Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 030706
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
206 AM EST WED FEB 3 2016

.SYNOPSIS...
A STRONG COLD FRONT WILL APPROACH LATER TONIGHT AND PUSH THROUGH THE
AREA ON WEDNESDAY BRINGING WIDESPREAD SHOWERS AND SOME
THUNDERSTORMS...SOME OF WHICH COULD BE STRONG TO SEVERE. IN THE
FRONTS WAKE...DRY HIGH PRESSURE WILL SPREAD BACK OVER THE REGION AND
PERSIST INTO THE WEEKEND. ANOTHER UPPER DISTURBANCE WILL APPROACH
THE CAROLINAS FROM THE WEST EARLY NEXT WEEK.

&&

.NEAR TERM /THROUGH TODAY/...
AS OF 1 AM...WIDE FRONTAL PRECIP BAND IS MOVING INTO THE AREA MORE
QUICKLY THAN PREVIOUSLY FORECAST...SO WILL ALLOW 100 POPS TO SPREAD
THROUGH THE WESTERN HALF OR SO OF THE FORECAST AREA THROUGH 12Z.
SOME RELATIVELY HEALTHY CONVECTION IS NOTED ACROSS NORTHERN ALABAMA
ATTM...WITHIN AXIS OF (BARELY) POSITIVE SBCAPE. THE LATEST SHORT
TERM GUIDANCE INDICATE THIS CAPE AXIS WILL WEAKEN EVEN FURTHER AS
THE CONVECTIVE BAND MOVES EAST...WHERE IT WILL ENCOUNTER AN AIR MASS
THAT IS COOLER OWING TO RESIDUAL COLD POOL AND UPSLOPE SHOWERS.
NEVERTHELESS...A PROMINENT WARM FRONT/CAD BOUNDARY IS LOCATED
ROUGHLY ALONG THE I-85 CORRIDOR...WHERE SRH IS BEING ENHANCED ABOVE
AND BEYOND THE ALREADY-IMPRESSIVE ENVIRONMENTAL SRH. SO THE
SITUATION WILL BEAR CLOSE MONITORING LATER THIS MORNING.
OTHERWISE...THE MAIN CONCERN WILL BE THE HEAVY RAIN POTENTIAL...
ESPECIALLY ALONG THE SOUTHERN ESCARPMENT...WHERE AROUND AN INCH OF
PRECIP HAS ALREADY FALLEN SINCE TUE EVENING...WITH MUCH MORE TO
COME.

UPDATED QPF BRINGS OVER 3.5 INCHES OF RAIN BETWEEN 00Z TONIGHT AND
18Z WEDNESDAY TO THE CLIMATOLOGICALLY FAVORED SOUTHWEST MOUNTAINS.
FOR NOW...BETWEEN FLASH FLOOD GUIDANCE AND CURRENT RIVER
LEVELS...THINKING THAT RIVER FLOOD THREATS ARE MINIMAL BUT CANNOT
RULE OUT SOME ISOLATED FLASH FLOODING. HOWEVER...WILL NOT ISSUE A
FLASH FLOOD WATCH AT THIS TIME DUE TO THE LOCALIZED NATURE OF THE
HIGHEST QPF AND FLASH FLOOD GUIDANCE VALUES INDICATING THAT SOILS
SHOULD BE ABLE TO HANDLE THIS AMOUNT OF RAIN...BUT IF QPF VALUES
RAMP UP OR UPSLOPE PRECIPITATION INCREASES MORE TONIGHT THAN
ANTICIPATED WILL HAVE TO REVISIT THIS ISSUE.

AS THE FRONT APPROACHES TONIGHT AND TOMORROW...INSTABILITY WILL
INCREASE IN A FAIRLY CLASSIC HIGH SHEAR LOW CAPE SCENARIO. SBCAPE
VALUES AROUND 100J/KG START CREEPING INTO WESTERN ZONES
AROUND 12Z...INCREASING DURING THE DAY AND SPREADING ACROSS
THE AREA...FINALLY EXITING AROUND THE END OF THE PERIOD. THE
NAM IS...AS USUAL...A LITTLE STRONGER WITH THE SBCAPE VALUES
AND ALSO HANGS THE FRONT BACK A LITTLE BIT...ALLOWING CAPES
TO INCREASE JUST A TAD. HOWEVER...AT BEST SBCAPE VALUES REMAIN
JUST UNDER 500J/KG...AND THIS IS PRETTY TALL SKINNY CAPE. THE
MORE IMPRESSIVE FEATURE IS THE SHEAR. HODOGRAPHS ARE CLASSICALLY
CURVED WITH DEEP-LAYER SHEAR OF 60-70KT AND 30-40KT 0-1KM SHEAR
ON THE GFS AND UPWARDS OF 50KT FOR THE NAM. WITH THIS...NAM EVEN
BRINGS A BULLSEYE OF 4 STP AROUND 21Z WEDNESDAY FOR PORTIONS OF THE
UPSTATE. LONG STORY SHORT...HIGH SHEAR LOW CAPE EVENT SEEMS LIKELY
TOMORROW WITH AT LEAST SOME DAMAGING WIND AND OF COURSE A NON-ZERO
TORNADO THREAT...LINING UP WELL WITH THE SPC MARGINAL DAY1 OUTLOOK.

TEMPERATURES WILL FEATURE A REDUCED DIURNAL RANGE WITH DEFINITELY
SOME BUST POTENTIAL BOTH TONIGHT...ASSOCIATED WITH THE DAMMING...AND
TOMORROW WITH CLOUD COVER...RAIN...AND PROGRESSION OF THE FRONT.

&&

.SHORT TERM /TONIGHT THROUGH FRIDAY/...
AT 230 PM TUESDAY...ON WEDNESDAY EVENING AN UPPER RIDGE WILL BE WELL
OFF THE EAST COAST...AND UPPER RIDGE WILL BE OVER THE CENTER OF THE
NATION...AND ANOTHER UPPER RIDGE WILL BE OVER THE WESTERN USA.
LITTLE OVERALL PROGRESSION OF THIS PATTERN OCCURS THROUGH FRIDAY
NIGHT...AS THE ORIGINAL TROUGH WEAKENS WHILE MOVING EAST OVER THE
APPALACHIANS ON FRIDAY...AND IS REPLACED BY ANOTHER TROUGH MOVING
FROM THE SOUTHERN ROCKIES TO THE PLAINS.

AT THE SURFACE....ON WEDNESDAY EVENING A COLD FRONT WILL BE SLOWLY
EXITING OUR AREA TO THE EAST...WHILE NW FLOW MOISTURE PERSIST OVER
THE NC MOUNTAINS BORDERING TN. LIGHT RAINFALL MAY BE SLOW TO EXIT
THE PIEDMONT AREA OVERNIGHT AND INTO THURSDAY. MEANWHILE...LIGHT
SNOW OR RAIN SHOWERS BRIEFLY SET UP IN THE WESTERN NC MOUNTAINS
AROUND DAWN ON THURSDAY...WITH THE RAIN SHOWERS AT LOWER ELEVATIONS.
DRYING OCCURS BY THURSDAY EVENING AS HIGH PRESSURE MOVES EAST ACROSS
THE GULF STATES...ALTHOUGH THE PRESSURE GRADIENT DOES NOT DECREASE
UNTIL FRIDAY...KEEPING WINDS UP A BIT...MAINLY IN THE MOUNTAINS.
TEMPERATURES WILL FALL TO NEAR MID WINTER NORMALS BEHIND THE
FRONT...WITH COLD ADVECTION OFFSETTING DOWNSLOPE WARMING.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
AS OF 130 PM TUE...DRY SFC HIGH PRESSURE WILL BLANKET MOST OF THE
ERN CONUS THRU EARLY SATURDAY UNDER CONFLUENT UPPER FLOW. THIS
BREAKS DOWN BY SAT NIGHT AS HEIGHTS FALL OVER THE INLAND EAST...AS
PHASED NRN AND SRN STREAM TROUGHS ADVANCE. THE NRN STREAM TROUGH
MOVES FASTER...SHEARING OFF THE SRN TROUGH OVER THE GULF COAST
REGION. THE TIMING AND EXACT LOCATION OF THAT OCCURRENCE IMPACTS OUR
FORECAST FOR SUNDAY INTO EARLY MONDAY...AS IT DETERMINES THE TRACK
OF A MILLER-A TYPE COASTAL LOW. MAJORITY OF THE LATEST AVBL GUIDANCE
PLACES THE SFC CYCLOGENESIS NEAR THE FLORIDA PANHANDLE...AND FAR
ENOUGH SOUTH AND EAST OF THE CWFA TO PRECLUDE SIGNIFICANT WINTER
WX. HOWEVER...NOTE E.G. THE 12Z GEM DEVELOPING THE LOW OVER THE
CENTRAL GULF WATERS INSTEAD...RESULTING IN A COLDER/WETTER PRECIP
EVENT FOR OUR CWFA. THE OTHER GUIDANCE /INCLUDING ENSEMBLE MEMBERS/
HAVE TRENDED TOWARD THE MORE OFFSHORE TRACK. THEREFORE I THINK
IT IS MOST LIKELY THE SYSTEM WILL BRUSH BY TO OUR SE. TEMPS WILL
REMAIN NEAR NORMAL...TRENDING SLIGHTLY UPWARD OVER THE WEEKEND.

JUST AS SOON AS THE COASTAL LOW DEPARTS THE REGION...A DEEPER
NRN STREAM TROUGH AND EMBEDDED CYCLONE DIG INTO THE MISSISSIPPI
VALLEY. GFS SUGGESTS PRECIP COULD RESULT AS EARLY AS MON MRNG AS
THE INITIAL COLD FRONT AND UPSLOPE FLOW ENCOUNTER THE MTNS...WITH
A SECOND ROUND COMING MON NIGHT-TUE WITH A SECONDARY FRONT. EC
DEVELOPS PRECIP ONLY FROM THE LATTER. NONETHELESS THIS SEEMS TO BE
WELL ENOUGH HANDLED BY GUIDANCE TO INTRODUCE LOW CHANCES FOR PRECIP
MAINLY OVER THE MTNS AND PORTIONS OF NC PIEDMONT...WHICH MAY RESULT
IN SOME LIGHT SNOW FOR THESE AREAS...PARTICULARLY TUE AS COOLER
TEMPS ARRIVE...AND MAX TEMPS DROP BACK TO 5-7 DEG BELOW NORMAL.

&&

.AVIATION /07Z WEDNESDAY THROUGH SUNDAY/...
AT KCLT...IFR CIGS HAVE RETURNED IN ASSOCIATION WITH MOIST LOW LEVEL
LIFT WITHIN SE FLOW REGIME. THE GOOD NEWS IS IT APPEARS THAT VISBY
IS NOT GOING TO BE AS PROBLEMATIC AS PREVIOUSLY ANTICIPATED...AS THE
STOUT SE WINDS SHOULD PREVENT ANY BR/FG FROM DEVELOPING.
HOWEVER...VISBY IS EXPECTED TO DETERIORATE AFTER SUNRISE...AS RAIN
ASSOCIATED WITH A COLD FRONT OVERSPREADS THE AREA FROM THE WEST.
EXPECT VISBY PRIMARILY IN THE 2-3SM RANGE...WITH BRIEF PERIODS OF
LOWER VISBY POSSIBLE IN HEAVY RAIN. IN TERMS OF CIGS...WILL FORECAST
THEM TO REMAIN AROUND 006 (GIVE OR TAKE 100 FT) THROUGH THE
AFTERNOON... ALTHOUGH WOULD NOT BE AT ALL SURPRISED TO SEE THEM LIFT
TO MVFR BY AROUND 18Z. ISOLATED THUNDER WILL BE POSSIBLE DURING THE
AFTERNOON...AND HAVE ACTUALLY BACKED UP THE PROB30 TO 18Z. WINDS
WILL GRADUALLY TURN TOWARD THE S AND SW AT 10-15 KTS...WITH GUSTS
AROUND 20 KTS POSSIBLE AT JUST ABOUT ANY TIME. PRECIP CHANCES WILL
DIMINISH DURING THE EVENING...CONCURRENT WITH RATHER QUICK
IMPROVEMENT IN FLT CONDITIONS.

ELSEWHERE...OCCL RAIN CAN BE EXPECTED AT THE TERMINALS OVER THE NEXT
FEW HOURS...FOLLOWED BY MORE PERSISTENT AND INCREASING RAINFALL
RATES BY AROUND SUNRISE...AND CONTINUING THROUGH A GOOD PART OF THE
DAY. THE GOOD NEWS IS VISBY IS NOT EXPECTED TO BE AS LOW AS
PREVIOUSLY FORECAST...AS THE INCREASING S/SE WINDS HAVE GENERALLY
CLEARED OUT MUCH OF THE BR. HOWEVER...OCCL 2-3SM VISBY IN RAIN WILL
CONTINUE THROUGH THE EARLY MORNING...WITH VISBY EXPECTED TO BECOME
MORE PERSISTENT IN THIS RANGE...WITH OCCL LOWER VISBY IN MODERATE TO
HEAVY RAIN. THUNDER CHANCES WILL INCREASE AT THE TERMINALS BY LATE
MORNING...AND PROB30S ARE CARRIED AT ALL LOCATIONS INTO THE
AFTERNOON. OTHERWISE...CIGS ARE EXPECTED TO SETTLE AT AROUND 005 BY
DAYBREAK. THE FORECAST CARRIED THESE THROUGH MUCH OF THE DAY...BUT
WOULD NOT BE SURPRISED TO SEE THEM LIFT TO MVFR BY EARLY AFTERNOON.
PRECIP CHANCES WILL DIMINISH DURING THE EVENING...CONCURRENT WITH
RATHER QUICK IMPROVEMENT IN FLT CONDITIONS.

OUTLOOK...IN THE WAKE OF THE FRONT...LARGE HIGH PRESSURE WILL BUILD
ACROSS THE REGION THROUGH THE WEEKEND...PROVIDING UNRESTRICTED
CONDITIONS.

CONFIDENCE TABLE...

            07-13Z        13-19Z        19-01Z        01-06Z
KCLT       HIGH  89%     HIGH  90%     HIGH  80%     MED   74%
KGSP       HIGH  91%     HIGH  85%     HIGH  81%     HIGH 100%
KAVL       HIGH  84%     HIGH  85%     MED   75%     HIGH 100%
KHKY       HIGH  86%     HIGH  87%     MED   73%     HIGH  94%
KGMU       HIGH  89%     HIGH  91%     HIGH  82%     HIGH 100%
KAND       HIGH  93%     HIGH  84%     MED   77%     HIGH 100%

THE PERCENTAGE REFLECTS THE NUMBER OF GUIDANCE MEMBERS AGREEING
WITH THE SCHEDULE TAF ISSUANCE FLIGHT RULE CATEGORY. COMPLETE 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...WIND ADVISORY UNTIL 10 AM EST THIS MORNING FOR NCZ033-048>052-
     058-059-062>064.
SC...NONE.

&&

$$
SYNOPSIS...JPT
NEAR TERM...JDL/TDP
SHORT TERM...JAT
LONG TERM...WIMBERLEY
AVIATION...JDL


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