FXUS62 KRAH 102346
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
646 PM EST THU DEC 10 2009
.SYNOPSIS...
COOL HIGH PRESSURE WILL CONTINUE TO BUILD INTO THE REGION THROUGH
FRIDAY. A LOW PRESSURE SYSTEM MOVING NORTH FROM THE GULF OF MEXICO
WILL AFFECT THE SOUTHEAST STATES OVER THE WEEKEND.
&&
.NEAR TERM /THROUGH FRIDAY NIGHT/...
AS OF 115 PM THURSDAY...
TONIGHT...
WITH PINNACLE OF COLD AIR IN PLACE BY 12Z FRIDAY(LOW-LEVEL
THICKNESSES BOTTOMING OUT AROUND 1265 TO 1270M)...AND WINDS DROPPING
OFF THE LESS THAN 05 KTS...THE MID TO UPPER 20 FORECAST BY MOS
STATISTICAL GUIDANCE LOOKS VERY REASONABLE...WITH SOME OF THE
TYPICAL CLIMATOLOGICAL COLDER SPOTS DIPPING DOWN INTO THE LOWER 20S.
FRIDAY AND FRIDAY NIGHT...
MODERATING SURFACE HIGH OVER THE LOWER MS VALLEY STRENGTHENS AS IT
BUILDS DIRECTLY OVER THE REGION...UNDER THE CONFLUENT FLOW ALOFT AND
DOWNSTREAM OF THE APPROACHING LOW AMPLITUDE S/W RIDGE. THICKNESSES
RISE SLOWLY THROUGH THE PERIOD...BUT REMAIN 30 TO 40 METERS BELOW
NORMAL. UNDER THE ACTIVE SOUTHERN STREAM JET...MODEL TIME HEIGHT
CROSS SECTIONS INDICATE INCREASING HIGH CLOUDS FRIDAY AFTERNOON AND
INTO FRIDAY NIGHT. WILL CONTINUE FAVOR COOLER MET STATISTICAL
GUIDANCE. HIGHS FRIDAY INTO THE LOWER TO MID 40S. DEPENDING ON
OPAQUENESS OF HIGH CLOUDS...LOWS FRIDAY NIGHT COULD POTENTIALLY
DIP DOWN INTO THE UPPER TEENS TO MID 20S (18-24 DEGREE RANGE)GIVEN
THE CALM WINDS AND THE EXPECTED DRY SINGLE DIGIT SFC DEWPOINTS.
NOT QUITE READY TO GO THAT COLD...BUT WILL KNOCK PREVIOUS MIN T
FORECAST DOWN A CATEGORY. LOWS IN THE LOWER TO MID 20S.
&&
.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
AS OF 230 PM THURSDAY...
ISENTROPIC LIFT OVER THE SURFACE RIDGE IS EXPECTED TO INCREASE
DURING THIS TIME FRAME WHILE THE AIR COLUMN ALSO BEGINS TO SATURATE
FROM THE TOP DOWN. CENTRAL NORTH CAROLINA SHOULD STAY DRY DURING THE
DAY ON SATURDAY AS ANY PRECIP THAT FORMS WILL EVAPORATE AS IT
ENCOUNTERS THE DRY SURFACE AIR MASS. AS THE RIDGE SHIFTS OFF TO THE
EAST LATE SATURDAY INCREASED LOW LEVEL FLOW WILL ALLOW MOISTURE TO
FINALLY INCREASE AT THE SURFACE. RAINFALL IS EXPECTED TO INCREASE IN
COVERAGE AFTER 00Z SUNDAY FROM THE SOUTHWEST TO NORTHEAST WITH THE
INCREASED ISENTROPIC LIFT AND A DEVELOPING INVERTED TROUGH OFF THE
CAROLINA COAST. THERE WILL BE A VERY SMALL WINDOW FOR SOME TYPE OF
WINTRY MIX AT THE ONSET OF THE EVENT LATE SATURDAY NIGHT ACROSS THE
EXTREME NORTHWESTERN PORTION OF THE CWA. WARM ADVECTION AT MID
LEVELS WILL INCREASE H85-H7 THICKNESSES ABOVE 1550M....WHILE H10-H85
THICKNESSES ARE PROGGED TO BE AT OR JUST ABOVE 1300M FROM THE TRIAD
AND NORTHWARD. THIS THERMAL PROFILE WOULD SUPPORT A SMALL CHANCE OF
FREEZING RAIN OR DRIZZLE. LATEST HPC FORECAST IS ALSO INDICATING A
POSSIBLE TRACE EVENT OVER THIS REGION...BEFORE THE PRECIP QUICKLY
CHANGES OVER TO RAIN AS INDICATED BY THE PREDOMINATE P-TYPE
NOMOGRAM. MODELS HAVE BEEN TRENDING WARMER OVER THE PAST FEW RUNS
AND IF THIS CONTINUES...THIS WOULD LIKELY TURN INTO AN ALL RAIN
EVENT. NEVERTHELESS...THIS WILL BE CLOSELY MONITORED BY FUTURE
SHIFTS. OTHERWISE...WILL SHOW LIKELY POPS ACROSS THE REGION THROUGH
18Z ON SUNDAY BEFORE THINGS FINALLY BEGIN TO TAPER OFF AS THE
SURFACE LOW OFF THE COAST MOVES NORTHEAST. AM NOT EXPECTING TOO MUCH
IN THE WAY OF QPF (AROUND 1/3 OF AN INCH) FOR THE DURATION OF THIS
EVENT...AS FORECAST SOUNDINGS DO NOT PROG A DEEP LAYER OF MOISTURE
(ONLY SATURATED BELOW ABOUT 600MB). ALSO...ONLY WEAK UPPER LEVEL
SUPPORT WILL BE IN PLACE ACROSS THE REGION OVER THE WEEKEND. MAY SEE
TWO QPF MAXIMUMS...ONE ALONG EASTERN PORTIONS OF THE CWA DUE TO THE
PROXIMITY OF THE SURFACE LOW AND ANOTHER ACROSS THE PIEDMONT DUE TO
THE UPSLOPE EFFECT. WITH PRECIP AND AMPLE CLOUD COVER IN
PLACE...WILL CONTINUE TO FORECAST TEMPS ON THE COOL SIDE OF
GUIDANCE...WITH AFTERNOON HIGH TEMPERATURES MOSTLY IN THE MID TO
UPPER 40S.
&&
.LONG TERM /MONDAY THROUGH WEDNESDAY/...
AS OF 245 PM THURSDAY...
BY MONDAY AND TUESDAY...LOW LEVEL SOUTH/SOUTHWESTERLY FLOW WILL
INCREASE AHEAD OF A COLD FRONT THAT WILL BE MOVING QUICKLY THROUGH
THE MIDWEST REGION. THIS WILL ALLOW TEMPS TO MODERATE INTO THE UPPER
50S TO LOW 60S ACROSS CENTRAL NORTH CAROLINA. PRECIP CHANCES WILL
RETURN ON TUESDAY AS THE COLD FRONT APPROACHES. HOWEVER...MODELS ARE
HAVING SOME DISCREPANCIES WITH RESPECT TO THE TIMING OF THE FRONTAL
PASSAGE...THEREFORE WILL SHOW CHANCE POPS AREAWIDE BEGINNING LATE
MONDAY AND LASTING THROUGH LATE TUESDAY. TEMPS WILL RETURN TO NEAR
NORMAL VALUES BY THE MIDDLE OF NEXT WEEK BEHIND THE FRONT.
&&
.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
AS OF 640 PM THURSDAY...
HIGH PRESSURE BUILDING INTO CENTRAL NC FROM THE WEST WILL PROVIDE
VFR CONDITIONS ACROSS THE AREA THROUGH SATURDAY. NEAR SURFACE WINDS
WILL REMAIN W-NW THROUGH FRIDAY AFTERNOON AT OR LESS THAN
10KTS.
A LOW PRESSURE SYSTEM WILL DEVELOP OVER THE NORTHERN GULF COAST
FRIDAY AND LIFT NORTHEAST FRIDAY NIGHT. THIS WEATHER SYSTEM MAY
CAUSE MVFR IR IFR CEILINGS ACROSS CENTRAL NC LATE SATURDAY NIGHT
INTO SUNDAY. VFR CONDITIONS ARE EXPECTED TO RETURN SUNDAY NIGHT
THROUGH TUESDAY AS HIGH PRESSURE BUILDS THEN SETTLES OVER THE
AREA.
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...RE
NEAR TERM...CBL
SHORT TERM...KRR
LONG TERM...KRR
AVIATION...WSS
