FXUS62 KGSP 061944
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
244 PM EST SUN DEC 6 2009
.SYNOPSIS...
AN AREA OF HIGH PRESSURE WILL SLIDE OFF THE EAST COAST ON MONDAY AS
A FAST MOVING COLD FRONT CROSSES THE FORECAST AREA. HIGH PRESSURE
WILL THEN RIDGE DOWN THE EASTERN SEABOARD ON TUESDAY AS MOISTURE
SPREADS ACROSS THE REGION ASSOCIATED WITH A STRONG AREA OF LOW
PRESSURE DEVELOPING OVER THE CENTRAL PLAINS. THIS SYSTEM WILL MOVE
INTO THE OHIO VALLEY ON WEDNESDAY...PUSHING A COLD FRONT ACROSS THE
SOUTHERN APPALACHIANS BY WEDNESDAY NIGHT.
&&
.NEAR TERM /THROUGH MONDAY/...
WEAK SHORTWAVES WILL CROSS THE FORECAST AREA IN WSW FLOW ALOFT
TONIGHT THROUGH MON. HIGH LEVEL CLOUDINESS WILL BE FAIRLY ABUNDANT
THROUGH THE PERIOD WITH A STOUT JET STREAK OVERHEAD AND TO THE N. A
BAND OF LOW LEVEL MOISTURE IN THE 900 TO 850 MB LAYER WILL MAKE A
RUN AT THE SOUTHEAST PIEDMONT FROM A COASTAL ATLANTIC SOURCE REGION
OVERNIGHT. THESE CLOUDS MAY REACH THE INTERSTATE 77 CORRIDOR AROUND
DAYBREAK BEFORE PIVOTING AWAY TO THE NE THROUGH THE DAY. NO
PRECIPITATION IS INDICATED...WITH THE SFC LAYER REMAINING DRY.
OTHERWISE...ANY DEEPER MOISTURE LOOKS FAIRLY SPARSE THROUGH THE
PERIOD. SLIGHTLY BETTER RH SHOULD ARRIVE FROM THE W DURING THE AFTN
HOURS MONDAY...WITH SLIGHT CHANCE POPS FOR SHOWERS IN THE MTNS.
CHILLY MINS IN THE 20S AND LOW 30S ARE EXPECTED OVERNIGHT...WITH
COOL MAXES IN THE 40S TO LOW 50S ON MONDAY.
&&
.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
AS OF 200 PM SUNDAY...WENT WITH A MODEL BLEND...AS GUIDANCE IN
GENERAL AGREEMENT ON EVOLUTION OF MIDWEEK CENTRAL CONUS STORM.
A POTENT SRN STREAM SHORTWAVE INVOF THE DESERT SOUTHWEST WITH DEEP
SFC LOW...WILL TRACK EASTWARD INTO THE SRN PLAINS STATES BY TUESDAY
EVENING. MODEL CONSENSUS PLACES THE LOW INVOF KS/OK BORDER 00Z
WED...AND TRACKS IT NEWD TO INVOF LAKE HURON BY 00Z THU. AN UPSTREAM
SFC HIGH IS PROGGED TO MIGRATE FROM UPSTATE NY TO LABRADOR DURING
THIS TIME FRAME. A HYBRID CAD LOOKS TO SET UP ACRS THE PIEDMONT FROM
VA TO ERN GA BY TUESDAY EVENING...AS PRECIP BREAKS OUT ACRS MUCH OF
THE SOUTHEAST STATES IN PERSISTENT STRONG LLVL WAA FLOW. THE PRECIP
SHOULD BE IN FORM OF RAIN...AS 850-700 MB THICKNESSES RISE
SIGNIFICANTLY...AND TEMPS SETTLE MAINLY IN THE 40S TO MID 50S.
SYNOPTIC MID-UPR LVL FORCING WILL BE MODEST AT BEST...AS MAIN
Q-VECTOR CONVERGENCE AND JET DYNAMICS WILL BE NORTHWEST OF THE AREA.
WITH THAT SAID...I MADE ONLY MINOR ADJUSTMENT TO POPS...AS TIMING OF
LOW-MID LVL LIFT IS BECOMING MORE CERTAIN. POPS RAMP UP TO
CATEGORICAL CWA-WIDE BY TUES EVENING...THEN TAPER OFF WEST TO EAST
AFTER DAYBREAK WED AS DRY SLOT AND COLD FRONT PUSH THRU FROM THE
WEST. QPF SHOULD STILL BE GENEROUS...AS GULF WILL BE WIDE OPEN FOR
THE EVENT...WITH PWATS PROGGED TO INCR IN THE 1-1.5" RANGE (300% OF
NORMAL) BY 12Z WED. THIS COUPLED WITH PROLONGED LLVL WAA OVR THE CAD
AND A STRONG UPSLOPE COMPONENT TO THE FLOW FOR A 6-12 HR PERIOD SHUD
RESULT IN WIDESPREAD 1.25-2.5" QPF BY WED AFTN (HIEST AMTS
CONCENTATED ALONG S-FACING SLOPES OF THE BLUE RIDGE).
THERE ARE A FEW CONCERNS WITH THIS EVENT. FIRST...MOST OF THE RIVER
BASINS ARE STILL RUNNING HIGH FROM LAST WEEK/S RAIN. SO THE CURRENT
QPF EXPECTED TUE NGT AND WED COULD CAUSE SOME FLOODING PROBLEMS.
SECOND...THE NAM AND GFS AGREE ON STRONG LLVL WINDS BOTH AHEAD OF
AND BEHIND THE COLD FRONT. RIDGE TOPS MAY HAVE WIND ADV CRITERIA
OVRNGT TUES NGT AS A SLY 50-60 KT H85 JET CROSSES THE AREA...THEN
LWA OR HIGHER GUSTS ARE POSSIBLE CWA-WIDE WEDNESDAY AFTN...WITH
W/SWLY WINDS 40-50 KTS ATOP BL IN STRONG CAA. THIRD...VERY STRONG
LLVL SHEAR IS EXPECTED LATE TUES NGT...AS THE WEDGE FRONT BEGINS TO
ADVANCE NWD. BASED ON THE CURRENT TIMING OF THE COLD FROPA (IN THE
MORNING)...I DON/T THINK THE WEDGE BNDRY WL BE ABLE TO ADVANCE NWD
MUCH AHD OF THE COLD FRONT AND MAY NOT REACH THE SRN TIER COUNTIES
BEFORE SHEAR AND INSTBY QUICKLY WANES. IN ANY CASE...THE SITUATION
FOR SOME EMBEDDED CONVECTION WITH DAMAGING WINDS OR ISOLD TORNADOES
SOUTH OF I-85 WILL NEED TO BE MONITORED.
&&
.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
AS OF 235 PM SUNDAY...WENT WITH HPC FAVORED GFS/ECMWF BLEND WED
NIGHT-SUN. H5 SHORTWAVE MOVES QUICKLY NE OF AREA WED NIGHT...LEAVING
ZONAL FLOW OVER REGION AS BROAD UPPER TROF MOVES SLOWLY ACROSS ERN N
AMERICA. SFC LOW ALSO TRACKS QUICKLY NE...LIMITING MOIST NW FLOW
INTO MTNS. STILL HELD ON TO SLIGHT CHC POPS OVER NC MTNS
OVERNIGHT...PSBLY MIXING WITH THEN TURNING TO LGT SNOW BEFORE
ENDING. SFC HI PRES BUILDS OVER AREA THU-FRI WITH PCLDY SKIES AND
NEAR AVG TEMPS THU...BLO AVG TEMPS FRI. SFC HI MOVES OFFSHORE FRI
NIGHT-SAT AS A LOW DEEPENS IN THE GULF AND TRACKS E TOWARD THE LOWER
SAVANNAH VLY. HI PRES CONT TO RIDGE IN FROM THE NE WITH WEDGE
DEVELOPING AND AS MOISTURE TRACKS NE...POPS WILL INCREASE FROM S TO
N FRI NIGHT. MODEL SOUNDINGS AND THKNS PROFILES HINT THAT A WINTRY
MIX WILL BE PSBL. KEPT IT SIMPLE ATTM WITH CHC RAIN MIXING WITH AND
TURNING TO SNOW OVERNIGHT...MAINLY NC MTNS...N FOOTHILLS AND NW
PIEDMONT...BUT A MIX APPEARS TO BE POSSIBLE INTO UPSTATE SC AS WELL.
WENT WITH CHC RAIN DURG DAY SAT WITH A SLIGHT CHC OF RAIN...PSBLY
MIXING WITH SNOW MTNS AND N ZONES SAT NIGHT. HIGH PRES BUILDS IN
FROM THE N SUN BUT DUE TO UNCERTAINTY THAT FAR OUT KEPT A SLIGHT CHC
OF RAIN ACROSS S TIER. TEMPS REMAIN BLO AVG.
&&
.AVIATION /20Z SUNDAY THROUGH FRIDAY/...
AT KCLT AND ELSEWHERE...HIGH CIRRUS CEILINGS WILL PERSIST THROUGH
THE PERIOD AT ALL TAF LOCATIONS WITH A JET AXIS OVERHEAD IN STIFF SW
FLOW ALOFT. SFC WINDS MAY STAY E TO NE AT KCLT THROUGH THE
PERIOD...WHILE A BRIEF ADJUSTMENT TO SE IS EXPECTED AT THE OTHER
SITES. A STRATOCUMULUS LAYER WILL LIKELY MAKE A RUN TOWARD KCLT LATE
TONIGHT...WITH VFR CIGS LIKELY TOWARD DAYBREAK. NO PRECIPITATION IS
EXPECTED AT ANY TAF SITES DURING THE PERIOD...BUT ISOLATED SHOWERS
MAY APPROACH KAVL TOWARD 18Z MONDAY. MOIST GROUND COULD LEAD TO SOME
PATCHY SHALLOW FOG OVERNIGHT FROM KAVL TO KHKY...BUT WILL NOT
ADVERTISE IN THE TAFS JUST YET SINCE IT IS NOT SUPPORTED BY MOS OR
THE SOUNDINGS.
OUTLOOK...VFR CONDITIONS ARE EXPECTED THROUGH MON NIGHT AS HIGH PRES
BUILDS OVER TO THE N. RAIN AND WIDESPREAD LOW CIGS AND VSBYS ARE
EXPECTED TUE THROUGH EARLY WED AS A LOW PRESSURE SYSTEM FROM THE
WEST BRINGS ABUNDANT MOISTURE INTO THE AREA. DRYING IS EXPECTED MID
TO LATE WEEK.
&&
.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.
&&
$$
SYNOPSIS...BSH
NEAR TERM...HG
SHORT TERM...ARK
LONG TERM...RB
AVIATION...HG
