FXUS62 KGSP 281929
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
229 PM EST SAT NOV 28 2009
.SYNOPSIS...
HIGH PRESSURE WILL REMAIN OVER THE AREA THROUGH THE WEEKEND ALLOWING
TEMPERATURES TO REACH A FEW DEGREES ABOVE NORMAL. LATE SUNDAY... A
COLD FRONT WILL APPROACH THE CAROLINAS AND NORTHEAST GEORGIA. THIS
FRONT WILL CROSS THE AREA ON MONDAY REACHING THE COAST BY LATE IN
THE DAY. HIGH PRESSURE WILL ONCE AGAIN BUILD BACK IN BRIEFLY UNTIL A
STORM SYSTEM APPROACHES FROM THE SOUTH WEDNESDAY.
&&
.NEAR TERM /THROUGH SUNDAY/...
AS THE UPPER FLOW TRANSITIONS TO MORE OF A SOUTHWESTERLY REGIME...
SOME CIRRUS WILL BEGIN STREAMING OVER THE AREA LATE TONIGHT. IT IS
DIFFICULT TO SAY AT THIS POINT HOW THICK THIS CLOUD COVER WILL BE...
AND THEREFORE WHAT EFFECT (IF ANY) IT WILL HAVE ON TEMPS. WE WILL
TREND TOWARD THE COOLER MAV GUIDANCE FOR OVERNIGHT MINS.
AS THICKNESS VALUES CONTINUE TO RISE AND DEEP SOUTHWEST FLOW BECOMES
WELL-ESTABLISHED...SUNDAY SHOULD BE A SOLID CATEGORY WARMER THAN
TODAY...WITH MAX TEMPS AVERAGING AS MUCH AS 10 DEGREES ABOVE NORMAL.
MOISTURE/DEWPOINTS SHOULD CONTINUE TO GRADUALLY INCREASE AS WELL...
SO LOW RH SHOULD NOT BE AS MUCH OF A CONCERN FOR FIRE WX INTERESTS
SUNDAY AFTERNOON.
&&
.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/...
AS OF 225 PM SATURDAY...GOOD AGREEMENT IS SEEN BTW THE NAM AND THE
GFS WRT THE FRONTAL TIMING MON. THE 12Z GFS HAS SLOWED ITS
PROGRESSIVE SOLN AND IS MUCH MORE INLINE WITH THE SREF AND THE GGEM.
SO...GOOD CONFIDENCE IS HAD IN BRING THE HIGHER MOISTURE TO THE NC
MTNS SHORTLY AFTER 00Z MON AND INCREASING POPS TO THE LOW 40S ACROSS
THE WESTERN ZONES BY 12Z MON. EXPECT A RATHER FAST FROPA DURING THE
DAY AND MOST OF THE ACTIVITY WILL BE EAST OF THE AREA BY 00Z
TUE...EXCEPT A SHORT LIVED AND RELATIVELY WARM WRAP AROUND SITUATION
FOR THE NORTHERN MTNS.
THE SOUNDINGS INDICATE SW/LY FLOW ONLY THROUGH A SHALLOW
LAYER...ABOUT 970 MB...WITH THE MAJORITY OF THE LLVL FLOW W/LY. THIS
SHOULD INHIBIT MUCH THETA/E ADV AND SUBSEQUENT DESTABILIZATION. THE
NAM KEEPS CONVECTIVE PRECIP WELL TO THE SW OF THE AREA AND THE LLVL
THETA/E RIDGE ALIGNED ALONG THE I-85 CORRIDOR SHOULD BE MORE OF A
FOCUSING MECHANISM FOR -SHRA THAN AN AXIS OF INSTABILITY. THE GFS
DOES SHOW SOME ELCAPE IN THE CROSS SECTIONS...HOWEVER IT/S LLVL
THERMAL AND WIND FIELD IS VERY SIMILAR TO THE MORE STABLE NAM. WITH
DEEPER MIXING ADVERTISED BY THE GFS...THE POTENTIAL IS THERE FOR
STRONG WIND ISSUES ACROSS THE MTNS AS A 45-50 KT LLVL JET TRAVERSES
THE AREA. THIS WILL BE ONE TO KEEP AN EYE ON...AS THE FAST MOVING
FRONT LOOKS TO ALSO HAVE DECENT CAA ASSOCIATED WITH IT.
A PACIFIC ORIGIN SFC HIGH BUILDS IN QUICKLY TUE NIGHT AND PERSISTS
THROUGHOUT THE DAY. NORTHERLY WINDS SHIFTING EAST THROUGH THE DAY
WILL KEEP TEMPS A FEW DEGREES BELOW NORMAL AND BELOW FREEZING SFC
TD/S WILL BE AWAITING THE NEXT SYSTEM OUT OF THE GOM WED. UPPER
LEVEL CLOUDS WILL BEGIN MOVING IN ACROSS THE S/RN ZONES LATE TUE IN
AN ACTIVE STJ PATTERN...AND BY 00Z WED LLVL CLOUDS WILL BEGIN QUICKLY
MOVING NORTH ACROSS THE CWFA. WITH LLVL E/LY FLOW SETTING UP...THE
MTNS WILL HAVE ADDED MECHANICAL LIFT TO ADD TO THE INCREASING
MOISTURE. THIS SHOULD BE ENOUGH TO INSTIGATE MTN PRECIP WHERE THE
SFC/BASED DRY AIR EVAPO COOLS AND MAKES FOR A P/TYPE CONCERN ACROSS
THE HIGHER ELEVATIONS. THIS SCENARIO SHOULD BE SHORT LIVED AS THE
SMALL SCALE INSITU HIGH YIELDS TO THE STRONGER AND WARMER SOUTHERN
STREAM SYSTEM.
&&
.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
AS OF 215 PM SATURDAY...WHILE THERE ARE MODEL DIFFERENCES IN THE
EVOLUTION OF THE NRN STREAM ENERGY IN THE LATER HALF OF THE
EXTENDED...THE GFS AND ECMWF ARE IN PRETTY GOOD AGREEMENT IN THE
TIMING AND LOCATION OF THE SRN STREAM LOW THAT COMES OUT OF THE GULF
ON WED. THE GFS DOES HOLD IN THE SFC RIDGE A LITTLE LONGER...THOUGH
IT/S STILL WEAK AND OUT OF POSITION FOR A GOOD CAD EVENT. THIS
RESULTS IN MUCH LOWER DEWPOINTS OVER THE REGION ON THE GFS THAN THE
EC TO START THE EVENT. THE AIRMASS THROUGH A DEEP LAYER STARTS OUT
QUITE DRY WED MORNING...WHICH SHOULD RESULT IN SOME MIXED PCPN JUST
THROUGH OUR TYPICAL WET-BULB EFFECTS. ONCE THE WARM ADVECTION REALLY
KICKS IN...THE EVENT SHOULD BE ALL RAIN. WHILE I HAVE SOME HIGH
ELEVATION SNOW IN THE MTNS EARLY IN THE DAY...THE ACTUAL PCPN TYPE
IS GOING TO BE HARD TO GAUGE. I IMAGINE WE WILL ALSO SEE A LITTLE
SLEET AND SOME FZRA IN THE HIGH NRN MTN VALLEYS. STILL...I DON/T
EXPECT THE MIXED PCPN TO BE OF ANY CONSEQUENCE FOR THIS EVENT.
I HAVE HIGH LIKELY TO CATEGORICAL POPS IN FOR WED. IT/S A LITTLE
RARE TO GO THAT HIGH ON DAY 5...BUT THE PAST SEVERAL MODEL RUNS HAVE
BEEN POINTING THIS WAY...AND IT MATCHES WELL WITH THE NEIGHBORING
OFFICES.
ONCE THE LOW PASSES WE SHOULD SEE DRY WEATHER FOR MOST OF THU-SAT.
THIS IS WHERE THE MODEL DIFFERENCES COME MORE INTO PLAY. THE GFS
DEVELOPS A STRONGER NRN STREAM UPPER LOW WHICH IS CENTERED FARTHER
SOUTH THAN THE EC/S. THIS KEEPS LLVL THICKNESSES COLDER AND RH/S
HIGHER ACROSS THE MTNS. THE GFS WOULD IMPLY A PRETTY GOOD CHANCE OF
SNOW SHOWERS THU AND FRI ALONG THE TN BORDER...WHILE THE EC IS
BASICALLY DRY AND WARMER. I HAVE CARRIED A FEW SHSN OVER THE HIGH
TERRAIN...BUT I STAYED CLOSER TO THE DRIER SOLUTION PER HPC/S
THOUGHTS ABOUT THE EXTENDED.
&&
.AVIATION /20Z SATURDAY THROUGH THURSDAY/...
AT KCLT AND ELSEWHERE...THE INFLUENCE OF DRY HIGH PRESSURE WILL
RESULT IN CLEAR SKIES/VFR CONDITIONS THROUGH THE PERIOD. LIGHT
SOUTHWEST WINDS WILL PERSIST THROUGH THE AFTERNOON...LIKELY BECMG
LIGHT AND VARIABLE THIS EVENING...BEFORE RETURNING TO THE SOUTHWEST
SUNDAY MORNING. THE EXCEPTION WILL BE AT KAVL...WHERE LIGHT UP-
VALLEY FLOW SHOULD BECOME L/V THIS EVENING.
OUTLOOK...A COLD FRONT WILL APPROACH FROM THE WEST SUNDAY. THE FRONT
WILL REACH THE NC MTNS LATE SUNDAY NIGHT AND MOVE EAST ACROSS THE
FOOTHILLS AND PIEDMONT DURING THE DAYTIME ON MONDAY. PERIODS OF
RESTRICTIONS WILL LIKELY ACCOMPANY THE PASSAGE OF THE FRONT. HIGH
PRESSURE WILL RETURN TO THE REGION MONDAY NIGHT AND WILL REMAIN
THROUGH TUESDAY. PRECIPITATION CHANCES WILL RETURN AGAIN WEDNESDAY.
&&
.FIRE WEATHER...
THERE IS SOME CONCERN ABOUT THE POTENTIAL FOR RH TO DROP THROUGH THE
FLOOR THIS AFTERNOON...ESPECIALLY SINCE DEWPOINTS ARE ALREADY QUITE
LOW AS OF 15Z (TEENS MTNS/20S PIEDMONT). HOWEVER...THERE ARE SOME
HINTS THAT DEWPOINTS WILL NOT CRATER MUCH MORE THAN THEY ALREADY
HAVE...AND MAY INCREASE SLIGHTLY THIS AFTERNOON. OWING TO FAIRLY
WARM AIR ALOFT...MIXING WILL NOT BE VERY DEEP THIS AFTERNOON. EVEN
IF MIXING BECOMES DEEPER THAN ANTICIPATED...IT APPEARS THAT SLIGHTLY
MORE MOIST AIR IS POISED TO MOVE INTO THE REGION THIS AFTERNOON FROM
THE TENN VALLEY. WE WILL CONTINUE TO FORECAST MIN RH JUST SLIGHTLY
ABOVE THE CRITICAL 25 PERCENT THRESHOLD.
&&
.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.
&&
$$
SYNOPSIS...PAT
NEAR TERM...JDL
SHORT TERM...SBK
LONG TERM...MCAVOY
AVIATION...JDL
