Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 221613
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1213 PM EDT TUE APR 22 2014

.SYNOPSIS...
A COLD FRONT WILL CROSS THE REGION FROM THE WEST TODAY. DRY HIGH
PRESSURE WILL THEN RETURN WEDNESDAY THROUGH THURSDAY. A WEAK COLD
FRONT WILL MOVE THROUGH THE AREA ON FRIDAY...WITH A REINFORCING
FRONT STALLING TO THE NORTH OF THE AREA OVER THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF NOON...LATEST MESOSCALE ANALYSIS INDICATES THAT WEAK CAPE HAS
DEVELOPED ACROSS THE UPPER SAVANNAH RIVER VALLEY AND UPSTATE...WITH
SHALLOW CIN ACROSS THE MAJORITY OF THE NC ZONES. RECENT RADAR
INDICATED THAT SHRA WERE DRIFTING EAST ACROSS THE MTNS. I WILL
UPDATE THE FORECAST TO FINE TUNE POPS INTO THIS EVENING. IN
ADDITION...TEMPS UNDER LIMITED CLOUD COVER HAVE SURGED WELL ABOVE
THE FORECAST...I WILL UPDATE TO AGREE WITH OBS AND LATEST MOS.

AS OF 940 AM...SUNNY CONDITIONS EAST OF THE MTNS HAVE RESULTED IN
RAPID WARMING THIS MORNING. KGSP LATEST READING WAS 70 DEGREES. I
WILL ISSUE A QUICK UPDATE TO ADJUST SKY TO SATELLITE OBSERVATIONS. I
WILL ALSO UPDATE TEMPERATURE AND DEWPOINTS TO ALIGN WITH RECENT OBS
TRENDS. POPS APPEAR ON TRACK.

AS OF 645 AM...SHWRS ARE JUST ENTERING WESTERN GRAHAM COUNTY ON
SCHEDULE...ALTHO THEY ARE VERY LIGHT PER MRX RADAR. MID CLOUDS
AROUND 10000 FT ARE INCREASING IN COVERAGE ACRS THE MTNS AND
ADJACENT FOOTHILLS EARLIER THAN EXPECTED. THEY ARE STILL SPLOTCHY IN
NATURE ON IR SAT IMAGERY...SO NOT SURE HOW MUCH IMPACT THEY WILL
HAVE ON DAYTIME HEATING/MAX TEMPS AND RESULTANT SBCAPE THIS AFTN.
WITH PREVIOUS UPDATE I BLENDED IN CONSHORT TEMP GRIDS...WHICH
RATCHETED BACK MAX TEMPS ACRS THE WRN 2/3RDS OF THE CWFA FOR THIS
AFTN. CONFIDENCE IN ROBUST CONVECTION AND SEVERE THIS AFTN IS
DECREASING BASED ON THESE TRENDS.

AS OF 500 AM...FOR THE 0830 UTC UPDATE...I TWEAKED TEMP/DWPT TO
MATCH UP WITH LATEST OBS. THE RADAR MOSAIC SHOWS AN AREA OF SHOWERS
CROSSING CENTRAL TN AND NRN AL. THE LEADING EDGE LOOKS TO REACH THE
SMOKIES AROUND 7 AM. THE POPS LOOK ON TARGET...BUT IF THE COVERAGE
CONTINUES TO BE AS HIGH AS IT IS NOW...I MAY BUMP THEM UP A LITTLE
WITH NEXT UPDATE.

AS OF 245 AM...A FULL LATITUDINAL TROF WITH SEVERAL EMBEDDED VORT
MAXES WILL CROSS THE CWFA TODAY. ONE OF THE LEADING VORT MAXES IS
ALREADY CROSSING THE AREA EARLY THIS MORNING...WITH INCREASING
MID-HIGH CLOUDINESS. AT THE SFC...A COLD FRONT IS CURRENTLY ENTERING
THE OH VLY...AND WILL CROSS THE AREA THIS EVENING. DISORGANIZED
PRE-FRONTAL SHOWERS ACRS THE OH/TN VLYS SHUD START TO ENTER THE NC
MTNS RIGHT AROUND DAYBREAK THIS MORNING.

FOR TODAY...GUIDANCE SEEMS TO BE BACKING OFF POPS A TAD...WHICH
ISN/T TOO SURPRISING...AS LLVL FLOW VEERS TO WLY BEFORE THE FRONT
ARRIVES. THERE IS SOME Q-VECTOR CONVERGENCE AND UPR JET DIVERGENCE
AROUND 18Z ACRS WRN NC. BUT EVEN THAT IS NOT THAT IMPRESSIVE IN ANY
OF THE PROGS. BLENDING IN THE 00Z NAM/GFS...I ACTUALLY GET A
DECREASE IN POPS EAST OF THE MTNS...IN THE HIGH-END CHC TO LOW-END
LIKELY RANGE. TEMPS SHUD BE ABLE TO WARM INTO THE MID-UPR 70S.
HOWEVER...WITH LEADING SHORTWAVE ENERGY WORKING IN THIS
MORNING...MID LVL CLOUDINESS MAY HAMPER DIURNAL HEATING SOMEWHAT. AS
FOR SEVERE POTENTIAL...IT STILL DOES NOT LOOK GOOD. FCST SNDGS SHOW
MOIST MID LVLS WITH WEAK LAPSE RATES AND GENERALLY LESS THAN 25 KTS
OF 0-6KM BULK SHEAR. HIGH RES MODELS SHOW SORT OF SHOTGUN CONVECTIVE
COVERAGE WITH A FEW STRONGER CELLS...PRIMARILY ACRS THE NC PIEDMONT.
SO I THINK WE WILL SEE MAINLY SCATTERED TO NUMEROUS SHWRS WITH
SCATTERED TSTMS...A FEW OF WHICH MAY APPROACH SEVERE LIMITS IF WE
CAN MANAGE TO DESTABILIZE TO 1500-2000 J/KG OF SBCAPE (AS THE GFS
SHOWS). BUT THE GFS SEEMS TOO HIGH WITH SFC DWPTS ACRS MUCH OF THE
WARM SECTOR...SO MAY BE AN OUTLIER. THE NEW DAY ONE CONVECTIVE
OUTLOOK STILL HAS ONLY GENERAL THUNDER TODAY ACRS THE REGION. WILL
MENTION THUNDER THREAT IN THE HWO...BUT IF ANY MENTION OF
SEVERE...JUST THAT IT CANNOT BE RULED OUT.

TONIGHT...GUIDANCE IN GOOD AGREEMENT ON DRY AIR AND CAA WORKING INTO
THE AREA QUICKLY THIS EVENING. SO POPS PRETTY MUCH END BY 00Z THIS
EVENING...SAVE FOR A FEW SHWRS LINGERING ALONG THE TN/NC BORDER WITH
HELP FROM NW UPSLOPE FLOW. FLOW STRENGTHENS TO 40-50 KTS AT 850 MB
IN THE NC MTNS WITH A STRONG BUT LOW INVERSION...HELPING PRODUCE
STRONG CHANNELED VALLEY WINDS. RIGHT NOW...IT LOOKS LIKE WINDS SHUD
GENERALLY STAY SUB-ADVISORY LEVELS. TEMPS SHUD BE ABLE TO FALL INTO
THE UPR 30S TO LWR 40S IN THE MTNS AND MID-UPR 40S ACRS THE PIEDMONT
BEHIND THE FRONT.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
AS OF 225 AM TUESDAY...DRY HIGH PRESSURE WILL BEGIN TO BUILD DOWN
OVER THE FORECAST AREA ON WEDNESDAY...WITH RESIDUAL BRISK NW FLOW
LINGERING THROUGH AT LEAST THE MORNING HOURS. THERE IS SOME
POTENTIAL FOR AN OROGRAPHICALLY INDUCED CIRRUS SHIELD TO FORM IN THE
MTN WAVE FLOW OVER WRN NC WED MORNING...BUT UPSTREAM MOISTURE
REMAINS A QUESTION MARK. OTHERWISE...EXPECT DRY CONDITIONS WED WITH
MAX TEMPS NEAR CLIMO IN THE SRN TIER AND ONE TO TWO CATEGORIES BELOW
NORMAL IN THE NRN TIER.

FLAT UPPER RIDGING WILL THEN BUILD IN FROM THE WEST LATE WED AND
LINGER THROUGH THU. SPOTTY 30S FOR OVERNIGHT LOWS WILL BE POSSIBLE
IN THE NC MTNS THU MORNING WITH GOOD RADIATION...BUT WITH TEMPS
PROBABLY A LITTLE TOO WARM FOR FROST. RETURN FLOW MOISTURE WILL
START TO SET UP FROM THE SW THU AFTN AND EVENING. THIS MIGHT
CONTRIBUTE A FEW MORE CLOUDS...BUT POPS STILL LOOK UNLIKELY. TEMPS
WILL HOVER NEAR CLIMATE NORMS.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
AS OF 230 AM EDT TUESDAY...A DEAMPLIFYING SHORTWAVE WILL CROSS THE
REGION EARLY FRI. THE ASSOCIATED SFC FRONT/TROUGH SHOULD ALSO CROSS
THE REGION BY EARLY AFTN...WITH THIS TIMING LIMITING INSTABILITY
SOMEWHAT. HOWEVER...ANY SLOWING OF THE FORWARD PROGRESS OF THE WEAK
FROPA COULD ALLOW CONVECTION TO CONTINUE THROUGH MID AFTN...WHEN SFC
BASED CAPE VALUES SHOULD BE 1000 TO 1500 J/KG ALONG THE SE PIEDMONT.
WILL FEATURE CHANCE POPS THROUGHOUT FOR SHOWERS AND THUNDERSTORMS
BUT SEVERE WEATHER PROBABILITIES REMAIN LOW.

A BROAD UPPER RIDGE SHOULD BE IN PLACE OVER THE SE THROUGH THE
WEEKEND. UNDER THE RIDGE...A BACKDOOR SFC COLD FRONT WILL STALL
NORTH OF THE FORECAST AREA SAT INTO SAT NIGHT. THIS WILL KEEP THE
REGION IN THE WARM SECTOR SUN THROUGH MON AS LOW PRES RIDES EAST
ALONG THE STALLED BOUNDARY TOWARD THE APPALACHIANS. DIURNAL SHOWER
CHANCES WILL STEADILY INCREASE SUNDAY THROUGH MONDAY AS MOISTURE AND
INSTABILITY BUILD IN THE SW FLOW.

&&

.AVIATION /16Z TUESDAY THROUGH SATURDAY/...
KCLT...THE MAIN CONCERN FOR THE 12Z TAFS WILL BE CONVECTION THIS
AFTN AHEAD OF AN APPROACHING COLD FRONT. GUIDANCE IN DECENT
AGREEMENT ON SCATTERED TO NUMEROUS SHRA ACROSS THE REGION FROM ABOUT
18Z TO 23Z...WITH AT LEAST A CHC OF TSTMS. SO WILL GO WITH
PREVAILING SHRA AND TEMPO TSRA FROM 19-22Z WHICH IS THE TIME FRAME
OF BEST CHC. THE BASES OF THE CLOUDS ARE HIGH (AROUND 7000-9000
FT)...SO EVEN ORDINARY SHRA MAY PRODUCE GUSTY WINDS. WILL INCLUDE
GUSTS IN THE TEMPO. OTHERWISE...GENERALLY BKN070-100 WITH A WSW WIND
(EXCEPT IN CONVECTION). THE ACTUAL FRONT SHUD PUSH THRU THIS EVENING
AFTER THE SHRA HAVE PUSHED OFF TO THE EAST...SO WIND DIR IS LOW
CONFIDENCE UNTIL THE FRONT IS THRU (AROUND 5Z WITH A NW WIND). SKIES
WILL CLEAR OUT...BUT OROGRAPHIC CIRRUS MAY DEVELOP AS UPPER JET
NOSES IN FROM THE NW TOWARD DAYBREAK WEDNESDAY.

ELSEWHERE...STILL LITTLE CHANGE IN THINKING FOR THE 12Z TAFS.
SCATTERED TO NUMEROUS SHRA EXPECTED WITH JUST A FEW EMBEDDED TSTMS
PRIMARILY ACRS THE PIEDMONT THIS AFTN. OTHER THAN A DIRECT IMPACT
FROM SHRA/TSRA...EXPECT VFR CONDITIONS WITH WSW WIND INCREASING TO
ABOUT 8-10 KTS. CONVECTION WILL EXIT TO THE EAST QUICKLY THIS
EVENING...THEN THE SFC COLD FRONT WILL PUSH THRU...CLEARING OUT THE
SKIES AND SWITCHING THE WINDS TO NW. WINDS MAY GET GUSTY AT KAVL
BEFORE DAYBREAK WEDNESDAY...AS PROFILES SUPPORT STRONG CHANNELED
VALLEY WINDS IN NW FLOW.

OUTLOOK...DRY HIGH PRES RETURNS FOR WEDNESDAY/THURSDAY. ANOTHER COLD
FRONT WITH POTENTIAL FOR SHOWERS/TSTMS IS THEN EXPECTED TO CROSS THE
REGION FRIDAY.

CONFIDENCE TABLE...

            16-22Z        22-04Z        04-10Z        10-16Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     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...HG
NEAR TERM...ARK/NED
SHORT TERM...HG
LONG TERM...HG
AVIATION...ARK






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