Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 041803
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
203 PM EDT WED MAY 4 2016

.SYNOPSIS...
A COLD FRONT WILL CROSS THE REGION TONIGHT AND USHER IN A COOL AIR
MASS FROM CANADA THROUGH THE END OF THE WORK WEEK. HIGH PRESSURE
RETURNS WITH A WARMING TREND FOR THE BALANCE OF THE WEEKEND...BEFORE
A COLD FRONT SLOWLY APPROACHES FROM THE NORTH ON SUNDAY. THIS FRONT
WILL MOVE NORTH AS A WARM FRONT EARLY MONDAY WITH ATLANTIC HIGH
PRESSURE DOMINATING THE REGION THROUGH TUESDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 1000 AM...A POTENT VORT MAX WILL BEGIN TO CLOSE OFF AN UPPER
LOW OVER THE IL/IN TODAY...THEN THE LOW WILL DROP SE ACROSS THE OH
VALLEY TONIGHT. THE LOW WILL BE ACCOMPANIED BY A STRONG COLD
FRONT...WHICH IS PROGGED TO ENTER THE NC MTNS AROUND 00Z. THE LOW
WILL HAVE COLD MID LVL TEMPS...RESULTING IN STEEP LOW-MID LVL LAPSE
RATES. A LINE OF SHOWERS AND PERHAPS A FEW EMBEDDED TSTMS WILL
DEVELOP ALONG THE FRONT...WITH THE CAMS IN GOOD AGREEMENT ON THAT
LINE ENTERING THE NC MTNS IN THE 21Z-00Z TIME FRAME LATE AFTN/EARLY
EVENING. SMALL HAIL AND GUSTY WINDS WILL BE POSSIBLE ALONG WITH THE
USUAL CLOUD-TO-GROUND LIGHTNING. ELSEWHERE...THERE ARE SOME
LINGERING HIGH-BASED CU ACRS THE NC PIEDMONT. THE NAM HAS A POCKET
OF 400-800 J/KG OF SBCAPE DEVELOPING IN THE SE CORNER OF THE
CWFA...WHERE DEWPTS REMAIN IN THE MID 50S. I THINK DRY AIR SHOULD
FILTER IN FROM THE NW...SO WILL GO WITH A DRY FCST OUTSIDE THE
FRONTAL BAND OF PRECIP. TEMPS WILL BE ABOUT A CATEGORY BELOW NORMAL.

THE PASSAGE OF THE COLD FRONT AND MID LEVEL LOW SHOULD SLOW DOWN AND
PROVIDE STEEP LAPSE RATES ACROSS THE REGION DURING THE EVENING
HOURS. I WILL FORECAST 30% COVERAGE TONIGHT AND OVER THE TN BORDER
COUNTIES. BROAD LOW PRESSURE WILL SETTLE ACROSS THE REGION THROUGH
THE REST OF THE NIGHT. LOW TEMPERATURES MAY RANGE FROM THE LOW 30S
ACROSS THE MTN RIDGES TO NEAR 50 ACROSS EASTERN CLT METRO. A
ROTATING LOW CENTER WILL TRACK NORTHWARD. RIDGE TOP SHOWER COULD
FALL AS A PERIOD OF SNOW ACROSS THE HIGHEST ELEVATIONS.

&&

.SHORT TERM /THURSDAY/...
AS OF 245 AM EDT WEDNESDAY...THE BIG STORY WITH THE LATTER PART OF
THE WEEK WILL BE THE PASSAGE OF A DEEP UPPER LOW THAT MOVES ACROSS
THE CAROLINAS ON THURSDAY. MODEL GUIDANCE DOES NOT SHOW MIXING TO BE
AS DEEP AS FCST SOUNDINGS ARE A BIT WARMER IN THE 850-700MB LAYER...
BUT EXPECT ENUF INSTABILITY THAT SHALLOW CONVECTION WILL DEVELOP BY
MIDDAY ACROSS MOST OF THE FCST AREA...EXCEPT FOR PROBABLY AREAS OF
UPSTATE SC AND NE GEORGIA TO THE IMMEDIATE LEE OF THE BLUE RIDGE.
THUS...THE FCST WILL STILL FEATURE A CHANCE OF SHOWERS MAINLY OVER
THE NC PART OF THE FCST AREA...AND PARTS OF THE UPSTATE WHERE
CONVERGENCE DOWNSTREAM OF THE MTNS SHOULD PROVIDE LOW LEVEL FORCING
FOR A BAND OF SHOWERS. UPSLOPE FLOW ON THE W SIDE OF THE MTNS WILL
SUPPORT A LIKELY POP ON THE TN BORDER. TEMPS WILL BE ON THE ORDER OF
10-15 DEG BELOW NORMAL FOR HIGHS. STILL THINK PRECIP CHANCES E OF
THE BLUE RIDGE WILL DIMINISH WITH LOSS OF HEATING ON THURSDAY
EVENING...SO PRECIP PROB GRADUALLY TAPERS BACK TO THE UPSLOPE AREAS
ON THE TN BORDER. MIN TEMPS WILL BE COOL AGAIN...BUT NOT NEARLY
CLOSE TO RECORDS...OR COLD ENOUGH TO WORRY ABOUT A FREEZE. A STEADY
NW WIND WILL PROBABLY ALSO PRECLUDE ANY FROST DEVELOPMENT. NO
SIGNIFICANT CHANGES ARE SUGGESTED FOR FRIDAY...EITHER...AS THE UPPER
LOW SPINS AWAY ACROSS THE MID-ATLANTIC. THE WESTERN EDGE OF THE COLD
POOL ALOFT WILL REMAIN ACROSS THE PIEDMONT...SO A SMALL PRECIP
CHANCE WAS KEPT ALONG AND E OF I-77. THAT TOO SHOULD END WITH LOSS
OF HEATING. TEMPS SHOULD REBOUND A BIT AS THE AIR MASS MODIFIES AND
THE UPPER LOW MOVES AWAY. FRIDAY NIGHT SHOULD BE DRY WITH TEMPS
ABOUT FIVE DEGREES WARMER THAN PREVIOUS NIGHTS.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
AS OF 155 PM EDT WEDNESDAY...NO NEED FOR ANY MAJOR CHANGES TO THE
GOING FCST. THE MODELS CONTINUE TO SHOW GOOD CONSISTENCY RUN TO RUN
AND WITH EACH OTHER WITH THE SYNOPTIC PATTERN AND EXPECTED SENSIBLE
WX THROUGH MOST OF THE PERIOD.

AN ERN UPPER LOW WILL CONTINUE TO DIG SOUTH SUN AND PUSH A BACKDOOR
COLD FRONT INTO THE NRN ZONES EARLY SUN. WITH A SFC HIGH CENTER
SITUATED OFFSHORE...THIS FRONT WILL BE SUPPLIED WITH A GOOD AMOUNT
OF GOM MOISTURE AND HIGH THETA/E AIR. AS THE FRONT SETTLES IN
SUN...SCT AFTERNOON -SHRA/TSTMS SHUD DEVELOP ACROSS THE I-40
CORRIDOR. SOUNDINGS AREN/T TOO IMPRESSIVE WITH THE AVAILABLE
CAPE...BUT A COUPLE OF THESE STORMS COULD BECOME QUITE STRONG GIVEN
THE EXPECTED ABOVE NORMAL SFC TEMPS AND HIGH TD/S. THIS ACTIVITY
WILL WANE QUICKLY SUN NIGHT AS THE FRONTAL ZONE MOVES NORTH AND A
LOW AMPLITUDE ULVL RIDGE BUILDS IN. THIS PATTERN WILL KEEP THE AREA
MOSTLY DRY THRU TUE...EXCEPT FOR THE NC MTNS WHERE POCKETS OF ULVL
ENERGY HELP INSTIGATE DIURNAL CONVECTION.

THE RIDGE AXIS SHIFTS EAST TUE AND THE CWFA WILL COME UNDER THE
INFLUENCE OF INCREASINGLY UPPER DIFLUENT FLOW AHEAD OF AN H5 LOW
TRACKING ACROSS THE LOWER MIDWEST. THE HIGHER UNSTABLE AIR WILL
REMAIN TO THE WEST OF THE AREA WED/THU...BUT GOOD MOISTURE FLUX WILL
KEEP POPS JUSTIFIED IN THE LOW/MID CHANCE RANGE ACROSS THE THE WRN
ZONES....WITH MAINLY ISOL CONVEC ACTIVITY ANTICIPATED EAST. TEMPS
WILL REMAIN FAIRLY PERSISTENT WITH HIGHS BEGINNING A COUPLE CATS
ABOVE NORMAL SUN THEN A SUBTLE DECREASE OF ABOUT 2-3 DEGREES BY WED.
MINS WILL LINGER A LITTLE BELOW OR NEAR NORMAL.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
AT KCLT AND ELSEWHERE EAST OF THE MTNS...VFR CONDITIONS THRU THE
PERIOD. A VIGOROUS UPPER DISTURBANCE WILL DROP SE FROM THE OH VLY
INTO THE WESTERN CAROLINAS BY THE END OF THE 18Z TAF PERIOD. AN
ASSOCIATED COLD FRONT WILL PUSH THRU OVERNIGHT. AHEAD OF THE
FRONT...A STOUT CU FIELD HAS DEVELOPED...WITH BASES IN THE 5-7 KFT
RANGE. A LEE TROF IS ALSO SETTING UP THANKS TO NWLY LLVL FLOW. SO
WINDS SHOULD FAVOR A SW TO WSW DIRECTION FROM LATE AFTN THRU THE
EVENING. THEN THE FRONT WILL PASS THRU AND SHIFT WINDS BACK TO NW
OVERNIGHT. A BAND OF SHOWERS IS EXPECTED TO ACCOMPANY THE FRONT AND
PUSH INTO THE MTNS EARLY THIS EVENING...BUT FIZZLE OUT BEFORE
REACHING THE PIEDMONT.

AT KAVL...WINDS WILL BE CHANNELED UP THE FRENCH BROAD VALLEY THRU
THE PERIOD...YIELDING NNW WINDS. WINDS ARE FORECAST TO FREQUENTLY
GUST INTO THE MID 20S DURING THE AFTERNOON...THEN AGAIN LATE TONIGHT
BEHIND THE PASSING COLD FRONT. A BAND OF SHOWERS WILL APPROACH KAVL
FROM THE NW EARLY THIS EVENING...AND MAY REACH THE TERMINAL...SO
WILL HIGHLIGHT WITH VCSH. LATER TONIGHT...GUIDANCE IS FORECASTING
SOME MVFR CIGS WITHIN THE NW FLOW...THEN LIFTING TO VFR AGAIN AFTER
DAYBREAK. AN UPPER LOW WILL BE NEARLY DIRECTLY OVER THE NC MTNS BY
18Z...AND ADDITIONAL SHRA ARE EXPECTED TO DEVELOP UNDERNEATH.

OUTLOOK...A STRONG UPPER LOW WILL SWING THRU THE AREA THRU
FRIDAY...AND WILL BRING SHRA AND TSRA MAINLY ACROSS THE NC SITES
BOTH THU AND FRI AFTN. DRY HIGH PRES RETURNS SATURDAY...WHILE
ANOTHER COLD FRONT APPROACHES FROM THE NORTH THRU SUNDAY.

CONFIDENCE TABLE...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     HIGH  99%     HIGH  92%     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 SCHEDULE TAF ISSUANCE FLIGHT RULE CATEGORY.  COMPLET HOURLY
EXPERIMENTAL AVIATION FORECAST CONSISTENCY TABLES AND ENSEMBLE FORECASTS
ARE AVAILABLE AT THE FOLLOWING LINK:

WWW.WEATHER.GOV/GSP/AVIATION

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.

&&

$$
SYNOPSIS...PM
NEAR TERM...ARK/NED
SHORT TERM...PM
LONG TERM...PM
AVIATION...ARK


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