Area Forecast Discussion
Issued by NWS Greer, SC

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS62 KGSP 010536
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1236 AM EST SUN MAR 1 2015

.SYNOPSIS...
COLD HIGH PRESSURE WILL PERSIST THROUGH SUNDAY. MOISTURE WILL
INCREASE AHEAD OF AN APPROACHING COLD FRONT WHICH WILL CROSS THE AREA
ON MONDAY. CANADIAN HIGH PRESSURE BUILDS BACK IN TUESDAY...WITH
ANOTHER MOIST COLD FRONT AFFECTING THE REGION LATE WEDNESDAY.

&&

.NEAR TERM /THROUGH TODAY/...
0535 UTC UPDATE...WINDS WERE UPDATED WITH A BLEND OF THE LATEST NAM
AND ADJMAV. SKY COVER WAS UPDATED BASED ON SATELLITE TRENDS.

1015 PM UPDATE...VERY LIGHT RADAR RETURNS NOW SPREADING INTO THE SRN
TIP OF THE CWFA...AND INCREASING IN COVERAGE. ASOS AT KGRD HAS
REPORTED A TRACE SO AT LEAST SOME OF IT IS REACHING THE GROUND.
LATEST GUIDANCE DOES STILL SHOW COVERAGE INCREASING OVERNIGHT...BUT
SOME OF THE MODELS DO NOT SHOW APPRECIABLE QPF OVER THE PIEDMONT
UNTIL WELL AFTER MIDNIGHT. MAINTAINED HIGH LIKELY POPS FOR THE
PIEDMONT AND BLUE RIDGE AREAS BUT KEPT QPF MODEST IN LIGHT OF THE
MESO MODEL RESULTS AND WPC PROBABILISTIC QPF SUGGESTING BEST
CONFIDENCE FOR UNDER A TENTH OF LIQUID THRU 12Z. MODEL TRENDS APPEAR
TO SUGGEST THE BEST ISENTROPIC FORCING WILL ARRIVE 12-18Z WHICH MAY
BE GOOD IN TERMS OF LIMITING THE AMOUNT OF THAT QPF THAT FALLS AS
FZRA.

TEMPS OVER MUCH OF THE AREA ARE ABOVE 0C ATTM...WITH A SLOW DECLINE
LIKELY RESULTING DIURNALLY. HOWEVER THERE SHOULD BE ENOUGH OF A WET
BULB EFFECT TO BRING TEMPS BELOW FREEZING AFTER PRECIP GETS GOING
OVER A LOCATION. THAT WILL ALLOW FOR THE ONSET OF FREEZING RAIN. IF
ANY LIGHT PRECIP OCCURS EARLIER THAN ANTICIPATED...IT IS POSSIBLE
RAIN MIGHT MIX WITH SOME SLEET OR SNOW INSTEAD...SINCE THE WARM NOSE
WILL TAKE TIME TO STRENGTHEN TONIGHT AND MELT ANY FROZEN
HYDROMETEORS. ACCUMULATION OF SLEET/SNOW APPEARS TO BE MINIMAL. I
HAVE REVISED ICE ACCUMS BASED ON THE LATEST FCST...WHICH PUTS MOST
OF THE ACCRETION BETWEEN 09-15Z BEFORE TEMPS START TO WARM. ACCUMS
MAX OUT AT ABOUT 0.15 INCH IN THE STATESVILLE/SALISBURY AREA...WITH
MAINLY UNDER A TENTH FURTHER S AND W. THIS ASSUMES THAT SOME OF THE
QPF WILL RUN OFF BEFORE FREEZING...GIVEN THE NECESSITY OF WET
BULBING TO DROP TEMPS. THIS MAY BE A LITTLE OPTIMISTIC.

IN LIGHT OF REVISED TEMPS AND PTYPES...I DID EXPAND THE FZRA ADVY TO
THE REST OF OCONEE/PICKENS AND ANDERSON COUNTIES. DID CONSIDER
CHANGING THE WINTER WX ADVY HEADLINE AREA TO FZRA...BUT STILL THINK
THERE MAY BE SOME MIXED PRECIP AT ONSET.

&&

.SHORT TERM /TONIGHT THROUGH TUESDAY/...
AS OF 305 PM SATURDAY...A SHORT WAVE PASSES BY TO OUR NORTH ON
MONDAY DROPPING HEIGHTS ACROSS THE REGION AND PUSHING A COLD FRONT
SOUTH OF THE AREA. COOLER HIGH PRESSURE BUILDS BEHIND THE FRONT AS
WELL. THIS WILL HELP END PRECIP OUTSIDE OF THE MTNS AS DRIER AIR
MOVES IN...BUT SOME WILL LINGER ACROSS THE MTNS AS THE FRONT MOVES
THRU AND THE MOIST NW FLOW BEHIND THE FRONT. ALL PRECIP WILL BE
LIQUID SUN NITE AND MON AS THE COLDEST AIR IS SLOW TO MOVE IN WITH
THE HIGH. LOWS SUN NITE NEAR TO A LITTLE ABOVE NORMAL WITH HIGHS
MONDAY NEAR TO A LITTLE BELOW NORMAL.

THE FRONT ATTEMPTS TO MOVE BACK NORTH AS A WARM FRONT...BUT IS
BLOCKED ACROSS OUR AREA AS THE HIGH PRESSURE TO OUR NORTHEAST SETS
UP AS A HYBRID CAD. HOWEVER...MOIST LOW LEVEL SLY FLOW AND
ISENTROPIC LIFT DO DEVELOP LATE MON NITE INTO TUE. TEMPS WILL BE
COLD ENUF AT ONSET FOR A BRIEF PERIOD OF FREEZING RAIN ACROSS THE
NRN MTNS AND BLUE RIDGE AREA...AND POSSIBLY NORTH OF I-40 ACROSS THE
NC FOOTHILLS AND PIEDMONT. BEST CHC FOR ANY ICE ACCRETION WILL BE
ACROSS THE NRN MTNS AND BLUE RIDGE...HOWEVER EVEN THESE AMOUNTS WILL
BE VERY LIGHT. LOWS MON NITE WILL BE AROUND 5 DEGREES ABOVE
NORMAL...BUT HIGHS TUE WILL BE 10 TO 15 DEGREES BELOW NORMAL IN THE
DEVELOPING PRECIP AND CAD.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
AS OF 230 PM SATURDAY...GUIDANCE STILL IN A LITTLE DISAGREEMENT ON
EXACT TIMING OF A WET FRONTAL ZONE THAT WILL SLOWLY SAG
SOUTHEASTWARD THRU THE CWFA WEDNESDAY THRU THURSDAY...BUT HAVE THE
SAME GENERAL IDEA. THE 12Z ECMWF HAS COME IN A LITTLE CLOSER TO THE
GFS/S FASTER TIMING ON WEDNESDAY...AND IS STILL QUICKER ON PUSHING
THE FRONTAL BAND ALL THE WAY THRU BY THURSDAY MORNING.
MEANWHILE...THE GFS AND CMC ARE A LITTLE SLOWER...AND KEEP
WIDESPREAD QPF ACRS THE CWFA THRU THE DAY THURSDAY. GOING WITH A
COMPROMISE/WPC FOR THIS FCST.

WEDNESDAY...STRONG SWLY WINDS AHEAD OF THE FRONT WILL SUPPORT TEMPS
5-10 DEG ABOVE NORMAL (WELL INTO THE 60S ACRS THE PIEDMONT). POPS
START RAMPING UP TO LIKELY IN THE EAST AND CATEGORICAL IN THE WEST
DURING THE AFTN HOURS. THE PERSISTENT LIFT ASSOCIATED WITH A STRONG
UPPER LEVEL JET NEARLY PARALLEL TO THE FRONT SHUD RESULT IN A SOLID
RAIN SHIELD...WITH SOME POTENTIALLY HEAVY RAIN. ALTHO...STILL NO
CLEAR SIGNALS THAT THERE WILL BE MUCH HYDRO/EXCESSIVE RAIN CONCERNS.
CATEGORICAL POPS CONTINUE FOR MOST OF THE AREA WEDNESDAY NIGHT. MAY
SEE SNOW LEVELS DROP TO AROUND 3500 FT ALONG THE TN LINE TOWARD
DAYBREAK THURSDAY...AS THE POLAR AIR MASS TO THE WEST STARTS TO PUSH
IN WHILE LIFT PERSISTS IN THE MID LVLS. MAY SEE LIGHT TO MODERATE
SNOW ACCUMS THERE BEFORE PRECIP ENDS. I HAVE POPS GRADUALLY TAPER
OFF THURSDAY INTO THURSDAY NIGHT...AS DRY AIR FILTERS IN FROM THE
NW. THURSDAY WILL BE A TRANSITION DAY FOR TEMPS...WITH NEAR NORMAL
ACRS THE PIEDMONT AND BELOW NORMAL IN THE MTNS. TEMPS WILL RETURN TO
BELOW NORMAL FROM THURSDAY NIGHT THRU SATURDAY NIGHT...AS THE HIGH
PRES SYSTEM SETTLES INTO THE SOUTHEAST STATES.

&&

.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
AT KCLT...GUIDANCE DISCREPANCIES YIELD LOW CONFIDENCE ON TIMING AND
VALUES OF CIGS AND VSBYS THIS FORECAST. A BLENDED APPROACH BRING
VSBY DOWN TO MVFR BY DAWN AS FREEZING RAIN SETS UP OVER THE
AREA...WITH A RETURN TO VFR BY MIDDAY...THEN MVFR TONIGHT. THE SAME
APPROACH BRINGS A LOW VFR CIG DOWN TO MVFR BEFORE DAWN...THEN BACK
TO LOW VFR THIS EVENING...THEN TO IFR LATE THIS EVENING. WINDS WILL
FAVOR THE NE IN COLD AIR DAMMING TODAY...BACKING TO THE SW THIS
EVENING AS THE COLD AIR WEDGE ERODES. FREEZING PRECIPITATION WOULD
CHANGE TO RAIN IN THE MORNING...WITH AS MUCH AS SEVEN TENTHS OF AN
INCH OF ICE ACCRETION. RAIN WOULD TAPER OF DURING THE EVENING.

ELSEWHERE...GUIDANCE VARIES CONSIDERABLY ON CIGS AND VSBYS AND THEIR
TIMING...YIELDING LOW CONFIDENCE. USING A BLENDED APPROACH...CIGS
WILL FALL TO MVFR OVERNIGHT WHILE FREEZING RAIN SETS UP AT ALL SITES
BUT KAND...WHERE RAIN WILL FALL. CIGS RISE TO VFR AT SC SITES AND
KAVL THIS EVENING...BUT FALL TO IFR AT KHKY. AN MVFR CIG MAY RETURN
TO KAND VERY LATE IN THE FORECAST. FOOTHILL VSBYS WOULD FALL TO MVFR
IN THE MORNING IN RAIN INDUCED FOG. BY THE TIME KAVL GOES TO MVFR
VSBY AT MIDDAY...SC SITES RETURN TO VFR. BY LATE AFTERNOON NC SITES
GO VFR...THEN IN THE EVENING ALL SITE RETURN TO MVFR. FREEZING
PRECIPITATION CHANGE TO RAIN IN THE MORNING...WITH ICE TOTALS
GENERALLY A LITTLE MORE THAN 5 TENTHS OF AN INCH...EXCEPT AT KAND
WHERE ONLY RAIN FALLS. RAIN WOULD TAPER OFF DURING THE EVENING.

OUTLOOK...CAD REGIME WILL WEAKEN LATE SUN INTO MON WITH ANOTHER
CANADIAN HIGH SLIDING NORTH OF THE CAROLINAS. AS THE HIGH MOVES NE
OF THE REGION...ANOTHER BRIEF CAD PATTERN IS POSSIBLE. PERIODS OF
PRECIP AND FLIGHT RESTRICTIONS THUS ARE LIKELY TUE-WED. A COLD FRONT
WILL MOVE THROUGH THE REGION BY THU BRINGING WET WEATHER AND
POSSIBLE RESTRICTIONS.

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...FREEZING RAIN ADVISORY UNTIL NOON EST TODAY FOR GAZ010-017.
NC...FREEZING RAIN ADVISORY UNTIL NOON EST TODAY FOR NCZ048-051>053-
     058-059-062>065-068>072-082-507>510.
     WINTER WEATHER ADVISORY UNTIL 5 PM EST THIS AFTERNOON FOR
     NCZ033-035>037-049-050-056-057-501>506.
SC...FREEZING RAIN ADVISORY UNTIL NOON EST TODAY FOR SCZ001>010-
     012>014.

&&

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


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.