Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 270516
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1216 AM EST FRI FEB 27 2015

.SYNOPSIS...
IN THE WAKE OF A COLD FRONT...COLD CANADIAN HIGH PRESSURE WILL BUILD
IN FRIDAY AND SLOWLY WARM THROUGH THE WEEKEND. ABOVE NORMAL
TEMPERATURES SHOULD RETURN TO THE AREA BY MONDAY.

&&

.NEAR TERM /THROUGH TODAY/...
0515 UTC UPDATE...AREAS OF FOG HAVE BEEN ADJUSTED BASED ON CURRENT
TRENDS. WINDS WERE UPDATED WITH A BLEND OF THE LATEST NAM AND
ADJMAV...FAVORING GUSTS DURING DAYLIGHT HOURS.

930 PM UPDATE...SEEING LESS SUPPORT FROM MESO MODEL QPF PROGS AND
FROM MODEL PROFILES FOR UPSLOPE SNOWFALL IN THE MTNS NEAR THE TENN
BORDER. ALSO CAN/T SEE THAT ANY SNOW HAS YET DEVELOPED FROM RADAR OR
WEBCAMS. BACKED OFF POPS FOR THIS ACTIVITY BUT RETAINED AT LEAST A
SCHC THRU THE NIGHT. CONSIDERING LINGERING SNOW COVER...AND MOIST
SOILS WHERE SNOW MELTED TODAY...IT IS NOT SURPRISING NUMEROUS SITES
ARE REPORTING LIGHT FOG. PROFILES ARE NOT CONDUCIVE TO DENSE OR
PROLONGED FOG...WHICH ACCOUNTS FOR THE RAPID CHANGES IN VSBY ON OBS.
THE FOG MENTION ADDED AT 630 PM UPDATE HAS BEEN EXPANDED IN LIGHT OF
SLIGHTLY HIGHER DEWPOINTS NOW EXPECTED. A CONCERN IS THAT IN AREAS
WHERE TEMPS ARE BELOW FREEZING THE FOG COULD ALLOW ADDITIONAL ICING
ON ROADWAYS. UPDATED THE WINTER WX ADVY THAT DAY SHIFT ISSUED FOR
BLACK ICE TO ALSO DISCUSS THIS CONCERN.

AS OF 630 PM...WEAK FROPA ON TAP FOR LATE EVENING AS HIGH PRESSURE
STARTS TO BUILD IN FROM THE NW. THIS STANDS TO BRING A PERIOD OF
INCREASED CLOUD COVER AND SOME LOW PRECIP CHANCES TO THE NW
PIEDMONT. SATELLITE CLOUD TRENDS APPEAR TO SHOW SOME LOW CLOUDINESS
DEVELOPING IN THIS AREA...SO THINK PREVIOUS EXPECTATIONS OF LIGHT
PRECIP ARE ON TRACK. SFC TEMPS AND THERMAL PROFILES INDICATE A
RA/FZRA SPLIT OVER THIS AREA...BUT MINIMAL ACCUMULATION IS EXPECTED.

AS OF 220 PM...SKY COVER SHOULD DIMINISH A BIT BY LATE
TOMORROW MORNING AND AFTERNOON AS PROFILES CONTINUE TO GRADUALLY
DRY. OTHERWISE...LOW TEMPS ARE STILL ON TRACK TO BOTTOM OUT BELOW
FRZ FOR ALL ZONES EXCEPT POSSIBLY THE VERY SOUTHERNMOST AREAS. A
WINTER WX ADVISORY WILL BE ISSUED FOR WIDESPREAD BLACK ICE FOR ALL
BUT OUR SOUTHERN TIER COUNTIES FOR TONIGHT THRU TOMORROW MORNING. AN
SPS FOR PATCHY BLACK ICE WILL BE ISSUED FOR THE REMAINING ZONES.
HIGHS TOMORROW WILL BE SIMILAR TO TODAY WITH 40S OVER MOST OF THE
LOWER ELEVATIONS AND COOLER TEMPS FOR MOST OF THE HIGHER TERRAIN.

&&

.SHORT TERM /TONIGHT THROUGH SUNDAY/...
AS OF 240 PM THURSDAY...FORECAST DOES NOT GET ANY LESS TRICKY FOR
THE WEEKEND. GUIDANCE SHOWS SOME WEAK WAVES MOVING ACROSS THE AREA
IN THE FLATTENING UPPER FLOW. AT THE SFC...HIGH PRESSURE BUILDS INTO
THE MID ATLANTIC STATES AND RIDGES SOUTHEAST INTO THE AREA AS A
HYBRID COLD AIR DAMMING EVENT DEVELOPS. THE GFS IS ALONE IN
DEVELOPING SOME LIGHT PRECIP FRI NITE AND SAT AS SOME WEAK
ISENTROPIC LIFT DEVELOPS AS THE THE CAD SETS UP. WILL LEAVE THE FCST
DRY FOR NOW. HOWEVER...DO KEEP CLOUD COVER QUITE HIGH AS THERE WILL
BE SOME MOISTURE TRAPPED UNDER THE DEVELOPING SUBSIDENCE INVERSION.
THE CONTINUED COLD THICKNESSES AND CLOUDS WILL KEEP LOWS AROUND 10
DEGREES BELOW NORMAL AND HIGHS 15 TO 20 DEGREES BELOW NORMAL. DEEP
MOISTURE INCREASES LATE SAT NITE INTO SUNDAY AS SLY LOW LEVEL FLOW
DEVELOPS AHEAD OF AN APPROACHING COLD FRONT. ALL GUIDANCE IS IN
AGREEMENT ON THIS DEVELOPMENT. HOWEVER...THE ECMWF AND GFS ARE
SLOWER TO DEVELOP THE DEEP MOISTURE AND LOW LEVEL ISENTROPIC LIFT
WHILE THE NAM AND SREF ARE FASTER. THE GEFS ENSEMBLE MEAN KEEPS BEST
CHC POP UNTIL AFTER 18Z...BUT MODEL BLENDS SHOW SLIGHT CHC POP
DEVELOPING LATE SAT NITE WITH CHC POP DEVELOPING BY NOON SUNDAY AND
EVEN SOME LIKELY POP ALONG THE NC/SC/GA BORDERS BY THE END OF THE
DAY. HAVE GONE WITH THE MODEL BLEND TIMING FOR NOW GIVEN THE
UNCERTAINTY. SFC TEMPS WILL BE COLD DURING THIS TIME AND ALL
OPERATIONAL AND ENSEMBLE MEAN GUIDANCE SHOWS FREEZING RAIN WOULD
DEVELOP IN MANY AREAS WITH THE EARLIER ONSET. HAVE FOLLOWED THIS
TREND AS WELL...BUT ALSO FOLLOW THE TREND OF WARMING TEMPS DURING
THE DAY WITH P-TYPE CHANGING TO ALL LIQUID AROUND NOON. THIS IS IN
LINE WITH THE CENTER OF THE HIGH PRESSURE MOVING OFF SHORE BUT
REMAINING RIDGED INTO THE AREA...LIMITING ANY MAINTENANCE FLOW OF
DRY AND COLD AIR INTO THE DAMMING REGION. STILL...HIGHS WILL REMAIN
ON THE COOL SIDE IN THE DAMMING REGION...WITH HIGHS 15 TO 20 DEGREES
BELOW NORMAL...AND HIGHS WARMING ACROSS MUCH OF THE MTNS TO 5 TO 10
DEGREES BELOW NORMAL. FOR NOW...EXPECT ANY EARLY QPF TO BE VERY
LIGHT WITH LITTLE TO NO ICE ACCRETION. LOWS SAT NITE 5 TO 10 DEGREES
BELOW NORMAL.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
AS OF 230 PM THURSDAY...THE MEDIUM RANGE WILL START OUT WITH A BROAD
UPPER RIDGE ACRS THE SOUTHEAST STATES...AND A RATHER DEEP TROF INVOF
THE CALIF COAST. AT THE SFC...A COLD FRONT WILL SLIDE THRU THE AREA
FROM THE NORTH ON MONDAY...WITH SOME MOISTURE AND LIFT AROUND TO
WARRANT MAINLY CHC POPS ACRS THE EASTERN HALF OF THE CWFA AND LIKELY
POPS IN THE WEST FOR SUNDAY NIGHT AND MONDAY. TEMPS LOOK TO BE WARM
ENUF TO KEEP PRECIP AS ALL RAIN.

MONDAY NIGHT THRU TUESDAY NIGHT...A 1028-1032 MB HIGH PRES WILL
QUICKLY TRANSLATE EAST ACRS THE GREAT LAKES AND THE NORTHEAST
STATES...RESULTING IN COLD AIR DAMMING SETTING UP ACRS THE REGION.
AT THIS POINT...THE GFS AND ECMWF REALLY DIVERGE ON THE SENSIBLE WX
FCST FOR THE CWFA...WITH THE GFS MUCH WETTER...WHILE THE EC IS DRY.
I WENT WITH THE SUPERBLEND/WPC GUIDANCE WHICH LOOKS LIKE A
COMPROMISE FOR POPS. THE ECMWF IS COLDER...AND LOCKS IN A MORE
NOTABLE IN-SITU WEDGE ONCE IT BRINGS PRECIP BACK IN TUESDAY NIGHT.
AGAIN...I WENT WITH COMPROMISE ON TEMPS...BUT LEANING TOWARD THE
COOL SIDE OF GUIDANCE FOR HIGHS TUESDAY.

WEDNESDAY THRU THURSDAY NIGHT...MODEL SPREAD CONTINUES TO INCREASE
WITH HANDLING A CYCLONE TRACKING THRU THE PLAINS INTO THE GREAT
LAKES...AS THE UPPER TROF PROGRESSES EAST FROM THE ROCKIES TO THE
PLAINS. THE GFS IS DEEPER AND FASTER WITH THE LOW...BUT HAS A
SECONDARY WAVE DEVELOP ALONG THE FRONT OVER THE GULF STATES AND
TRACK THRU THE AREA WEDNESDAY NIGHT. THE ECWMF IS OVERALL SLOWER
WITH THE FRONT...SHOWING MORE OF AN ANAFRONT PRECIP PATTERN THRU
THURSDAY. IN EITHER CASE...WE COULD SEE A HEAVY RAIN EVENT...WITH
ONE OR TWO ROUNDS OF DECENT QPF...AS THE FRONT SLOWLY PUSHES THRU
FROM THE NORTHWEST. THE LATEST DAYS 6-7 QPF GUIDANCE FROM WPC SHOWS
OVER AN INCH OF QPF ACRS THE PIEDMONT AND 1-3" ACRS THE MTNS. GOING
WITH LIKELY TO CATEGORICAL POPS FOR WED-WED NIGHT...AND CHC POP FOR
THU-THU NIGHT. THE AREA SHUD BE IN THE WARM SECTOR OF THE PLAINS LOW
ON WEDNESDAY...SO ABOVE NORMAL TEMPS IN THE 60S FOR MOST OF THE AREA
EXPECTED. NEAR NORMAL TEMPS FOR THURSDAY...AS COLD FRONT PUSHES THRU.

&&

.AVIATION /05Z FRIDAY THROUGH TUESDAY/...
AT KCLT...GUIDANCE APPEARS TO BE TOO OPTIMISTIC ON CIGS...AND MODEL
TIME HEIGHTS SUGGEST A LOW VFR CIG THROUGH THIS EVENING. SOME IFR
VSBY HAD BEEN NOTED TO THE NE...BUT GUIDANCE INSISTS ON VFR. THE
FORECAST WILL BRING THE VSBY TO MVFR AROUND DAWN. WINDS WILL VEER
FROM NW TO NE TODAY.

ELSEWHERE...AT MOST SITES...GUIDANCE WAS TOO OPTIMISTIC ON CIG
COMPARED TO CURRENT OBSERVATIONS. MODEL TIME HEIGHTS SUGGEST LOW VFR
CIGS FOR MOST OF THE TIME THROUGH THIS EVENING...BUT OBSERVATIONS
SUPPORT MVFR AT KAND...WHICH SHOULD LAST AT LEAST UNTIL DAYBREAK.
GUIDANCE IS NOT SUPPORTIVE OF VSBY RESTRICTIONS AT TAF SITES. WINDS
WILL VEER FROM NW TO NE TODAY...EXCEPT AT KAVL...WHERE WINDS WILL
REMAIN FROM THE N.

OUTLOOK...LOW LEVEL MOISTURE WILL LINGER THROUGH THE REMAINDER OF
THE WEEK AND INTO THE WEEKEND AS COLD AIR DAMMING BUILDS FROM
THE NORTH ON SATURDAY. FLIGHT RESTRICTIONS WILL BE POSSIBLE DURING
THIS TIMEFRAME...ESPECIALLY ON SUNDAY ONCE MOISTURE SPREADS IN FROM
THE SOUTH AND CIGS LOWER.

CONFIDENCE TABLE...

            13-19Z        19-01Z        01-07Z        07-12Z
KCLT       HIGH  95%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       MED   74%     HIGH 100%     HIGH 100%     HIGH 100%
KHKY       MED   77%     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 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...WINTER WEATHER ADVISORY UNTIL 10 AM EST THIS MORNING FOR
     GAZ010-017-018.
NC...WINTER WEATHER ADVISORY UNTIL NOON EST TODAY FOR NCZ033-
     048>053-058-059-062>065-501-503-505-507-509.
     WINTER WEATHER ADVISORY UNTIL 10 AM EST THIS MORNING FOR
     NCZ035>037-056-057-068>072-082-502-504-506-508-510.
SC...WINTER WEATHER ADVISORY UNTIL 10 AM EST THIS MORNING FOR
     SCZ001>009.

&&

$$
SYNOPSIS...CSH
NEAR TERM...JAT/JPT/WIMBERLEY
SHORT TERM...RWH
LONG TERM...ARK
AVIATION...JAT


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