Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 030717
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
317 AM EDT TUE MAY 3 2016

.SYNOPSIS...
A COLD FRONT WILL MOVE SLOWLY ACROSS THE REGION TODAY. A COOLER AND
DRIER AIR MASS WILL MOVE IN BEHIND THE FRONT ON WEDNESDAY. ANOTHER
COLD FRONT WILL CROSS THE REGION ON WEDNESDAY NIGHT AND WILL USHER
IN A MUCH COOLER AIR MASS FROM CANADA FOR THE END OF THE WORK WEEK.
HIGH PRESSURE SHOULD RETURN WITH A WARMING TREND FOR THE BALANCE OF
THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 315AM TUESDAY MORNING...THUNDERSTORMS ARE WORKING THEIR WAY
SOUTHEASTWARD OUT OF THE CWA.  THERE WAS SOME CONCERN ABOUT POSSIBLE
FLASH FLOODING FROM TRAINING OF STORMS...HOWEVER...STORMS HAVE MADE
ENOUGH SOUTHEASTWARD PROGRESS TO AVOID TRAINING.  MORE WIDELY
SCATTERED LIGHT SHOWERS EXIST OVER MOST OF THE REST OF THE CWA.
LIGHT SHOWER ACTIVITY WILL CONTINUE OVER NIGHT WITH THUNDERSTORMS
EXPECTED AGAIN THIS AFTERNOON OVER THE SOUTHEASTERN 2/3S OF THE
CWA.  ALL THIS ACTIVITY IS ALONG AND AHEAD OF A SURFACE BOUNDARY
ORIENTED SW-NE SOUTHEAST OF THE APPALACHIANS.  THIS BOUNDARY WILL
MAKE GRADUAL SOUTHEASTWARD PROGRESS DURING THE DAY...EXITING THE CWA
TUESDAY EVENING.  CHANCES FOR THUNDERSTORMS DECLINE RAPIDLY BEHIND
THE FRONT.  WITH FROPA...WINDS WILL VEER FROM THE SOUTHWEST TO
NORTHWEST AND MAY REACH 15 TO 20 KTS AT HIGHER ELEVATIONS.

COLD FRONT IS AHEAD OF A DEEP POSITIVELY TILTED UPPER TROUGH.  AS THE
TROUGH APPROACHES...MID LEVEL FLOW IMPROVES GIVING INCREASED DEEP
LAYER SHEAR THIS AFTERNOON ALONG THE FRONT OF 50 TO 55 KTS.  THIS
COMBINES WITH LI TO -6 AHEAD OF THE FRONT TO PROVIDE AN ENVIRONMENT
FOR POSSIBLE SEVERE STORMS WITH FROPA THIS AFTERNOON.  VEERED
LOW-LEVEL WINDS ARGUE AGAINST STRONG SUPERCELLS...WITH SEVERE WIND
GUSTS AND FLASH FLOODING BEING THE PRIMARY THREATS.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
AS OF 130 AM EDT TUESDAY...THE BIG STORY FOR THE LATTER HALF OF THE
WEEK WILL BE THE BIG COOL DOWN COURTESY OF A DEEP UPPER LOW THAT
ROLLS DOWN FROM THE GT LAKES AND ACROSS THE WESTERN CAROLINAS ON
THURSDAY. NOT EXACTLY BLACKBERRY WINTER...AS IT DOES NOT APPEAR THAT
LOW TEMPS WILL GET ANYWHERE NEAR RECORDS...BUT UNSEASONABLY COOL
NONETHELESS. WE BEGIN ON WEDNESDAY MORNING IN A RELATIVE LULL AS A
DRY SLOT CROSSES THE FCST AREA IN THE WAKE OF AN INITIAL VORT LOBE.
THE LACK OF FORCING AND MOISTURE SHOULD MAKE IT DIFFICULT FOR PRECIP
TO DEVELOP...SO PRECIP CHANCES WERE BROUGHT DOWN BELOW 15 PCT THRU
MOST OF THE MORNING HOURS. THE MODELS ARE IN DECENT AGREEMENT OF
BRINGING THE MAIN VORT CENTER DOWN FROM THE NW AS THE UPPER LOW
APPROACHES ON WEDNESDAY AFTERNOON. EXCELLENT FORCING AND DEEP
MOISTURE SHOULD REACH THE MTNS AROUND MIDDAY SO PRECIP CHANCES GO UP
FROM THERE. THE PASSAGE OF THE VORT CENTER ACROSS THE FCST AREA
SHOULD FORCE SHOWERS TO BREACH THE MTNS AND MOVE OUT E OF THE BLUE
RIDGE MAINLY WEDNESDAY EVENING. AFTER THE VORT PASSES...PRECIP
PRODUCTION SHOULD SCALE BACK TO THE UPSLOPE AREAS ON THE TN BORDER
FOR THE REST OF THE NIGHT AND EARLY THURSDAY MORNING. THE UPPER LOW
CENTER IS EXPECTED TO CROSS THE FCST AREA DURING THE DAY ON
THURSDAY. AS THIS HAPPENS...THE COLD POOL ALOFT WILL MOVE OVERHEAD
AND RESULT IN VERY STEEP LOW LEVEL LAPSE RATES. CONVECTION SHOULD
BREAK OUT DURING THE AFTERNOON ACROSS THE ENTIRE FCST AREA. FCST
SOUNDINGS SHOW A WET BULB ZERO AROUND 5K FEET...SO SMALL HAIL WILL
PROBABLY REACH THE GROUND IN THE STRONGER CONVECTION. HIGH TEMPS
WILL BE ON THE ORDER OF 10 TO 15 DEG BELOW NORMAL. THE CONVECTIVE
ACTIVITY SHOULD TAPER OFF WITH LOSS OF HEATING...AND PRECIP CHANCES
WILL ONCE AGAIN TAPER BACK TO THE NW FLOW UPSLOPE AREAS ON THE TN
BORDER THROUGH EARLY FRIDAY MORNING. THE COLDEST TEMPS WILL BE
THURSDAY NIGHT...WITH LOW TEMPS ON THE ORDER OF 5 TO 10 DEG BELOW
NORMAL...REACHING THE MID/UPPER 30S IN PARTS OF THE NC MTNS.
HOWEVER...LINGERING CLOUD COVER AND STRONG NW WINDS WILL PROBABLY
PRECLUDE ANY FROST...AND TEMPS WILL NOT BE COLD ENUF FOR AN
ADVECTIVE FREEZE. THE PRECIP CHANCES SHOULD DIMINISH ON FRIDAY AND
TEMPS WILL REBOUND A BIT AS THE UPPER LOW SPINS SLOWLY AWAY ALONG
THE MID-ATLANTIC COAST. SOME LINGERING PRECIP CHANCE IS WARRANTED
OVER THE NRN MTNS...AND PERHAPS E OF I-77 CLOSER TO THE DEPARTING
COLD AIR ALOFT.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
AS OF 245 AM EDT TUESDAY...THE LATEST OPERATIONAL MODEL GUIDANCE
SUGGESTS THAT THE NEXT CLOSED LOW DROPPING DOWN ACROSS THE GT LAKES
AND ERN CANADA LATE IN THE WEEKEND MIGHT BE A BIT DEEPER THAN
PREVIOUSLY INDICATED...AND IN RESPONSE THE MODEL GUIDANCE PUSHES A
SFC BOUNDARY FARTHER S INTO THE WESTERN CAROLINAS. THE CONSENSUS OF
THE GUIDANCE STILL ONLY SHOWS A SLIGHT CHANCE OF PRECIP OVER THE NRN
ZONES ON SUNDAY INTO MONDAY...WHICH IS HARDLY COMPELLING ENOUGH TO
CHANGE AN ONGOING DRY FCST. HOWEVER...IT NOW APPEARS THAT OUR
WEATHER MIGHT NOT BE QUITE AS FAIR LATE IN THE PERIOD THAN
PREVIOUSLY THOUGHT. NO SIGNIFICANT CHANGES WERE MADE OVERALL...JUST
SOME TWEAKS TO PRECIP CHANCES OVER THE NRN PART OF THE FCST AREA.
TEMPS STILL LOOK LIKE THEY WILL CONTINUE TO RECOVER TOWARD NORMAL
OVER THE WEEKEND...BUT IF THE FRONT CONTINUES ITS SWD TREND IN THE
GUIDANCE...WE MIGHT NOT BE SEEING THE ABOVE NORMAL TEMPS CURRENTLY
CARRIED EARLY NEXT WEEK.

&&

.AVIATION /07Z TUESDAY THROUGH SATURDAY/...
KCLT...SHOWERS AND THUNDERSTORMS WILL CONTINUE FOR THE NEXT
SEVERAL HOURS AND GRADUALLY MOVE EASTWARD.  THIS WILL BE FOLLOWED BY
A RESPITE FROM 6AM UNTIL TUESDAY AFTERNOON WHEN MORE CONVECTIVE
ACTIVITY IS ANTICIPATED.  SHOWERS ARE ALONG AND AHEAD OF A
SOUTHWEST-NORTHEAST ORIENTED COLD FRONT JUST EAST OF THE
APPALACHIANS.  THIS FRONT WILL MAKE GRADUAL SOUTHEAST PROGRESS
DURING THE DAY...PASSING KCLT BY 8PM.  AS FRONT EXITS THE
AREA...WINDS WILL SHIFT FROM SOUTHWESTERLY TO NORTHWESTERLY AND
CHANCES FOR CONVECTION RAPIDLY DECLINE.

ELSEWHERE...AREA OF SHOWERS CURRENTLY FROM KAND TO KCLT WITH TRW
AROUND KCLT.  THIS ACTIVITY WILL CONTINUE TO MOVE EASTWARD
OVERNIGHT.  KAVL AND KHKY ARE CURRENTLY FREE OF SHOWERS...BUT WILL
LIKELY EXPERIENCE MORE BEGINNING EARLY THIS MORNING.  THIS ACTIVITY
IS ALONG AND AHEAD OF A SURFACE BOUNDARY ORIENTED SW TO NE JUST EAST
OF THE APPALACHIANS.  BOUNDARY WILL MAKE GRADUAL SOUTHEASTWARD
PROGRESS DURING THE DAY WITH MORE THUNDERSTORMS EXPECTED ALONG IT
EARLY THIS AFTERNOON.  FOLLOWING FROPA...WINDS WILL SHIFT FROM
SOUTHWEST TO NORTHWEST AND INCREASE AT HIGHER ELEVATIONS TO 15KTS
WITH HIGHER GUSTS.  MODELS ARE INDICATING LESS FOG OVERNIGHT THAN
PREVIOUS NIGHTS AND I HAVE LEFT IT OUT OF THE FORECAST.

OUTLOOK...DRY AIR WILL WORK IN FROM THE WEST TUESDAY NIGHT THRU
WEDNESDAY. A STRONG UPPER LOW WILL SWING THRU THE AREA WED NIGHT
THRU THU...AND WILL BRING SHRA AND TSRA MAINLY TO THE MTNS.

CONFIDENCE TABLE...

            07-13Z        13-19Z        19-01Z        01-06Z
KCLT       HIGH  82%     HIGH  92%     HIGH 100%     HIGH  80%
KGSP       HIGH  91%     HIGH  91%     HIGH 100%     HIGH  80%
KAVL       MED   62%     HIGH  82%     HIGH 100%     MED   70%
KHKY       MED   61%     MED   79%     HIGH 100%     HIGH  80%
KGMU       HIGH  92%     HIGH  82%     HIGH 100%     HIGH  80%
KAND       HIGH  86%     MED   69%     HIGH 100%     HIGH  80%

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...HG
NEAR TERM...WJM
SHORT TERM...PM
LONG TERM...PM
AVIATION...JAT/WJM


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