO...TEMPERATURES NOT MUCH COOLER UNTIL WEDNESDAY. OVERNIGHT LOWS
TUESDAY NIGHT STILL UP INTO THE LOWER TO MIDDLE 70S.
WEDNESDAY AND WEDNESDAY NIGHT...UPPER TROUGH DEEPENING AND PUSHING
COLD FRONTAL BOUNDARY INTO THE REGION. INCREASED MOISTURE FLUX AS
GFS PWATS RISE TO 2.3 INCHES. LATEST MOS GUIDANCE GIVES ABOUT 40
PERCENT FOR WEDNESDAY BUT DECIDED TO 50 PERCENT WITH FRONTAL
BOUNDARY PROVIDING A FOCUSING MECHANISM. WILL ALSO GO 50 PERCENT
WEDNESDAY NIGHT AS A MODEL BLEND BETWEEN MAV 65 AND MET 40 PERCENT.
COOLER TEMPERATURES WITH MORE CLOUDS AND HIGHER RAIN CHANCES...
DECIDED ON HIGHS MAINLY IN THE MIDDLE 80S. LOWS WEDNESDAY NIGHT
UPPER 60S NORTH TO LOWER 70S SOUTH.
&&
.LONG TERM /THURSDAY THROUGH TUESDAY/...
MEDIUM RANGE MODELS ARE IN GOOD AGREEMENT SHOWING A DEEP UPPER
TROUGH IN THE EASTERN CONUS THURSDAY AND FRIDAY EXTENDING ALL THE
WAY SOUTH TO THE GULF OF MEXICO. AN UPPER LOW IS EXPECTED TO FORM
JUST WEST OF THE UPPER TROUGH IN THE LOWER MISSISSIPPI VALLEY
SATURDAY AND PERSIST THROUGH MONDAY. THIS UPPER LOW MAY DRIFT
SLOWLY TO THE EAST APPROACHING THE APPALACHIANS BY MONDAY. THIS
SETUP WILL CREATE AN UNSETTLED WEATHER PATTERN FOR THE PERIOD.
BOTH THE GFS AND THE ECMWF HAVE THE STALLED OUT FRONTAL BOUNDARY
THAT MOVED TO THE SOUTH EARLIER IN THE WEEK STRETCHING FROM THE
GULF COAST TO JUST OFFSHORE OF THE CAROLINAS THURSDAY THROUGH
SATURDAY. THEN BOTH MODELS BEGIN TO LIFT THE FRONTAL BOUNDARY BACK
NORTHWARD SUNDAY AND MONDAY. PLENTY OF MOISTURE SHOULD BE
AVAILABLE WITH GFS PWAT VALUES 2.2-2.3 INCHES THURSDAY AND FRIDAY.
PWAT VALUES INCREASE TO OVER 2.6 INCHES IN THE GULF SATURDAY AS
TROPICAL MOISTURE BEGINS TO MOVE NORTHWARD INTO THE REGION. THE
TROPICAL MOISTURE MODIFIES A BIT TO 2.3-2.4 INCHES AS IT
ENCOUNTERS SOME MID LATITUDE AIR SUNDAY AND MONDAY. HIGH MOISTURE
MAY LEAD TO A FLOODING THREAT AS DEEPER MOISTURE MOVES INTO THE
REGION. THE GFS HAS LOW PRESSURE ASSOCIATED WITH THE TROPICAL
MOISTURE IN THE GULF FRIDAY AND SATURDAY. IT IS UNCLEAR IF THIS
LOW PRESSURE WILL BECOME A TROPICAL SYSTEM BUT IT WILL MOVE INTO
AN UNFAVORABLE ENVIRONMENT FOR DEVELOPMENT AS IT MOVES NORTHWARD
WHERE A TROUGH COVERS THE REGION. TEMPERATURES ARE EXPECTED TO BE
BELOW NORMAL. USED MOS GUIDANCE GIVING HIGHS MAINLY IN THE LOWER
TO MIDDLE 80S DURING THE PERIOD. HOWEVER...GFS MOS GUIDANCE GAVE
HIGHS ONLY IN THE 70S THURSDAY THROUGH SATURDAY. NEAR OVERCAST
CONDITIONS WITH A HIGH CHANCE OF RAIN...SAY OVER 80
PERCENT...WOULD MAKE THESE COOLER HIGHS MORE REPRESENTATIVE.
NIGHT-TIME LOWS IN THE UPPER 60S TO BEGIN THURSDAY NIGHT AND
FRIDAY NIGHT SHOULD LEVEL OFF TO AROUND 70 BY SUNDAY NIGHT AS
MOISTURE INCREASES.
&&
.AVIATION /07Z TUESDAY THROUGH SATURDAY/...
VFR CONDITIONS GENERALLY EXPECTED THROUGH THE 24 HOUR TAF FORECAST
PERIOD. HOWEVER...WIDELY SCATTERED SHOWERS/THUNDERSTORMS CONTINUE TO
DEVELOP ACROSS THE CSRA/EASTERN MIDLANDS. WILL NEED TO MENTION A
TEMPO GROUP AT DNL/AGS/OGB FOR A PERIOD OF SHRA/TSRA.
OTHERWISE...SKIES WILL REMAIN PARTLY TO MOSTLY CLEAR SKIES WITH LOW
DEWPOINT DEPRESSIONS OVERNIGHT. THIS ALONG WITH SOME RAINFALL...MAY
LEAD TO SOME CONCERNS FOR FOG DEVELOPMENT TOWARD MORNING.
HOWEVER...MODEL INDICATIONS OF A WESTERLY BOUNDARY LAYER FLOW AROUND
20 KT AND CURRENT VWP SHOWS 15 TO 20 KT WEST WINDS...WOULD LIMIT FOG
POTENTIAL. LATEST GFS LAMP IS INDICATING MVFR VSBYS AT FOG PRONE
AGS/OGB. SCATTERED CONVECTION EXPECTED TUE AFTN/EVE...THINK A LATE
AFTN VCTS MENTION IS REASONABLE.
EXTENDED AVIATION OUTLOOK...RESTRICTIONS POSSIBLE IN AFTERNOON
CONVECTION AS WELL AS LATE NIGHT/EARLY MORNING FOG/STRATUS.
&&
.CAE WATCHES/WARNINGS/ADVISORIES...
SC...NONE.
GA...NONE.
&&
$$