FXUS62 KGSP 291137
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
637 AM EST SUN NOV 29 2009
.SYNOPSIS...
HIGH PRESSURE WILL WEAKEN AND MOVE OFF THE EAST COAST BY MONDAY
MORNING AS A COLD FRONT APPROACHES FROM THE WEST. THIS FRONT WILL
CROSS THE AREA ON MONDAY WITH A BRIEF PERIOD OF HIGH PRESSURE
RETURNING TO THE REGION ON TUESDAY. THE NEXT SYSTEM IS THEN EXPECTED
TO AFFECT NORTHEAST GEORGIA AND THE WESTERN CAROLINAS FROM THE SOUTH
STARTING ON WEDNESDAY.
&&
.NEAR TERM /THROUGH TONIGHT/...
SFC HIGH PRESSURE WILL REMAIN OVER THE WESTERN ATLANTIC AS A COLD
FRONT ADVANCES EAST ACROSS THE MID MISSISSIPPI RIVER VALLEY TODAY.
THIS PATTERN WILL SUPPORT WEAK SOUTH-SOUTHWEST RETURN FLOW ACROSS
THE CWA TODAY. SCT TO BKN HIGH CLOUDS ARE EXPECTED TO REMAIN OVER
THE REGION FOR MOST OF THE DAY. THE HIGH CLOUDS WILL LIMIT THE
AMOUNT OF INSOLATION THIS AFTERNOON. HOWEVER...MILD THICKNESSES WILL
LIKELY SUPPORT HIGH TEMPERATURES AROUND 10 DEGREES ABOVE
NORMAL...MID 60S WITHIN THE MTN VALLEYS AND U60S EAST. MIN RH VALUES
WILL FALL NEAR 30 PERCENT DURING THE MID AFTERNOON HOURS.
MODELS AGREE FAIRLY WELL WITH THE TIMING AND PLACEMENT OF THE COLD
FRONT AND ASSOCIATED MOISTURE TONIGHT. CLOUD COVER WILL THICKEN
ACROSS THE CWA THROUGH THE NIGHT WITH SOUTHWEST WINDS REMAINING
AROUND 5 KTS. MILD LLVL PROFILES...INCREASING SKY COVER...AND A
MIXING WIND WILL SLOW DIURNAL COOLING. I WILL FAVOR THE 2M TEMPS IN
THE GFS40 AND SREF GUIDANCE FOR LOW TEMPS. THIS APPROACH WILL YIELD
LOW TEMPERATURES IN THE MID 40S ACROSS THE MTNS AND U40S EAST. A
LINE OF SCATTERED TO NUMEROUS SHOWERS ASSOCIATED WITH THE COLD FRONT
WILL LIKELY REACH THE MTNS BETWEEN 9-12Z TONIGHT. THE ADJACENT
FOOTHILLS MAY SEE WIDELY SCATTERED SHRA LATE TONIGHT...WITH THE
PIEDMONT REMAINING DRY. QPF WILL REMAIN LESS THAN 0.25 OF AN INCH
TONIGHT.
&&
.SHORT TERM /MONDAY THROUGH WEDNESDAY NIGHT/...
AS OF 230 AM SUNDAY...IT LOOKS LIKE THE SHORT RANGE OF THE FORECAST
IS SHAPING UP TO BE ACTIVE WITH THE PASSAGE OF A COLD FRONT MONDAY
AND A DEEPENING LOW PRESSURE AREA ON WEDNESDAY.
AS FOR THE FIRST SYSTEM...THE OTHER MODELS HAVE MORE OR LESS COME
AROUND TO THE FASTER PREVIOUS GFS SOLUTION WHICH PUTS THE COLD FRONT
ON OUR WESTERN BORDER AT SUNRISE ON MONDAY. THE UPPER TROF MOVES
QUICKLY EAST WHICH SHOULD PUSH THE FRONT RAPIDLY ACROSS THE FORECAST
AREA...INTO THE MTNS IN THE MORNING AND EAST OF THE PIEDMONT BY
SUNSET. DEEP MOISTURE AND DECENT UPPER FORCING SUGGEST THAT OUR POP
COULD BE RAISED A BIT IN THE MORNING OVER THE WESTERN ZONES...SO
HAVE BUMPED THE POP TO CATEGORICAL ON THE TN BORDER. THERE IS STILL
SOME CONCERN FOR HOW THE FRONT WILL COME OFF THE MTNS IN THE
AFTERNOON BUT THINK THAT OVER THE PIEDMONT MORE PLACES THAN NOT WILL
SEE A PASSING SHOWER. HIGH TEMPS REFLECT A GUIDANCE BLEND. THE
CONSENSUS OF THE MODELS IS THAT PRECIP WILL BE LONG GONE BY EVENING
SO HAVE STARTED THE DRYING TREND LATE IN THE DAYTIME PERIOD OVER THE
WEST...THEN COMPLETELY ELIMINATED ANY MENTION OF PRECIP IN THE
MONDAY NIGHT TIME FRAME. MADE A CORRESPONDING DOWNWARD ADJUSTMENT TO
MIN TEMPS TO REFLECT FASTER CLEARING.
TUESDAY STILL LOOKS LIKE A BREAK IN THE ACTION AS HIGH PRESSURE
SCOOTS WEST TO EAST ACROSS THE CAROLINAS...BUT ALREADY A LOW
PRESSURE CENTER WILL ORGANIZE ALONG THE OLD FRONT OVER THE NW GULF.
MADE A SIGNIFICANT UPWARD ADJUSTMENT TO HIGH TEMPS OF ABOUT 5
DEGREES BASED ON SUNNY SKY AND MODEL GUIDANCE. WHICH BRINGS US TO
THE NEXT SYSTEM...
THE GUIDANCE HAS BEEN FAIRLY CONSISTENT WITH THE NEXT SYSTEM WHICH
IS SEEN AS A SRN STREAM UPPER LOW SPINNING EAST ACROSS NRN MEXICO
AND TEXAS TUESDAY AND TUESDAY NIGHT. THE SURFACE LOW OVER THE NW
GULF WILL START TO LIFT NE ALONG THE NRN GULF COAST TUESDAY NIGHT IN
RESPONSE TO THE APPROACHING UPPER LOW. THE GFS AND ECMWF ARE FAIRLY
CONSISTENT WITH DEVELOPING ISENTROPIC UPGLIDE AND RETURN MOISTURE UP
FROM THE SOUTHWEST LATE AT NIGHT. THIS SHOULD BRING THE LEADING EDGE
OF LIGHT RAIN INTO THE AREA ROUGHLY WEST OF I-26 BY SUNRISE
WEDNESDAY. THERE HAS BEEN SOME CONCERN ABOUT PRECIP TYPE AT THE
ONSET...BUT THE LATEST GUIDANCE SHOWS WARM THICKNESSES AND STRONG
WARM ADVECTION AT 850MB WITH TEMPS GENERALLY PLUS 6 TO PLUS 8. THIS
SHOULD BE A SITUATION WITH WARMER RIDGETOP TEMPS AND THINK IT WILL
CLOUD UP TOO EARLY TO ALLOW VALLEYS TO COOL BELOW FREEZING.
SO...HAVE RAISED MIN TEMP ABOVE FREEZING AND CHANGED ALL PRECIP
TYPES TO RAIN.
WEDNESDAY LOOKS LIKE A WASHOUT WITH ALL INDICATIONS POINTING TOWARD
A SOAKING RAIN EVERYWHERE...SO POP WAS RAISED TO CATEGORICAL ACROSS
THE ENTIRE FORECAST AREA. WHAT REMAINS TO BE SEEN IS IF WE MANAGE TO
GET ANY SORT OF INSTABILITY INTO THE SOUTHEAST FRINGE...WHICH WOULD
SUPPORT A SMALL SEVERE WEATHER THREAT BECAUSE OF THE VERY STRONG
SHEAR. WE MIGHT ALSO HAVE A HIGH WIND PROBLEM. THE SURFACE LOW WILL
MOVE GRADUALLY NORTHEAST AND DEEPEN ACROSS THE CAROLINAS LATE IN THE
DAY SO POP WAS RAISED FOR THE EVENING HOURS AS WELL. COLD AIR SPILLS
IN BEHIND THE LOW AFTER MIDNIGHT...SO THERE COULD BE A CHANGEOVER TO
SNOWSHOWERS AT ELEVATIONS ABOVE ABOUT 4000 FEET IN THE PRE-DAWN
HOURS.
&&
.LONG TERM /THURSDAY THROUGH SATURDAY/...
AS OF 230 AM SUNDAY...I HAVE UPDATED THE MEDIUM RANGE FORECAST
MAINLY TO REFLECT COOLER TEMPS AS SUPPORTED BY THE 00Z GFS AND
ECMWF. OVERALL THE PERIOD WILL BE A TRANSITIONAL ONE BETWEEN THE
SYSTEM DEPARTING TO THE NORTHEAST ON THURSDAY AND THE EASTERN CONUS
LONGWAVE TROF THAT SETTLES IN THEREAFTER. LINGERING WRAP AROUND LOW
LEVEL MOISTURE AND UPSLOPE FLOW WILL RESULT IN ISOLATED TO SCATTERED
RAIN AND SNOW SHOWERS ALONG THE TN BORDER TUESDAY AND TUESDAY NIGHT.
THE UPSLOPE FLOW IS FAIRLY WEAK AND THE MOISTURE FLEETING SO POPS
DECREASE RAPIDLY THROUGH THURSDAY NIGHT. OTHERWISE...HIGH PRESSURE
WILL BUILD IN THROUGH SATURDAY LEAVING THE REGION IN RELATIVELY DRY
CONDITIONS THROUGH THAT TIME. WITH UPPER HEIGHTS AND LOW LEVEL
THICKNESSES DECREASING THURSDAY THROUGH SATURDAY...TEMPS DURING THE
PERIOD WILL BE ON THE COOL SIDE. IN FACT...CAA SHOULD DOMINATE AT
H85 THROUGH SATURDAY AND I HAVE GONE WITH TEMPS 4-6 DEGREES BELOW
CLIMO THROUGHOUT THE FORECAST.
&&
.AVIATION /12Z SUNDAY THROUGH THURSDAY/...
AT KCLT AND ELSEWHERE...SOUTH TO SOUTHWEST WINDS WILL REMAIN LIGHT
EARLY THIS MORNING. WIND SPEEDS SHOULD INCREASE TO 6-9KTS AROUND MID
DAY AS MIXING INCREASES AND PRESSURE GRADIENT STEEPENS AHEAD OF A
COLD FRONT WEST OF THE MTNS. WINDS WILL LIKELY BECOME LIGHT SHORTLY
AFTER SUNSET. OTHERWISE...SCT TO BKN MID AND HIGH CLOUDS WILL REMAIN
ACROSS THE WESTERN CAROLINAS THROUGH THE TAF PERIOD. BETWEEN 10-12Z
SUNDAY NIGHT...A BAND OF SHRA WILL PUSH ACROSS MOST OF THE NC
MTNS...ISO SHRA MAY REACH FOOTHILLS. I WILL FORECAST 6SM FOR SHRA AT
KAVL AT 10Z...KAND/KHKY MAY SEE A VCSH BY 10Z.
OUTLOOK...A SOLID BAND OF SHRA ALONG AND AHEAD OF A COLD FRONT WILL PUSH
EAST ACROSS THE WESTERN CAROLINAS DURING THE DAY ON MONDAY. THESE
SHOWERS WILL LIKELY PRODUCE PERIODS OF VISIBILITY AND CEILING
RESTRICTIONS ON MONDAY. ONCE THE FRONT PUSHES EAST...GUSTY
WEST-NORTHWEST WINDS WILL DEVELOP AND LINGER INTO MONDAY NIGHT. DRY
HIGH PRESSURE WILL BUILD OVER THE REGION ON TUESDAY. TUESDAY NIGHT
THROUGH WEDNESDAY NIGHT...A SIGNIFICANT AREA OF LOW PRESSURE WILL
LIFT FROM THE NRN GULF OF MEXICO ACROSS THE WESTERN CAROLINAS.
WIDESPREAD RA AND CEILING/VIS RESTRICTIONS WILL ACCOMPANY THE
PASSAGE OF THE LOW.
&&
.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.
&&
$$
SYNOPSIS...BSH
NEAR TERM...NED
SHORT TERM...PM
LONG TERM...BSH
AVIATION...NED
