FXUS62 KGSP 230111
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
811 PM EST TUE DEC 22 2009
.SYNOPSIS...
HIGH PRESSURE WILL REMAIN OVER THE AREA THROUGH WEDNESDAY. STRONG
LOW PRESSURE WILL MOVE FROM THE PLAINS TO THE GREAT LAKES LATER IN
THE WEEK...PUSHING A COLD FRONT THROUGH THE WESTERN CAROLINAS AND
NORTHEAST GEORGIA ON FRIDAY. DRY HIGH PRESSURE WILL THEN RETURN OVER
THE WEEKEND.
&&
.NEAR TERM /THROUGH WEDNESDAY/...
AN UPPER RIDGE WILL AMPLIFY OVER THE TN AND OH RIVER VALLEY TONIGHT.
A SURFACE RIDGE WILL REMAIN ALONG THE COAST...WHILE UPPER LEVEL
CLOUD COVER SPREADS OVER IT FROM THE WEST IN ADVANCE OF LOW PRESSURE
ENTERING THE MS RIVER VALLEY. THIS CLOUD COVER HAS ALREADY CROSSED
THE MOUNTAINS...AND WILL REACH THE PIEDMONT WITHIN HOURS. DESPITE
THE ADVANCING CIRRUS...MINIMUM TEMPERATURES WILL BE LOWERED SLIGHTLY
PER CURRENT TRENDS AND GUIDANCE. ALTHOUGH MET GUIDANCE BRINGS FOG TO
KAVL...THE MAV DOES NOT. WITH CLOUDS INCREASING...ONLY PATCHY FOG
WILL BE ADDED TO THE NC MOUNTAIN VALLEYS AT THIS TIME...DESPITE
LOCAL RESTRICTIONS IN THE KAVL TAF.
MODELS IN GOOD AGREEMENT THAT HIGH CLOUDS WILL CONTINUE TO INCREASE
WED AS UPPER LEVEL MOISTURE IS ENHANCED BY AN H5 SHORTWAVE
APPROACHING FROM THE W AND MOVG ACROSS THE AREA IN THE AFTN INTO
EARLY EVE. WEAK HIGH PRESSURE WILL BUILD IN FROM THE NE WED AFTN AND
LGT NE WINDS ARE EXPECTED IN THE MORNING...VEERING TO SOUTHEAST IN
THE AFTERNOON. WED HIGHS WILL REACH THE L-M50S ACROSS THE PIEDMONT
WITH M40S TO AROUND 50 MTNS AS HEIGHTS RISE ALOFT.
&&
.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/...
AS OF 200 PM TUE...DEEP LOW PRES SYSTEM IS EXPECTED TO BE OVER THE
SOUTHERN PLAINS WED EVENING WITH A RIDGE ACROSS THE SE STATES AND
DEVELOPING CAD. LOOKS LIKE DRY CONDITIONS WILL CONTINUE WED NIGHT
UNDER THE DRY RIDGE.
NUMERICAL MODEL SUITE IN GENERAL AGREEMENT WITH THE EVOLUTION OF THE
SENSIBLE WEATHER OVER THE REGION THU THROUGH FRI. THE EXCEPTION IS THE
OPERATIONAL NAM WHICH IS ABOUT 12 HOURS SLOWER WITH THE ONSET OF
PRECIP AND THE FRONTAL PASSAGE. WILL DISCARD THIS SOLUTION AS THE
MODEL CONSENSUS...INCLUDING THE SREF SUPPORTS A FASTER PROGRESSION.
POP FIELD WAS PARED BACK SOMEWHAT ON THU USING A BLEND OF MAV/SREF.
THIS KEEPS POPS FOR THU ESSENTIALLY OVER THE WESTERN HALF OVER THE
FORECAST AREA. WILL THEN SPREAD CATEGORICAL RAIN ACROSS MOST ALL OF
THE FORECAST AREA THU NIGHT. SFC COLD NOSE LOOKS TO GET REINFORCED
BY THE CAD THU NIGHT...SO SOME ICE ACCUMS FROM FREEZING RAIN WILL BE
POSSIBLE NEAR THE BLUE RIDGE AND NC FOOTHILLS THU NIGHT INTO EARLY
FRI. AT THIS POINT...LOOKS LIKE DURATION OF ICE SHOULD BE SHORT
ENOUGH TO PRECLUDE LARGE ACCUMULATIONS OF ICE...BUT AN ADVISORY WILL
LIKELY BE NEEDED AT SOME POINT FOR THU NIGHT. OCCLUDING FRONT
WILL BE FORECAST TO CROSS THE AREA ON CHRISTMAS. A TRIPLE POINT LOW
STILL LOOKS LIKE IT WILL DEVELOP OVER THE SAVANNAH RIVER VALLEY
FRIDAY...AND TRACK ACROSS THE SC MIDLANDS. THIS SHOULD KEEP
INSTABILITY AT BAY...SO NO MENTION OF THUNDER FOR NOW. A TRACK A
LITTLE FARTHER N WOULD ALLOW FOR SOME SHALLOW CONVECTION ACROSS THE
SC PIEDMONT AS CAD ERODES. IF THIS OCCURS IT WOULD BE A CONCERN AS
HELICITY IS OFF THE CHARTS. IN ADDITION...850 MB WINDS SHOULD EASILY
TOP 50 KT IN THE PEAK WARM ADVECTION FLOW LATE THU NIGHT...SO MTN
WINDS COULD APPROACH ADVISORY LEVELS IN THE HIGHER TERRAIN. WILL
FORECAST THE FRONT CLEARING THE AREA TO THE EAST LATE FRI
AFTERNOON...SO NO MENTIONABLE POPS FRI NIGHT AS DRYER AIR QUICKLY
OVERSPREADS THE AREA. USED MAV/MET BLEND FOR WED NIGHT AND MAV FOR
MAX TEMPS ON THU. FOR THU NIGHT...USED A BLEND OF MAV/GMOS/SREF THEN
GMOS ON FRI.
SIGNIFICANT HYDROLOGY PROBLEMS ARE NOT ANTICIPATED AT THE MOMENT DUE
TO THE RATHER FAST MOVING WEATHER SYSTEM...BUT 1.0 TO 1.5 INCHES OF
RAIN IS STILL A GOOD BET ACROSS A LARGE PORTION OF THE FORECAST
AREA. SNOW MELT HAS CAUSED STREAM AND RIVER LEVELS TO REMAIN FAIRLY
STEADY THE PAST FEW DAYS IN WESTERN NC/NORTHERN UPSTATE...SO TRIBUTARIES
WILL BE SOMEWHAT PRIMED FOR RAPID RISES...SO WILL HAVE TO MONITOR
CLOSELY.
&&
.LONG TERM /SATURDAY THROUGH TUESDAY/...
AS OF 230 PM TUESDAY...LOW CONFIDENCE FCST FOR THE LONG TERM AS THE
MEDIUM RANGE MDLS CONTINUE TO VARY FROM RUN TO RUN REGARDING THE
DISPOSITION OF THE UPPER LOW THAT STARTS OUT OVER THE WRN GREAT
LAKES AT THE BEGINNING OF THE PERIOD. THE MDLS NOW SHOW THE LOW
SLOWLY MOVING MOVING EAST...REACHING THE EAST COAST BETWEEN 00Z AND
12Z TUESDAY. THIS KEEPS GENERAL TROFINESS ACROSS THE SOUTHEAST THRU
THIS PERIOD. RIDGING THEN BUILDS OVER THE AREA TUESDAY AHEAD OF THE
NEXT STORM SYSTEM. AT THE SFC...LOW PRESSURE ACROSS THE GREAT LAKES
SLOWLY MOVES EASTWARD THEN NE INTO CANADA MONDAY OR MONDAY NIGHT.
HIGH PRESSURE RIDGES IN JUST SOUTH OF THE AREA FROM THE WEST DURING
THIS TIME. THIS WILL KEEP MOST OF THE AREA DRY...XCPT FOR THE TN
BORDER COUNTIES. THERE IS A CHANCE OF NW FLOW SNOW SHOWERS DURING
THIS TIME. HOWEVER...THE MDLS CONTINUE TO DIFFER FROM RUN TO RUN ON
THE BEST PERIOD. THIS IS DUE TO THE H85 FLOW BEING WEAK AND MAINLY
WESTERLY EARLY ON WITH ONLY MINIMAL CAA. THE WILL BE A BETTER PERIOD
OF NWLY FLOW AND CAA. HOWEVER...IT COULD OCCUR ANY TIME FROM SUNDAY
TO MONDAY NIGHT DEPENDING ON THE MDL OR RUN. GIVEN THE CONTINUED
VARIABILITY...WILL KEEP POP LIMITED TO SLIGHT CHC FOR NOW. THERE
WILL BE A DRY PERIOD FROM THEN THRU TUESDAY AS THE RIDGING BUILDS
INTO THE AREA SFC AND ALOFT. THE LATEST GUIDANCE KEEPS THE NEXT
STORM SYSTEM TO OUR SOUTHWEST THRU THE END OF THE PERIOD. MDLS ALSO
CONTINUE TO VARY FROM RUN TO RUN ON THE AMOUNT AND TIMING OF THE
COLD AIR MOVING IN. HAVE GONE WITH THE NATIONAL GUIDANCE WHICH HAS
THE AREA BELOW NORMAL UNTIL THE VERY END WITH NEAR NORMAL READINGS.
THIS IS BASED ON THE GEFS H85 MEAN TEMP 1 TO 1.5 STANDARD DEVIATIONS
BELOW NORMAL EARLY THEN NEAR NORMAL AT THE END OF THE PERIOD.
&&
.AVIATION /01Z WEDNESDAY THROUGH SUNDAY/...
AT KCLT...A FEW CIRRUS WILL DRIFT OVERHEAD WHILE WINDS REMAIN CALM.
DEW POINT DEPRESSIONS WILL BE LOW AROUND DAWN...BUT GUIDANCE CARRIES
NO VISIBILITY RESTRICTION. LOW VFR FOG WILL BE CARRIED IN THE TAF AT
SUNRISE. LIGHT NORTHEAST WINDS SET UP BY MID MORNING...WITH CIRRUS
BECOMING BROKEN. BY AFTERNOON WINDS VEER TO SOUTHEAST...AND THE VFR
CEILING LOWERS AS ALTOCUMULUS MOVE IN.
ELSEWHERE...VFR THROUGH THE PERIOD WITH SCATTERED CIRRUS...BECOMING
BROKEN WEDNESDAY MORNING...WITH ALTOCUMULUS MOVING IN THE AFTERNOON.
MODEL TIME HEIGHTS SHOW SOME LOW LEVEL MOISTURE OVER UPSTATE SC ON
WEDNESDAY...BUT CONFIDENCE IN THIS LAYER IS LOW. EXPECT LOW VFR FOG
AROUND DAWN. THE EXCEPTION WILL BE KAVL...WITH MVFR AFTER 06Z...THEN
IFR 09-12Z...BEFORE IMPROVING TO VFR BY 14Z. WINDS WILL GO CALM
OVERNIGHT...THEN LIGHT NORTHEAST VEERING TO SOUTHEAST WEDNESDAY.
OUTLOOK...VFR WED NIGHT EXCEPT FOR BRIEF FOG NEAR DAWN. A STORM WILL
APPROACH FROM THE WEST LATE THURSDAY...PRODUCING WIDESPREAD MVFR/IFR
RESTRICTIONS...WITH WINTRY WEATHER POSSIBLE THURSDAY NIGHT INTO FRI
BETWEEN KAVL AND KHKY. CONDITIONS SHOULD IMPROVE FRI NIGHT-SAT AS
DRY AIR COMES IN FROM THE W.
&&
.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.
&&
$$
SYNOPSIS...DEO
NEAR TERM...JAT/RB
SHORT TERM...LG
LONG TERM...RWH
AVIATION...JAT
