Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 281131
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
731 AM EDT SAT MAR 28 2015

.SYNOPSIS...
CHILLY CONTINENTAL HIGH PRESSURE WILL PREVAIL INTO SUNDAY. WEAK
COLD FRONTS WILL PUSH INTO THE REGION LATE MONDAY AND AGAIN
WEDNESDAY...AND BOTH FRONTS SHOULD DISSIPATE OVER OR CLOSE TO THE
AREA. WARMER ATLANTIC HIGH PRESSURE WILL THEN BUILD OVER THE
REGION THROUGH LATE WEEK. A STRONGER COLD FRONT WILL ARRIVE LATE
WEEK OR EARLY NEXT WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
FOR TODAY...A HIGHLY ANOMALOUS LONG WAVE TROUGH THAT IS SOME 2 TO
3 STANDARD DEVIATIONS DEEPER THAN NORMAL FOR LATE MARCH WILL
REMAIN ANCHORED OVER THE EASTERN THIRD OF THE COUNTRY. AT THE
SURFACE WE FIND AN INTENSE 996 MB LOW LIFTING NE FROM OFF THE MID
ATLANTIC REGION EARLY TO EAST/SE OF NEW ENGLAND THIS
AFTERNOON...WHILE UPSTREAM A COLD 1027 MB HIGH WILL STRETCH FROM
THE WESTERN GREAT LAKES TO THE GULF OF MEXICO. THIS WILL PROVIDE
THE AREA WITH DRY AND STABLE CONDITIONS WITH A RATHER COOL WEST/NW
SYNOPTIC FLOW TO PREVAIL. THE RESULTING 850 MB TEMPS WILL BE
AROUND 2 STANDARD DEVIATIONS BELOW NORMAL...AS COLD AS -3C SOUTH
AND -5C NORTH. ASIDE FROM SOME THIN CIRRUS/PATCHY ALTOCUMULUS FROM
THE WEST AND FEW-SCATTERED FLAT CUMULUS...THERE IS CONSIDERABLE
INSOLATION TODAY. THAT ALONG WITH DOWNSLOPE TRAJECTORIES OFF THE
APPALACHIANS...WILL NEGATE A LITTLE OF THE COLDER AIR...BUT
SUPPORTIVE OF MAX TEMPS ONLY IN THE MID AND UPPER 50S FAR NORTH
AND NW TO THE LOWER 60S SOUTH. THIS IS SOME 10-13 DEGREES BELOW
SEASONAL NORMS.

TONIGHT...COLD ADVECTION BECOMES MORE NEUTRAL TONIGHT AS THE
THERMAL TROUGH SHIFTS INTO THE ATLANTIC. HOWEVER...THE AXIS OF THE
LOW AND MID LEVEL TROUGH...ACTING ALMOST LIKE A SECONDARY COLD
FRONT WILL PUSH THROUGH OVERNIGHT. THIS ALLOWS THE UPSTREAM AND
COLD SURFACE HIGH IN THE OHIO VALLEY TO BUILD FROM THE NW WITH
STEADILY RISING PRESSURES. BUT IT ALSO ARRIVES WITH ANOTHER INFLUX
OF COLD CANADIAN AIR...ENOUGH TO ALLOW FOR FREEZING TEMPS TO
PENETRATE INTO AT LEAST OUR NW TIER. AFTER COORDINATION WITH
NEIGHBORING OFFICES WE HAVE UPGRADED THE EARLIER FREEZE WATCH TO A
FREEZE WARNING FROM INLAND BERKELEY COUNTY TO ALLENDALE AND
HAMPTON...SCREVEN AND JENKINS. THIS IS DUE TO MIN TEMPS OF 30-32F
FOR 3-5 HOURS LATE TONIGHT AND EARLY SUNDAY...ALONG WITH PATCHY
FROST. FORTUNATELY IT WON/T BE A HARD FREEZE...BUT THESE
CONDITIONS ARE ENOUGH TO CAUSE DAMAGE TO TENDER AND SENSITIVE
VEGETATION AND UNPROTECTED PLANTS.

WE CONSIDERED A FROST ADVISORY FROM INLAND CHARLESTON TO INLAND
JASPER IN SC AND THEN SOUTH/SW THROUGH INLAND CHATHAM...TO
CANDLER...TATTNALL AND LONG COUNTIES. BUT THERE ARE TWO FACTORS
GOING AGAINST ANYTHING MORE THAN PATCHY FROST. FIRST WOULD BE THAT
THE DEW POINT DEPRESSIONS ARE QUITE LARGE...SOME 6-10F. AND
SECONDLY THERE WILL BE TOO MUCH MIXING IN SOME OF THESE AREAS DUE
TO THE HIGH BUILDING IN AND GEOSTROPHIC WINDS HOLDING UP NEAR 10
OR 15 KT. EVEN SO...THOSE WITH FROST SENSITIVE PLANTS MIGHT WANT
TO TAKE PRECAUTIONS AS WELL...WITH LOWS IN THE MIDDLE 30S. IT/S
ALSO CONCEIVABLE THAT IF THE FREEZING TEMPS ARE ABLE TO PENETRATE
A BIT FURTHER SE THAT A FEW PARTS OF THIS CORRIDOR OF COUNTIES MAY
ALSO REQUIRE A FREEZE WARNING. THE ONLY PLACES THAT SHOULD ESCAPE
ANY FROST AND/OR FREEZE WILL BE THE COASTAL SE GA ZONES.

LOWS TONIGHT WILL BE VERY CLOSE TO RECORDS FOR MARCH 29...COMING
WITHIN ABOUT 2 DEGREES AT THE THREE CLIMATE SITES. SEE CLIMATE
SECTION BELOW FOR MORE INFORMATION.

&&

.SHORT TERM /SUNDAY THROUGH TUESDAY/...
SUNDAY...THE SURFACE HIGH WILL SHIFT OVER THE AREA. STRONG
SUBSIDENCE WILL PROVIDE A DRY AND SUNNY DAY. DESPITE FULL
INSOLATION...AFTER A COLD START TEMPERATURES WILL ONLY RECOVER INTO
THE UPPER 50S ACROSS MOST OF SE SC TO THE LOWER 60S ACROSS MUCH OF
SE GA. THESE TEMPERATURES WILL AVERAGE SOME 10 TO 13F BELOW NORMAL
FOR LATE MARCH.

SUNDAY NIGHT WILL START WITH MAINLY CLEAR SKIES/LIGHT
WINDS...SUPPORTING EXCELLENT RADIATIONAL COOLING CONDITIONS.
THEN...AS THE GRADIENT TIGHTENS BETWEEN HIGH PRESSURE SHIFTING SOUTH
OF THE REGION AND A COLD FRONT APPROACHING FROM THE NORTHWEST...AND
AS CLOUDS BEGIN TO INCREASE...OVERNIGHT TEMPERATURES COULD HOLD
STEADY OR EVEN BEGIN TO RISE. THUS...HOURLY TEMPERATURES INDICATE
LOWS WITHIN A COUPLE OF HOURS OF MIDNIGHT...PERHAPS DIPPING INTO THE
UPPER 30S AT INLAND LOCATIONS BUT IN THE LOWER TO MID 40S MOST
LOCATIONS...FOLLOWED BY SLIGHTLY HIGHER TEMPS AROUND DAYBREAK
MONDAY. IF THIS SCENARIO IS DELAYED...LOWER TEMPS AND EVEN A TOUCH
OF FROST CANNOT BE RULED OUT WELL INLAND.

MONDAY...GUIDANCE HAS TRENDED TOWARD AN EARLIER ARRIVAL OF A COLD
FRONT FROM THE NORTHWEST...DUE IN PART TO A FAST-MOVING SHORTWAVE
TROUGH ALOFT WHICH WILL PASS NORTH OF THE REGION. GUIDANCE DEPICTS
SUFFICIENT FORCING FOR ASCENT AND ASSOCIATED DEEP LAYERED MOISTURE
TO JUSTIFY CHANCE POPS ADVANCING FROM N/NW TO S/SE AS THE DAY
PROGRESSES. ALSO...ISOLATED THUNDERSTORMS CANNOT BE RULED OUT...BUT
LATEST GUIDANCE SUGGESTS THAT A PLUME OF ENHANCED LOW-LEVEL
INSTABILITY WILL BE CUT OFF WEST OF THE FORECAST AREA...LEAVING ONLY
WEAK INSTABILITY IN PLACE OVER THE REGION. THUS...MAINTAINED NO
MENTION OF THUNDERSTORMS FOR NOW...BUT WILL CONTINUE TO ASSESS.
OTHERWISE...DESPITE CLOUD COVER COMPRESSIONAL HEATING AHEAD OF THE
COLD FRONT WILL HELP TEMPERATURES RECOVER INTO THE MID/UPPER 60S
NORTH AND LOWER TO MID 70S SOUTH...CLOSER TO NORMAL FOR LATE MARCH.

MONDAY NIGHT AND TUESDAY...THE COLD FRONT WILL WEAKEN...STALL AND
BEGIN TO DISSIPATE OVER OR CLOSE TO SOUTHERN COUNTIES OF THE
FORECAST AREA. MODEL SOLUTIONS DIFFER REGARDING THE SOUTHWARD
PROGRESS OF THE FRONT AND THE ASSOCIATED POOL OF ENHANCED MOISTURE.
PER LATEST TRENDS...SLIGHT CHANCE POPS ARE JUSTIFIED MONDAY NIGHT
THROUGH TUESDAY ACROSS SOUTHERN COUNTIES. OTHERWISE...LOWS IN THE
40S/50S MONDAY NIGHT WILL GIVE WAY TO NEAR-NORMAL TEMPERATURES
MAINLY IN THE 70S AWAY FROM THE COAST TUESDAY.

&&

.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
THROUGH LATE WEEK...ABOVE NORMAL TEMPERATURES WILL PREVAIL... EXCEPT
PERHAPS THURSDAY IF SHOWERS/THUNDERSTORMS BECOME MORE WIDESPREAD
THAN CURRENTLY FORECAST. THEN...NORMAL TO BELOW-NORMAL TEMPERATURES
SHOULD RETURN NEXT WEEKEND.

ANOTHER COLD FRONT IS EXPECTED TO SETTLE INTO THE REGION FROM THE
NORTH WEDNESDAY. DISCOUNTING THE 28/00 UTC CANADIAN SOLUTION
DEPICTING A PROGRESSIVE FRONT FOLLOWED BY STRONG HIGH PRESSURE
BUILDING FROM THE N/NE...THIS FRONT SHOULD REMAIN WEAK AND WILL
LIKELY STALL AND DISSIPATE OVER OR CLOSE TO THE REGION. MEANWHILE...
A SHORTWAVE TROUGH ALOFT WILL ADVANCE THROUGH THE LOWER MS RIVER
VALLEY TOWARD THE NORTHERN GULF COAST...AND TO VARYING DEGREES
GUIDANCE DEPICTS AN EXPANDING PLUME OF MOISTURE/PRECIPITATION AHEAD
OF THIS FEATURE. GIVE THE SHORTWAVE RIDGING ALOFT OVER THE
REGION...FEEL THAT GUIDANCE COULD BE PUSHING CONVECTIVE PRECIPITATION
TOO QUICKLY TOWARD THE EAST/INTO THE REGION. THUS...HELD POPS BELOW
15 PERCENT WITH NO MENTION OF PRECIPITATION WEDNESDAY...BUT FORECAST
CONFIDENCE IS LOW. A BETTER CHANCE FOR SHOWERS AND PERHAPS
THUNDERSTORMS SHOULD DEVELOP WEDNESDAY NIGHT THROUGH AT LEAST
THURSDAY NIGHT AS THE UPPER TROUGH PASSES OVER THE REGION. A
STRONGER COLD FRONT WILL ARRIVE LATER FRIDAY OR SATURDAY...
JUSTIFYING AT LEAST CHANCE POPS AND A MENTION THUNDERSTORMS.

&&

.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
KCHS...VFR CONDITIONS THROUGH 12Z SUNDAY. NW WINDS MAY BECOME A
LITTLE GUSTY THIS AFTERNOON.

KSAV...VFR THROUGH 12Z SUNDAY. WEST/NW WINDS WILL BE GUSTY THIS
AFTERNOON WITH DEEP MIXING TO OCCUR...PEAKING CLOSE TO 20 KT.

EXTENDED AVIATION OUTLOOK...FLIGHT RESTRICTIONS POSSIBLE IN SHOWERS
MONDAY. OTHERWISE...MAINLY VFR.

&&

.MARINE...
TODAY...COLD ADVECTION AND STEADY ISALLOBARIC PRESSURE RISES WILL
RESULT IN A CONTINUATION OF THE SMALL CRAFT ADVISORIES ACROSS THE
GA WATERS OUT 60 NM WHERE THE BEST LOW LEVEL JETTING WILL TAKE
PLACE. ELSEWHERE ACROSS THE MARINE COMMUNITY WE/LL REMAIN JUST
BELOW ADVISORY THRESHOLDS. CONDITIONS WILL IMPROVE THIS AFTERNOON
AS COLD ADVECTION WANES...PRESSURE RISES STOP AND THE PRESSURE
PATTERN BECOMES MORE RELAXED.

TONIGHT...THE IMPROVEMENT IN CONDITIONS FROM EARLIER WILL BE
SHORT-LIVED AS A STRENGTHENING CONTINENTAL HIGH BUILDS FORM THE
OHIO VALLEY AND EXPANDS ACROSS THE LOCAL WATERS DURING THE LATE
EVENING AND OVERNIGHT. IT WILL ALSO ARRIVE WITH ANOTHER SHOT OF
COLD ADVECTION AND PRESSURE RISES...AND A DECENT NORTH/NE SURGE
WILL OCCUR LATE. WE MAY ACTUALLY FLIRT WITH SMALL CRAFT ADVISORIES
ON THE CHARLESTON COUNTY ATLANTIC WATERS AS SUNRISE APPROACHES.

SUNDAY THROUGH THURSDAY...A SURGE OF NORTHEAST WINDS AND LOCALIZED
SMALL CRAFT ADVISORY CONDITIONS COULD PERSIST INTO SUNDAY MORNING...
THEN A MUCH WEAKER PRESSURE PATTERN AND SLACKENING WINDS/SUBSIDING
SEAS SHOULD DEVELOP SUNDAY AFTERNOON INTO SUNDAY EVENING.
THEN...AHEAD OF AN APPROACHING COLD FRONT LATER SUNDAY NIGHT THROUGH
MONDAY...SW WINDS WILL INCREASE AND SEAS WILL BUILD...PERHAPS
PUSHING TO SCA LEVELS ESPECIALLY ACROSS AMZ350 AND AMZ374. THE COLD
FRONT WILL STALL AND DISSIPATE BY TUESDAY...THEN ANOTHER WEAK COLD
FRONT WILL LIKELY STALL AND DISSIPATE IN THE AREA WEDNESDAY.
THUS...A RELATIVELY BENIGN PRESSURE PATTERN PRIMARILY GOVERNED BY
OFFSHORE HIGH PRESSURE SHOULD HOLD WINDS/SEAS BELOW SCA LEVELS UNTIL
LATE WEEK OR EARLY NEXT WEEKEND.

&&

.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 FROM 4 AM TO 9 AM EDT SUNDAY FOR GAZ087-088.
SC...FREEZE WARNING FROM 4 AM TO 9 AM EDT SUNDAY FOR SCZ040-042>045.
MARINE...SMALL CRAFT ADVISORY UNTIL 11 AM EDT THIS MORNING FOR AMZ354.
     SMALL CRAFT ADVISORY UNTIL 1 PM EDT THIS AFTERNOON FOR AMZ374.

&&

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


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