Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 221751
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
151 PM EDT TUE JUL 22 2014

.SYNOPSIS...
EXPECT A BRIEF RETURN TO MORE TYPICAL SUMMER WEATHER ON WEDNESDAY
BEFORE A FRONT APPROACHES AND MOVES 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 145 PM EDT TUESDAY... NO MAJOR CHANGES TO THE FORECAST FOR THE
REST OF THE AFTERNOON.

PREVIOUS DISCUSSIONS...
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.

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 200 PM EDT TUESDAY...ALL NUMERICAL GUIDANCE IS FORECASTING A
STRONG SHORT WAVE TO MOVE THROUGH THE GREAT LAKES WED NIGHT INTO THU
WHICH WILL DRIVE A SURFACE COLD FRONT SOUTHEASTWARD INTO THE
SOUTHEAST STATES. THE NAM AND GFS HAVE SETTLED INTO SIMILAR TIMING
IN REGARD TO THE FRONT WITH BOTH MODELS BRINGING IT TO JUST NW OF
THE NC MOUNTAINS BY 12Z THU...AND THEN BRINGING IT ACROSS THE
MOUNTAINS INTO THE LOWER PIEMDONT BY THURSDAY EVENING. THE FRONT IS
THEN FORECAST TO CLEAR THE AREA BY MIDNIGHT. A DRYER AND MORE STABLE
AIR MASS IS EXPECTED TO OVERSPREAD THE AREA ON FRIDAY AS HIGH
PRESSURE RIDGES SOUTHEASTWARD FROM THE OHIO VALLEY.

IN REGARD TO SENSIBLE WEATHER...SOME LINGERING SHOWERS AND STORMS
MAY BE OVER THE AREA WED EVENING...BUT THEY SHOULD DISSIPATE WITH
LOSS OF HEATING WED NIGHT. HOWEVER...WILL NEED TO RAMP POPS UPWARD
LATE THURSDAY NIGHT AS SOME PREFRONTAL SHOWERS MAY REACH THE
MOUNTAINS BY SUNRISE THURSDAY. WILL CONTINUE TO ADVERTISE LIKELY
POPS IN THE MOUNTAINS ON THU...BUT CONVECTION SHOULD BE SCATTERED
OUTSIDE OF THE MOUNTAINS AS WINDS IN PROFILES ARE DECIDELY DOWNSLOPE
IN NATURE. HOWEVER..THERE SHOULD BE PLENTY OF INSTABILITY WITH CAPES
POOLING TO 1500-2000J OVER THE PIEMDONT. HENCE...A FEW SEVERE STORMS
ARE POSSIBLE. WILL FORECAST DECREASING POPS THU NIGHT AND THEN A DRY
DAY ON FRI. MAX TEMPS WILL BE BELOW CLIMO BOTH THU AND FRI IN THE
MOUNTAINS...BUT NEAR CLIMO OUTSIDE THE MOUNTAINSON THU AND THEN
ABOUT A CATEGORY BELOW CLIMO ON FRIDAY.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
AS OF 215 PM TUESDAY...THE MEDIUM RANGE GUIDANCE SUGGESTS THAT THE
EASTERN U.S. TROUGH WILL FLATTEN AS HEIGHTS RISE IN RESPONSE TO
ANOTHER STRONG UPPER WAVE DIGGING INTO THE NORTHERN PLAINS OVER THE
WEEKEND. THIS WAVE IS FORECAST TO SWING ACROSS THE GREAT LAKES AND
RE-ESTABLISH THE EASTERN U.S TROUGH BY MONDAY.

LOOKS LIKE WE SHOULD BE ABLE TO SQUEEZE OUT ONE MORE NICE DAY ON
SATURDAY BEHIND THE THURSDAY FRONTAL PASSAGE AS HIGH PRESSURE
REMAINS WEEKLY RIDGED OVER THE AREA AND MOISTURE LEVELS REMAIN
RELATIVELY LOW. HOWEVER...IT LOOKS LIKE THE FIRST PART OF NEXT
WEEK WILL TURN STORMY. ALL THE MEDIUM RANGE MODELS HINT AT A
POSSIBLE MCS MAKING A RUN AT THE SOUTHERN APPALACHIANS ON SUNDAY. IT
IS DIFFICULT TO SAY WHETHER ANY OF THE PARENT STORMS WILL MAKE IT
ACROSS THE MOUNTAINS...BUT THE OUTFLOW MAY TRIGGER ADDITIONAL STORMS
ACROSS THE PIEDMONT SUNDAY AFTERNOON AND NIGHT. ALSO..AS THE UPPER
TROUGH DIGS OVER THE GREAT LAKES EARLY NEXT WEEK A COLD FRONT IS
FORECAST TO ARRIVE ON MONDAY PROVIDING THE TRIGGER FOR MORE
THUNDERSTORMS. SEVERE STORMS ARE A POSSIBILITY FROM SUNDAY INTO
MONDAY.

THE FRONT IS FORECAST TO CLEAR THE AREA MONDAY NIGHT WHICH SHOULD
ALLOW FOR DRYER AND MORE STABLE AIR TO OVERSPREAD THE AREA FROM THE
NW ON TUESDAY. MAX TEMPS ARE FORECAST TO BE NEAR OR EVEN SLIGHTLY
ABOVE CLIMO SAT THROUGH MONDAY...AND THEN BELOW CLIMO ON TUE BEHIND
THE COLD FRONT

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
AT KCLT... EXTENSIVE CLOUD COVER WILL CONTINUE ACROSS THE AERODROME
AND VICINITY INTO THE EVENING... HOWEVER THE EARLIER STRATUS LAYER
HAS EVOLVED INTO A CUMULUS AND STRATOCUMULUS CLOUD FIELD WITH BASES
NEAR 4K FT. VISIBILITY WILL REMAIN UNRESTRICTED EXCEPT IN SCATTERED
SHOWERS AND ISOLATED THUNDERSTORMS PRIMARILY BETWEEN 21Z AND 00Z.
OVERNIGHT CONVECTIVE CLOUDS WILL DIMINISH AND GIVE WAY TO MORE
STRATIFORM SCATTERED TO BROKEN CLOUD WITH BASES 1-2K FT. OVERNIGHT
VISIBILITY WILL LOWER TO NEAR 5 MILES IN FOG AND HAZE VICINITY
KCLT... BUT CONFIDENCE NOT YET SUFFICIENT TO FORECAST SIGNIFICANT
RESTRICTIONS TOWARD DAYBREAK. NEITHER THE NAM MOS OR NGM MOS
INDICATE A PROLONGED PERIOD OF LOW CEILING OR VISIBILITY AT THIS
TIME. LATEST GFS LAMP POINTS TOWARD MVFR CEILING AND VISIBILITY FROM
09Z TO 12Z. AFTER 13Z WEDNESDAY... VISIBILITY WILL BECOME
UNRESTRICTED SURFACE HEATING WILL PRODUCE CUMULUS CLOUDS WITH BASES
NEAR 4K FT.

ELSEWHERE... CUMULUS AND STRATOCUMULUS CLOUD BASES 3-5K FT WILL
PERSIST INTO THE EVENING. NO RESTRICTIONS EXCEPT IN SCATTERED RAIN
SHOWERS AND ISOLATED THUNDERSTORMS THROUGH APPROXIMATELY 02Z.
OVERNIGHT... CONVECTIVE CLOUD WILL EVOLVE TO SCATTERED TO BROKEN
STRATUS WITH BASES 1-2K FT. AREAS OF FOG WITH VISIBILITY NEAR 1 MILE
MOST LIKELY AT KAVL. AFTER 14Z VISIBILITY WILL BECOME UNRESTRICTED
AND SURFACE HEARING WILL PRODUCE CUMULUS CLOUDS WITH BASES NEAR 4K
FT.

OUTLOOK... SHOWERS AND THUNDERSTORMS THURSDAY WITH THE PASSAGE OF A
COLD FRONT THURSDAY. SCATTERED SHOWERS AND THUNDERSTORMS MAINLY
DURING THE AFTERNOONS AND EVENINGS THROUGH THE END OF THE WEEK.

CONFIDENCE TABLE...

            17-23Z        23-05Z        05-11Z        11-17Z
KCLT       HIGH  95%     HIGH 100%     HIGH  98%     HIGH  93%
KGSP       HIGH  94%     HIGH 100%     HIGH  95%     HIGH  86%
KAVL       HIGH  97%     HIGH  98%     MED   65%     MED   75%
KHKY       HIGH  86%     HIGH 100%     HIGH  97%     HIGH  97%
KGMU       HIGH  94%     HIGH 100%     HIGH  96%     HIGH  95%
KAND       HIGH  82%     HIGH  94%     HIGH  91%     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
SHORT TERM...PM
LONG TERM...PM
AVIATION...LGL





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