FXUS62 KGSP 252358
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
658 PM EST FRI DEC 25 2009
.SYNOPSIS...
WEAK HIGH PRESSURE WILL BUILD ACROSS THE SOUTHEAST STATES THROUGH
THE WEEKEND WHILE A LARGE UPPER LEVEL TROUGH CROSSES OVERHEAD. A
STRONG UPPER LEVEL RIDGE WILL THEN BRING IN MUCH COOLER HIGH
PRESSURE MONDAY AND DROP TEMPERATURES BLOW NORMAL THROUGH THE MIDDLE
OF NEXT WEEK.
&&
.NEAR TERM /THROUGH SATURDAY/...
NOT EXPECTING ANY ADDITIONAL PRECIP TONIGHT SO A NEW FORECAST WILL
BE RUN TO ELIMINATE THAT WORDING OVER THE EASTERN ZONES.
OTHERWISE...CLOUD COVER MAY PERSIST WELL INTO THE OVERNIGHT HOURS AS
LOW LEVEL FLOW REMAINS SW AND SATELLITE IMAGERY SHOWS MVFR CEILINGS
UPSTREAM ACROSS GA.
LOWER OVC ACRS THE FTHLS/PIEDMONT WITHIN LINGERING WEAK WEDGE SHOULD
EVENTUALLY SCOUR...BUT TIMING REMAINS UNCERTAIN...ESPECIALLY AS ANY
MIXING LOOKS TO LIMITED WITHIN THE WEAK FLOW AND HEADING INTO THE
NIGHTTIME HOURS. AS DRYING ALOFT CONTINUES...AREAS OF FOG MAY ALSO
DEVELOP.
WITH TEMPERATURES EXPECTED TO FALL TO FREEZING AND BELOW BY EARLY
SATURDAY MORNING...ANY WATER LINGERING ON ROADS WILL FREEZE. THE
GREATEST THREAT IS ACRS THE NC MTNS/FTHLS WHERE ICE ACCUMULATED
EARLIER...SNOWMELT CONTINUES AND TEMPERATURES WILL BE THE LOWEST.
THUS A WINTER WX ADVISORY FOR BLACK ICE WAS ISSUED FOR THESE AREAS.
THE FA TO REMAIN WITHIN DEEP MID/UPPER LEVEL CYCLONIC FLOW ON
SATURDAY...BUT WEAK SFC RIDGING AND THE PRESENCE OF DEEP DRYING
TO RESULT IN A QUICK RETURN TO FAIR WX CONDITIONS AND MAX TEMPS A
LITTLE ABOVE CLIMO.
&&
.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
AS OF 350 PM FRI...AN INTENSE UPPER LOW WILL FINALLY GET PICKED UP
BY THE WESTERLIES SUNDAY NIGHT AND MONDAY. WITH A WEAK SURFACE RIDGE
AND A DRY AIRMASS IN PLACE...THE WEATHER WILL BE FAIR SAT NGHT AND
SUNDAY. AS THE AXIS OF THE UPPER LOW SWINGS JUST NORTH OF THE
REGION OVERNIGHT...NORTHWEST FLOW...COLDER TEMPERATURES AND CYCLONIC
CURVATURE WILL BEGIN TO AFFECT THE MOUNTAINS. THE RESULTING UPSLOPE
FLOW SHOULD YIELD GOOD SNOWSHOWER COVERAGE ALONG THE TN LINE. THE
HEIGHTS ARE A LITTLE HIGH...BUT WITH A MOIST LAYER EXTENDING UP TO
AROUND 750 MB AND H8 TEMPS FALLING TO AROUND -10 DEG C...THE
SNOWSHOWER ACTIVITY SHOULD BE VIGOROUS ENOUGH TO CAUSE ACCUMULATING
SNOWFALL. THE PREVIOUS SHIFT HAD 1 TO 2 INCHES OF SNOW...AND MY
NUMBERS ARE SIMILAR...WITH THE HIGHEST TOTALS ACROSS THE NRN MTNS
AND ALONG THE IMMEDIATE TN LINE DOWN ACROSS THE CENTRAL AND
SOUTHWEST MTNS.
&&
.LONG TERM /TUESDAY THROUGH FRIDAY/...
AS OF 245 PM FRIDAY...H5 SHRTWV MOVES E OF AREA MON NIGHT. LOW LVL
MOISTURE IN NW FLOW OVER NC MTNS ALONG TN BORDER WILL ALLOW SNOW
SHWRS TO LINGER THRU THE DAY MON BEFORE ENDING MON NIGHT. H5 RIDGE
BUILDS OVER REGION TUE AND SFC HIGH RIDGES DOWN OVER CWA WITH COOL
NE FLOW DEVELOPING. THERE SHOULD BE ENOUGH SUNSHINE FOR TEMPS TO
WARM TO WITHIN A COUPLE DEG OF AVG TUE AFTN. UPPER RIDGE MOVES E AND
NEXT S STREAM SHORTWAVE APPROACHES THE AREA FROM THE SW TUE
NIGHT-WED. MODELS CONTINUE TO STRUGGLE WITH RUN TO RUN CONTINUITY
AND DIVERGE FROM EACH OTHERS SOLUTIONS REGARDING THIS SYSTEM. IN ANY
CASE THERE IS ENOUGH AGREEMENT TO SEE THAT AS SFC HIGH PRESSURE
RIDGES INTO THE CWA FROM THE NE WED...A SFC LOW DEVELOPS IN THE N
GULF AND TRACKS ENE INTO N FL BEFORE WEAKENING AND REDEVELOPING OFF
THE CAROLINA COAST IN WHAT APPEARS TO BE A PSBL MILLER B SCENARIO.
THE S EXTENT OF THIS TRACK INDICATES A RAIN-SNOW MIX BUT KEPT POPS
IN THE CHC RANGE ATTM DUE TO RELATIVELY HIGH DEGREE OF UNCERTAINTY
REGARDING DETAILS AND TIMING.
&&
.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
AT KCLT...A TRICKY FORECAST BECAUSE OF A LACK OF CONFIDENCE IN MODEL
GUIDANCE. FOG WAS DEVELOPING ACROSS THE PIEDMONT AT SUNSET WHILE LOW
STRATUS HANGS ON. CONDITIONAL CLIMATOLOGY SUGGESTS THAT IFR/LOW IFR
CONDITIONS WILL PERSIST FOR THE BETTER PART OF THE NIGHT BUT THE
DATA SET IS SMALL. UP UNTIL THE RECENT 23Z ISSUANCE...THE GFS LAMP
GUIDANCE HAS BEEN BEHIND ON ITS HANDLING OF THE FOG. WATER VAPOR
IMAGERY SHOWS DRYING ALOFT MOVING OVER WRN PIEDMONT...WHICH IS BORNE
OUT IN THE MODEL GUIDANCE. IN MOST SITUATIONS WITH DRYING ALOFT AND
LOTS OF LOW LEVEL MOISTURE FROM VERY RECENT RAINFALL...WE SHOULD
EXPECT A PERIOD OF POOR VISIBILITY FROM FOG. SO...THIS IS WHAT WAS
DONE. EITHER IFR OR LOW IFR IN VIS OR CEILING UNTIL AFTER SUNRISE
SATURDAY. DECLINED TO GO VERY LOW IFR...BUT DENSE FOG CERTAINLY A
POSSIBILITY AND WILL MONITOR. BY 13Z-14Z...RAPID CLEARING SHOULD
TAKE PLACE AND AFTER THAT...VFR WITH LIGHT SW WIND AND JUST SOME
HIGH CLOUDINESS.
ELSEWHERE...SW LOW LEVEL FLOW SHOULD ADVECT MVFR/IFR CLOUD DECK FROM
GEORGIA ACROSS THE FORECAST AREA. SO...IN SPITE OF SOME LOCATIONS
VFR AT 23Z...THINK LOW CLOUDS WILL RETURN. NOT AS CERTAIN ABOUT FOG
POSSIBILITY AS WITH KCLT...BUT EXPECT MVFR VIS WILL REDEVELOP.
AGAIN...SOME LOWER STUFF SHOULD BE EXPECTED...BUT TIMING IS
UNCERTAIN SO NO TEMPOS ARE INCLUDED AT THIS TIME. EXPECTING VFR
CONDITIONS TO RETURN BY MID-MORNING.
OUTLOOK...VFR CONDITIONS EXPECTED SATURDAY THRU WEDNESDAY. MOISTURE
AHEAD OF A WEAK COLD FRONT WILL RETURN TO THE AREA ON WEDNESDAY.
&&
.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...WINTER WEATHER ADVISORY UNTIL 9 AM EST SATURDAY FOR NCZ033-
048>053-058-059-062>065-501>510.
SC...NONE.
&&
$$
SYNOPSIS...SBK
NEAR TERM...CSH/PM
SHORT TERM...MCAVOY
LONG TERM...RB
AVIATION...PM
