Area Forecast Discussion
Issued by NWS Greer, SC

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS62 KGSP 221445
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1045 AM EDT TUE JUL 22 2014

.SYNOPSIS...
A WEAK UPPER LOW WILL MOVE AWAY TO THE WEST TODAY WHICH SHOULD ALLOW
FOR A BRIEF RETURN TO MORE TYPICAL SUMMER WEATHER FOR WEDNESDAY.
HOWEVER...A FRONT WILL APPROACH AND MOVE ACROSS THE REGION ON
THURSDAY. THE PASSAGE OF THE FRONT WILL NOT BRING COOLER AIR...BUT
IT SHOULD BRING DRIER AIR FOR FRIDAY AND INTO THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
AT 1030 AM EDT TUESDAY... CUTOFF LOW ALOFT APPEARS TO BE MOVING VERY
SLOWLY WESTWARD PER THE RECENT GUIDANCE. 500 MB CYCLONIC SHEAR AXIS
EXTENDING NORTHEASTWARD FROM THE LOW THROUGH THE COL REGION CROSSES
THE CWA AND WILL ROTATE SLOWLY WESTWARD AROUND THE LOW. 12Z NAM
INDICATES A VERY SUBTLE REGION OF ANTICYCLONIC VORTICITY ADVECTION..
FROM THE EAST FOLLOWING THE SHEAR AXIS... WILL AFFECT THE AREA
DURING THE AFTERNOON. VORTICITY ADVECTION PATTERN AND ONLY MODEST
VALUES OF CAPE SUGGEST AFTERNOON CONVECTIVE STORMS WILL NOT BE
PARTICULARLY ENERGETIC. HOWEVER... MOIST ATMOSPHERE  AND SLOW STORM
MOVEMENT DUE TO WEAK DEEP-LAYER WIND CAN PRODUCE LOCALLY HEAVY
RAIN.DIFFICULT TO PINPOINT DISTRIBUTION OF AFTERNOON SHOWERS AND
THUNDERSTORMS... BUT WESTERN PORTION OF CWA NEAR THE FOOTHILLS AND
MOUNTAINS SEEMS MOST LIKELY FOR BEST COVERAGE.

PREVIOUS DISCUSSION...
AS OF 6 AM...REGIONAL RADAR CONTINUES TO SHOW NUMEROUS AREAS OF
DRIZZLE OR LIGHT RAIN ACROSS THE REGION. A CLUSTER OF SHOWERS ACROSS
THE MIDLANDS EARLY THIS MORNING WAS TRACKING NORTHWEST. THESE
SHOWERS MAY REACH THE I-85 CORRIDOR BY 13Z. I WILL UPDATE THE
FORECAST TO TWEAK POP TIMING AND PLACEMENT. IN ADDITION...I HAVE
POPULATED THE VIS FORECAST WITH A BLEND OF LATEST
GUIDANCE...WEIGHTED TOWARDS THE LAMP.

AS OF 330 AM...RECENT W/V IMAGES INDICATE THAT THE CENTER OF THE MID
LEVEL LOW WAS LOCATED NEAR THE PANHANDLE OF FL. DEEP MOISTURE HAS
SPREAD ACROSS MOST OF THE SOUTHEAST U.S...LIFTING PW UP TO 2
INCHES...OR 125 PERCENT OF NORMAL. FORECAST SOUNDINGS SHOW THAT DEEP
SKINNY CAPE WILL EXIST ACROSS THE REGION TODAY...WITH CAPE VALUES
AROUND 1000 J/KG. THE COMBINATION OF WEAK ISENTROPIC LIFT...EAST H85
WINDS...AND LFC BETWEEN 3-4 KFT SHOULD RESULT SCT TO NUMEROUS
SHOWERS AND THUNDERSTORMS TODAY. STORM MOTIONS WILL LIKELY REMAIN
LESS THAN 10M/S. HEAVY DOWNPOURS AND CLOUD TO GROUND LIGHTNING WILL
BE THE PRIMARY THREATS. OVERCAST TO MOSTLY CLOUDY SKY AND PERIODS OF
RAIN SHOULD LIMIT HEATING TODAY. HIGH TEMPERATURES ARE FORECAST TO
RANGE FROM THE U70S WITHIN THE MTN VALLEYS TO THE LOW 80S EAST.

TONIGHT...NEAR TERM MODELS INDICATE THAT THE MID LEVEL LOW WILL
TRACK WEST...ALLOWING HEIGHTS TO RISE ACROSS THE FORECAST AREA. H85
WINDS WILL VEER FROM THE SW...RESULTING IN DOWNSLOPE FLOW ACROSS THE
FOOTHILLS AND ENDING LLVL ISENTROPIC LIFT. POPS WILL QUICKLY
DECREASE AFTER SUNSET...FALLING TO SCHC LATE TONIGHT. LOW
TEMPERATURES WILL REMAIN NEAR NORMAL.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
AS OF 230 AM EDT TUESDAY...IT LOOKS LIKE A TRANSITION OF SORTS WILL
BE COMPLETE BY WEDNESDAY MORNING...AS THE WEAK UPPER LOW WILL HAVE
RETROGRADED FAR ENOUGH FOR THE CYCLONIC FLOW TO HAVE MOVED WEST OF
THE FCST AREA. THAT WILL BRING THE FLOW AROUND TO SOMETHING MORE SW
TO W FOR THE FIRST PART OF THE SHORT RANGE...WITH STILL PLENTY OF
LOW LEVEL MOISTURE REMAINING TO FUEL DIURNAL SHOWERS AND
THUNDERSTORMS. AM A BIT SURPRISED WITH THE LACK OF COVERAGE IN THE
NAM SOLUTION FOR WEDNESDAY AFTERNOON/EVENING AND THINK THAT THE
ENTIRE FCST AREA WILL SEE SCATTERED STORMS...SO THE FCST STAYS MORE
IN LINE WITH THE GREATER COVERAGE SEEN ON THE GFS. EXPECT MOST OF
THE ACTIVITY TO WEAKEN/END GRADUALLY WITH LOSS OF HEATING WEDNESDAY
NIGHT E OF THE MTNS...BUT BY THEN A COLD FRONT WILL APPROACH FROM
THE NW WHICH WARRANTS KEEPING THE CHANCE POP OVERNIGHT OVER THE
MTNS. THE NEW GUIDANCE SHOWS A STRONGER PUSH BY A SHORT WAVE HELPING
TO CARVE OUT A NEW EASTERN UPPER TROF ON THURSDAY. THIS FEATURE IS
NOW EXPECTED TO PUSH THE COLD FRONT ALL THE WAY THROUGH THE FCST
AREA THURSDAY AFTERNOON AND EVENING...BUT THE PROBLEM NOW IS THE
TIMING. THE NAM BRINGS IT THROUGH EARLIER AND DRIVES THE FRONT
FARTHER S THAN THE OTHER GUIDANCE. THE FRONT APPEARS A BIT STRONGER
WHICH MAKES ME THINK WE ARE LIKELY TO SEE SHOWERS AND STORMS OVER
MOST OF THE FCST AREA...HOWEVER...UNCERTAINTY ABOUT WHEN THE MOST
LIKELY TIME OF THE STORMS WILL BE ACTUALLY RESULTS IN A SLIGHT
DECREASE IN THE PRECIP PROBABILITY FOR THE DAY AS A WHOLE. ONCE THE
TIMING IS MORE CERTAIN...EXPECT THIS TO CREEP BACK TOWARD THE LIKELY
CATEGORY. THE PRECIP CHANCES SHOULD SLOWLY DIMINISH AND PUSH OFF TO
THE S THROUGH EARLY FRIDAY MORNING. TEMPS WILL ALSO COOL DOWN A BIT
THURSDAY NIGHT AS DRY AIR COMES IN BEHIND THE FRONT.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
AS OF 315 AM TUESDAY...THE NEW GUIDANCE FOR THE START OF THE MEDIUM
RANGE CONFIRMS THAT THE SURFACE FRONT WILL PROBABLY BE DRIVEN SOUTH
OF THE FCST AREA BY FRIDAY MORNING GIVING US A CLEANER FRONTAL
PASSAGE THAN EARLIER THOUGHT. WITH THIS TREND ESTABLISHED IN THE
GUIDANCE...THE PRECIP CHANCES WERE LOWERED INITIALLY ON FRIDAY.
HOWEVER...IT IS HARD TO RULE OUT SOME SHOWER ACTIVITY BEHIND THE
FRONT ON FRIDAY AFTERNOON AS THERE DOES NOT APPEAR TO BE ENUF TO
SUPPRESS DEEP CONVECTION...SO A SLIGHT CHANCE WAS KEPT OVER MOST OF
THE FCST AREA PER THE MOSGUIDE...WITH A CHANCE ON THE SE FRINGE.
TEMPS WILL NOT DROP MUCH AT ALL BEHIND THE FRONT...BUT HOPEFULLY
THERE WILL BE ENUF DROP IN THE DEWPOINT TO MAKE THE RH FALL. NO
OTHER CHANGES WERE MADE TO THE MEDIUM RANGE. THE GFS SUGGESTS SOME
MCS-LIKE ACTIVITY MOVING IN FROM THE WEST ON SUNDAY BUT CONFIDENCE
IN THAT IS LOW. THERE IS DECENT AGREEMENT BETWEEN THE GFS AND ECMWF
WITH THE PASSAGE OF ANOTHER FRONT NEXT MONDAY...SO WE WILL CONTINUE
TO FEATURE THE HIGHEST PRECIP CHANCES IN THE MEDIUM RANGE ON THAT
DAY.

&&

.AVIATION /15Z TUESDAY THROUGH SATURDAY/...
AT KCLT...CEILING RESTRICTION IN LOW STRATUS HAS BEEN IMPROVING AT
REGIONAL AIRFIELDS. SEE NO REASON NOT TO EXPECT IMPROVEMENT AT KCLT
IN THE 15Z TO 17Z TIME FRAME AS BOUNDARY LAYER STEADILY WARMS AND
MIXING OCCURS. THE MOST RECENT LAMP FITS THIS IMPROVING
TREND... SO PLAN TO CONTINUE FORECAST OF CLOUDS BECOMING MORE
CONVECTIVE IN NATURE WITH BASES 3-5K FT BY 19Z. VISIBILITY WILL BE
GENERALLY UNRESTRICTED... BUT LOCAL CEILING AND VISIBILITY
RESTRICTIONS ARE POSSIBLE IN SCATTERED SHOWERS AND ISOLATED
THUNDERSTORMS PRIMARILY BETWEEN 21Z AND 00Z. SURFACE WIND SHOULD
FAVOR A NORTHEAST DIRECTION AT SPEED OF LESS THAN 10 KT. SURFACE
PRESSURE GRADIENT IS RATHER WEAK... SO WIND CAN BE LIGHT AND
VARIABLE AT TIMES. OVERNIGHT... EXPECT NO SIGNIFICANT CLOUDS OR
WEATHER ALTHOUGH VISIBILITY AROUND 5 MILES IN FOG POSSIBLE TOWARD
SUNRISE. CONFIDENCE RATHER LOW AT THIS TIME... SO NOT INCLUDED IN
TAF.

ELSEWHERE... BOUNDARY LAYER WARMING AT ALL SITES WILL RESULT IN
LIFTING OF REMAINING LOW MORNING STRATUS THROUGH 16Z. BY 18Z...
CLOUDS WILL BE MOSTLY CONVECTIVE IN NATURE WITH BASES NEAR 3-4K FT.
VISIBILITY GENERALLY UNRESTRICTED BUT LOCAL RESTRICTIONS IN
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS WILL OCCUR AFTER 18Z.
CONVECTIVE STORMS WILL DIMINISH AFTER 00Z. LOW CLOUDS AND FOG MAY
DEVELOP ACROSS THE REGION LATE TONIGHT.

OUTLOOK...A GRADUAL RETURN TO A MORE TYPICAL PATTERN WITH DIURNAL
SHOWERS AND STORMS IS EXPECTED WEDNESDAY. A FRONTAL SYSTEM
APPROACHING FROM THE NORTHWEST WILL CROSS THE REGION THURSDAY
NIGHT...BRINGING STRONGER CONVECTION AND POSSIBLE FLIGHT
RESTRICTIONS THROUGH FRIDAY.

CONFIDENCE TABLE...

            14-20Z        20-02Z        02-08Z        08-14Z
KCLT       HIGH  87%     HIGH 100%     HIGH  98%     HIGH  85%
KGSP       HIGH  89%     HIGH  98%     HIGH  98%     HIGH  96%
KAVL       HIGH  85%     HIGH  95%     MED   74%     HIGH  83%
KHKY       HIGH  83%     HIGH  99%     HIGH  84%     HIGH  91%
KGMU       HIGH  87%     HIGH 100%     HIGH  98%     HIGH  96%
KAND       HIGH  83%     HIGH  98%     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...PM
NEAR TERM...LGL/NED
SHORT TERM...PM
LONG TERM...PM
AVIATION...LGL/NED





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.