FXUS62 KGSP 260517
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1217 AM EST SAT DEC 26 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 TODAY/...
EXCELLENT DENSE FOG CONDITIONS THIS EVENING ACROSS A LARGE PART OF
THE WESTERN CAROLINAS WITH DRYING ABOVE THE BOUNDARY LAYER...LOTS OF
LOW LEVEL MOISTURE FROM RECENT RAINFALL...AND LIGHT WIND. SURFACE
OBS HAVE FINALLY REACHED CRITICAL MASS SO THE TIME IS NOW FOR
ISSUING A DENSE FOG ADVISORY FOR THE AREA FROM THE FRENCH BROAD
VALLEY AND NRN MTNS EAST ACROSS THE FOOTHILLS AND WRN PIEDMONT.
DENSE FOG MIGHT THIN OUT AND LIFT DURING THE EARLY MORNING HOURS IN
WHICH CASE PARTS OF THE ADVISORY MIGHT GET CANCELLED EARLY...
OTHERWISE IT WILL RUN UNTIL JUST AFTER SUNRISE. IF THE FOG DOES NOT
LIFT...THIS COULD GET INTERESTING AS WE MIGHT END UP WITH A DENSE
FREEZING FOG SITUATION AS TEMPS FALL SLOWLY BELOW 32F TOWARD DAWN.
SEEN THIS HAPPEN BEFORE AND IT LEADS TO SOME SLIPPERY PATCHES ON
ROADS THAT ESSENTIALLY GET COVERED WITH A THIN LAYER OF RIME ICE.
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 /TONIGHT 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 /05Z SATURDAY THROUGH WEDNESDAY/...
AT KCLT...LIFR WITH TEMPORARY VLIFR IN FOG AND STRATUS SHOULD
PERSIST IN CALM WINDS UNTIL SUNRISE...WHEN QUICK IMPROVEMENT TO VFR
WILL OCCUR. LIGHT NORTHWEST WIND AFTER DAWN WILL BACK TO THE
SOUTHWEST IN THE AFTERNOON. MODEL TIME HEIGHTS SUGGEST THAT
SCATTERED CIRRUS WILL ARRIVE AFTER DAYBREAK...AND PERSIST THROUGH
SATURDAY EVENING.
ELSEWHERE...LIFR CONDITIONS WILL TEMPORARILY LOWERING TO VLIFR IN
FOG AND STRATUS WITH LIGHT WINDS OVERNIGHT...EXCEPT AT KAND WHERE
VFR WILL LOWER TO MVFR IN FOG. FORECAST MINIMUM TEMPERATURES SUPPORT
FREEZING FOG AT MOST SITES BY DAWN...BUT OBSERVED DEW POINTS SUGGEST
THAT MINIMUM TEMPERATURES MAY HAVE TROUBLE GETTING TO FREEZING.
RAPID IMPROVEMENT TO VFR WILL TAKE PLACE AFTER SUNRISE...WITH LIGHT
WEST OR NORTHWEST WINDS BACKING TO THE SOUTHWEST IN THE AFTERNOON...
EXCEPT AT KAVL WHERE A LIGHT NORTH WIND WILL PERSIST UNTIL IT
BECOMES VARIABLE AT SUNSET. SCATTERED CIRRUS WILL ARRIVE AFTER
DAYBREAK AND PERSIST THROUGH SATURDAY EVENING ACCORDING TO MODEL
TIME HEIGHTS.
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...DENSE FOG ADVISORY UNTIL 7 AM EST THIS MORNING FOR NCZ033-
035>037-049-050-053-056-057-064-065-068>072-082-501>510.
WINTER WEATHER ADVISORY UNTIL 9 AM EST THIS MORNING FOR NCZ033-
048>053-058-059-062>065-501>510.
SC...DENSE FOG ADVISORY UNTIL 7 AM EST THIS MORNING FOR SCZ001>014-
019.
&&
$$
SYNOPSIS...SBK
NEAR TERM...CSH/PM
SHORT TERM...MCAVOY
LONG TERM...RB
AVIATION...JAT
