000
FXUS62 KGSP 231340
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
940 AM EDT THU MAY 23 2013

.SYNOPSIS...
AN APPROACHING UPPER LEVEL TROUGH WILL CONTINUE TO INFLUENCE THE 
REGION TODAY. A COLD FRONT MOVES THROUGH THE AREA TONIGHT...BEFORE A 
COOLER AND DRIER AIRMASS SETTLES IN FOR THE WEEKEND. THE AIRMASS 
MODIFIES THROUGH THE EARLY PART OF NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF MID MORNING...THE KGSP RADAR SHOWED A PATCH OF VERY LIGHT RAIN 
MOVING ACROSS METRO CLT AND SOME OTHER SHOWER ACTIVITY SKIRTING THE 
NRN MOUNTAINS. THE POP FOR THE NEXT HOUR OR TWO WAS ADJUSTED 
ACCORDINGLY. AS FOR THE REST OF THE DAY...THE LATEST RUNS OF THE 
CONVECTION ALLOWING MODELS ARE NOT AS EXCITED COMPARED TO YESTERDAY. 
THINK THE MOST LIKELY SCENARIO WILL BE FOR SCATTERED SHOWERS 
DEVELOPING OVER THE PIEDMONT DURING THE MIDDLE PART OF THE DAY AND 
THEN MOVING OFF TO THE EAST BEFORE BECOMING MORE NUMEROUS. THESE 
MODELS WERE VERY GOOD YESTERDAY. WITH THAT IN MIND...HAVE LOWERED 
THE EXPECTATIONS FOR THIS AFTERNOON AND TRIMMED POP BACK TO THE 
CHANCE RANGE ACROSS ALL BUT THE NORTHERNMOST ZONES. TEMP TRENDS WERE 
ALSO ADJUSTED DOWNWARD FOR THE MORNING BECAUSE OF THE EXTENSIVE 
CONVECTIVE DEBRIS CLOUDS.

PREVIOUS DISCUSSION...

AT 300 AM EST THURSDAY...AN UPPER TROUGH AXIS WILL CROSS THE OH AND 
TN VALLEYS TODAY...CROSS THE SOUTHERN APPALACHIANS THIS EVENING... 
THEN MOVES SLOWLY OVER THE EASTERN SEABOARD TONIGHT. THE REMAINS OF 
A COLD FRONT WILL CONTINUE TO CROSS OUR AREA EARLY TODAY..EXITING 
THE AREA TO THE EAST THIS AFTERNOON. A STRONG COLD FRONT WILL 
APPROACH FROM THE NW TODAY...REACHING THE MOUNTAINS BY THIS 
EVENING...AND CROSSING THE ENTIRE AREA SHORTLY AFTER MIDNIGHT.

THE ATMOSPHERE WILL DESTABILIZE AGAIN TODAY...WITH MODEST WIND 
SHEAR...AND SUFFICIENT DRY AIR ALOFT FOR DOWNDRAFT PRODUCTION. MODEL 
TIME HEIGHTS SHOW THE BEST LIFT BETWEEN 18 AND 21Z. A VEERING LOW 
LEVEL FLOW WILL DRY OUT THE LOWER LEVELS BEFORE LIFT IS MAXIMIZED IN 
THE FOOTHILLS...BUT DEEPER MOISTURE WILL REMAIN IN THE PIEDMONT... 
WHERE HEAVIER RAINFALL CAN BE EXPECTED. MAXIMUM TEMPERATURES WILL BE 
SLIGHTLY ABOVE NORMAL TODAY.

AS THE COLD FRONT CROSSES THE ARE THIS EVENING...WINDS WILL VEER NW. 
MODEL TIME HEIGHTS SHOW SOME LOW LEVEL MOISTURE PERSISTING EAST OF 
THE BLUE RIDGE...DESPITE A DOWNSLOPE FLOW...AND LIGHT RAINFALL MAY 
PERSIST INTO THE EVENING. POST FRONTAL PRECIPITATION WILL BE BEST 
AND MOST PROLONGED ALONG THE TN BORDER WITH NC...WHERE A PRONOUNCED 
MOIST NW UPSLOPE FLOW WILL SET UP AND LINGER OVERNIGHT. MINIMUM 
TEMPERATURES WILL BE NEAR NORMAL.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
AS OF 210 AM THURSDAY...AXIS OF AN UPPER TROF SWINGS ACROSS THE AREA 
FRI. AT THE SFC...PRESSURE GRADIENT TIGHTENS ACROSS THE AREA AS A 
COLD FRONT SLOWLY MOVES EAST AND HIGH PRESSURE SLOWLY MOVES IN FROM 
THE WEST. LOW LEVEL MOISTURE LINGERS OVER THE MTNS DURING THE 
MORNING...KEEPING SOME SCT RAIN SHOWERS THERE IN THE NWLY UPSLOPE 
FLOW. THE SHRA DISSIPATE BY AFTERNOON AS THE MOISTURE DIMINISHES. 
THE WIND AND COOLER AIR MASS WILL BE THE BIGGER STORIES. MODERATELY 
STRONG LOW LEVEL WINDS MOVE IN AND MIXING SHUD BE ABLE TO TAP THOSE 
WINDS DURING THE DAY. ALTHOUGH A WINDY DAY IS EXPECTED...GUSTS SHUD 
REMAIN BELOW WIND ADV LEVELS. WITH THE COOLER AIR MASS MOVING IN... 
HIGHS WILL BE 5 TO 10 DEGREES BELOW NORMAL.

HIGH PRESSURE WILL CONTINUE TO BUILD INTO THE ARE FRI NITE AS NWLY 
FLOW DEVELOPS ALOFT. THE GUSTY WINDS SHUD COME TO AN END DURING THE 
EVENING. HOWEVER...THE COLD AIR MASS WILL DROP LOWS TO AROUND 15 
DEGREES BELOW NORMAL. IN FACT...TEMPS IN THE NC MTN VALLEYS WILL BE 
COLD ENUF FOR FROST. IF THE WIND CAN DIMINISH ENUF...WHICH LOOKS 
QUITE POSSIBLE FOR THE SWRN VALLEYS...THEN A FROST ADV WOULD BE 
NEEDED.

NWLY FLOW ALOFT REMAINS OVER THE AREA SAT AND SAT NITE AS A FEW WEAK 
SHORT WAVES MOVE THRU. AT THE SFC...A WEAK BACK DOOR COLD FRONT 
DROPS INTO THE AREA LATE SAT OR SAT NITE. ALTHOUGH MOISTURE 
INCREASES SIGNIFICANTLY AND THERE IS SOME FORCING...THE FCST REMAINS 
DRY. HIGHS REMAIN NEARLY STEADY OUTSIDE OF THE MTNS...BUT REBOUND A 
FEW DEGREES OVER THE MTNS SAT. LOWS SAT NITE ALSO INCREASE...BUT 
REMAIN ABOUT 10 DEGREES BELOW NORMAL.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
AS OF 345 AM THURSDAY...THE GFS AND ECMWF ARE IN GENERAL AGREEMENT 
ON THE OVERALL PATTERN DURING THE MEDIUM RANGE. HOWEVER...THERE ARE 
SOME SIGNIFICANT DETAIL DIFFERENCES...ESPECIALLY AT THE SFC. NWLY 
FLOW ALOFT STARTS OUT OVER THE AREA BETWEEN AN UPPER LOW OVER NEW 
ENGLAND AND A RIDGE OVER THE CENTRAL CONUS. THIS FLOW CONTINUES THRU 
MON ON THE GFS UNTIL THE RIDGE MOVES EAST OVER THE AREA ON TUE WITH 
THE RIDGE REMAINING IN PLACE THRU WED. ON THE ECMWF...THE RIDGE DOES 
NOT MOVE IN UNTIL WED.

AT THE SFC...A BACK DOOR COLD FRONT STARTS OUT OVER THE AREA. THE 
ECMWF TAKES THE FRONT SOUTH OF THE AREA SUN...KEEPS IT THERE MON 
THEN MOVES IT BACK NORTH INTO THE AREA TUE AND KEEPS IT STATIONARY 
WED. THE GFS KEEPS THE FRONT OVER OR JUST NORTH OF THE AREA SUN AND 
MON...THEN SLIDES IT NORTHWARD TUE AND EASTWARD WED. THE GFS WOULD 
INDICATE MORE OF A DIURNAL CHC OF CONVECTION EACH DAY...WHILE THE 
ECMWF SUGGESTS MORE OF A STEADY CHC OF CONVECTION. THE GFS HAS BEEN 
PRETTY CONSISTENT WITH ITS FORECAST FROM RUN TO RUN...WHILE THE 
ECMWF HAS NOT. THEREFORE...SINCE NATIONAL GUIDANCE IS CLOSER TO THE 
GFS...HAVE FOLLOWED THOSE TRENDS AS WELL. HIGHS A LITTLE BELOW NORMAL 
SUN RISE TO AROUND 5 DEGREES ABOVE NORMAL BY WED. LOWS A FEW DEGREES 
BELOW NORMAL AT THE BEGINNING OF THE PERIOD RISE TO A FEW DEGREES 
ABOVE NORMAL BY THE END.

&&

.AVIATION /14Z THURSDAY THROUGH MONDAY/...
AT KCLT...MVFR CIG RESTRICTION HAS FINALLY DEVELOPED AND WILL BE 
CARRIED INITIALLY. THE LATEST GUIDANCE SUPPORTS VFR...SO THE 
RESTRICTION WILL ONLY BE TEMPORARY FOR NOW. SW WINDS WILL APPROACH 
10 KNOTS THIS MORNING. ANOTHER ROUND OF CONVECTION WITH POSSIBLE 
RESTRICTIONS IS EXPECTED THIS AFTERNOON AS A COLD FRONT MOVES 
THROUGH FROM THE W... AND ANOTHER APPROACHES FROM THE NW. CONVECTION 
WILL MOVE OFF TO THE EAST BY THIS EVENING....WHILE SW WINDS VEER TO 
NW AND BECOME GUSTY. MODEL TIME HEIGHTS SUGGEST THE A LOW VFR CIG 
WILL PERSIST INTO THIS EVENING.

ELSEWHERE...RESTRICTIONS WILL END BY MID MORNING AS WINDS COME UP 
FROM THE SW IN THE FOOTHILLS AND NW IN THE MOUNTAINS. ADDITIONAL 
CONVECTION AND RESTRICTIONS ARE EXPECTED BY MIDDAY BETWEEN A 
DEPARTING COLD FRONT...AND ANOTHER STRONGER FRONT ARRIVING FROM THE 
NW. WINDS WILL VEER TO THE WEST DURING THE DAY IN THE FOOTHILLS AND 
BECOME GUSTY...VEERING FURTHER TO BECOME NW IN THE EVENING. 
OVERNIGHT PRECIPITATION WILL BE MAINLY CONFINED TO THE MOUNTAINS 
BORDERING TN THIS EVENING IN NW UPSLOPE FLOW.

OUTLOOK...VFR WEATHER FRIDAY AND SATURDAY.

CONFIDENCE TABLE...

            13-19Z        19-01Z        01-07Z        07-13Z 
KCLT       HIGH  97%     HIGH 100%     HIGH 100%     HIGH 100%     
KGSP       HIGH  95%     HIGH 100%     HIGH 100%     HIGH 100%     
KAVL       HIGH  95%     HIGH 100%     HIGH  95%     MED   79%     
KHKY       HIGH  88%     HIGH 100%     HIGH 100%     HIGH 100%     
KGMU       HIGH  95%     HIGH 100%     HIGH 100%     HIGH 100%     
KAND       HIGH  97%     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...RWH
NEAR TERM...JAT/PM
SHORT TERM...RWH
LONG TERM...RWH
AVIATION...JAT