Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 130550
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1250 AM EST SAT FEB 13 2016

.SYNOPSIS...
AS A WEAK SURFACE TROUGH DEPARTS THE FORECAST AREA TONIGHT...
NORTHWEST WINDS IN ADVANCE OF AN ARCTIC HIGH PRESSURE SYSTEM WILL
USHER IN VERY COLD TEMPERATURES FOR THIS WEEKEND. THE HIGH PRESSURE
WILL SETTLE OVER THE EASTERN U.S. THROUGH EARLY MONDAY. A STRONG LOW
PRESSURE SYSTEM BRINGING HEAVY PRECIPITATION MOVES SLOWLY ACROSS THE
AREA DURING THE DAY ON MONDAY AND DEPARTS THE AREA TUESDAY MORNING.

&&

.NEAR TERM /THROUGH TODAY/...
AS OF 1230 AM...THE NEXT 2-3 HOURS LOOK LIKE ABOUT THE PEAK OF THIS
NWFS EVENT PER RADAR MOSAIC AND IR SATELITE TRENDS. WINDS ARE REALLY
BEGINNING TO INCREASE ACROSS THE NORTHERN MTNS...DROPPING WIND
CHILLS AND HELPING IMPROVE UPSLOPE FORCING. THE CURRENT POP TREND
LOOKS GOOD WITH LIKELY TO CATEGORICAL FOR NEXT COUPLE HOURS...THEN
GRADUALLY TAPERING OFF AS MOISTURE BEGINS TO DIMINISH.
OTHERWISE...CLEAR TO MOSTLY CLEAR SKIES AND LIGHTER WINDS EAST OF
THE MOUNTAINS.

AS OF 10 PM...RECENT RADAR RETURNS FROM KMRX CONTINUED TO INDICATE
WEAK REFLECTIVITY ACROSS EASTERN TN AND ALONG THE SPINE OF THE
APPALACHIANS. IN ADDITION...CLOUD TOPS WITH TEMPS BELOW -15C EXISTED
FROM THE SOUTHERN APPALACHIANS NW TO THE CENTRAL OHIO RIVER VALLEY.
BASED ON THE LATEST OBSERVATIONS...STEADY NWFS SHOULD CONTINUE
ACROSS THE TN BORDER COUNTIES OF NC FOR THE NEXT 4 TO 6 HOURS.
ALSO...TEMPERATURES HAVE COOLED THIS EVENING...BUT NOT AS FAST AS
THE CURRENT FORECAST. I WILL UPDATE THE FORECAST TO ALIGN COOLING
TRENDS TO LATEST MOS TIMING. OTHERWISE...THE MIN FORECAST FOR
TONIGHT LOOKS RIGHT ON TRACK. THE WSW HAS BEEN UPDATED...WITH NO
SIGNIFICANT CHANGES.

AS OF 7 PM...STEADY WNW WINDS WILL REMAIN ACROSS THE FOOTHILLS AND
PIEDMONT AS THE CENTER OF STRONG HIGH PRESSURE SLIDES ACROSS THE MID
WEST. MID LEVEL CLOUDS WILL LIKELY CONTINUE TO THIN ACROSS THE
REGION THROUGH TONIGHT. LOW TEMPERATURES IN THE SINGLE DIGITS AND
TEENS ACROSS THE MTNS COMBINED WITH GUSTY WINDS TO SUPPORT A WIND
CHILL ADVISORY FOR TONIGHT ACROSS THE TN BORDER. I WILL UPDATE THE
FORECAST WITH THE LATEST OBSERVATIONS FOR TEMP AND DEWPOINT. IN
ADDITION...I WILL UPDATE THE HWO.

BY MID SATURDAY MORNING...DEEPENING MIXING SHOULD SUPPORT GUSTS
INTO THE HIGH TEENS. WINDS GUSTS WILL LIKELY LINGER ACROSS THE
REGION UNTIL MID TO LATE AFTERNOON.

AT 230 PM FRIDAY...AN UPPER TROUGH WILL PROGRESS OVER THE EAST COAST
TONIGHT AND SATURDAY. CHANNELED VORTICITY ROUNDING THE TROUGH WILL
OFF THE CAROLINA COAST TONIGHT...WHILE MORE CHANNELED ENERGY REMAINS
FARTHER NORTH. MEANWHILE...A SURFACE LOW WILL MOVE OFF THE CAROLINA
COAST THIS AFTERNOON...WHILE SURFACE WINDS VEER FROM SW TO NW...
BECOMING QUITE GUSTY AT HIGHER ELEVATIONS...AND DOWNSLOPE FLOW
LEADS TO DRYING IN THE LEE OF THE MOUNTAINS. MOIST NW FLOW INTO THE
NC MOUNTAIN BORDERING TN WILL KEEP SNOW SHOWERS GOING THERE
OVERNIGHT...WITH A DIMINISHING TREND ON SATURDAY.

LOW TEMPERATURES OVERNIGHT WILL RUN AROUND 10 DEGREES BELOW NORMAL.
THE WINTER WEATHER ADVISORY FOR SNOW ACCUMULATIONS OF OVER TWO
INCHES WILL BE LEFT UP IN THE NC MOUNTAINS BORDERING TN...ANS WILL
THE WIND CHILL AND WIND ADVISORY FOR LATE TONIGHT AND EARLY SATURDAY
FOR THE NORTHERN NC MOUNTAINS AND HIGH ELEVATIONS OF THE SOUTHERN
AND CENTRAL NC MOUNTAINS BORDERING TN. HIGH TEMPERATURES ON SATURDAY
WILL RUN AROUND 18 DEGREES BELOW NORMAL.

&&

.SHORT TERM /TONIGHT THROUGH MONDAY NIGHT/...
AS OF 245 PM EST FRIDAY...THE SHORT TERM IS A MESS...BUT I
SUPPOSE MOST USERS WANT MORE INFORMATION THAN JUST THAT. THE
SYNOPTIC PATTERN FOR THE FIRST PART OF THE SHORT TERM IS FAIRLY
STRAIGHTFORWARD WITH A DEEP UPPER TROUGH OVER THE EASTERN SEABOARD
AND A VERY COLD ARCTIC SURFACE HIGH BUILDING IN FROM THE NORTHWEST
WITH DEEP-LAYER STRONG CAA SPREADING ACROSS THE AREA. WINDS
AND RESULTING WIND CHILLS WILL CONTINUE TO BE AN ISSUE AT THE
BEGINNING OF THE PERIOD BUT SHOULD TAPER OFF AS THE SURFACE HIGH
BUILDS IN. WITH THAT...EXPECT LOW TEMPERATURES SUNDAY MORNING TO
BE VERY COLD...TEENS AND LOW 20S ACROSS THE UPSTATE...WITH SINGLE
DIGITS IN THE NORTHERN MOUNTAINS. RECOVERY ON SUNDAY AFTERNOON
WILL BE MINUSCULE WITH BARELY HALF THE FORECAST AREA GETTING ABOVE
FREEZING...MAYBE SOME UPPER 30S DOWN SOUTH.

MEANWHILE THE AFOREMENTIONED MESS GETS GEARED UP OVER THE NORTHERN
PLAINS AND UPPER MIDWEST AS A SHORTWAVE DIVES DOWN...WITH A
SECONDARY WAVE DIPPING INTO THE PLAINS OUT OF THE NORTHERN
ROCKIES. MOISTURE WILL INCREASE ACROSS THE DEEP SOUTH AHEAD OF
THE APPROACHING FRONT...WHILE THE SURFACE HIGH SHIFTS EAST AND
TRIES TO DAM DOWN THE EASTERN SEABOARD IN A VERY PROGRESSIVE
HYBRID CAD. DEFINITELY SOME UNCERTAINTY HERE AS BY THE TIME THE
PRECIPITATION STARTS TO OVERSPREAD OUR FORECAST AREA...THE PARENT
HIGH IS OFFSHORE THEREBY NO LONGER SUPPLYING A SOURCE OF GOOD LOW
LEVEL CAA...BUT EVAPORATIONAL COOLING INTO THE COLD AND DRY SURFACE
LAYER MAY HELP TO CREATE A BIT OF INSITU DAMMING. A LOT WILL DEPEND
ON WHERE EXACTLY THE DEWPOINTS ARE AT PRECIPITATION /VIRGA/ ONSET.

ADDITIONALLY...AS IF TAKING DIABATIC PROCESSES INTO ACCOUNT ISN`T
DIFFICULT ENOUGH...THERE IS STILL SIGNIFICANT UNCERTAINLY ON
LOCATION OF THE SURFACE LOW. 12Z GFS HAS SHIFTED FARTHER SOUTH
/SAY FROM AUGUSTA TO RALEIGH/...WHICH WOULD NATURALLY RESULT IN
GREATER CHANCES FOR WINTRY PRECIP. HOWEVER...THE NEW 12Z ECMWF
TAKES THE SURFACE LOW ON THE NW SIDE OF THE APPALACHIANS...WHICH
WOULD CUT OFF ANY WINTRY POTENTIAL FOR MOST OF OUR AREA BY MIDDAY
MONDAY. WPC GUIDANCE SUGGESTED STICKING WITH THE 12Z ECMWF/00Z
ECMWF ENSEMBLE MEAN POSITION...WHICH IS ALL WELL AND GOOD EXCEPT
THOSE DATA ARE NOT AVAILABLE FOR US TO USE OPERATIONALLY. TRIED
TO TAKE A BLEND OF THE OPERATIONAL 12Z GFS AND ECMWF...BUT AGAIN
ECMWF DATA ARE LIMITED...SO IN THE END OUR FORECAST IS PROBABLY
ON THE COOL /AND PESSIMISTIC/ SIDE OF GUIDANCE. AS AN EXAMPLE
HOWEVER...TAKING THE RAW GFS VS. ECMWF...THE DIFFERENCES IN HIGH
TEMPS MONDAY FOR GSP ARE 33 VS 39 RESPECTIVELY...AND FOR CLT IT
IS WORSE WITH 34 VS. 46 RESPECTIVELY.

SO WHAT WE HAVE AS THE SYSTEM APPROACHES IS A VERY COLD COLUMN
AND WHEN PRECIPITATION BEGINS...IT WILL BEGIN AS ALL SNOW. AS THE
SURFACE LOW APPROACHES...WHILE SURFACE WINDS REMAIN NORTHEASTERLY
IN RESPONSE TO THE INSITU DAMMING...WINDS ALOFT WILL PICK UP OUT OF
THE SOUTH AND WAA ATOP THE COLD DOME WILL INSTIGATE A CHANGEOVER
FROM SNOW TO SLEET TO FREEZING RAIN FROM SOUTH TO NORTH. PROBABLY
ALL RAIN ACROSS MOST OF THE AREA...EXCEPT MAYBE THE MOUNTAINS AND
NORTHERN TIER...BY MONDAY EVENING. I CANNOT EMPHASIZE ENOUGH THAT
CONFIDENCE IS --VERY-- LOW ON ACTUAL TEMPERATURES AND THUS PTYPE
TRANSITION...AND THUS SNOW AND ICE ACCUMS. BUT SPEAKING OF THE
LATTER...CURRENTLY OUR GRIDS HAVE FROM A TRACE SNOW ACROSS THE
UPSTATE TO 3-4 INCHES ACROSS THE MOUNTAINS THROUGH THE END OF THE
SHORT TERM /12Z TUESDAY...MORE SNOW WITH WRAPAROUND PRECIP AS WE
TRANSITION INTO THE EXTENDED/...WITH TRACE ICE ACROSS THE UPSTATE
TO A MAX OF AROUND 1/4 INCH ACROSS THE NORTHERN MOUNTAINS. THIS
ACTUALLY LINES UP PRETTY WELL WITH WPC GUIDANCE FOR NOW...BUT
I WILL REEMPHASIZE ONCE AGAIN THAT CONFIDENCE IS LOW AND THERE
IS QUITE A BIT OF UNCERTAINTY ESPECIALLY ON SOUTHERN EXTENT OF
WINTRY PRECIPITATION. HIGHEST CONFIDENCE /BIG SURPRISE/ IS ACROSS
THE MOUNTAINS.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
AS OF 230 PM EST FRIDAY...THE THINKING WITH REGARD TO THE END OF THE
EARLY-WEEK EVENT HAS NOT CHANGED MUCH. THE LATEST MODEL GUIDANCE
STILL SHOWS THE PRIMARY SURFACE LOW TO OUR EAST OR NORTHEAST AT
DAYBREAK TUESDAY...AND THE LOW SHOULD PULL AWAY RAPIDLY TO THE
NORTHEAST DURING THE MORNING. THAT SHOULD BRING A GRADUAL END TO THE
PRECIP PROBABILITY FROM SW TO NE OVER MOST OF THE REGION DURING THE
MORNING AND EARLY AFTERNOON...WITH THE THINKING THAT THE ECMWF
PROBABLY HOLDS ONTO THE PRECIP A BIT TOO LONG ACROSS THE NC
PIEDMONT. THE TRANSITION TO A NW FLOW EVENT WILL TAKE PLACE DURING
TUESDAY AFTERNOON AND EVENING. IF THERE IS SOME CONTROVERSY...IT IS
BETWEEN THE GFS AND ECMWF WITH REGARD TO THE TIMING AND TRACK OF A
FOLLOW-UP WAVE. THE GFS HAS A DISTINCT BREAK IN THE ACTION AROUND
DUSK ON TUESDAY...AND THEN MOVES THE WAVE MUCH FARTHER N...ACROSS
THE CENTRAL APPALACHIANS WEDNESDAY MORNING. MEANWHILE...THE ECMWF
SHOWS NO SUCH BREAK...AND HAS THE FOLLOW UP WAVE ACTUALLY DIVING S
OF THE FCST AREA LATE TUESDAY NIGHT. THE PROBLEM WITH THAT SOLUTION
IS THAT IT COULD SPELL ANOTHER STRIPE OF LIGHT SNOW EARLY WEDNESDAY
MORNING ACROSS NE GEORGIA AND UPSTATE SC...SIMILAR TO WHAT HAPPENED
EARLIER TODAY. THAT WOULD BE A LOW PREDICTABILITY EVENT OUT AT DAY
6...SO A SCENARIO CLOSER TO THE GFS IS FAVORED. PRECIP CHANCES RAMP
BACK UP A BIT...IN THE CHANCE RANGE...ALONG THE TN BORDER FOR
TUESDAY NIGHT AND THRU MUCH OF THE DAY WEDNESDAY. IF THE GFS IS
CORRECT...THE MOISTURE GRADUALLY DIMINISHES WEDNESDAY EVENING. THE
POTENTIAL FOR SIGNIFICANT SNOW WITH THIS EVENT IS NOT PARTICULARLY
HIGH. THE FLOW LOOKS TO BE MORE WESTERLY...AND BACKWARDS
TRAJECTORIES CALCULATED AT 12Z WEDNESDAY SHOW THAT AIR STREAMS WILL
ORIGINATE OR PASS OVER THE NRN PLAINS...MISSING THE GT LAKES
ENTIRELY. WITH NO GT LAKES CONNECTION AND SNOW ALREADY ON THE GROUND
IN KY AND TN TO LIMIT SFC FLUXES OF HEAT AND MOISTURE...THIS
PROBABLY WILL NOT EVEN REACH ADVISORY CRITERIA. AFTER THE NW FLOW
WINDS DOWN...THE REST OF THE FCST IS BENIGN WITH HEIGHTS STEADILY
RISING IN A PROGRESSIVE UPPER PATTERN. SFC HIGH PRESSURE WILL BUILD
BACK IN THURSDAY THROUGH FRIDAY...AND TEMPS SHOULD MODERATE
CONSIDERABLY...BACK TO FIVE DEGREES OR SO ABOVE NORMAL.

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
AT KCLT AND ELSEWHERE EAST OF THE MTNS...VFR...WITH GENERALLY SKC OR
FEW250 FOR MOST OF THE PERIOD. WINDS WILL REMAIN OUT OF THE
NW...WITH SOME LOW-END GUSTS EXPECTED AS MIXING DEEPENS LATE MORNING
THRU THE MIDAFTERNOON.

AT KAVL...NORTH-NORTHWEST WINDS WILL REMAIN ACROSS THE TERMINAL
THROUGH THE TAF PERIOD AS HIGH PRESSURE APPROACHES FROM THE
NORTHWEST. WIND GUSTS HAVE BEEN INTERMITTENT THRU THE EVENING...BUT
ARE EXPECTED TO BE MORE FREQUENT BY 9Z...AND CONTINUE THRU THE
AFTERNOON. A TEMPO FOR THE GUSTS AND FOR POTENTIAL MVFR CIG FROM THE
TN BORDER WILL BE KEPT THRU 9Z. SKIES SHOULD CLEAR OUT BY 14Z...AS THE
LLVL MOISTURE TAPERS OFF.

OUTLOOK...AN ARCTIC AIR MASS WILL BUILD IN ACROSS THE REGION OVER THE
WEEKEND. A SIGNIFICANT WINTER WEATHER SYSTEM IS POSSIBLE EARLY NEXT
WEEK.

CONFIDENCE TABLE...

            06-12Z        12-18Z        18-24Z        00-06Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH  87%     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 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...WINTER WEATHER ADVISORY UNTIL 6 AM EST EARLY THIS MORNING FOR
     NCZ033-048>052.
     WIND CHILL ADVISORY UNTIL 10 AM EST SUNDAY FOR NCZ033-049-050.
     WIND CHILL ADVISORY UNTIL NOON EST TODAY FOR NCZ048-051-052-
     058-059.
SC...NONE.

&&

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


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