Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 290802
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
402 AM EDT SUN MAR 29 2015

.SYNOPSIS...
COLD HIGH PRESSURE WILL PREVAIL TODAY...THEN SHIFTS INTO THE
ATLANTIC TONIGHT. WEAK COLD FRONTS WILL PUSH INTO THE REGION LATE
MONDAY AND AGAIN WEDNESDAY...AND BOTH FRONTS SHOULD DISSIPATE OVER
OR CLOSE TO THE AREA. ATLANTIC HIGH PRESSURE WILL THEN BUILD OVER
THE REGION THROUGH LATE WEEK.  A STRONGER COLD FRONT WILL ARRIVE
FROM THE NORTHWEST NEXT WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
EARLY THIS MORNING...THE DEW POINT FRONT WILL CONTINUE TO SWEEP
SOUTHWARD AND CLEAR THE ENTIRE AREA BEFORE SUNRISE. BEHIND THIS
FEATURE IS A LARGE AND COLD ARCTIC HIGH THAT WILL CONTINUE TO FEED
AN INFLUX OF COLDER AIR INTO THE REGION FROM THE NORTH. THIS WILL
ALLOW FOR TEMPS TO FALL BELOW FREEZING FOR 2-4 HOURS ALONG OUR NW
TIER...WHERE THE FREEZE WARNING REMAINS IN EFFECT. THIS WILL ALSO
ALLOW FOR NEAR RECORD COLD AS SHOWN IN THE CLIMATE SECTION BELOW.
THIS TRANSITION HAS ALSO CAUSED MIXING TO INCREASE AS THE COLDER AIR
CONTINUES ITS PENETRATION SOUTHWARD. THIS WILL RESULT IN NORTH/NE
WINDS APPROACHING LAKE WIND ADVISORY CONDITIONS ON LAKE
MOULTRIE...WHERE WE HAVE WINDS OF 15-20 KT AND WAVES 1-2 FT.

FOR THE BULK OF TODAY...WITH THE ARRIVAL OF A FRESHER CANADIAN AIR
MASS THERE ISN/T MUCH MODIFICATION THAT IS ABLE TO OCCUR. ALTHOUGH
COLD ADVECTION THIS MORNING WILL SHUT OFF AND BECOME NEUTRAL OR
EVEN SHOW SLIGHT WARM ADVECTION FOR THIS AFTERNOON. THE FULL
INSOLATION UNDERNEATH THE SURFACE HIGH AS IT SLIDES DIRECTLY
OVERHEAD WILL ALLOW FOR A LARGE DIURNAL SWING IN TEMPS...SOME
20-30F...LEADING TO MAX TEMPS SIMILAR TO YESTERDAY. ONSHORE
TRAJECTORIES WILL HOLD SHORELINE COMMUNITIES SEVERAL DEGREES
COOLER THAN THOSE INLAND.

TONIGHT...THE SURFACE HIGH IS JUST STARTING TO MOVE INTO THE
ATLANTIC THIS EVENING...AND THE GRADIENT IS RATHER NEBULOUS. THIS
WILL ALLOW FOR RAPID DECOUPLING AND EXCELLENT RADIATIONAL COOLING
WILL TRANSPIRE...CAUSING TEMPS TO PLUMMET QUICKLY INTO THE UPPER
30S AND LOWER 40S INLAND WELL BEFORE MIDNIGHT. WE/LL EXPERIENCE A
GOOD 5-8 HOURS OF RADIATIONAL COOLING NORTH AND UP TO 8-10 HOURS
SOUTH. WHILE IT WON/T BE AS COLD AS THIS MORNING...MANY SECTIONS
INLAND WILL FALL INTO THE MIDDLE 30S. THIS COMBINED WITH SMALL
DEW POINT DEPRESSIONS WILL LEAD TO AT LEAST SCATTERED FROST
ACROSS MUCH THE REGION INLAND FROM US-17. AS SUCH WE/LL MOST
LIKELY NEED TO ISSUE A FROST ADVISORY AT SOME POINT LATER TODAY.
FOR LATE TONIGHT OUR TEMPS WILL STEADY OFF OR EVEN RISE AS THE
SYNOPTIC FLOW VEERS AROUND TO THE SOUTH/SW AND WARM ADVECTION
TAKES HOLD AS A LOW LEVEL JET MOVES INTO THE AREA. CLEAR SKIES
EARLY ON WILL GIVE WAY TO SOME MID/HIGH LEVEL CLOUDS ARRIVING FROM
THE WEST/NW LATE IN ADVANCE OF THE NEXT COLD FRONT THAT WILL BE
NEARING THE APPALACHIANS BY SUNRISE.

&&

.SHORT TERM /MONDAY THROUGH WEDNESDAY/...
MONDAY...A PREFRONTAL BAND OF MOISTURE...MAINLY SUPPORTED BY AN 850
MB WESTERLY JET AND ASSOCIATED CONVERGENCE/MOISTURE TRANSPORT...WILL
TRANSLATE QUICKLY TOWARD THE SOUTH/ SOUTHEAST AND THROUGH THE
FORECAST AREA. THIS FORCING SHOULD WEAKEN WITH TIME...AND THE AXIS
OF ENHANCED 850-500 MB RELATIVE HUMIDITY SHOULD BECOME LESS WELL-
DEFINED WITH TIME. GIVEN THE PERSISTENT CAP DEPICTED BY MODEL
SOUNDINGS AND THE GENERAL WEAKENING TRENDS EVIDENT IN
FORCING/ASSOCIATED MOISTURE FIELDS...CAPPED MAXIMUM POPS AT 30-40
PERCENT LATE MORNING INTO MONDAY AFTERNOON. MEANWHILE...ADJUSTED
TIMING OF TO FAVOR A FASTER TREND FAVORED BY ALL OPERATIONAL
GUIDANCE EXCEPT THE 29/00 UTC NAM. ALSO OF NOTE...A NARROW AXIS OF
SURFACE BASED INSTABILITY WILL ATTEMPT TO SPREAD EAST ESPECIALLY
MONDAY AFTERNOON...THUS A MENTION OF THUNDER REMAINS JUSTIFIED
ACROSS MAINLY SOUTHERN COUNTIES.

MONDAY AFTERNOON TEMPERATURES ARE FORECAST TO RANGE FROM THE MID 60S
FAR NORTH TO THE MID 70S FAR SOUTH. HOWEVER...IF CLOUDS/
PRECIPITATION REMAIN LESS PROMINENT THAN EXPECTED...INCREASING W/SW
WINDS COULD PUSH TEMPERATURES WELL INTO THE 70S ACROSS A WIDER SWATH
OF THE FORECAST AREA.

MONDAY NIGHT...THE PROGRESS OF THE AFOREMENTIONED/WEAKENING BAND OF
MOISTURE WILL BECOME PARALLEL TO THE UPPER FLOW AND WILL SLOW
SOUTHWARD PROGRESS...WHILE A WEAK SURFACE COLD FRONT WILL ADVANCE
INTO THE FORECAST AREA FROM THE NORTH. WHILE THE 29/00 UTC NAM IS
LIKELY OVERDONE DEPICTING A RATHER ACTIVE CONVECTIVE REGIME
ALONG/SOUTH OF I-16...A SLIGHT CHANCE OF SHOWERS/THUNDERSTORMS IS
STILL JUSTIFIED IN THIS AREA MONDAY EVENING. AFTER MIDNIGHT...POPS
ACROSS THE SOUTH TAPER TO LESS THAN 15 PERCENT WITH NO MENTION OF
PRECIPITATION. OTHERWISE...LOWS IN THE 40S/50S WILL BE COMMON
MONDAY NIGHT.

TUESDAY THROUGH WEDNESDAY...AN INITIAL COLD FRONT WILL STALL AND
DISSIPATE OVER THE REGION TUESDAY...THEN ANOTHER WEAK SURFACE COLD
FRONT WILL PUSH INTO THE AREA FROM THE NORTH WEDNESDAY. THIS SECOND
FRONT WILL ALSO STALL AND DISSIPATE OVER OR PERHAPS JUST SOUTH OF
THE REGION. MEANWHILE...A PLUME OF DEEP-LAYERED MOISTURE WILL RESIDE
JUST SOUTH AND WEST OF THE FORECAST AREA...AND THIS MOISTURE WILL
ATTEMPT TO RIDE THE WEST/NORTHWEST STEERING FLOW TOWARD THE
SOUTHEAST COAST. MODEL SOUNDINGS REMAIN SUFFICIENTLY DRY TO MAINTAIN
RAIN-FREE FORECASTS THROUGH TUESDAY NIGHT...BUT AT LEAST SLIGHT
CHANCE POPS INCLUDING A MENTION OF THUNDER ARE WARRANTED ACROSS
SOUTHERN COUNTIES WEDNESDAY. FORECAST CONFIDENCE REGARDING POPS
DURING THIS PERIOD ARE NOT HIGH...AS PRECIPITATION COULD EITHER
STREAM MORE QUICKLY INTO THE REGION LATE TUESDAY/TUESDAY NIGHT OR
COULD BE HELD MAINLY WEST OF THE REGION AS A SHORTWAVE RIDGE BUILDS
INTO THE REGION WEDNESDAY. OTHERWISE...NORMAL TO SLIGHTLY ABOVE
NORMAL HIGH TEMPERATURES IN THE 70S WILL BE COMMON BOTH DAYS...AND
NIGHTTIME LOWS MAINLY IN THE 50S CAN BE EXPECTED.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
THROUGH LATE WEEK...ABOVE NORMAL TEMPERATURES WILL PREVAIL
THEN...NORMAL TO BELOW-NORMAL TEMPERATURES SHOULD RETURN NEXT
WEEKEND.

AS AN UPPER SHORTWAVE TROUGH EJECTS EAST/NORTHEAST ACROSS THE
REGION...AT LEAST CHANCE POPS FOR SHOWERS AND THUNDERSTORMS ARE
JUSTIFIED ESPECIALLY THURSDAY. BETWEEN THE DEPARTING SHORTWAVE AND
AN APPROACHING COLD FRONT...FRIDAY COULD TURN OUT TO BE A VERY WARM
DAY WITH HIGHS IN THE 80S AND POPS BELOW 15 PERCENT WITH NO MENTION
OF PRECIPITATION. A STRONGER COLD FRONT WILL ARRIVE FRIDAY NIGHT OR
SATURDAY. TIMING REMAINS UNCERTAIN...BUT CHANCE POPS AND A MENTION
THUNDERSTORMS ARE CENTERED ON SATURDAY. DRIER AND COOLER CONDITIONS
ARE THEN EXPECTED SUNDAY.

&&

.AVIATION /08Z SUNDAY THROUGH THURSDAY/...
VFR AT KCHS AND KSAV THROUGH 06Z MONDAY. FOR THE SAKE OF
SIMPLICITY WE HAVE SHOWN MORE OF AVERAGE WINDS IN THE 06Z
TAFS...BUT THERE WILL BE SOME GUSTS THIS MORNING AND WINDS
TONIGHT WILL ACTUALLY GO LIGHT/VARIABLE OR EVEN CALM.

EXTENDED AVIATION OUTLOOK...MAINLY VFR.

&&

.MARINE...
THIS MORNING...A SOLID NORTH/NE SURGE OF WINDS WILL OVERSPREAD THE
MARINE DISTRICT IN RESPONSE TO A 1030 MB HIGH BUILDING OUT OF THE
VIRGINIAS. THE ENSUING COLD ADVECTION AND ISALLOBARIC PRESSURE
RISES OF CLOSE TO 1 MB/HOUR THROUGH MID TO LATE MORNING WILL BUMP
WINDS UP TO 15 OR 20 KT EVERYWHERE. BUT THE GRADIENT WILL BE
GREATEST ON THE CHARLESTON COUNTY ATLANTIC WATERS...AND IT IS HERE
WHERE WE HAVE HOISTED A SMALL CRAFT ADVISORY THROUGH MIDDAY FOR
FREQUENT GUSTS OF 25 KT. THE OTHER WATERS WILL BE CLOSE TO
ADVISORY CONDITIONS...BUT AT PRESENT THEY LOOK TO REMAIN JUST
BELOW THE CRITERIA.

THIS AFTERNOON...RAPID IMPROVEMENT WILL OCCUR AS THE COLD
ADVECTION HALTS...PRESSURE RISES STOP AND THE CORE OF THE
CONTINENTAL HIGH SHIFTS ALMOST DIRECTLY OVERHEAD. WINDS WILL CLOCK
AROUND TO THE EAST AND DIMINISH TO 10 KT OR LESS AS SEAS ALSO FALL.

TONIGHT...WE/LL START THE NIGHT UNDERNEATH THE OFFSHORE
TRANSITIONING HIGH...RESULTING IN VERY LITTLE WIND AND LIMITED
SEAS. BUT THE HIGH DOES SLIDE SE OVERNIGHT IN ADVANCE OF THE
UPSTREAM COLD FRONT MOVING THROUGH THE OHIO/TENNESSEE VALLEYS.
THIS ALONG WITH A DECENT NOCTURNAL LOW LEVEL JET AFTER 06Z WILL
ALLOW FOR SOUTH/SW WINDS TO CLIMB AS HIGH AS 10 OR 15 KT AS SEAS
RISE MAYBE A FOOT.

MONDAY THROUGH FRIDAY...A SURGE OF SOUTHWEST WINDS IS EXPECTED AHEAD
OF AN APPROACHING COLD FRONT MONDAY. HOWEVER...GIVEN THE STABLE
MARINE ENVIRONMENT...HELD WINDS/SEAS BELOW SCA LEVELS. THE COLD
FRONT SHOULD ARRIVE FROM THE NORTH MONDAY NIGHT INTO EARLY
TUESDAY...PERHAPS ACCOMPANIED BY A MODEST SURGE OF NORTHEAST
WINDS...BUT THE PROBABILITY FOR ANY SCA CONDITIONS REMAINS VERY
LOW. THE FRONT WILL STALL AND DISSIPATE...GIVING WAY TO A WEAK
PRESSURE PATTERN TUESDAY AFTERNOON/NIGHT. ANOTHER COLD FRONT WILL
ARRIVE FROM THE NORTH WEDNESDAY...AND THIS FRONT SHOULD ALSO STALL
AND DISSIPATE OVER OR JUST SOUTH OF THE WATERS BY THURSDAY.
SOUTH/SOUTHWEST WINDS SHOULD AGAIN INCREASE AHEAD OF A STRONGER COLD
FRONT APPROACHING FROM THE NORTHWEST LATE THIS WEEK...BUT ONCE AGAIN
MARINE LAYER STABILITY COULD PREVENT SCA WINDS/SEAS.

ALSO OF NOTE...INCREASING DEWPOINTS COULD SUPPORT SOME SEA FOG OVER
NEAR SHORE WATERS ESPECIALLY THURSDAY UNTIL A COLD FROPA OCCURS
FRIDAY NIGHT OR SATURDAY. WILL CONTINUE TO ASSESS.

&&

.CLIMATE...
RECORD LOWS MARCH 29TH...
KCHS...32 SET IN 1969.
KSAV...33 SET IN 1955.
KCXM...37 SET IN 1982.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...FREEZE WARNING UNTIL 9 AM EDT THIS MORNING FOR GAZ087-088.
SC...FREEZE WARNING UNTIL 9 AM EDT THIS MORNING FOR SCZ040-042>045.
MARINE...SMALL CRAFT ADVISORY UNTIL NOON EDT TODAY FOR AMZ350.

&&

$$
SYNOPSIS...
NEAR TERM...
SHORT TERM...SPR
LONG TERM...SPR
AVIATION...
MARINE...
CLIMATE...


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