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Area Forecast Discussion

951
FXUS62 KGSP 010021
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
721 PM EST SAT FEB 28 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 SUNDAY/...
630 PM UPDATE...CLOUD COVER HAS BEEN SLOW TO INCREASE OVER THE
WEDGE...SO SKY GRIDS HAVE BEEN REVISED CLEARER THIS EVENING. NAM
FAMILY OF GUIDANCE SEEMS TO HAVE A GOOD HANDLE ON THIS.
LIKEWISE...POPS WERE BACKED OFF CONCURRENTLY. WITH AT LEAST
PARTIALLY CLEAR SKIES THE TEMP FCST IS MADE A LITTLE MORE DIFFICULT
EVEN THOUGH BREEZY CONDITIONS WILL INHIBIT RADIATION.
OVERALL...REVISED TEMPS TO NEAR SHORT TERM CONSENSUS VALUES...BUT AT
ONSET OF PRECIP I ALLOWED THEM TO DIP TO NEAR THE WET BULB TEMPS.
RELATIVELY MOIST DEWPOINTS WILL KEEP WET BULBS RELATIVELY HIGH BUT
THERE SHOULD BE ENOUGH OF AN EFFECT TO BRING TEMPS BELOW FREEZING.
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. THIS MAY BE A LITTLE OPTIMISTIC HOWEVER
FOR THE NC PIEDMONT...THE AREA MOST UNDER THE CONTROL OF THE WEDGE.

&&

.SHORT TERM /SUNDAY NIGHT 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 /01Z SUNDAY THROUGH THURSDAY/...
AT KCLT...COLD AIR DAMMING IN PLACE WILL SET THE STAGE FOR COLD
AND DAMP CONDITIONS LATER TONIGHT...WITH FZRA LIKELY TO RESULT. VFR
WILL CONTINUE THRU THE EVENING BEFORE A SURGE OF MOISTURE AND WARM
UPGLIDE MOVES ATOP THE WEDGE...CIGS LOWERING TO MVFR AND EVENTUALLY
IFR WITH ONSET OF PRECIP. TEMP FCST IS TRICKY BUT CRITICAL TO
DETERMINE PRECIP TYPE. TEMPS ARE LIKELY TO REMAIN ABOVE FREEZING
UNTIL PRECIP GETS UNDERWAY...WHEN EVAPORATIVE COOLING IS LIKELY TO
BRING THEM BELOW 0C. FZRA IS BY FAR THE MOST LIKELY TYPE BY THE
ONSET OF STEADY PRECIP. HOWEVER IF ANY LIGHT PRECIP FELL EARLIER
SLEET AND SNOW MIGHT MIX WITH RAIN. WE WILL JUST NEED TO MONITOR
RADAR AND SHORT RANGE GUIDANCE THRU THE NIGHT. IFR CIGS COULD LOWER
TO LIFR AS RAIN CONTINUES INTO THE DAY SUNDAY. SOLIDLY NE WINDS
WITHIN THE WEDGE...BUT THESE MAY TURN SELY VERY LATE IN THE PERIOD
AS IT BEGINS TO WEAKEN.

ELSEWHERE...BASICALLY THE SAME CONCERNS AS AT KCLT. THE RESTRICTIVE
CIGS WILL ARRIVE FROM S TO N LATER THIS EVENING. A PERIOD IF FZRA IS
EXPECTED AT ALL SITES EXCEPT KAND WHERE TEMPS DO NOT APPEAR LIKELY
TO DROP BELOW FREEZING. THE CHANGEOVER TO RAIN SHOULD OCCUR IN THE
COUPLE HRS AFTER SUNRISE...WITH PRECIP CHANCES TAPERING OFF AFTER
NOON FROM W TO E. ONCE IFR DEVELOPS IT IS UNLIKELY TO GO ANYWHERE
BEFORE 00Z MON. WINDS MAY START TO VEER TO MORE SWLY OVER THE MTNS
LATE IN THE DAY...AND KAVL WILL BE CHANNELED SE BY THE VALLEY...BUT
OTHERWISE THE WEDGE-FORCED NE WINDS WILL PREVAIL THRU THE PERIOD.

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 FROM MIDNIGHT TONIGHT TO NOON EST
     SUNDAY FOR GAZ010-017.
NC...FREEZING RAIN ADVISORY FROM MIDNIGHT TONIGHT TO NOON EST
     SUNDAY FOR NCZ048-051>053-058-059-062>065-068>072-082-
     507>510.
     WINTER WEATHER ADVISORY FROM 3 AM TO 5 PM EST SUNDAY FOR
     NCZ033-035>037-049-050-056-057-501>506.
SC...FREEZING RAIN ADVISORY FROM MIDNIGHT TONIGHT TO NOON EST
     SUNDAY FOR SCZ001>003-006>009-012>014.

&&

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



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