Area Forecast Discussion
Issued by NWS Greer, SC

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442
FXUS62 KGSP 181454
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1054 AM EDT MON MAY 18 2015

.SYNOPSIS...
BERMUDA HIGH PRESSURE WILL PERSIST OVER THE REGION TODAY...WITH
SCATTERED AFTERNOON SHOWERS AND THUNDERSTORMS EXPECTED. A COLD FRONT
WILL MOVE SLOWLY SOUTHEAST OVER THE AREA THROUGH TUESDAY
NIGHT...BRINGING INCREASED PRECIPITATION CHANCES TO THE REGION.
SLIGHTLY COOLER AND DRIER HIGH PRESSURE WILL RETURN ON
WEDNESDAY...BUT WITH SOMEWHAT UNSETTLED WEATHER LINGERING THROUGH
LATE WEEK AS WAVES OF LOW PRESSURE RETURN ALONG THE FRONTAL ZONE.
DRIER HIGH PRESSURE WILL SET UP OVER THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 1030 AM...DEEPER CONVECTION ACRS THE NORTH GEORGIA MOUNTAINS
GETTING AN EARLY START TODAY WITHIN THE ABOVE CLIMO PWAT REGIME.
WITHIN THE STEADILY EXPANDING...BUT GENERALLY WEAK INSTABILITY
AXIS...CVRG SHOULD INCREASE ACRS THE MOUNTAINS OF THE CWFA BECOMING
NUMEROUS...AND EVENTUALLY SCATTERED TSTMS SHOULD BE SEEN IN THE
PIEDMONT LATER TODAY. STEERING FLOW IS STILL WEAK BUT EXHIBITING
SOME MOTION 10-15 KTS...SO ANYTHING MORE THAN AN ISOLATED EXCESSIVE
RAINFALL RISK IS DOUBTFUL.

AS OF 645 AM...A FEW LIGHT SHOWERS CONTINUE THE NRN NC MTNS AND
ADJACENT FOOTHILLS/PIEDMONT. THESE SEEM TO BE THE RESULT OF A SLIGHT
MTN LEE TROUGH WHICH IS CREATING ENOUGH CONVERGENCE TO TOSS UP A FEW
PARCELS. WILL MAINTAIN A MINOR PRECIP MENTION FOR THESE
SHOWERS...WHICH BLENDS INTO THE DIURNALLY DRIVEN POPS LATER IN THE
MRNG. FEELING A LITTLE MORE CONFIDENT ON FOG IN THE MTNS AND
VICINITY TONIGHT...BUT WIDESPREAD DENSE FOG IS NOT EXPECTED WHERE
RAIN DOES NOT FALL.

TODAY THE THE SERN STATES WILL REMAIN UNDER THE INFLUENCE OF
OFFSHORE HIGH PRESSURE AND RELATIVELY WEAK FORCING. A COLD FRONT
ASSOCIATED WITH LOW PRESSURE CROSSING THE GREAT LAKES WILL PROGRESS
ACRS THE WRN HALF OF THE MISSISSIPPI VALLEY...BUT ANY APPRECIABLE
CONVERGENCE WILL REMAIN WELL TO OUR WEST. HOWEVER AS THE LOW MOVES
EWD IT WILL WEAKEN THE DEEP RIDGE PRESENT OVER THE EAST
COAST...CREATING SLIGHTLY BETTER LAPSE RATES ALOFT AND ALLOWING THE
AREA TO DESTABILIZE MORE THAN THE PAST COUPLE OF DAYS. THIS IS
ESPECIALLY TRUE OVER THE PIEDMONT WHICH WAS SEEMINGLY KEPT CAPPED BY
THE RIDGE. SHEAR WILL CONTINUE TO BE WEAK AND NOT ENOUGH TO ALLOW
FOR ORGANIZED CONVECTION...AND THE COLUMN LOOKS A BIT TOO MOIST TO
EXPECT A SIGNIFICANT DOWNBURST THREAT. HEAVY RAIN WILL CERTAINLY BE
A CONCERN GIVEN SLOW STORM MOTION. AS FAR AS POP TRENDS...A NOTABLE
CONSENSUS BETWEEN MESO MODELS IS THEIR EXPECTATION THAT CONVECTION
WILL FIRE A LITTLE BEFORE NOON NEAR THE BLUE RIDGE...BUT BASICALLY
DIMINISH IN PLACE OVER THE FOLLOWING 3-4 HRS. THE FOCUS GRADUALLY
SHIFTS TO THE PIEDMONT AS THAT AREA TOWARD THE PEAK IN HEATING...BUT
THE MTNS SEE A DROP IN ACTIVITY. IN THE FCST I MERGED THIS IDEA WITH
A CLIMO TYPE TREND. MAX TEMPS ARE EXPECTED TO EDGE A BIT WARMER THAN
SUNDAY...SEVERAL DEGREES ABOVE NORMAL.

CONVECTION WILL GENERALLY WANE IN THE EVENING WITH THE FRONT STILL
WEST OF THE MTNS...BUT THERE IS A CHANCE SOME OUTFLOW BOUNDARIES MAY
ENTER FROM TN/GA AND KICK OFF SOME ACTIVITY OVER THE WRN THIRD OF
THE CWFA. FURTHERMORE...INCREASING MOISTURE AND NWLY UPSLOPE FLOW
WARRANTS CHC POPS REMAINING OR EVEN SLOWLY INCREASING NEAR THE TENN
BORDER TOWARD DAWN TUE. MIN TEMPS WILL BE 7-10 DEGREES ABOVE NORMAL
UNDER MOSTLY CLOUDY SKIES.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
AS OF 230 AM EDT MONDAY...A BROAD UPPER RIDGE WILL REMAIN OVER THE
SE TUE THROUGH WED. EXPECT W TO NW DOWNSLOPING FLOW ACROSS THE
REGION ON TUE AS A SFC TROUGH SHARPENS OVER THE ERN PIEDMONT OF THE
CAROLINAS...AND AN APPROACHING FRONTAL BOUNDARY LAYS OVER NW OF THE
AREA. SCATTERED STRONG THUNDERSTORM DEVELOPMENT IS POSSIBLE...MAINLY
OVER THE MTNS LATE DAY...AND ALSO EAST OF THE AREA CLOSER TO THE
PIEDMONT TROUGH...AS DRIER AIR WILL BE SLOW TO ARRIVE.

SOME MODEL TIMING DIFFERENCES THEN DEVELOP WITH RESPECT TO THE
HANDLING OF THE SURFACE COLD FRONT TUE NIGHT/WED. THE GFS REMAINS
THE MOST PROGRESSIVE IN BRINGING THE BOUNDARY STEADILY THROUGH THE
FORECAST AREA...WHILE THE ECM/NAM STALL THE BOUNDARY OVER OR JUST N
OF THE FORECAST AREA INTO WED. EVEN THE GFS WITH THE FROPA HOLDS
ONTO WARMER LOW LEVEL THICKNESSES IN THE SRN PART OF THE AREA ON
WED. THUS EXPECT ONLY MODEST COOLING IN THE NRN TIER...COMPARABLE
MAXES WED AFTN TO TUE AFTN IN THE SRN PART...AND LINGERING ISOLD
SHOWER POPS ALONG THE SRN ESCARPMENT AREA. OTHERWISE...WILL PLAY UP
A WEAK FROPA AND WITH GENERALLY DRIER HIGH PRESSURE BUILDING OVER TO
THE N FROM THE SRN SHORES OF THE GREAT LAKES THROUGH WED NIGHT.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
AS OF 230 AM EDT MONDAY...A NRN STREAM SYSTEM WILL TRAVERSE THE
GREAT LAKES ON THU AND FLATTEN THE UPPER FLOW ACROSS THE SE. WEAK
SURFACE WAVES WILL RIDE EAST ALONG THE OLD FRONTAL ZONE TO IMPROVE
PRECIPITATION CHANCES ACROSS THE DEEP AND MID SOUTH THU. THE MAIN
QUESTION IS WHERE THE SFC BOUNDARY WILL BE AT THIS POINT...WITH THE
DRIER GFS KEEPING PRECIP SHUNTED BACK ACROSS THE ARKLATEX REGION AND
ALSO EAST IN THE COASTAL PLAIN TROUGH...WHILE THE ECMWF SPREADS
PRECIPITATION BACK INTO THE APPALACHIANS. WILL COMPROMISE AND
FEATURE MAINLY ISOLD THU POPS...WITH TEMPERATURES COOLING ANOTHER
COUPLE OF DEGREES FROM THE N.

UPPER HEIGHTS WILL START RISING AGAIN ON FRI...WITH THE PATTERN
STRONGLY AMPLIFYING OVER THE EAST INTO THE WEEKEND. SFC HIGH
PRESSURE WILL STRETCH FROM ONTARIO TO THE CAROLINAS. SOME ATLANTIC
FLOW MOISTURE COULD WRAP INTO THE BASE OF THE SRN APPALACHIANS...BUT
WITH SHOWER CHANCES FAIRLY LOW AND FOCUSED MAINLY ON THE MTN
ESCARPMENT AREAS. MAXES SHOULD BE NEAR CLIMO...WITH MINS AT LEAST 5
DEGREES ABOVE CLIMO EACH DAY IN MOST AREAS.

&&

.AVIATION /15Z MONDAY THROUGH FRIDAY/...
AT KCLT...OFFSHORE HIGH PRESSURE WILL PREDOMINATE THE PATTERN
TODAY...BUT UNDER INFLUENCE OF APPROACHING COLD FRONT AND
TROUGH...THE RIDGE WILL BREAK DOWN ENOUGH TO ALLOW SOME TSRA ACRS
THE AREA THIS AFTN. SCT LOW VFR CU ARE EXPECTED TO BREAK OUT BY
MIDDAY...WITH TSRA DEVELOPING NEAR PEAK HEATING. A TSRA PASSING
DIRECTLY OVER THE FIELD WOULD LIKELY BRING A BRIEF PERIOD OF IFR
VSBY...BUT ONLY WENT MVFR IN TEMPO GIVEN LOW LIKELIHOOD OF A DIRECT
HIT. RESTRICTIONS ARE UNLIKELY TONIGHT UNLESS HEAVY RAIN FALLS AT
THE SITE. FLOW WILL FAVOR SW THROUGH THE DAY...OCCASIONALLY HELD
CLOSER TO S EARLY THIS AM DUE TO LEE TROUGH OVER VIRGINIA. IF WINDS
DO NOT GO CALM TONIGHT THEY WILL LIKELY FLIP TO NW AFTER MIDNIGHT.

ELSEWHERE...SIMILAR TRENDS TO KCLT BUT WITH VARIED TIMING. MTN
CONVECTION EXPECTED TO FIRE NEAR THE BLUE RIDGE AROUND NOON...WITH A
SECOND ROUND DEVELOPING OVER THE PIEDMONT LATER IN THE AFTN. A
MENTION OF TSRA IS MADE AT ALL SITES...GENERALLY WITH A PROB30 OR
TEMPO DEPENDING ON HOW EARLY THEY APPEAR IN THE TAF. MTN VALLEY FOG
LIKELY TO RETURN TONIGHT AS WELL AS IN PORTIONS OF THE
FOOTHILLS...INCLUDING KHKY. ANY SITE THAT GETS SOAKED BY AFTN RAIN
IS LIKELY TO HAVE AT LEAST BRIEF RESTRICTIONS TONIGHT.

OUTLOOK...THE REGION WILL REMAIN WITHIN A PLUME OF MOISTURE THROUGH
MID WEEK. MORNING FOG AND STRATUS WILL BE POSSIBLE EACH MORNING
ABOVE WET GROUND. OTHERWISE...EXPECTING LIGHT WINDS WITH AFTERNOON
AND EVENING TSRA. THE MID WEEK PASSAGE OF A COLD FRONT SHOULD BRING
BACK SOMEWHAT DRIER CONDITIONS...THOUGH THE FRONT MAY HANG UP OVER
THE SOUTHEAST ALLOWING PERIODS OF UNSETTLED WEATHER TO RETURN.

CONFIDENCE TABLE...

            15-21Z        21-03Z        03-09Z        09-12Z
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  80%
KHKY       HIGH 100%     HIGH 100%     HIGH 100%     MED   77%
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...CSH/WIMBERLEY
SHORT TERM...HG
LONG TERM...HG
AVIATION...WIMBERLEY



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