FXUS62 KGSP 050224
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
924 PM EST FRI DEC 4 2009
.SYNOPSIS...
AN AREA OF LOW PRESSURE WILL MOVE ACROSS THE GULF OF MEXICO THROUGH
TONIGHT...AND THEN UP THE SOUTHEAST COASTLINE ON SATURDAY. AS THE
LOW PULLS AWAY FROM THE EASTERN SEABOARD SATURDAY NIGHT...HIGH
PRESSURE WILL BUILD IN ACROSS THE FORECAST AREA FROM THE WEST ON
SUNDAY. A FAST MOVING COLD FRONT WILL PUSH ACROSS THE REGION ON
MONDAY WITH ANOTHER AREA OF HIGH PRESSURE MOVING IN BEHIND IT.
&&
.NEAR TERM /THROUGH SATURDAY/...
MOISTURE CONTINUES TO INCREASE OVER THE AREA AS H5 SHORTWAVE MOVES
ACROSS THE LOWER MS VALLEY TO APPROACH THE CWA FROM THE W. LATEST
MODEL RUNS IN GOOD AGREEMENT WITH CURRENT FCST/TRENDS AND GRIDS ARE
IN GOOD SHAPE FOR OVERNIGHT...DEPICTING INCRSNG MOISTURE/POPS AND
LOWERING THKNS AS UPSLOPE FLOW AND ISENTROPIC LIFT SPIN UP. ONLY
MINOR TWEAKS MADE TO GOING FCST...UPDATED PRODUCTS ARE GENERATING
NOW AND WILL BE AVAILABLE SOON.
PREVIOUS DISCUSSION...HERE ARE THE HIGHLIGHTS OF WARNING/ADVISORY
DECISIONS FOR SNOW WITH THIS PACKAGE...WINTER STORM WARNING WILL BE
ISSUED AVERY TO MADISON TO HAYWOOD FOR ALL ELEVATIONS. A HIGH
ELEVATION WARNING WILL BE ISSUED FROM THE SMOKIES TO BUNCOMBE TO WRN
CALDWELL...WITH LOW ELEVATION ADVISORIES FOR THE SAME ZONES. AND...A
WINTER WEATHER ADVISORY WILL BE ISSUED FOR THE SRN MOST NC MTN
COUNTIES FROM GRAHAM AROUND TO HENDERSON. ALL HAZARDS WILL BE VALID
MIDNIGHT TONIGHT TO 8 PM SATURDAY EVENING.
SEVERAL FORCING MECHANISMS WILL COME TOGETHER ACROSS THE WRN
CAROLINAS AND NE GA TONIGHT THROUGH SATURDAY. SFC LOW PRES WILL MOVE
FROM THE GULF OF MEXICO TO THE SOUTHEAST COAST. A POSITIVE TILT
UPPER TROUGH WILL MOVE EAST THROUGH THE CENTRAL CONUS TONIGHT...WITH
THE SRN STREAM BECOMING OUT OF PHASE AND SHARPENING UP IN THE MS
RIVER VALLEY. LEAD VORT LOBES AHEAD OF THIS FEATURE WILL REACH THE
SRN APPALACHIANS CIRCA 06Z...BUT THE STRONGEST Q VECTOR CONVERGENCE
WILL CROSS WESTERN NORTH CAROLINA 12Z TO 18Z...AND POSSIBLY LINGER
ALONG THE INTERSTATE 40 CORRIDOR THROUGH 21Z SAT. UPPER JET
DIVERGENCE SHOULD IMPACT THE FORECAST AREA MAINLY LATE
TONIGHT...WITH PRECIPITATION POSSIBLY FOCUSED A LITTLE EARLIER THAN
PREVIOUSLY EXPECTED ALONG PIEDMONT SECTIONS TOWARD DAYBREAK.
MEANWHILE...A LOW LEVEL MOIST SE WARM ADVECTION FLOW AT 850 MB
SHOULD GET GOING IN EARNEST BY 06Z. SNOW LEVELS SHOULD START OUT
ABOVE 3500 FEET AT THE ONSET...BUT WILL LIKELY PLUMMET QUICKLY TO
THE VALLEY FLOORS BY DAYBREAK. PLENTY OF DECENT FORCING SHOULD THUS
BE IN PLACE FOR THIS EVENT...BUT IT DOES LOOK LIKE A FAIRLY SHORT
DURATION EVENT LASTING FROM 06Z TONIGHT TO AROUND 21Z SAT AFTN.
THE 12Z OPERATIONAL MODELS ARE NOW HIGHER ON QPF...HOWEVER...SREF
AND GMOS ENSEMBLE MEANS REMAIN QUITE A BIT DRIER. ALTHOUGH THE EVENT
WILL BE SHORT...THE 850 MB LOW CENTER TRANSITING THE PIEDMONT OF THE
WRN CAROLINAS CERTAINLY LOOKS FAVORABLE FOR SOME HEAVY MTN SNOW.
PLUS...THE SURFACE LOW NOW APPEARS TO HUG THE COAST FAIRLY TIGHTLY
THROUGH SAT. WILL UPGRADE THE WATCH AS MENTIONED ABOVE TO FEATURE 3
TO 5 INCH SNOW ACCUMULATIONS...WITH A TIER OF LOWER ELEVATION AND
SOUTHERN MOUNTAIN ADVISORIES WITH SNOW TOTALS 1 TO 2 INCHES.
THE RAPID ONSET OF COLD ADVECTION DURING THE DAY SAT SHOULD DRAG
SNOW LEVELS DOWNWARD ACROSS THE FOOTHILLS AND PIEDMONT...ESPECIALLY
ALONG THE INTERSTATE 40 CORRIDOR IN WRN NC. WILL ADVERTISE A GRADUAL
MIXOVER TO SNOW ACROSS MUCH OF THE NC FOOTHILL AND PIEDMONT FROM
MIDDAY ONWARD...HOWEVER...QPF AMOUNTS WILL DWINDLE. THE ONLY
LINGERING ISSUE FOR POSSIBLE ACCUMULATING SNOW OUT INTO THE PIEDMONT
WOULD BE IF FRONTOGENESIS CAN CREATE SOME BANDING AS THE LOW
DEPARTS. IF THAT HAPPENED...A QUICK INCH COULD ACCUMULATE ALONG
INTERSTATE 40 OUT INTO THE PIEDMONT...BUT THIS IS TOO UNCERTAIN TO
FORECAST PRESENTLY. WHERE PRECIP DOES NOT MIX OVER...IT WILL STILL
BE A RAW CHILLY DAY.
&&
.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
AS OF 145 PM FRIDAY...POTENT S/W TROF EXITS THE CWFA TO THE E BY
SATURDAY EVE...WITH ANY LINGERING LGT RA/SN SHWRS ENDING BY
MIDNIGHT. DURING THE OVERNIGHT...FCST SNDGS INDICATE RAPID DRYING
ALOFT...AND CLEARING SKIES. THE CLR SKIES COUPLED WITH DECENT LLVL
CAA WL ALLOW TEMPS TO DROP INTO THE 20S (MAYBE A FEW TEENS IN THE
SHELTERED HIGH VALLEYS IN THE NRN MTNS). THERE MAY BE A FEW HRS
BETWEEN THE END OF PRECIP AND THE TIME SFC TEMPS DROP BLO FRZG E OF
THE MTNS. STILL THINK BLACK ICE THREAT WL BE HIEST IN THE MTNS...BUT
STILL POSSIBLE ACRS THE PIEDMONT.
SUNDAY AND SUNDAY NIGHT...UPR FLO BECOMES QUASI-ZONAL...WITH A
TRANSIENT POLAR HI DOMINATING OUR WX. THE MAIN JET WILL RMN OVR THE
SRN TIER STATES...AND TEMPS WL RMN SLIGHTLY BLO NORMAL (ESP IN THE
MTNS WHERE SNOW WL BE MELTING). AFTN HIGHS WL RANGE FM ARND 40 ON
RIDGETOPS TO LWR 50S SRN/WRN UPSTATE UNDER SUNNY/MSUNNY SKIES.
OVERNIGHT LOWS A CAT OR TWO ABV SATURDAY NGT/S LOWS.
MONDAY AND MONDAY NIGHT...A CLIPPER WAVE WL TRACK THRU THE GREAT
LAKES TO THE CANADIAN MARITIMES...PUSHING A VERY WEAK COLD FRONT
THRU THE CWFA LATE MONDAY. SYNOPTIC FORCING AND OVERALL AVAILABLE
MOISTURE ARE LACKING WITH THE FROPA. THERE WL BE ENUF ISENTROPIC
LIFT AND MOISTURE FOR AT LEAST LAYERS OF LOW-MID LVL CLOUDINESS AND
A MENTION OF SLGT CHC POP. ANY PRECIP THAT DEVELOPS COULD BE A
WINTRY MIX IN THE MORNING MAINLY IN THE MTNS. THE DETAILS ARE TOO
UNCERTAIN...AND WITH SUCH A LOW POP/QPF FCST...I HAVE OPTED TO KEEP
IT A RA/SN MIX FOR NOW (EVEN THO FCST SNDGS INDICATE POTENTIAL FOR
SOME FZRA/SLEET MIXED IN). NO SIGNIFICANT ACCUM IS EXPECTED WITH
THIS FEATURE...AS THICKNESSES IN INCR SUCH THAT PRECIP SHUD
TRANSITION TO ALL RAIN. THE GFS IS FASTEST ON FROPA...WITH THE
NAM/SREF/GEM/ECMWF IN BETTER AGREEMENT ON A MON NGT PASSAGE. SO HAVE
KEPT A SLGT CHC POP MON NGT...WITH A MENTION OF RA/SN MIXING IN THE
HIGH ELEVATIONS AS TEMPS DROP INTO THE 30S.
&&
.LONG TERM /TUESDAY THROUGH FRIDAY/...
AS OF 2 PM FRIDAY...LITTLE IN THE WAY OF A PATTERN CHANGE IS IN
SITE...AS THE GLOBAL MODELS CONTINUE TO DEPICT VERY PROGRESSIVE/
ACTIVE LARGE-SCALE FLOW THROUGH THE END OF THE FORECAST CYCLE. THE
12Z GFS...AND NOW THE 12Z ECMWF ARE IN VERY GOOD AGREEMENT IN
DEPICTING A MILLER-B SCENARIO DURING MID-WEEK...AS A STRONG VORT MAX
LIFTS OUT OF THE MISS VALLEY. THE MODELS ARE IN FAIRLY GOOD
AGREEMENT IN TIMING PRECIP INTO THE CAROLINAS BY THE END OF THE DAY
TUESDAY. HOWEVER...LIGHT/PATCHY PRECIP WILL BE POSSIBLE TUE
MORNING...AS THE LOW-LEVEL FLOW BEGINS TO RESPOND TO HEIGHT FALLS TO
OUR WEST. A BRIEF PERIOD OF WINTRY MIX IS POSSIBLE...MAINLY ACROSS
THE MTNS EARLY TUESDAY. HOWEVER...THERMAL PROFILES SHOULD RAPIDLY
WARM TO SUPPORT ALL-LIQUID. PRECIPITATION CHANCES APPEAR TO REACH A
NADIR TUE NIGHT (WHEN LIKELY POPS WILL BE ADVERTISED)...BEFORE
ENDING ACROSS MOST OF THE AREA WEDNESDAY...AS THE COASTAL LOW
BECOMES THE DOMINANT SYNOPTIC FEATURE.
COOLER AIR MOVES IN BEHIND THE FRONT WED NIGHT/THURSDAY...WITH A
BRIEF PERIOD OF UPSLOPE/NORTHWEST FLOW -SHSN POSSIBLE. AFTER BRIEF
DRYING THURSDAY...THE GLOBAL MODELS FEATURE YET ANOTHER STORM SYSTEM
TAKING AIM ON THE REGION BY THE END OF DAY 7. SLIGHT-TO-LOW CHANCE
POPS WILL BE FEATURED BY FRIDAY AFTERNOON.
&&
.AVIATION /03Z SATURDAY THROUGH WEDNESDAY/...
KCLT AND ELSEHWERE...THERE MAY BE A FEW BREAKS IN CIGS EARLY THIS
EVE BUT EXPECT CIGS TO LOWER STEADILY TO MVFR BY LATE EVE AS UPSLOPE
FLOW AND MOISTURE INCREASE ACROSS THE CWA. CHC PRECIP WILL INCRS
WITH LIKELY START AS LGT RAIN BETWEEN 05-06Z. CIG/VSBY WILL CONT TO
DECREASE OVERNIGHT WITH IFR EXPECTED AROUND DAYBREAK...EARLIER AT
KAVL DUE TO SNOW MIXING IN AFTER 09Z...BECMG ALL SNOW KAVL BY 16Z.
COULD SEE SOME SNOW MIX IN LOWER ELEVS...MAINLY KHKY IN THE MRNG BUT
ALL SITES IN THE AFTN. LGT MLY WINDS WILL INCRS TO 10KT IN HTE AFTN
WITH G20 KAVL.
OUTLOOK...CONDITIONS WILL IMPROVE QUICKLY SAT NIGHT AS THE LOW PRES
SYSTEM PULLS AWAY TO THE NE. FREEZING TEMPERATURES WILL LEAD TO
BLACK ICE CONDITIONS ON RUNWAYS SUNDAY MORNING. DRY WEATHER IS
EXPECTED SUNDAY. A WEAK FRONT WILL PASS MONDAY. DRY HIGH PRESSURE IS
THEN EXPECTED AGAIN TUESDAY BEFORE OUR NEXT MAJOR SYSTEM MOVES IN
FROM THE W TUE NIGHT-WED.
&&
.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...WINTER WEATHER ADVISORY UNTIL 8 PM EST SATURDAY FOR NCZ051-053-
058-059-062>065-501-503-505.
WINTER STORM WARNING UNTIL 8 PM EST SATURDAY FOR NCZ033-
048>053-059-501-503-505.
SC...NONE.
&&
$$
SYNOPSIS...BSH
NEAR TERM...HG/RB
SHORT TERM...ARK
LONG TERM...JDL
AVIATION...RB
