Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 012001
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
401 PM EDT SUN MAY 1 2016

.SYNOPSIS...
HIGH PRESSURE WILL STRETCH ACROSS THE REGION TONIGHT AS LOW
PRESSURE AND A COLD FRONT REMAIN OFF TO THE DISTANT NORTHWEST. A
SERIES OF LOW PRESSURE AREAS WILL GRADUALLY PUSH A COLD FRONT
TOWARD THE REGION MONDAY THROUGH TUESDAY...PRODUCING UNSETTLED
CONDITIONS. THE COLD FRONT WILL ADVANCE THROUGH THE REGION TUESDAY
NIGHT AND WILL PUSH OFFSHORE WEDNESDAY...FOLLOWED BY ANOTHER COLD
FRONT THURSDAY. HIGH PRESSURE WILL THEN EXPAND INTO THE REGION
THROUGH NEXT WEEKEND.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
CONVECTION HAS FORMED INTO A NARROW QLCS AND IS HEADING EAST/NE AND
WILL TRAVERSE THE WEST AND NW ZONES LATE THIS AFTERNOON...PERHAPS
REACHING THE CHARLESTON METRO...BEAUFORT AND THE SAVANNAH DISTRICT
AROUND 22-24Z BEFORE NOCTURNAL INFLUENCES TAKE OVER AND
CONVECTION STARTS TO WANE. THERMODYNAMIC PARAMETERS ARE STILL
FAVORABLE FOR ISOLATED SEVERE WEATHER...BUT ORGANIZED SEVERE
WEATHER IS NOT EXPECTED WITH THE LACK OF SUFFICIENT SHEAR. DCAPES
800-1000 J/KG OVER SOUTHERN ZONES SUGGEST AT LEAST ISOLATED
DOWNBURSTS OF DAMAGING WINDS COULD STILL OCCUR IN A COUPLE OF THE
STRONGEST STORMS...ESPECIALLY IF A COLLISION OF THE SEA BREEZE
WITH THE CONVECTIVE LINE OCCURS. HAIL IN THE -10 TO -30C LAYER IS
AROUND 400- 500 J/KG OR ENOUGH FOR MARGINALLY SEVERE HAIL AT
BEST. THERE IS ALSO A RISK OF LOCALLY HEAVY RAINFALL WITH PWATS IN
EXCESS OF 1.5 INCHES. THAT ALONG WITH THE SLOW MOVEMENT OF THE
CELLS IN WEST/SW TO EAST/NE ORIENTATION WHICH IS ALIGNED WITH THE
MEAN FLOW WHICH SUGGESTS TRAINING COULD STILL OCCUR...AND SIMILAR
TO WHAT WE SAW IN SOUTHERN DORCHESTER COUNTY EARLIER IN THE
AFTERNOON. WE ARE SHOWING SCATTERED AND LIKELY POPS THROUGH
DARK...GREATEST COVERAGE INLAND.

FOR TONIGHT...THE BULK OF THE CONVECTION WILL FADE AFTER SUNSET WITH
NOCTURNAL INFLUENCES OVERSPREAD THE REGION. HOWEVER...FORCING FROM
THE APPROACH OF THE NEXT SHORT WAVE FOUND IN THE TN VALLEY TO THE
LOWER MS VALLEY MIGHT STILL ALLOW FOR ISOLATED SHOWERS AND T-STORMS
DURING THE LATE EVENING AND OVERNIGHT. IN ADDITION...ISOLATED
SHOWERS AND T-STORMS COULD BRUSH THE CHARLESTON COUNTY COASTLINE
FROM OFF THE ATLANTIC LATE WITH LOW LEVEL CONVERGENCE WITHIN
A SOUTH/SW SYNOPTIC FLOW.

WHILE MUCH OF THE INITIAL CLOUD COVER ACROSS SOUTHERN SC AND SE GA
WILL THIN OUT THIS EVENING...CONSIDERABLE HIGH LEVEL CLOUDS FROM THE
DISTANT UPSTREAM CONVECTION WILL CONTINUE TO SPREAD EAST AND THAT
ALONG WITH THE FORMATION OF LATE NIGHT STRATUS WILL LEAD TO
MOSTLY CLOUDY SKY CONDITIONS. THIS ALONG WITH GEOSTROPHIC WINDS OF
10-15 KT WILL LIKELY LIMIT THE POTENTIAL FOR ANY SIGNIFICANT FOG
CONCERNS. ALTHOUGH CONDENSATION PRESSURE DEFICITS ARE LOW ENOUGH
WHERE IF THE HIGHER LEVEL CLOUDS ARE LESS THAN EXPECTED THERE
COULD BE SOME FOG...MOST ESPECIALLY SOUTH OF I-16.

IT/LL BE ANOTHER WARM AND MUGGY NIGHT BY THE STANDARDS OF EARLY MAY
WITH THE CLOUD COVER AND WARM SOUTH/SW FLOW...AND IT/S POSSIBLE THAT
NEW RECORD HIGH MINIMUMS COULD BE SET AT SOME OR ALL THREE CLIMATE
SITES FOR MAY 1ST DEPENDING ON HOW MUCH CONVECTION OCCURS PRIOR TO 1
AM MONDAY. OVERNIGHT LOWS WILL BE FORTUNATE TO EVEN FALL BELOW
70...AND WILL AVERAGE AS MUCH AS 8-15F ABOVE NORMAL.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/...
MONDAY AND MONDAY NIGHT...UNSETTLED CONDITIONS WILL CONTINUE AS A
SERIES OF SHORTWAVE TROUGHS EMBEDDED WITHIN A WSW FLOW ALOFT CROSS
THE REGION AND INTERACT WITH A PLUME OF ENHANCED DEEP-LAYERED
MOISTURE/PWATS 1.50 TO 1.75 INCHES. LOCALLY HEAVY RAIN COULD OCCUR
IF/WHERE THUNDERSTORM TRAINING/CELL MERGERS DEVELOP...AND AN
ISOLATED SEVERE THUNDERSTORM OR TWO CANNOT BE DISCOUNTED ESPECIALLY
IF/WHERE CONVECTION INTERACTS WITH MESOSCALE BOUNDARIES MONDAY
AFTERNOON/EVENING. MONDAY NIGHT...THE ALREADY LIMITED SEVERE
POTENTIAL WILL DIMINISH...BUT THE POTENTIAL FOR LOCALLY EXCESSIVE
RAINFALL WILL PERSIST.

WHILE THE LOCATION OF BEST THUNDERSTORM COVERAGE MONDAY/MONDAY NIGHT
REMAINS UNCERTAIN AND WILL DEPEND IN LARGE MEASURE ON THE
ANTECEDENT/DEVELOPING MESOSCALE ENVIRONMENT...PER RECENT GUIDANCE
MAINTAINED HIGHEST POPS ACROSS INLAND/NORTHERN COUNTIES MONDAY
AFTERNOON/NIGHT.

HIGH TEMPERATURES MONDAY WILL REMAIN HIGHLY DEPENDENT ON CLOUD COVER
AND PRECIPITATION DISTRIBUTION...PERHAPS AS LOW AS THE LOWER 80S
WHERE CLOUDS/PRECIPITATION PERSIST AND AS HIGH AS THE MID/UPPER 80S
WHERE LESS CLOUD COVER/PRECIPITATION COVERAGE PREVAIL. TEMPERATURES
SHOULD BOTTOM OUT IN THE 65-70F RANGE MONDAY NIGHT.

TUESDAY AND TUESDAY NIGHT...AN UNSETTLED REGIME WITH PWATS STILL AT
OR EXCEEDING 1.50 INCHES WILL PERSIST ACROSS THE REGION. IN ADDITION
TO MESOSCALE BOUNDARIES CREATED BY EARLIER/ONGOING CONVECTION...A
COLD FRONT WILL PRESS INTO THE REGION FROM THE NORTHWEST AND WILL BE
ACCOMPANIED BY A BROAD AREA OF 500 MB HEIGHT FALLS AND WEAK 500-300
MB Q VECTOR CONVERGENCE. DYNAMIC FORCING FOR ASCENT SHOULD COMBINE
WITH A FAVORABLE THERMODYNAMIC/KINEMATIC ENVIRONMENT TO PRODUCE AT
LEAST SCATTERED TO NUMEROUS SHOWERS/THUNDERSTORMS. LOCALLY EXCESSIVE
RAINFALL AND A FEW SEVERE THUNDERSTORMS COULD OCCUR ESPECIALLY
TUESDAY MIDDAY INTO TUESDAY EVENING.

ELEVATED POPS REMAIN IN FORECASTS TUESDAY INTO TUESDAY
EVENING...WITH HIGHEST POPS INITIALLY ACROSS INLAND/NORTHERN
COUNTIES IN THE MORNING THEN EXPANDING INTO MUCH OF THE AREA TUESDAY
AFTERNOON. HIGHEST POPS THEN SHIFT OFFSHORE WITH THE COLD FRONT
TUESDAY EVENING...AND POPS DIMINISH WITH TIME AS THE COLD FRONT
ADVANCES OFFSHORE AND DRIER AIR BEGINS TO SPREAD INTO THE REGION
LATER TUESDAY NIGHT.

AGAIN...HIGH TEMPERATURES TUESDAY REMAIN UNCERTAIN AND WILL DEPEND
ON TIMING/COVERAGE OF SHOWERS/THUNDERSTORMS. THE LATEST FORECAST
INDICATES HIGH TEMPS IN THE LOWER TO MID 80S...BUT LOCALLY
SIGNIFICANT VARIANCES COULD DEVELOPMENT.

WEDNESDAY...RECENT GUIDANCE HAS TRENDED TOWARD A MORE PROGRESSIVE
COLD FRONT AND ASSOCIATED DRYING TREND. THUS...MAINTAINED LOW POPS
FOR SHOWERS/THUNDERSTORMS NEAR THE COAST DURING THE FIRST HALF OF
THE DAY...THEN LOWERED POPS WELL BELOW 15 PERCENT WITH NO MENTION OF
PRECIPITATION DURING THE AFTERNOON. MEANWHILE...EXPECT COOLER AND
DRIER CONDITIONS WITH DEWPOINTS FALLING INTO THE 50S AND HIGH TEMPS
RANGING FROM THE MID 70S TO LOWER 80S.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
MODELS ARE NOW IN FAIRLY GOOD AGREEMENT SHOWING WEAK HIGH PRESSURE
OVER THE AREA WEDNESDAY NIGHT WHILE A STORM SYSTEM IMPACTS THE
NORTHEASTERN STATES. A DRY COLD FRONT IS FORECAST TO MOVE THROUGH ON
THURSDAY...BRINGING COOLER TEMPERATURES FOR FRIDAY. DESPITE A TROUGH
REMAINING OVER THE EAST COAST DURING THIS ENTIRE TIME PERIOD...POPS
ARE LOW BECAUSE HIGH PRESSURE WILL BE SPREAD ACROSS OR NEAR THE
SOUTHEAST STATES FRIDAY AND SATURDAY.

&&

.AVIATION /20Z SUNDAY THROUGH FRIDAY/...
MAINLY VFR AT THE TERMINALS. BUT PERIODIC FLIGHT RESTRICTIONS COULD
OCCUR AT BOTH SITES TOWARD EVENING AS A LINE OF SHRA/TSRA
APPROACHES FROM  THE WEST AROUND 22-24Z. WHILE CONVECTION WILL
FADE EARLY TONIGHT...THERE IS THE RISK FOR SOME LATE NIGHT/EARLY
MORNING STRATUS AND PERHAPS A LITTLE GROUND FOG AND PERIODIC MVFR
OR IFR CONDITIONS TO OCCUR.

EXTENDED AVIATION OUTLOOK...PERIODIC FLIGHT RESTRICTIONS WITHIN
SCATTERED SHOWERS/THUNDERSTORMS MONDAY NIGHT THROUGH TUESDAY NIGHT.
THEN...VFR THROUGH LATE WEEK.

&&

.MARINE...
TONIGHT...HIGH PRESSURE NESTLED BETWEEN THE MID ATLANTIC STATES AND
BERMUDA WILL BECOME ABSORBED BY A STRONGER AREA OF HIGH PRESSURE IN
THE NW ATLANTIC OVERNIGHT. THE ASSOCIATED RIDGE WILL EXPAND WEST/SW
ACROSS THE MARINE REGION...RESULTING IN MODERATE SOUTH/SW BREEZES
AND SEAS NO MORE THAN 2-3 FT WITHIN 20 NM AND 3-4 FT FURTHER OUT. NO
MORE THAN ISOLATED SHOWERS AND T-STORMS WILL OCCUR...EXCEPT
SCATTERED COVERAGE THIS EVENING IN CHARLESTON HARBOR IF STORMS
UPSTREAM ARE ABLE TO SURVIVE BEFORE CINH INCREASES.

MONDAY THROUGH FRIDAY...AHEAD OF AN APPROACHING COLD FRONT A SURGE
OF S/SW WINDS IS EXPECTED ESPECIALLY MONDAY AFTERNOON/EVENING INTO
TUESDAY. FOR NOW...CAPPED WINDS AT 20 KT AND SEAS BELOW 6 FT...BUT A
PERIOD OF SMALL CRAFT ADVISORY CONDITIONS CANNOT BE RULED OUT. AFTER
THE COLD FRONT PASSES TUESDAY NIGHT/EARLY WEDNESDAY...OFFSHORE WINDS
WILL PREVAIL THROUGH LATE WEEK...WITH WINDS/SEAS REMAINING BELOW
SMALL CRAFT ADVISORY LEVELS.

&&

.CLIMATE...
RECORD HIGH MINIMUMS FOR 1 MAY...
KCHS 70/1989...
KCXM 73/2012...
KSAV 73/1953...

&&

.EQUIPMENT...
THE CHARLESTON HARBOR NOS TIDE GAUGE HAS STOPPED REPORTING ALL
METEOROLOGICAL AND TIDE DATA. THE NATIONAL OCEAN SERVICE IS
INVESTIGATING THE CAUSE OF THE OUTAGE. AN ESTIMATED TIME FOR DATA
RESTORATION IS UNKNOWN AT THIS TIME.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...NONE.

&&

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



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