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Area Forecast Discussion

184
FXUS62 KGSP 301048
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
648 AM EDT THU OCT 30 2014

.SYNOPSIS...
A COOL AND DRY AIRMASS WILL REMAIN ACROSS THE SOUTHERN APPALACHIAN
REGION THROUGH FRIDAY. A STRONG MID LEVEL AREA OF LOW PRESSURE IS
FORECAST TO TRACK ACROSS THE REGION FRIDAY NIGHT INTO SATURDAY. A
STRONG SURFACE LOW PRESSURE SYSTEM WILL DEVELOP OFF THE CAROLINA
COAST ON SATURDAY...THEN WILL TRACK QUICKLY NORTH BY SATURDAY NIGHT.
CIRCULATION AROUND THE COASTAL LOW WILL BRING A CANADIAN AIR MASS TO
THE REGION FOR THE FIRST HALF OF NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 640 AM...COOL AND FAIR WEATHER ACROSS THE CWA THIS MORNING. I
WILL UPDATE THE FORECAST WITH THE LATEST TEMP/TD OBS. OVERALL...THE
CURRENT FORECAST APPEARS ON TRACK.

AS OF 330 AM...SFC HIGH PRESSURE WILL BUILD ACROSS THE SOUTHERN
APPALACHIAN REGION THROUGH THIS AFTERNOON. WINDS ARE FORECAST TO
REMAIN LIGHT FROM THE NNE THROUGH THE DAYLIGHT HOURS. AT THE MID
LEVELS...THE AXIS OF AN AMPLIFYING TROF WILL RIPPLE ACROSS THE
CENTRAL MISSISSIPPI RIVER VALLEY. MID LEVEL HEIGHTS SHOULD GRADUALLY
FALL ACROSS THE REGION TODAY. THE COOL LLVL THICKNESSES AND LIGHT
NNE WINDS SHOULD FAVOR HIGHS IN THE U50S WITHIN THE MTN VALLEYS TO
MID TO UPPER 60S EAST.

TONIGHT...THE AXIS OF A DEEP L/W TROF WILL REACH THE SOUTHERN
APPALACHIANS BY 12Z FRI. HEIGHTS WILL FALL ACROSS THE CWA
TONIGHT...HOWEVER...H85 TEMPS WILL NOT COOL BY MORE THAN TWO
DEGREES. AS THE TROF APPROACHES...CIRRUS LEVEL MOISTURE WILL BEGIN
TO BUILD ACROSS THE WESTERN CAROLINAS. LOWER MOISTURE/CLOUDS ARE
FORECAST TO ARRIVE ACROSS THE WEST FACING MTN SLOPES LATE
TONIGHT...SUPPORTING INCREASING UPSLOPE CLOUD COVER. MIN
TEMPERATURES SHOULD RANGE FROM MID TO UPPER 30S ACROSS THE MTNS TO
LOW TO MID 40S EAST.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
AS OF 315 AM THURSDAY...THE 00Z GUIDANCE (EXCEPT THE CMC)...HAVE
COME INTO BETTER AGREEMENT ON A VERY POTENT COMPACT VORTMAX/CLOSED
500 MB LOW...DIVING SOUTH OUT OF CANADA FRIDAY...AND ROUNDING THE
BASE OF A SHARP/DEEP TROF OVER THE CWFA ON SATURDAY. THE ENERGY OF
THE SYSTEM WILL LIKELY INDUCE CYCLOGENESIS EAST OF THE OUTER BANKS
DURING THE DAY ON SATURDAY...WITH A DEFORMATION ZONE SETTING UP ACRS
CENTRAL VA/NC. A SURGE OF VERY COLD AIR WILL ALSO ACCOMPANY THE
SYSTEM...WITH 850 MB TEMPS PLUMMETING TO -6 TO -8C ALONG THE TN LINE
AND GENERALLY 0 TO -4C ACRS THE PIEDMONT. THE LLVL WINDS WILL BE
AROUND 40-50 KTS OUT OF THE NW...AS THE MID-UPR LOW SWINGS BY...WITH
STRONG CAA...SHUD RESULT IN PROBABLY WIND ADV LVL WINDS IN THE MTNS
(EVEN HIGHER AT THE HIGHEST PEAKS). BREEZY TO WINDY CONDITIONS WILL
THEN SPREAD ACRS THE PIEDMONT DURING THE DAY ON SATURDAY...AS THE
LLVL SYSTEM DEEPENS NEAR THE OUTER BANKS...AND CONTINUED NLY CAA
FLOW PERSISTS. THIS EVENT IS ONLY 48-60 HOURS AWAY...AND YET
CONFIDENCE IS LOW ON THE DETAILS ON SENSIBLE WX. IF THE 00Z GFS
VERIFIES...IT/S 500 MB HEIGHTS WILL BE ABOUT 5.5 STANDARD DEVIATIONS
BELOW NORMAL (OR ABOUT A 50-YEAR RETURN INTERVAL). HOWEVER...ONE
THING SEEMS ALMOST A SLAM DUNK...AND THAT IS ACCUMULATING SNOW ALONG
THE TN BORDER...AS A VERY GOOD NW FLOW SNOW SET UP SHUD OCCUR.

FRIDAY SHUD SEE INCREASING CLOUDS...AS THE SYSTEM APPROACHES FROM
THE NW. SHOWERS MAY START AS EARLY AS MID AFTN IN THE NRN
MTNS...THEN SPREAD ACRS THE MUCH OF THE AREA...AS DEEP LYR RH WILL
ACCOMPANY VERY STRONG QG FORCING. MODELS IN DECENT AGREEMENT ON SNOW
LEVELS FALLING TO THE VALLEY FLOORS BY DAYBREAK SATURDAY...WITH
PERHAPS A LULL IN SHWR ACTIVITY OUTSIDE THE USUAL NW FLOW AREAS.
HIGHS WILL BE 1-2 CATEGORIES BELOW NORMAL ON FRIDAY...THEN DROP WITH
ONSET OF CAA...ESP IN THE HIGH TERRAIN FRIDAY NIGHT...WITH LOWS IN
THE 20S TO MID 30S MTNS...AND UPR 30S TO LWR 40S PIEDMONT.
ELEVATIONS ABOVE 3500 FT ALONG THE TN BORDER MAY SEE A FEW INCHES OF
SNOW...DEPENDING ON HOW ROBUST THE SHOWER ACTIVITY IS.

SATURDAY...TAKING A GFS/ECMWF BLEND...IT LOOKS LIKE THERE SHUD BE A
PERIOD OF WRAP-AROUND RAIN/SHWR ACTIVITY ACRS THE I-77
CORRIDOR...WHILE THE NW FLOW SNOW SHWRS CONTINUE ALONG THE TN
BORDER. TEMPS/POPS FOR THE DAY ARE LOW CONFIDENCE...GIVEN THE
DYNAMIC NATURE OF THE SYSTEM. SNOW LEVELS MAY RISE BACK UP TO ABOUT
3500 FT...AS THE COMPACT MID LVL LOW EXITS TO THE EAST. SOME
PORTIONS OF THE NC FOOTHILLS/PIEDMONT MAY SEE A FEW SNOW FLAKES
EARLY SATURDAY MORNING...BUT IT LOOKS LIKE THE DEFORMATION ZONE
PRECIP SHUD REMAIN LIQUID...AS THE SFC LAYER IS JUST TOO WARM. EVEN
IF SOME SNOW FALLS OUTSIDE THE MTNS ON SATURDAY...ANY SIGNIFICANT
ACCUMS LOOKS HIGHLY UNLIKELY...AS SOIL TEMPS ARE RUNNING MID 50S TO
MID 60S AHEAD OF THE SYSTEM. CHARLOTTE HAS NOT HAD MEASURABLE SNOW
EARLIER THAN NOV 11TH GOING BACK TO 1878. I BLENDED IN THE STRAIGHT
GFS TEMPS TO ACCOUNT FOR THE ANOMALOUSLY LOW THICKNESSES AND
LINGERING DEFORMATION ZONE IN THE EAST. HIGHS IN THE MTNS MAINLY IN
THE 30S TO LWR 40S...AND MID 40S EAST TO MID 50S WEST IN THE
PIEDMONT.

SATURDAY NIGHT...SNOW SHWR ACTIVITY SHUD SUBSIDE...AND GUIDANCE
AGREES ON POPS TAPERING OFF BY 12Z SUNDAY. MIN TEMPS WILL BE
TRICKY...AS LOW PRES EXITS TO THE EAST...ALLOWING SKIES TO CLEAR AND
WINDS TO DIMINISH...BUT TO WHAT EXTENT? SO DEPENDING ON HOW GOOD THE
RADIATIONAL COOLING CONDITIONS CAN GET...MAY A LIGHT FREEZE ACRS
MUCH OF THE PIEDMONT. THE GOING FCST IS FOR MAINLY LWR TO MID 30S
ACRS THE PIEDMONT. MTNS WILL BE MAINLY IN THE 20S.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
AS OF 345 AM THURSDAY...GIVEN THE FCST CONCERNS IN THE SHORT
TERM...THERE WAS NO TIME TO MAKE ANY CHANGES TO THE EXTENDED THIS
MORNING. DRY CANADIAN HIGH PRES WILL BUILD IN FOR SUNDAY AND
MONDAY...WITH GENERALLY CLEAR SKIES AND WELL BELOW NORMAL TEMPS. A
WARMING TREND IS EXPECTED EARLY TO MIDDLE OF NEXT WEEK AS THE HIGH
SLIDES EAST AND AN UPPER RIDGE BUILDS IN FROM THE WEST.

AT 230 PM EDT WEDNESDAY...ON SATURDAY EVENING...A STRONG...ANOMALOUS
UPPER LOW WILL BE LOCATED OFF THE NC COAST...WHILE AN UPPER RIDGE
WILL BE OVER THE PLAINS. THE UPPER LOW WILL WEAKEN AND FILL AS IT
LIFTS NE OFF THE NEW ENGLAND COAST ON SUNDAY. BY MONDAY THE UPPER
RIDGE REACHED THE OH AND TN RIVER VALLEYS...AND ON TUESDAY THIS
RIDGE CROSSES THE EAST COAST. AN UPPER TROUGH PROGRESSES FROM THE
GREAT LAKES TO THE SOUTHERN AND CENTRAL APPALACHIANS BY WEDNESDAY IN
THE GFS...BUT IS LESS PROGRESSIVE IN THE ECMWF.

DRY HIGH PRESSURE WILL BUILD SOUTHEAST ACROSS OUR AREA FROM SATURDAY
NIGHT THROUGH MONDAY. AS A RESULT...VERY TIGHT PRESSURE GRADIENT
WILL GRADUALLY RELAX ON SATURDAY NIGHT AND SUNDAY. BY LATE
TUESDAY...A LIGHT MOIST UPSLOPE FLOW ON THE BACK SIDE OF THE
DEPARTING SURFACE HIGH WILL REACH OUR AREA...STARTING IN THE
MOUNTAINS...WHILE A COLD FRONT MOVES INTO THE OH AND MID MS RIVER
VALLEY. THIS COLD FRONT IS EXPECTED TO STALL TO OUR WEST BY
WEDNESDAY MORNING. POPS WILL BE ALLOWED TO RAMP UP LATE TUESDAY INTO
WEDNESDAY... HOWEVER PRECIPITATION ACCUMULATIONS WILL BE LIGHT...AND
MAINLY LIMITED TO THE MOUNTAINS.

TEMPERATURES WILL START OUT AROUND 15 DEGREES OR SO BELOW NORMAL IN
A COLD AIR MASS BEHIND THE DEPARTING UPPER LOW AND AN ASSOCIATED
COLD FRONT. TEMPERATURES WILL MODERATE TO NEAR NORMAL VALUES BY
MIDWEEK AHEAD OF THE NEXT FRONT.

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
AT KCLT AND ELSEWHERE...VFR CONDITIONS EXPECTED THROUGH THE TAF
PERIOD ACROSS THE WESTERN CAROLINAS. BROAD HIGH PRESSURE WILL BUILD
ACROSS THE REGION...RESULTING IN LIGHT NNE WINDS AND DRY CONDITIONS.
CIRRUS LEVEL MOISTURE WILL BEGIN TO INCREASE LATE THIS EVENING AND
OVERNIGHT AS MID LEVEL TROF AMPLIFIES ACROSS THE REGION.

OUTLOOK...ANOTHER COLD FRONT APPROACHES ON FRIDAY AFTERNOON BRINGING
CLOUDS AND A CHANCE FOR SHOWERS AS IT MOVES THROUGH BY FRIDAY
EVENING. SOME RESTRICTIONS ARE POSSIBLE...ESPECIALLY IN THE
MOUNTAINS WHERE EVEN SOME SNOW SHOWERS ARE EXPECTED FRIDAY NIGHT AND
SATURDAY.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...FROST ADVISORY UNTIL 9 AM EDT THIS MORNING FOR NCZ033-049-050-
     053.
     WINTER STORM WATCH FROM FRIDAY EVENING THROUGH SATURDAY
     EVENING FOR NCZ033-048>053-058-059.
SC...NONE.

&&

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



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