Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 201933
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
233 PM EST SAT DEC 20 2014

.SYNOPSIS...
LOW LEVEL MOISTURE WILL LINGER ATOP A WEDGE OF HIGH PRESSURE...AS A
SERIES OF WEAK WAVES TRACK BY TO OUR SOUTH TONIGHT THROUGH MONDAY.
DEEPER MOISTURE ARRIVES ON TUESDAY AHEAD OF A SHARP COLD FRONT. THE
COLD FRONT WILL CROSS THE AREA FROM THE WEST ON WEDNESDAY. COLD AND
WINDY CONDITIONS WILL SET UP IN THE MOUNTAINS THROUGH THURSDAY...
WITH DRIER CONDITIONS EXPECTED EAST OF THE MOUNTAINS.

&&

.NEAR TERM /THROUGH SUNDAY/...
AT 200 PM...FAST MOVING VORT MAX HAS EXITED TO THE EAST ALONG WITH
MOST OF THE PRECIP. RADAR DOES CONTINUE TO SHOW SOME WEAK RETURNS
OVER THE UPSTATE BUT THIS IS JUST DRIZZLE. NORTHERN MOUNTAIN PRECIP
ALSO LOOKS TO HAVE ENDED PER RADAR AND OBSERVATIONS. HENCE...POPS
FOR MEASURABLE PRECIP NOW GENERALLY <15%.

MODEL SOUNDINGS AND TIME HEIGHTS INDICATE THAT LOW LEVEL FLOW WILL
REMAIN MOSTLY NE-E THROUGH SUNDAY AS WEAK CAD CONDITIONS CONTINUE.
BOUNDARY LAYER ALSO IS FORECAST TO REMAIN MOIST. HENCE...EXPECT
CLOUDS TO STUBBORNLY HANG IN. ALSO AS THE BOUNDARY LAYER COOLS
OVERNIGHT AND UPPER LEVELS DRY... EXPECT WIDESPREAD FOG TO DEVELOP.
RIGHT NOW IT DOES NOT LOOK LIKE VSBY`S WILL LOWER ENOUGH TO WARRANT
AN ADVISORY...BUT THIS WILL BE REACCESSED THROUGH THE EVENING
FORECAST UPDATES. A WEAK UPSLOPE COMPONENT INTO THE BLUE RIDGE MAY
PRODUCE PATCHY DRIZZLE THERE OVERNIGHT. SOME OF THE HIGHER
EVELATIONS COULD COOL ENOUGH FOR SOME FREEZING DRIZZLE...BUT AGAIN
NOT WIDESPREAD ENOUGH FOR ANY ADVISORY.

ON SUNDAY...LITTLE CHANGE IS EXPECTED AS WEAK CAD PERSISTS. SUNDAY
SHOULD BE A MOSTLY CLOUDY DAY WITH TEMPS PERHAPS RECOVERING A
CATEGORY ABOVE TODAY AS CLOUDS THIN SOME DURING THE AFTERNOON.
HOWEVER...MAX TEMPS WILL BE BELOW CLIMO OUTSIDE OF THE MOUNTAINS.







MAIN PRECIP AREA HAS MOVED EAST OF THE REGION. AREAS OF DRIZZLE
REMAIN OVER MAINLY THE WESTERN UPSTATE AND NE GA DUE TO MOIST E-NE
FLOW. NOT MUCH PRECIP LEFT IN THE MOUNTAINS...JUST SOME SCT FLURRIES
ABOVE 4000FT AND SCT LIGHT SHOWERS VALLEYS. DRIZZLE SHOULD GRADUALLY
END DURING THE AFTERNOON AS WINDS BECOME LIGHTER AND ATMOSPHERE
TRIES TO DRY FROM THE TOP DOWN.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
AS OF 200 PM EST SAT...SUN NIGHT AND MONDAY...A SOUTHWESTERLY UPPER
DIFFLUENT FLOW REGIME WILL SET UP ACROSS THE REGION BY MON NIGHT AS
A SOUTHERN STREAM UPPER SHORTWAVE APPROACHES FROM THE SW AND A WEAK
UPPER RIDGE AXIS PUSHES OFF THE EAST COAST. AHEAD OF THIS UPPER
FEATURE...BEST 290K ISENTROPIC LIFT WILL OCCUR BETWEEN 00Z AND 12Z
MON. THE UPPER WAVE IS FORECAST TO LIFT NE ACROSS THE CWA BETWEEN
12Z AND 18Z MON...OFF THE NC/VA COAST BY 00Z TUE. AT THE
SURFACE...COLD AIR DAMMING WEDGE WILL PERSIST ACROSS THE REGION AS
1030MB HIGH REMAINS CENTERED OVER THE NE STATES. MEANWHILE...A
CYCLOGENESIS WILL TAKE PLACE JUST OFF THE SE COAST ON
MONDAY...OVERSPREADING DEEP MOISTURE FROM THE SE. THE
COMBINATION OF THE BEST 290K ISENTROPIC LIFT AND DEEP LAYER MOISTURE
ADVECTION WILL SUPPORT LIKELY POPS OVER THE PIEDMONT AND SOLID
CHANCE POPS IN THE MTN ZONES LATE SUN NIGHT INTO MON MORNING. GIVEN
ABOVE FREEZING SURFACE TEMPS AND WARM NOSE ALOFT...FROZEN PRECIP IS
NOT EXPECTED AT THIS TIME. POPS RAMP DOWN TO THE END CHANCE
RANGE THRU MON AFTERNOON AS THE LOW PULLS FARTHER NE AWAY AND THE
UPPER FORCING EJECTS TO THE NE. WITH ONGOING PRECIP AND CAD...TEMPS
WILL REMAIN 3-7 DEGREES BELOW NORMAL.

MON NIGHT AND TUE...A RESIDUAL CAD AND MOIST SWLY FLOW ALOFT OVER
THE AREA WILL KEEP LOW END CHANCE POPS OVER THE PIEDMONT WITH SLIGHT
CHANCE POPS OVER THE MTNS ZONES ON MON NIGHT. A HIGH AMPLITUDE UPPER
TROUGH WILL DIG INTO THE WESTERN GULF STATES ON TUE...PUSHING AN
ASSOCIATED SHARP COLD FRONT THROUGH THE MISSISSIPPI VALLEY.
MEANWHILE...THE HIGH CENTERED OVER THE NE STATES WILL SHIFT
OFFSHORE...WITH NE FLOW BECOMING EASTERLY OVER THE FORECAST AREA BY
TUE AFTERNOON. POPS THEN RAMP UP TO CATEGORICAL OVER THE ESCARPMENT
OF THE BLUE RIDGE AND LIKELY RANGE ELSEWHERE THRU LATE TUE
AFTERNOON/EVENING AS STRONG UPPER SSWLY DIFFLUENT FLOW ALOFT
DEVELOPS WHILE ATLANTIC MOISTURE ADVECTION INCREASES IN EASTERLY
FLOW REGIME. TEMPS WILL WARM INTO NEAR NORMAL RANGE ON TUE.

&&

.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
AS OF 130 PM SATURDAY...A DEEP UPPER TROUGH AND ASSOCIATED CYCLONE
WILL MOVE ACROSS THE EASTERN CONUS EARLY IN THE MEDIUM RANGE
PERIOD...LIKELY RESULTING IN WIDESPREAD RAIN ACROSS THE FORECAST
AREA EARLY ON CHRISTMAS EVE. QPF WILL BE THE PRIMARY CHALLENGE
SURROUNDING THIS PERIOD OF THE FORECAST OVER THE NEXT COUPLE OF
DAYS...AS THERE APPEARS TO BE A GOOD CASE FOR A CONSIDERABLE AMOUNT
OF GULF COAST CONVECTION POTENTIALLY INTERRUPTING TRANSPORT OF THE
RICHEST GULF MOISTURE INTO THE AREA. NEVERTHELESS...MOST AREAS
SHOULD SEE RAIN LATE TUE NIGHT/EARLY WED...AND HIGH-END LIKELY TO
CATEGORICAL POPS WILL BE CARRIED DURING THIS TIME. ANOTHER
POTENTIALLY PROBLEMATIC FACET TO THE FORECAST IS THE POTENTIAL FOR
CONVECTION ACROSS OUR AREA WITHIN HIGH SHEAR/LOW CAPE REGIME WED
MORNING...AS STRONG/DEEP MERIDIONALLY-ORIENTED FORCING ACCOMPANIES
THE COLD FRONT INTO THE AREA. THE LATEST GFS HAS BECOME A LITTLE
MORE PRONOUNCED WITH ITS SURFACE-BASED INSTABILITY DURING THIS
TIME...AND A SLIGHT CHANCE FOR THUNDER WILL BE CARRIED...MAINLY
ACROSS THE PIEDMONT.

ALTHOUGH A BRIEF NORTHWEST FLOW SNOW EVENT MAY UNFOLD LATER WED INTO
WED NIGHT...THE LOW LEVEL FLOW REMAINS QUITE BACKED AS SNOW LEVELS
START TO FALL...OWING TO A CONSIDERABLE AMOUNT OF UPPER LEVEL SHORT
WAVE ENERGY REMAINING UPSTREAM OF THE REGION. MEANWHILE...THE UPPER
TROUGH AXIS IS EXPECTED TO LIFT QUICKLY OFF THE COAST INTO EARLY
THURSDAY...SO MOISTURE DOES NOT LINGER FOR VERY LONG ONCE THE FLOW
FINALLY TURNS NORTHWEST. THIS SPELLS A LOW IMPACT EVENT.

CHRISTMAS WILL BE UNSEASONABLY COOL BUT DRY UNDER ANOMALOUSLY LOW
HEIGHTS...BUT TEMPS WILL BEGIN TO MODERATE BY FRIDAY AS HEIGHTS RISE
OVER THE EAST IN RESPONSE TO DEPARTING TROUGH...AND A NEW ROUND OF
HEIGHT FALLS ACROSS THE WESTERN CONUS. THIS AREA OF HEIGHT FALLS AND
ATTENDANT FRONTAL ZONE MAY BRING THE NEXT CHANCE FOR PRECIP TO THE
AREA BY DAY 7.

&&

.AVIATION /20Z SATURDAY THROUGH THURSDAY/...
AT KCLT...MAIN AREA OF PRECIP HAS MOVED EAST OF THE AIRFIELD ALONG
WITH VORT MAX THAT TRIGGERED IT. IN ITS WAKE...A MOIST BOUNDARY
LAYER WILL REMAIN AS LIGHT NE FLOW CONTINUES. EXPECT CIGS TO HOVER
AROUND 030 AND THEN SLOWLY LOWER OVERNIGHT AS BOUBNDARY LAYER COOLS.
PLAYED IT CONSERVATIVE FOR NOW AND JUST LOWERED CIGS TO 015
OVERNIGHT AND VSBY TO 4SM IN BR. WOULD NOT BE SURPRISED IF IT WENT A
BIT LOWER THAN THAT. ONLY A SLOW IMPROVEMENT AFTER SR ON SUNDAY.

ELSEWHERE...FOR THE SC TAF SITES LOW MVFR TO IFR CONDITIONS ARE
EXPECTED TO PREVAIL DUE TO THE VERY MOIST BOUNDARY LAYER AND WINDS
REMAINING LIGHT E-NE. DRIZZLE SHOULD GRADUALLY END BY 00Z...BUT THEN
VSBYS WILL GRADUALLY LOWER TO AT LEAST 3SM IN BR BY 12Z.

OUTLOOK...LINGERING LOW LEVEL MOISTURE IS LIKELY TO KEEP LOW STRATUS
AND NIGHT TIME FOG AROUND THRU MONDAY...WITH SOME IMPROVEMENT DURING
THE DAYLIGHT HOURS. A COLD FRONT WILL APPROACH ON TUESDAY FROM THE
WEST AND MOVE THROUGH ON WED. WIDESPREAD SHOWERS WITH RESTRICTIONS
SHOULD ARRIVE TUESDAY AFTERNOON AND WILL CONTINUE UNTIL THE FRONT
CLEARS THE AREA LATE WEDNESDAY.

CONFIDENCE TABLE...

            19-01Z        01-07Z        07-13Z        13-18Z
KCLT       HIGH  81%     HIGH  86%     HIGH  88%     HIGH  80%
KGSP       HIGH  91%     HIGH  96%     HIGH 100%     HIGH  88%
KAVL       HIGH  88%     HIGH  91%     HIGH  81%     HIGH  94%
KHKY       LOW   58%     HIGH  81%     HIGH  94%     HIGH  90%
KGMU       HIGH  91%     HIGH  96%     HIGH 100%     HIGH  88%
KAND       HIGH  91%     HIGH  84%     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...NONE.
NC...NONE.
SC...NONE.

&&

$$
SYNOPSIS...ARK
NEAR TERM...LG
SHORT TERM...JOH
LONG TERM...JDL
AVIATION...LG


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