FXUS62 KGSP 230541
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1241 AM EST WED DEC 23 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 TODAY/...
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 /TONIGHT 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 /06Z WEDNESDAY THROUGH SUNDAY/...
AT KCLT...THERE IS NO SIGNIFICANT WEATHER EXPECTED FOR THE TAF
PERIOD AND THE FORECAST PRIMARILY BOILS DOWN TO A WIND DIRECTION
FORECAST. THIN CIRRUS WILL PERSIST THROUGH THE MORNING...GRADUALLY
LOWERING TO AN AS DECK BY THE AFTERNOON. WINDS WILL REMAIN CALM OVER
NIGHT...BECOMING MORE EASTERLY AND THEN SOUTH OF EASTERLY DURING THE
AFTERNOON. TAKING A BLEND OF THE NAM AND THE GFS YIELDS WINDS FROM
AROUND 110 AFTER 18Z BEFORE THEY BECOME SOLID NORTHEASTERLY BY THE
EVENING.
ELSEWHERE...MAIN CHANGES WERE TO SCALE BACK THE INTENSITY OF FOG AT
KAVL AND KHKY FOR THIS MORNING. AT KAVL...CURRENT TEMP DP SPREAD IS
HOVERING AROUND 2-3 DEGREES WHICH IS GREATER THAN THIS TIME LAST
NIGHT. GUIDANCE STILL DOES NOT SHOW ANY LIFR FOG DEVELOPMENT AND I
HAVE REMOVED THE 1/2 MILE FOG MENTION AT 09Z...INSTEAD HANGING ON TO
SOME MVFR LEVEL FOG. AT KHKY...SIMILAR STORY AS I HAVE REMOVED THE
3SM FOG AND GONE WITH 5SM INSTEAD. EVERYWHERE...WINDS WILL REMAIN
CALM OVERNIGHT BEFORE BECOMING MORE EASTERLY AND SOUTHEASTERLY
DURING THE AFTERNOON. FLOW THEN TURNS MORE NORTHEASTERLY IN THE
EVENING AS HIGH PRESSURE CONTINUES TO RIDGE DOWN THE EASTERN
SEABOARD. EXPECT CIRRUS TO GRADUALLY LOWER TO A 12-15 KFT AS DECK IN
THE AFTERNOON...BUT NO RESTRICTIONS EXPECTED.
OUTLOOK...A STORM WILL APPROACH FROM THE WEST LATE THURSDAY
PRODUCING WIDESPREAD MVFR/IFR RESTRICTIONS. A BRIEF PERIOD OF WINTRY
WEATHER WILL BE POSSIBLE THURSDAY NIGHT INTO FRI BETWEEN KAVL AND
KHKY...MAINLY AT THE ONSET OF PRECIP. 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...BSH
