Lake Wind Advisory 38, NWS Charleston, SC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
331 PM EST SAT NOV 26 2011

.SYNOPSIS...
HIGH PRESSURE WILL PREVAIL THROUGH SUNDAY NIGHT. A COLD FRONT WILL
APPROACH FROM THE WEST ON MONDAY...AND PUSH THROUGH THE AREA FROM
WEST TO EAST MONDAY INTO MONDAY EVENING. HIGH PRESSURE WILL THEN
SLOWLY BUILD BACK INTO THE REGION THROUGH THE MIDDLE AND LATTER
PORTIONS OF NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
A DEEP RIDGE OF HIGH PRESSURE WILL CONTINUE TO DRIFT EAST OVER THE
ATLANTIC THIS EVENING THROUGH TONIGHT AS A LONGWAVE TROUGH SHIFTS
FROM THE CENTRAL PLAINS TOWARDS THE SOUTHEASTERN UNITED STATES. AS
THIS OCCURS...SFC HIGH PRESSURE TO OUR NORTH WILL DRIFT FURTHER
OFFSHORE...THUS ALLOWING LIGHT ONSHORE FLOW TO REMAIN OVER THE
FORECAST AREA. ONSHORE FLOW IN COMBINATION WITH INCREASING ISENTROPIC
ASCENT WILL LIKELY EXPAND CLOUD COVER OVERNIGHT. ALTHOUGH STRONG
RADIATIONAL COOLING IS NOT ANTICIPATED...OVERNIGHT LOWS WILL
APPROACH CROSSOVER TEMPS...LOW/MID 50S. THIS MAY PRODUCE SOME PATCHY
FOG...ESPECIALLY AS WINDS BECOME LIGHT AND VARIABLE LATE. THE BEST
CHANCES OF FOG WILL BE OVER SOUTHEAST GEORGIA WHERE SFC DEWPTS
WILL BE HIGHEST. RAINFALL CHANCES WILL BE LOW THROUGH TONIGHT AS
FORCING MECHANISMS REMAIN WEAK.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY/...
ON SUNDAY...THE SURFACE RIDGE WILL MOVE FURTHER OUT INTO THE
ATLANTIC...WHILE A COLD FRONT GRADUALLY MOVES THROUGH THE
SOUTHEASTERN STATES. THE CWA WILL STILL BE IN THE WARM ADVECTION
PATTERN ON THE BACKSIDE OF THE ATLANTIC HIGH ON SUNDAY...GIVING THE
AREA TEMPERATURES WELL ABOVE NORMAL DESPITE A FAIR AMOUNT OF CLOUD
COVER AROUND. VERY STRONG INVERSION ABOVE 900 MB WILL KEEP CLOUD
DECK SHALLOW...SO I DO NOT EXPECT ANYTHING BESIDES SOME LOCAL
SPRINKLES TOMORROW ON THE PRECIP FRONT.

MOISTURE PROFILES THICKEN A LITTLE SUNDAY NIGHT...BUT VERY LOW RH
AIR WILL KEEP MOST OF THE SHOWER ACTIVITY AT BAY. THE EXCEPTION MAY
BE THE FAR WESTERN AREAS WHERE THE CAP BEGINS TO BREAK DOWN UNDER
THE INFLUENCE OF HEIGHT FALLS FROM THE STRONG UPPER LOW APPROACHING
FROM THE WEST. TEMPS WILL CONTINUE WELL ABOVE NORMAL WITH MILD
SOUTHEASTERLY WINDS.

BY MONDAY...THE COLD FRONT STARTS TO MAKE PROGRESS INTO THE AREA
FROM THE WEST. THERE IS STILL SOME UNCERTAINTY WITH THE SPEED OF THE
FRONT AS THE ECMWF AND CMC REMAIN SLOWER THAN THE NAM AND GFS...BUT
THERE ARE ALL WELL INTO THE CWA BY LATE MONDAY. POPS WILL RAMP UP
ACCORDINGLY. MAX TEMPS WILL VARY QUITE A BIT ACROSS THE AREA
MONDAY...WITH THE WARMEST BEING IN THE NORTHEASTERN PART OF THE FA
SINCE THEY WILL BE AHEAD OF THE FRONT THE LONGEST AND ALSO HAVE THE
BEST CHANCE OF SEEING A FEW PEAKS OF SUNSHINE. MAX TEMPS WILL
ACTUALLY BE COOLER TO THE SOUTHWEST WHERE THE FRONT MOVES THROUGH
EARLIER AND THE CLOUDS ARE THICKER.

FOR PRECIP...IT LOOKS LIKE EVERYWHERE WILL GET SOME NEEDED RAIN WITH
THE FRONTAL PASSAGE. THE MAIN REASON FOR NOT GOING ABOVE 80 POPS IN
ANY ONE PERIOD IS THE TIMING ISSUES...BUT VERY STRONG DYNAMICS
SUPPORT WIDESPREAD CONVECTION WITH AN EXTENDED AREA OF RAIN BEHIND
THE FRONT AS THE UPPER LOW GOES NEGATIVE TILT OVER THE SOUTHEAST.
THERE IS STILL A SMALL THREAT FOR SEVERE RIGHT ALONG THE FRONT
MONDAY AFTERNOON IN A NARROW CORRIDOR...BUT FAR TOO MANY QUESTIONS
ON LOCATION OF INSTABILITY...OR LACK THEREOF...TO FEEL CONFIDENT IN
BRINGING UP THE THREAT IN ANY OF OUR PUBLIC PRODUCTS THIS EARLY IN
THE GAME.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
MEDIUM RANGE SOLUTIONS ARE IN DECENT AGREEMENT WITH THE OVERALL
SYNOPTIC PATTERN EVOLUTION THROUGH THE LONG TERM PERIODS. HIGH
PRESSURE IS SLOWLY EXPECTED TO BUILD BACK INTO THE REGION TUESDAY
NIGHT AND REMAIN THE DOMINANT WEATHER FEATURE THROUGH NEXT SATURDAY.
AS A RESULT...WILL KEEP THE FORECAST RAIN FREE WITH GENERALLY CLEAR
TO PARTLY CLOUDY SKIES. EXPECT TEMPERATURES TO RUN SLIGHTLY BELOW
NORMAL TUESDAY NIGHT THROUGH THURSDAY NIGHT...THEN REBOUND TO NEAR
NORMAL LEVELS FRIDAY THROUGH SATURDAY.

&&

.AVIATION /21Z SATURDAY THROUGH THURSDAY/...
VFR CONDITIONS WILL PREVAIL AT KCHS AND KSAV THROUGH THE FIRST 24
HOUR PERIOD. CEILINGS WILL LOWER OVERNIGHT BUT ARE ANTICIPATED TO
REMAIN VFR. REDUCTIONS IN VSBYS ARE POSSIBLE LATE TONIGHT AS LOW
LVL MOISTURE INCREASES WITH ONSHORE FLOW AND CROSSOVER TEMPS ARE
APPROACHED. HOWEVER...15 KT WINDS BETWEEN 1-2K FT ABOVE THE SFC WILL
LIKELY KEEP THE THREAT OF ANY SIGNIFICANT VSBY REDUCTION AT A
MINIMUM. HAVE OPTED TO KEEP OUT MENTION OF MVFR VSBYS FOR THE TIME
BEING SINCE IT APPEARS THAT THIS IS MAINLY A LOW END VFR STRATUS
EVENT.

EXTENDED AVIATION OUTLOOK...MVFR CIGS APPEAR LIKELY SUNDAY NIGHT
THROUGH MONDAY NIGHT IN ASSOCIATION WITH A SLOW MOVING COLD FRONT
COLD FRONT...WITH PERIODS OF IFR CIGS/VSBYS IN RAIN AND FOG.
THUNDERSTORMS WILL ALSO BE POSSIBLE MONDAY AFTERNOON AND MONDAY
NIGHT. MVFR CIGS MAY LINGER INTO TUESDAY MORNING...BUT IMPROVING
CONDITIONS TO VFR LEVELS ARE EXPECTED TUESDAY AFTERNOON THROUGH
THURSDAY.

&&

.MARINE...
SFC HIGH PRESSURE WILL CONTINUE TO DRIFT OFF THE SOUTH CAROLINA AND
NORTH CAROLINA COAST THIS EVENING THROUGH TONIGHT. THIS WILL ALLOW
WINDS TO CLOCK FROM EAST TO SOUTHEAST THROUGH TONIGHT. A WEAK
PRESSURE GRADIENT WILL GENERALLY KEEP WINDS AT 10 KT OR LESS
THROUGH EARLY TONIGHT. SEAS WILL BE IN THE 2-4 FT RANGE...HIGHEST
ACROSS THE OUTER GEORGIA WATERS. THE SURFACE PRESSURE GRADIENT
WILL THEN BEGIN TO TIGHTEN ACROSS THE WATERS LATE AS HIGH PRESSURE
DRIFTS FURTHER OFFSHORE WHILE A COLD FRONT BEGINS TO APPROACH FROM
THE WEST. WIND SPEEDS SHOULD INCREASE UPWARDS TO 10-15 KT
TONIGHT...RESULTING IN A SLIGHT INCREASE IN SEAS.

SUNDAY THROUGH THURSDAY...WINDS AND SEAS WILL BE ON THE INCREASE
SUNDAY AS THE PRESSURE GRADIENT TIGHTENS BEHIND RETREATING HIGH
PRESSURE. SEAS ARE EXPECTED TO REACH 6 FEET SUNDAY NIGHT...FIRST IN
THE OUT GEORGIA WATERS...THEN ALL COASTAL WATERS LATER IN THE
NIGHT...SO SCAS WILL BE HOISTED. AT THIS TIME...I DO NOT EXPECT
WINDS TO REACH SCA CRITERIA...BUT THEY WILL BE CLOSE MONDAY AHEAD OF
THE FRONT...AND THEN AGAIN MONDAY NIGHT BEHIND THE FRONT. WINDS AND
SEAS WILL GRADUALLY COME BACK DOWN TUESDAY AS LOW PRESSURE PULLS
AWAY TO THE NORTHEAST AND WEAKER HIGH PRESSURE BUILDS IN BEHIND THE
SYSTEM.

&&

.TIDES/COASTAL FLOODING...
THERE IS A CHANCE OF EXCEEDING COASTAL FLOOD ADVISORY CRITERIA
DURING THE MORNING HIGH TIDE CYCLE ON SUNDAY AS THE ASTRONOMICAL
PREDICTIONS AT BOTH CHARLESTON AND SAVANNAH ARE JUST BELOW
ADVISORY CRITERIA. THE ONSHORE FLOW MAY PROVIDE ENOUGH OF A
POSITIVE DEPARTURE TO PRODUCE TIDE LEVELS HIGH ENOUGH SUCH THAT
SHALLOW COASTAL FLOODING COULD OCCUR. THUS...COASTAL FLOOD
ADVISORIES MAY EVENTUALLY BE NEEDED...BUT A SIGNIFICANT FLOOD EVENT
IS NOT EXPECTED.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 3 AM MONDAY TO 10 AM EST TUESDAY FOR
     AMZ350-352.
     SMALL CRAFT ADVISORY FROM 9 PM SUNDAY TO NOON EST TUESDAY FOR
     AMZ374.
     SMALL CRAFT ADVISORY FROM 3 AM MONDAY TO 2 AM EST TUESDAY FOR
     AMZ354.

&&