Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 290003
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
803 PM EDT THU MAY 28 2015

.SYNOPSIS...
BERMUDA HIGH PRESSURE WILL PERSIST ACROSS THE REGION THROUGH THE
WEEKEND AND INTO EARLY NEXT WEEK. DEEPER MOISTURE WILL GRADUALLY
POOL ALONG THE SOUTHERN APPALACHIANS IN THE SOUTHERLY FLOW BETWEEN
LOW PRESSURE APPROACHING THE MID MISSISSIPPI VALLEY FROM THE WEST
AND THE OFFSHORE BERMUDA HIGH TO THE EAST. A COLD FRONT WILL PUSH
SOUTHWARD INTO THE REGION AROUND MID WEEK AND THEN LIKELY STALL
NEARBY.

&&

.NEAR TERM /THROUGH FRIDAY/...
745 PM UPDATE...REMAINING CONVECTION MOSTLY PERSISTS ALONG OUTFLOW
BOUNDARIES IN AREAS WHERE INSTABILITY WAS NOT REALIZED DURING THE
AFTERNOON. ONE SUCH BOUNDARY MOVING INTO OUR NC FOOTHILLS AND NW
PIEDMONT CONTINUES TO DRIVE NEW DEVELOPMENT...AND MAY DO SO FOR A
BIT LONGER UNTIL IT REACHES MORE STABLE AIR OVER THE NOW-SOAKED NRN
MTNS. ACTIVITY OVER THE ERN UPSTATE IS LIKELY TO DO THE SAME...AND
SEEMS TO BE ALREADY TRENDING DOWNWARD. NONETHELESS IT STILL APPEARS
THERE IS A CHANCE SOME PRECIP MIGHT OCCUR THRU THE NIGHT NEAR THE
ESCARPMENT GIVEN SE UPSLOPE FLOW. DENSE FOG IS LIKELY TO BECOME AN
ISSUE IN THE AREAS THAT SAW HEAVY RAIN. EVEN BEFORE THE STORMS
FORMED OVER THE NRN FOOTHILLS/PIEDMONT AND I-40 CORRIDOR...GUIDANCE
SUPPORTED SOME FOG DEVELOPMENT THERE AND IN THE MTN VALLEYS. WILL
HAVE TO SEE EXACTLY WHERE THE FOG FORMS BEFORE RAISING ANY HEADLINES.

PREVIOUS DISCUSSION...WHILE COVERAGE OF CONVECTION SHOULD DIMINISH
THIS EVENING...A LIGHT S/SE LOW LEVEL UPSLOPE FLOW AND THE LINGERING
DEEP MOIST PLUME COULD ALLOW AT LEAST ISOLATED CONVECTION COULD
PERSIST FOR MUCH OF THE OVERNIGHT NEAR THE BLUE RIDGE...AND 20-30
POPS WILL BE CARRIED IN THESE AREAS THROUGH THE PERIOD.

FOR FRIDAY...SHORT TERM GUIDANCE INDICATES THE MOIST PLUME WILL LIFT
NORTH AND BECOME DIFFUSE THROUGH THE DAY...AS UPPER SHEAR ZONE/WEAK
TROUGH CONTINUES TO SHEAR OUT. AS SUCH...FORECAST SOUNDINGS ARE
QUITE DRY ACROSS THE FORECAST AREA BY AFTERNOON. IN FACT...SHORT
TERM MODEL QPF RESPONSE AND CONVECTION-ALLOWING MODELS SUGGEST
TOMORROW AFTERNOON WILL BE QUITE INACTIVE. POPS MAY THEREFORE
ACTUALLY PEAK IN THE MORNING HOURS. NEVERTHELESS...MODERATE
INSTABILITY SHOULD SUPPORT AT LEAST ISOLATED CONVECTION ACROSS MUCH
OF THE AREA THROUGH THE AFTERNOON...WHILE THE HIGHEST POPS (ABOUT 50
PERCENT) WILL BE RESERVED FOR THE TENN BORDER COUNTIES...NEARER THE
RETREATING MOIST PLUME.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
AT 200 PM EDT THURSDAY...ON FRIDAY EVENING AN UPPER RIDGE WILL BE
ALONG THE EAST COAST...WHILE AN UPPER TROUGH WILL BE OVER THE
PLAINS. THE TROUGH AXIS SLOWLY PROGRESSES TO THE MS RIVER VALLEY BY
LATE SUNDAY...WHILE THE RIDGE PROGRESSES OFF THE EAST COAST.

AT THE SURFACE...ATLANTIC HIGH PRESSURE REMAINS OVER THE CAROLINAS
AND GA INTO SATURDAY...BUT WITH A WEAKENING TREND AS THE CENTER OF
THE HIGH DRIFTS FARTHER OFFSHORE...AND A COLD FRONT APPROACHES FROM
THE NW. THE MODELS INDICATE A MODEST DECREASE IN LOW LEVEL MOISTURE
OVER MUCH OF OUR AREA FRIDAY NIGHT AND SATURDAY...AS A LEE TROUGH
DEVELOPS IN THE PIEDMONT. AS THE TROUGH APPEARS TO SHIFT EAST ON
SUNDAY...MOISTURE SPREADS ACROSS OUR AREA FROM THE WEST IN ADVANCE
OF THE SLOW MOVING AND WEAKENING COLD FRONT.

THE GREATEST INSTABILITY WILL BE ALONG THE LEE TROUGH IN THE
PIEDMONT...BUT SHEAR APPEARS TO BE QUITE LIMITED. WITH ONLY WEAK
ISENTROPIC UPGLIDE AND UPSLOPE FLOW...PRECIPITATION SHOULD NOT BE
EXCESSIVE OUTSIDE OF LOCALLY ROBUST CONVECTION. TEMPERATURES WILL
RUN SLIGHTLY ABOVE NORMAL.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
AS OF 230 PM THURSDAY...MODELS ARE IN GOOD AGREEMENT AT THE START OF
THE EXTENDED PERIOD. A FRONTAL BOUNDARY WILL HAVE SLOWED ITS
SOUTHEASTWARD MOTION CONSIDERABLY AND BECOME ALMOST STATIONARY OVER
THE SOUTHERN APALACHIANS BY SUNDAY NIGHT...LEADING TO A HEALTHY
INCREASE IN POPS. THE BOUNDARY WASHES OUT SOMEWHAT BUT REMAINS IN
PLACE MONDAY AND TUESDAY...KEEPING POPS ELEVATED THROUGH TUESDAY
NIGHT. A LACK OF SIGNIFICANT UPPER LEVEL FORCING AND SHEAR SHOULD
KEEP THE PROBABLITY OF ORGANIZED SEVERE STORMS RELATIVELY
LOW...THOUGH ISOLATED PULSE-TYPE STRONG TO SEVERE STORMS CAN`T BE
RULED OUT DUE TO MARGINAL INSTABILITY EACH AFTERNOON. WEAK MEAN FLOW
AND POSSIBLE WEAK MECHANICAL UPSLOPE FORCING WILL MAKE LOCALLY HEAVY
RAINFALL THE MAIN THREAT FOR THE EXTENDED PERIOD.

GUIDANCE DIVERGES SOMEWHAT IN THE SECOND HALF OF THE PERIOD...WITH A
SURFACE HIGH EXPANDING OVER THE NORTHEAST AND PUSHING THE NOW
BACKDOOR FRONTAL BOUNDARY OUT OF THE AREA. DUE TO DIFFERENCES IN
MODEL POSITION AND STRENGTH OF A POTENTIAL CUT-OFF UPPER LEVEL LOW
OVER MS/LA...THE 12Z GFS SWEEPS THE BACKDOOR FRONT IN MORE QUICKLY
THAN THE 00Z ECMWF. CONSEQUENTLY THE GFS DISPLAYS A DRIER SOLUTION
FOR WEDNESDAY AND THURSDAY THAN THE WET ECMWF...RESULTING IN POPS
JUST SLIGHTLY ABOVE CLIMO. THE OFFICAL FORECAST IS CLOSER TO A GFS
SOLUTION WITH THE FASTER FRONTAL PASSAGE...BUT THE WETTER/SLOWER
ECMWF BEARS WATCHING UNTIL THE GUIDANCE COMES INTO BETTER AGREEMENT.

MAX TEMPS WILL REMAIN ABOVE CLIMO MONDAY...WITH MIN TEMPS REMAINING
A CATEGORY OR TWO ABOVE AVERAGE. A VERY MOIST AIRMASS AND HEFTY
CLOUD COVER DURING THE SECOND HALF OF THE PERIOD WILL KEEP HIGHS
RIGHT AROUND NORMAL WHILE LIMITING THE DIURNAL TEMPERATURE RANGE
CONSIDERABLY.

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
AT KCLT...THE THREAT OF ANY CONVECTION THIS EVENING IS SMALL...BUT A
CELL OR TWO COULD FIRE ALONG A LEFTOVER OUTFLOW BOUNDARY. HAVE JUST
HANDLED THIS WITH VCSH. LIGHT S TO SE FLOW IN THE BOUNDARY LAYER
COULD BRING IN SOME LOW CLOUDINESS...BUT GUIDANCE MEMBERS SHOWING
RESTRICTIVE CIGS ARE IN THE MINORITY. THIS IS NOT WELL SUPPORTED BY
ANALYSIS OF NAM/GFS PROFILES. WITH MODEST CONFIDENCE HAVE KEPT IT
VFR WITH A MENTION OF SPOTTY LOW VFR CLOUDS OVERNIGHT. DIURNAL CU
JUST ABOVE VFR THRESHOLD WILL FORM MID-MRNG AND THESE WILL PREVAIL
THRU THE DAY. PRECIP CHANCES IN THE EARLY AFTN ARE TOO LOW TO
INCLUDE AT THIS ISSUANCE.

ELSEWHERE...SCT TSRA WILL LINGER NEAR KGSP/KGMU AND OVER KHKY EARLY
THIS EVENING. LIGHT PRECIP IS POSSIBLE AT KAND/KAVL BUT WITH
EXPECTED LOW IMPACT...NO MENTION WAS MADE. WHILE ACTIVITY SHOULD
WANE BY 02-03Z...A PRECIP CHANCE WILL LINGER OVER THE BLUE RIDGE
LATER INTO THE NIGHT. ATTENTION AT THAT TIME TURNS TO LOW CIGS
FORMING IN MOIST SELY FLOW /ESP NEAR THE BLUE RIDGE ESCARPMENT/ AND
FOG...THE LATTER BEING LIKELY WHERE HEAVY RAIN FELL THIS EVENING.
IFR AT KAVL/KHKY. SOUTHERLY FLOW CONTINUES THRU THE DAY TOMORROW
WITH RIDGE BUILDING OVER THE SOUTHEAST. MENTIONABLE DIURNAL PRECIP
CHANCES ARE MAINLY OVER THE MTNS AND FOOTHILLS...WITH PROB30S AT
KAVL/KHKY AND VC WORDING AT KGSP/KGMU.

OUTLOOK...MOIST SW FLOW WILL CONTINUE TO AFFECT THE TERMINAL
FORECAST AREA THROUGH THE UPCOMING WEEKEND...AS A COLD FRONT LAYS
OVER TO THE NORTH OF THE AREA. EXPECT POCKETS OF MORNING FOG AND/OR
STRATUS MOST DAYS...WITH CONTINUED CHANCES OF AFTN/EVENING SHRA/TSRA
EACH DAY.

CONFIDENCE TABLE...

            00-06Z        06-12Z        12-18Z        18-00Z
KCLT       HIGH 100%     HIGH 100%     HIGH  98%     HIGH 100%
KGSP       HIGH 100%     MED   72%     HIGH  92%     HIGH 100%
KAVL       HIGH  97%     HIGH  85%     MED   72%     HIGH  95%
KHKY       HIGH  93%     HIGH  85%     HIGH  88%     HIGH 100%
KGMU       HIGH 100%     MED   74%     HIGH  83%     HIGH 100%
KAND       HIGH  94%     MED   64%     MED   71%     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...JDL/WIMBERLEY
SHORT TERM...JAT
LONG TERM...LEV
AVIATION...WIMBERLEY



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