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Area Forecast Discussion

798
FXUS62 KGSP 270708
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
308 AM EDT MON APR 27 2015

.SYNOPSIS...
A LARGE COOL AND DRY AIR MASS WILL DOMINATE THE WEATHER ACROSS THE
SOUTHERN APPALACHIAN REGION THROUGH TUESDAY. A WELL ORGANIZED LOW
PRESSURE SYSTEM WILL LIFT ACROSS THE DEEP SOUTH...TRACKING ACROSS
THE ATLANTIC COAST DURING THE MID WEEK. ANOTHER CANADIAN AIR MASS
WILL SETTLE BACK OVER THE REGION DURING THE LATE WEEK AND WILL
REMAIN INTO THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 230 AM MONDAY...THE NEAR TERM IS OVERALL FAIRLY QUIET. LARGE
UPPER LOW SPINNING OFF NEW ENGLAND KEEPS US IN NORTHWEST FLOW IN THE
WAKE OF THE COLD FRONT THAT PUSHED THROUGH YESTERDAY. ANOTHER
SHORTWAVE SPINS AROUND THE WESTERN PERIPHERY OF THE LOW...PUSHING
THROUGH THE SOUTHERN APPALACHIANS TONIGHT. SURFACE HIGH PRESSURE
LOCKED ACROSS THE GREAT LAKES UNDER THE CONFLUENT FLOW TONIGHT WILL
CONTINUE TO RIDGE TOWARD THE SOUTHEAST...KEEPING THE SENSIBLE
WEATHER DRY THROUGH THE NEAR TERM. NEXT WEATHER-MAKER IS A CUTOFF
LOW OVER THE SOUTHERN PLAINS THAT WILL BRING A SURFACE LOW FROM THE
GULF INTO THE LOWER MISSISSIPPI VALLEY AND SOUTHEAST...BUT WITH NO
IMPACTS UNTIL THE SHORT TERM PERIOD. THE FEW CLOUDS OUT THERE AT AFD
TIME WILL CONTINUE TO DISSIPATE THROUGH THE MORNING HOURS...THOUGH
BUFR SOUNDINGS DO INDICATE ENOUGH RH AT THE TOP OF THE MIXED LAYER
THAT WE COULD SEE SOME FAIR-WEATHER CUMULUS DEVELOPING THIS
AFTERNOON.

THE PRIMARY CONCERN THROUGH THE NEAR-TERM WILL BE TEMPERATURES
OVERNIGHT TONIGHT...WHICH ARE PROGGED TO BE 5 OR SO DEGREES BELOW
NORMAL FOR MOST OF THE UPSTATE/PIEDMONT/FOOTHILLS. THE PROBLEM MIGHT
BE IN THE MOUNTAINS WITH DEEP LAYER /ALBEIT WEAK/ CAA THROUGH THE
COLUMN. THIS COMBINED WITH THE DECREASING SURFACE PRESSURE GRADIENT
AS THE HIGH CONTINUES TO RIDGE IN...AND WINDS WILL DROP OFF TONIGHT.
BASED ON TEMPS...DEWPOINT DEPRESSIONS...AND WINDS...EXPECT TO SEE
SOME FROST DEVELOPING JUST BEFORE SUNRISE AT THE HIGHER ELEVATIONS
OF THE NORTH CAROLINA MOUNTAINS. HOWEVER...AREAL EXTENT OF CURRENTLY
FORECAST FROST COVERAGE IS NOT ENOUGH TO WARRANT AN ADVISORY AT THIS
TIME. OVERNIGHT TEMPS/DEWPOINTS/WINDS WILL HAVE TO BE CLOSELY
REEVALUATED THROUGH THE DAY WITH UPDATED GUIDANCE IN CASE AN
ADVISORY BECOMES WARRANTED.

&&

.SHORT TERM /TUESDAY THROUGH THURSDAY/...
AS OF 230 AM MONDAY...SHORT RANGE MODELS AGREE THAT TUESDAY WILL SEE
DRY CONDITIONS UNDER S/W RIDGING. FORECAST SOUNDINGS INDICATE THAT
MOISTURE WILL INCREASE STEADILY FROM THE TOP-DOWN DURING THE
DAYLIGHT HOURS...DEEPEST ACROSS THE SW. A CONSENSUS OF THE
TEMPERATURE GUIDANCE SUPPORT HIGH TEMPERATURES RANGING FROM THE MID
60S WITHIN THE MTN VALLEYS TO THE UPPER 60S EAST...OR 5 TO 7 DEGREES
BELOW NORMAL.

ON WEDNESDAY...SHORT RANGE MODELS REMAIN IN GENERAL AGREEMENT...ALL
MAINSTREAM SOLUTIONS INDICATE THAT THE SFC LOW WILL LIFT NORTH
ACROSS THE FL PANHANDLE EARLY WEDNESDAY...REACHING THE CAROLINA
COAST BY WEDNESDAY EVENING. AT THE MID LEVELS...A DEEP TROF WILL
SLIDE EAST...REACHING THE SOUTHERN APPALACHIANS BY WEDNESDAY
AFTERNOON. A WIDE FIELD OF MODERATE Q-VECTOR CONVERGENCE IS FORECAST
TO SWEEP ACROSS THE CAROLINAS WEDNESDAY AFTERNOON. AT THE LOW
LEVELS...THE LOW CIRCULATION WILL RESULT IN EAST WINDS AT
H85...PROVIDING UPSLOPE FLOW DURING THE MORNING HOURS. THE
COMBINATION OF DEEP MOISTURE...DEEP SYNOPTIC SCALE FORCING...AND
LLVL UPSLOPE FLOW SHOULD RESULT IN RAPID INCREASE IN RAINFALL
COVERAGE ON WEDNESDAY. TEMPERATURES MAY BEGIN THE DAY AROUND
50...RISING TO AROUND 60 DURING THE AFTERNOON. THE EXPANDING
RAINFALL AND THICK CLOUD COVER SHOULD LIMIT DAYTIME TEMPERATURES TO
NEARLY 20 DEGREES BELOW NORMAL.

THURSDAY...THE ECMWF INDICATE THAT A BROAD MID LEVEL TROF WILL SWING
ACROSS THE REGION...THE GFS INDICATES THAT THE CORE OF A 540 CLOSED
LOW WILL TRACK OVER THE NC MTNS BY 0Z FRI. I WILL USE A BLEND OF THE
TWO SOLUTIONS...WHICH WILL YIELD MORE CLOUDS AND PRECIP THAN THE
INHERITED FORECAST. I WILL INCREASE SKY TO MOSTLY CLOUDY THROUGH
MID DAY...THEN INDICATE CLOUD COVER ERODING WITHIN THE DOWNSLOPE
AREAS THURSDAY AFTERNOON. IN ADDITION...I WILL KEEP CHC POPS THROUGH
THE DAYLIGHT HOURS. LIGHT RAIN TO RAIN SHOWERS SHOULD OCCUR BOTH
WEDNESDAY AND THURSDAY...MODEL INSTABILITY IS VERY WEAK.
TEMPERATURES ARE FORECAST TO WARM ABOVE WEDNESDAY/S VALUES BY 5 TO 8
DEGREES. QPF ON THURSDAY SHOULD REMAIN LESS THAN A QUARTER OF AN
INCH.

&&

.LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/...
AS OF 300 AM MONDAY...THROUGH THE EXTENDED...THE COASTAL SFC LOW
WILL LIKELY CONTINUE TO TRACK NORTHEAST AND INTENSIFY. DRY CANADIAN
HIGH PRESSURE WILL SWEEP ACROSS THE SOUTHERN APPALACHIAN REGION
DURING THE LATE WEEK AND REMAIN INTO THE WEEKEND. AT THE MID
LEVELS...A BROAD TROF WILL SLOWLY GIVE WAY TO RISING HEIGHTS FROM
THE WEST. FRIDAY-SUNDAY SHOULD SEE MODERATING
TEMPERATURES...BEGINNING BELOW NORMAL AND ENDING WITH TEMPERATURES
VERY CLOSE TO NORMALS. OVERALL...CONDITIONS WILL REMAIN DRY WITH
PARTLY CLOUDY SKY COVER.

&&

.AVIATION /07Z MONDAY THROUGH FRIDAY/...
AT KCLT...EXPECT VFR THROUGH THE PERIOD. CLOUDS AT TAF TIME
RANGE FROM SCT TO BKN 6-8KFT AND THESE WILL CLEAR OUT THROUGH THE
MORNING AS THE FRONT CONTINUES PUSHING SOUTH. CANNOT RULE OUT SOME
BRIEF FEW-SCT 5-6KFT CU THIS AFTERNOON. OTHERWISE JUST HIGH CLOUDS
THROUGH THE PERIOD. ONLY CAVEAT TO PREVAILING VFR CONDITIONS REMAINS
THAT SOME GUIDANCE...NAMELY THE RUC...DOES STILL WANT TO DEVELOP IFR
TO LIFR FOG ACROSS THE NC PIEDMONT THIS MORNING INCLUDING AT KCLT.
BASED ON DEWPOINT DEPRESSIONS AND CONDENSATION PRESSURE DEFICIT...
NOT INCLINED TO BELIEVE THIS OUTLIER SOLUTION BUT CANNOT RULE OUT
SOME PATCHY MVFR FOG. NW WINDS GENERALLY THROUGH THE PERIOD BUT
PICKING UP TO BETWEEN 5-10KT THIS AFTERNOON...WITH POTENTIAL FOR A
BRIEF VERY LOW-END GUSTS.

ELSEWHERE...VERY SIMILAR TREND TO CLT. SOME MVFR CIGS STILL HANGING
OUT ACROSS THE UPSTATE...BUT CIGS SHOULD LIFT AND BEGIN TO SCATTER
IN THE NEXT COUPLE OF HOURS. GENERALLY NNW TO BRIEFLY NNE WINDS
EVERYWHERE BETWEEN 5-10KT THIS AFTERNOON...BUT WILL PROBABLY SEE
SLIGHTLY STRONGER WINDS AT KAVL...10KT OR JUST ABOVE WITH GUSTING
POTENTIAL TO 20KT OR SO.  OTHERWISE JUST HIGH CLOUDS THROUGH THE
PERIOD.

OUTLOOK...DRY HIGH PRESSURE WILL CONTINUE THROUGH TUESDAY. ANOTHER
LOW PRESSURE SYSTEM WILL TRACK ACROSS THE DEEP SOUTH WEDNESDAY AND
THURSDAY...WITH CEILING AND VSBY RESTRICTIONS POSSIBLE.

CONFIDENCE TABLE...

            07-13Z        13-19Z        19-01Z        01-06Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH  91%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH  94%     HIGH 100%     HIGH 100%     HIGH 100%
KHKY       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGMU       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAND       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%

THE PERCENTAGE REFLECTS THE NUMBER OF GUIDANCE MEMBERS AGREEING
WITH THE SCHEDULED TAF ISSUANCE FLIGHT RULE CATEGORY. COMPLETE HOURLY
EXPERIMENTAL AVIATION FORECAST CONSISTENCY TABLES AND ENSEMBLE FORECASTS
ARE AVAILABLE AT THE FOLLOWING LINK: (MUST BE LOWER CASE)

WWW.WEATHER.GOV/GSP/AVIATION_TABLES

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.

&&

$$
SYNOPSIS...NED
NEAR TERM...TDP
SHORT TERM...NED
LONG TERM...NED
AVIATION...TDP



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