Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 250202
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1002 PM EDT FRI APR 24 2015

.SYNOPSIS...
HIGH PRESSURE WILL SHIFT OFFSHORE EARLY TONIGHT. A WARM FRONT WILL
LIFT NORTH LATE TONIGHT INTO SATURDAY WITH A COLD FRONT MOVING SOUTH
THROUGH THE AREA SUNDAY NIGHT. DRY HIGH PRESSURE WILL PREVAIL
MONDAY INTO TUESDAY. ANOTHER STORM SYSTEM COULD IMPACT THE REGION
BY MID-WEEK.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
MID LEVEL RIDGING WILL EXTEND ACROSS THE SOUTHEAST WHILE SFC HIGH
PRESSURE SHIFTS FURTHER OFFSHORE EARLY TONIGHT. THE SETUP WILL
LIKELY RESULT IN DRY CONDITIONS FOR MOST OF THE NIGHT WHILE
SUBSIDENCE DOMINATES. AS THE HIGH SHIFTS MORE INTO THE ATLANTIC A
WARM FRONT WILL GRADUALLY LIFT NORTHWARD TOWARD THE AREA WITH
INCREASING MID/UPPER LEVEL MOISTURE THAT PRODUCES PARTLY TO MOSTLY
CLOUDY SKIES. WARM AIR ADVECTION ALONG WITH ISENTROPIC ASCENT
ALONG/NEAR THE FRONT COULD PRODUCE A FEW SHOWERS IN WESTERN ZONES
NEAR DAYBREAK.

THERE HAS BEEN ENOUGH RADIATIONAL COOLING WITHIN THE DRY AIR MASS
OVER EAST/NE SECTIONS TO ADJUST SOME TEMPS DOWN IN THESE LOCALES.
BUT THICKER CLOUD COVER HAS SLOWED THE DIURNAL CURVE SOUTH/SW
ZONES. THIS WILL MAKE FOR AN ATYPICAL TEMP CURVE THROUGH THE
NIGHT...AS ONCE CLOUDS MOVE IN/THICKEN THE TEMPS WILL STEADY OUT
OR EVEN RISE. WE/RE CURRENTLY SHOWING LOWS IN THE LOWER-MIDDLE 50S
NORTH/NE WITH UPPER 50S-LOWER 60S SOUTH/SW AND ALONG ALL COASTAL
COMMUNITIES.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/...
SATURDAY...THE WARM FRONT WILL LIKELY BE IN THE VICINITY OF THE
SANTEE RIVER BY SUNRISE SATURDAY...THEN PROGRESSING NORTH THROUGH
THE DAY. TEMPERATURES WILL RISE STEADILY THROUGH THE MORNING HOURS--
POSSIBLY BEING TEMPERED BY A CONSIDERABLE CLOUD CANOPY--MAXING
OUT IN THE UPPER 70S NORTH TO LOWER 80S ACROSS THE SOUTH. THE
STRONGEST ISENTROPIC ASSENT WILL SHIFT NORTH WITH THE WARM
FRONT...OFFERING A SLIGHT CHANCE FOR SHOWERS ACROSS THE FAR
WESTERN ZONES AND THE CHARLESTON TRI-COUNTY AREA THROUGH 8-9
AM...WITH THE MORNING LIKELY REMAINING DRY THEREAFTER.
SHOWERS/TSTMS ARE THEN EXPECTED TO REDEVELOP QUICKLY DURING THE
AFTERNOON AS DEEP LAYERED ASSENT INTENSIFIES WITH THE APPROACH OF
MID-LEVEL SHORTWAVE ENERGY AND THE RIGHT ENTRANCE REGION OF 125 KT
JET STREAK. THIS COUPLED WITH MODEST INSTABILITY AND PWATS
APPROACHING 2 INCHES WILL SUPPORT QUITE A BIT OF CONVECTIVE
ACTIVITY. CATEGORICAL POPS OF 80-90 PERCENT LOOK REASONABLE AND
WERE MAINTAINED. RAIN CHANCES WILL DIMINISH STEADILY SATURDAY
EVENING WITH DRY CONDITIONS PREVAILING OVERNIGHT.

THERE IS CERTAINLY A POTENTIAL FOR SEVERE WEATHER SATURDAY
AFTERNOON...BUT THE DEGREE OF SURFACE-BASED INSTABILITY THAT WILL BE
IN PLACE REMAINS UNCERTAIN. WIND PROFILES WILL BE SUFFICIENTLY
STRONG TO SUPPORT LINES OF STRONG TO SEVERE TSTMS WITH 0-6KM BULK
SHEAR 65-75 KT DURING PEAK HEATING...BUT SURFACE BASED INSTABILITY
PER MODIFIED FORECAST SOUNDINGS ONLY SUPPORT ABOUT 1200-1500 J/KG OF
SBCAPE WITH LIFTED INDICES OF -3 TO -4C. THIS WILL TEND TO LIMIT THE
SEVERE POTENTIAL SOMEWHAT...DESPITE THE FAVORABLE SHEAR PROFILES
THAT WILL BE IN PLACE. IF THE HIGH CLOUDS ARE NOT AS THIN AND/OR
SIGNIFICANT BREAKS CAN DEVELOP...THEN MORE FOCUSED CORRIDORS OF
HIGHER INSOLATION WILL BE POSSIBLE RESULTING FOR A MORE SUBSTANTIAL
RISK FOR SEVERE TSTMS. IT APPEARS THE MOST LIKELY SEVERE WEATHER
SCENARIO ATTM IS FOR SOME SORT OF QUASI-LINEAR CONVECTIVE SYSTEM
/QLCS/ TO AFFECT THE WESTERN ZONES BY EARLY-MID AFTERNOON AND
SPREADING EAST TO THE COAST LATE AFTERNOON/EARLY EVENING. THE
PRIMARY HAZARDS WILL BE DAMAGING WINDS AND CLOUD-TO-GROUND
LIGHTNING...BUT ISOLATED TORNADOES WILL BE POSSIBLE WHERE
SUPERCELLULAR STRUCTURES CAN EVOLVE WITHIN THE HIGHLY SHEARED
ENVIRONMENT. THE RISK FOR TORNADOES LOOKS HIGHEST OVER SOUTHEAST
SOUTH CAROLINA WHERE NAM12 0-1KM HELICITY VALUES ARE PROGGED TO
INCREASE TO 300-400 M2/S2 WITH 0-1KM EHI RISING TO 1.5-2 UNITS.

SUNDAY...SUNDAY COULD POTENTIALLY BE THE WARMEST DAY OF THE YEAR SO
FAR WITH STRONG WESTERLY FLOW AND 850 HPA TEMPERATURES RISING TO
NEAR 16C. MOSTLY SUNNY SKIES AND A PINNED SEA BREEZE WILL ALLOW
TEMPERATURES TO RISE QUICKLY AFTER SUNRISE WITH DEWPOINTS MIXING OUT
INTO THE UPPER 50S IN THE AFTERNOON. HIGHS LOOK TO APPROACH OF NOT
SURPASS 90 DEGREES FOR MOST AREAS WITHIN A CLASSIC PRE-FRONTAL
COMPRESSIONAL ENVIRONMENT AHEAD OF A BACKDOOR COLD FRONT. FORECAST
SOUNDINGS SUGGEST THE ATMOSPHERE WILL REMAIN CAPPED FOR MUCH OF THE
DAY SO EXPECT DRY CONDITIONS. THE RISK FOR ISOLATED TO PERHAPS LOW-
END SCATTERED SHOWERS/TSTMS COULD DEVELOP AND/OR ACCOMPANY THE
BACKDOOR FRONT SUNDAY EVENING AS THE BOUNDARY DROPS SOUTH OF THE
SANTEE RIVER. THE RISK LOOKS HIGHEST OVER THE CHARLESTON TRI-COUNTY
WHERE POTENTIAL INSTABILITY WILL BE THE HIGHEST JUST AFTER SUNSET
WITH RAIN CHANCES DIMINISHING GREATLY SOUTH OF THE EDISTO RIVER AS
INSTABILITY WANES AND MID-LVL CAPPING WILL BE THE STRONGEST. WILL
CARRY 20-30 PERCENT ACROSS SOUTHEAST SOUTH CAROLINA...HIGHEST
CHARLESTON TRI-COUNTY AREA...WITH NON-MENTIONABLE POPS FOR SOUTHEAST
GEORGIA. ALTHOUGH ISOLATED...THERE WILL BE A RISK FOR DAMAGING WINDS
WITH ANY TSTMS THAT CAN DEVELOP. THE RISK FOR SEVERE IS HIGHLY
CONDITIONAL AS THERE IS CHANCE THE CAP COULD HOLD WITHIN THE WARM
PRE-FRONTAL ENVIRONMENT. LOWS WILL RANGE FROM THE MID 50S FAR NORTH
TO THE MID 60S FAR SOUTH WITH UPPER 50S/LOWER 60S FOR MOST
LOCATIONS.

MONDAY...COOL/DRY HIGH PRESSURE WILL EXTEND OVER THE AREA MONDAY. IT
WILL BE CONSIDERABLY COOLER WITH HIGHS ONLY REACHING THE LOWER-MID
70S.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
DRY HIGH PRESSURE TO PREVAIL MONDAY NIGHT INTO TUESDAY BEFORE SOME
SHOWERS RETURN TO AT LEAST SOUTHEAST GEORGIA TUESDAY AFTERNOON AS
MOISTURE INCREASES AHEAD OF DEVELOPING LOW PRESSURE ALONG THE GULF
COAST...MORE LIKE A WINTER PATTERN. RAIN CHANCES LOOK TO PEAK
TUESDAY NIGHT INTO WEDNESDAY AS THE LOW MOVES THROUGH WITH DRIER
CONDITIONS PREVAILING THEREAFTER THROUGH FRIDAY...ALTHOUGH WILL
LIKELY STILL SEE A FEW SHOWERS AROUND INTO THURSDAY /MAINLY OVER SC/
AS THE UPPER LOW MOVES THROUGH. TEMPERATURES WILL START OFF BELOW
NORMAL THROUGH AT LEAST WEDNESDAY BEFORE POSSIBLY GETTING BACK
CLOSER TO NORMAL ASSUMING A PROGRESSIVE UPPER LOW.

&&

.AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
VFR CONDITIONS TONIGHT AND SATURDAY MORNING WITH DETERIORATING
CONDITIONS SATURDAY AFTERNOON AND EVENING IN RESPONSE TO
SCATTERED-NUMEROUS SHRA AND SCATTERED TSRA THAT MOVES THROUGH IN
ASSOCIATION WITH A WARM FRONT. WHILE WE ARE PRESENTLY SHOWING
LOW-END VFR AFTER 17Z SATURDAY AT BOTH KSAV AND KCHS THERE REMAINS
A HIGH PROBABILITY OF AT LEAST MVFR WEATHER ONCE RADAR TRENDS
BECOME BETTER ESTABLISHED. STRONG WINDS...HEAVY RAINS AND LIGHTNING
STRIKES WILL BE COMMON IN AND NEAR CONVECTION. EVEN OUTSIDE OF
SHRA/TSRA SOUTHERLY WINDS WILL BE BREEZY THE SECOND HALF OF THE
DAY.

EXTENDED AVIATION OUTLOOK...POSSIBLE IFR CIGS NEAR DAYBREAK SUNDAY
DUE TO LINGERING LOW-LEVEL MOISTURE. IT WILL ALSO BE BREEZY
SUNDAY AFTERNOON WITH GUSTS TO 25-30 KT LIKELY. VFR CONDITIONS
SHOULD THEN PREVAIL INTO TUESDAY BEFORE SHOWERS AND TSTMS RETURN
MAINLY TUESDAY NIGHT/WEDNESDAY.

&&

.MARINE...
TONIGHT...CONDITIONS WILL BE RELATIVELY QUIET UNDER THE INFLUENCE
OF A 1018 MB HIGH THAT PULLS FURTHER OFF THE SE COAST EAST AND SE
WINDS OF LESS THAN 10 OR 15 KT WILL VEER TO THE SE AND SOUTH
OVERNIGHT WITH LITTLE CHANGE IN SPEEDS. SEAS WILL WILL HOLD AROUND
2-4 FT EARLY AND AT 1-3 FT LATE.

SATURDAY...WINDS WILL VEER SOUTHERLY IN THE WAKE OF THE WARM FRONT.
SPEEDS WILL INCREASE DURING THE AFTERNOON IN RESPONSE TO A
TIGHTENING PRESSURE GRADIENT. SPEEDS LOOK TO MAX OUT IN THE 10-15 KT
RANGE NEARSHORE...15-20 KT RANGE OFFSHORE BY LATE AFTERNOON AND
INCREASING FURTHER TO 15-20 KT NEARSHORE AND 20-25 KT OFFSHORE
OVERNIGHT. SEAS WILL ALSO STEADILY BUILD...PEAKING 3-5 FT NEARSHORE
WATERS AND 5-7 FT OFFSHORE WATERS JUST AFTER MIDNIGHT EARLY SUNDAY
MORNING. A SMALL CRAFT ADVISORY WILL LIKELY BE NEEDED FOR THE
GEORGIA OFFSHORE LEG IN LATER FORECASTS.

SUNDAY...SOUTHWEST WINDS WILL TURN WEST SUNDAY EVENING AND
EVENTUALLY NORTH TO NORTHWEST OVERNIGHT AS A BACKDOOR COLD FRONT
DROPS SOUTH THROUGH THE LOCAL MARINE AREA. WINDS LOOK TO MAX OUT AT
15-20 KT DURING THIS TIME WITH SEAS DIMINISHING ONLY SLIGHTLY WITH
THE MORE OFFSHORE COMPONENT...2-4 FT NEARSHORE...3-5 FT OFFSHORE.

MONDAY THROUGH WEDNESDAY...HIGH PRESSURE BUILDING FROM THE NORTH
SHOULD LEAD TO A WEAKENING PRESSURE GRADIENT AND WEAKER WINDS MONDAY
INTO TUESDAY. CONDITIONS WORSEN SLIGHTLY WEDNESDAY AS LOW PRESSURE
APPROACHES THE AREA.

&&

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

&&

$$
SYNOPSIS...
NEAR TERM...
SHORT TERM...
LONG TERM...RJB
AVIATION...
MARINE...



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