Area Forecast Discussion
Issued by NWS Charleston, SC

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450
FXUS62 KCHS 052347
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
747 PM EDT THU MAY 5 2016

.SYNOPSIS...
AN UPPER LEVEL LOW WILL SHIFT OVER THE AREA TONIGHT...THEN LINGER
ALONG COAST THROUGH FRIDAY. LOW PRESSURE WILL MEANDER IN THE
NORTHEAST THROUGH THE WEEKEND AS HIGH PRESSURE BUILDS TO THE SOUTH.
ATLANTIC HIGH PRESSURE WILL THEN ESTABLISH ITSELF ACROSS THE AREA
DURING THE EARLY AND MIDDLE PART OF NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
COLD UPPER LOW MOVING THROUGH THE CAROLINAS ALONG WITH DAYTIME
HEATING WILL HELP SPARK A FEW SHOWERS MOVING SOUTHEAST ACROSS THE
AREA THIS EVENING. FREEZING LEVELS NEAR 6500 FT AS OBSERVED FROM
THE 00Z CHS SOUNDING COULD YIELD SOME SMALL HAIL WITH THE
HEAVIER/STRONGER SHOWERS...ALTHOUGH THIS THREAT APPEARS TO BE
DIMINISHING QUICKLY BASED ON THE WEAKENING RADAR RETURNS. WIND GUSTS
OVER 20 MPH WILL BE POSSIBLE THROUGH EARLY EVENING...MAINLY
ASSOCIATED WITH THE SHOWERS.

MOSTLY CLEAR SKIES ALONG THE VERY COLD AIR ALOFT WILL CREATE A
FAVORABLE SCENARIO FOR UNUSUALLY LOW TEMPS TONIGHT. IN
GENERAL...TEMPS WILL DIP INTO THE UPPER 40S INLAND TO LOWER/MID 50S
ALONG THE COAST. THIS WILL BE CLOSE TO RECORD LOWS...ESPECIALLY AT
SAVANNAH AIRPORT AND IN DOWNTOWN CHARLESTON. SEE CLIMATE SECTION
FOR DETAILS.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/...
FRIDAY...ALTHOUGH THE ANOMALOUS UPPER LEVEL LOW WILL LIFT AWAY FROM
THE AREA AND TOWARD THE DELMARVA...ANOTHER SHORT WAVE AND ASSOCIATED
COLD POOL FEATURING 500 MB TEMPS AS COLD AS -22 OR -23C WILL SWEEP
THROUGH. DESPITE LIMITED MOISTURE WITH PWATS NO MORE THAN AROUND 3/4
INCHES AND 20-30F SURFACE DEW POINT DEPRESSIONS...THE ASSOCIATED
STEEP LAPSE RATES AND MODEST QG FORCING WILL SUPPORT THE RISK FOR
ISOLATED TO SCATTERED SHOWERS AND LOW TOPPED T-STORMS FOR MAINLY THE
CHARLESTON QUAD-COUNTY DISTRICT. HIGHEST PROBABILITIES ARE NORTH OF
I-16 AT 30 PERCENT. SUCH COLD AIR ALOFT AND WET BULB ZERO HEIGHTS
NEAR 6-7K FT...FREEZING LEVELS DOWN AS LOW AS 7-8K FT AND HAIL CAPE
VALUES OF 200-300 J/KG SUPPORT THE POTENTIAL FOR SMALL HAIL OR
GRAUPEL IN A FEW OF THE STRONGER STORMS. THE DAY WILL START MOSTLY
SUNNY...BUT LOOK FOR A QUICK DEVELOPMENT TO CUMULUS WITH THE STEEP
LAPSE RATES DURING DIURNAL HEATING AND LOW CONVECTIVE TEMPS IN THE
60S. 850 MB TEMPS ARE CLOSE TO 2 STANDARD DEVIATIONS BELOW NORMAL
AND THUS MAX TEMPS WILL BE FORTUNATE TO ACHIEVE THE LOWER OR MIDDLE
70S.

FRIDAY NIGHT...CONVECTION WILL RAPIDLY DIMINISH WITH SUNSET WITH
NOCTURNAL INFLUENCES AND EVENTUALLY THE PASSAGE OF THE TROUGH ALOFT.
SKIES WILL CLEAR OUT AND THIS LEADS TO ANOTHER UNSEASONABLY COOL
NIGHT WITH LOWS NOT FAR FROM 50 INLAND AND MID AND UPPER 50S NEAR
THE COAST. A FEW UPPER 40S IN RURAL SECTIONS ARE CERTAINLY POSSIBLE.

SATURDAY THROUGH SUNDAY...STEADILY CLIMBING HEIGHTS IN WAKE OF THE
EAST COAST TROUGH PULLING AWAY THROUGH THE ATLANTIC AND SURFACE HIGH
PRESSURE FROM THE GULF MOVING EAST WILL SUPPORT A WARMING TREND FOR
THIS WEEKEND. 850 MB TEMPS AND LOW LEVEL THICKNESS ARE STILL BELOW
AVERAGE VALUES SATURDAY BUT ON AN INCREASE...BOUNCING BACK TO ABOVE
NORMAL FOR SUNDAY. WITH PLENTY OF INSOLATION AND DOWNSLOPE
TRAJECTORIES WE STAYED VERY CLOSE TO THE IDEAL 1000-850 MB THICKNESS
FORECAST FOR MAX TEMPS BOTH AFTERNOONS. UPPER 70S AND LOWER 80S
SATURDAY...THEN MID AND UPPER 80S OR PERHAPS 90 IN SPOTS ON SUNDAY.
A LITTLE COOLER AT THE COAST SUNDAY WITH RESULTANT SEA BREEZE
CIRCULATIONS TO OCCUR.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
MID LEVEL RIDGING EARLY NEXT WEEK WILL GRADUALLY BREAK DOWN THROUGH
MID WEEK. SURFACE HIGH PRES OVER THE ATLANTIC WILL BE THE DOMINANT
SYNOPTIC FEATURE FOR OUR REGION. TEMPS WILL REMAIN ABOVE CLIMO FOR
MUCH THE PERIOD. IT LOOKS LIKE WE WILL RETAIN A DECENT MID LEVEL CAP
ON MONDAY AND PROBABLY AGAIN ON TUESDAY. WE MAINTAINED SLIGHT CHANCES
FOR MAINLY DIURNAL SHOWERS AND TSTMS IN THE MID WEEK TIME FRAME.

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
VFR CONDITIONS ARE EXPECTED TO PREVAIL AT BOTH CHS AND SAV
TERMINALS THROUGH 00Z SATURDAY. HOWEVER...CAN/T RULE OUT A
SHOWER/THUNDERSTORM CAUSING FLIGHT RESTRICTIONS AT KCHS FRIDAY
AFTERNOON. ANY SHOWERS THAT MAY HIT THE TERMS EARLY THIS EVENING
SHOULD NOT CAUSE ANY SIGNIFICANT IMPACTS. LASTLY...GUSTS NEAR 20
KT WILL CONTINUE THROUGH ABOUT 02Z...SLIGHTLY STRONGER IN SHOWERS.

EXTENDED AVIATION OUTLOOK...VFR WEATHER WILL BE THE RULE.

&&

.MARINE...
THIS EVENING AND TONIGHT...SMALL CRAFT ADVISORIES WILL REMAIN IN
EFFECT FOR ALL WATERS INCLUDING THE CHS HARBOR THROUGH THIS EVENING
AS STRONG COLD AIR ADVECTION ASSOCIATED WITH A MID/UPPER LVL LOW
PROMOTES DEEP MIXING IN THE ATMOSPHERE. IN GENERAL...WEST/NORTHWEST
WINDS WILL RANGE BETWEEN 15-20 KT WITH GUSTS UP TO 25-30
KT...HIGHEST ALONG THE LAND/WATER INTERFACE AND IN OFFSHORE GEORGIA
WATERS. SEAS WILL RANGE BETWEEN 2-4 FT IN NEARSHORE WATERS AND 4-6
FT IN OFFSHORE GEORGIA WATERS. CONDITIONS WILL BEGIN TO IMPROVE LATE
THIS EVENING IN THE CHS HARBOR AS DIURNAL HEATING IS LOST...BUT
ADVISORY CONDITIONS WILL PERSIST FOR AT LEAST A FEW HOURS IN
NEARSHORE WATERS...AND INTO LATE NIGHT HOURS IN OFFSHORE GEORGIA
WATERS.

FRIDAY...THE CYCLONIC FLOW OFFSHORE FLOW AROUND LOW PRESSURE IN THE
MID ATLANTIC REGION WILL EASE A LITTLE ALLOWING FOR WEST/NW WINDS
THAT ARE AS HIGH AS 15-20 KT EARLY TO DIMINISH TO 15 KT OR LESS IN
THE AFTERNOON. TRAJECTORIES FROM LAND TO THE OCEAN WILL LIMIT SEAS
TO NO MORE THAN 2-4 FT AND HIGHEST NEAR 50-60 NM OFF THE GA COAST.

FRIDAY NIGHT THROUGH SATURDAY...LOW PRESSURE WILL MEANDER IN THE NE
QUADRANT OF THE NATION AS HIGH PRESSURE BUILDS EAST FROM THE GULF OF
MEXICO. WHERE SITUATED WITHIN AN OFFSHORE FLOW BETWEEN THESE TWO
FEATURES WITH WEST/NW BREEZES NO HIGHER THAN ABOUT 15 KT AND SEAS 3
FT OR LESS.

SUNDAY THROUGH TUESDAY...HIGH PRESSURE IN THE GULF WILL SHIFT INTO
THE SW ATLANTIC AND THE OFFSHORE SYNOPTIC FLOW WILL TRANSITION INTO
AN ONSHORE DIRECTION. SEA BREEZE CIRCULATIONS AND DEEP MIXING WILL
CAUSE HIGHER BUMPS IN CHARLESTON HARBOR...NEAR THE COAST AND OVER
THE INTRA-COASTAL EACH DAY...BUT WINDS AND SEAS WILL REMAIN BELOW
ADVISORY THRESHOLDS THROUGH THE PERIOD.

&&

.TIDES/COASTAL FLOODING...
DESPITE THE OFFSHORE FLOW TO WINDS FRIDAY AND SATURDAY...GIVEN THE
PERIGEAN SPRING TIDES THERE MIGHT BE A NEED FOR COASTAL FLOOD
ADVISORIES WITH THE EVENING HIGH TIDE CYCLES. THEN ON SUNDAY THE
FLOW ATTEMPTS TO SHIFT A LITTLE MORE ONSHORE...AGAIN CAUSING A RISK
FOR SHALLOW COAST FLOOD CONCERNS WITH THE EVENING HIGH TIDE.

&&

.CLIMATE...
RECORD LOWS FOR MAY 6...

CHARLESTON AIRPORT /CHS/...44/1973
SAVANNAH AIRPORT /SAV/...46/1957
DOWNTOWN CHARLESTON /CXM/...53/1921

&&

.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...AND A SITE VISIT WILL BE
PERFORMED LATE THIS WEEK.

THE GRAYS REEF BUOY 41008 ALSO REMAINS OUT OF SERVICE...AND A SITE
VISIT BY NDBC IS EXPECTED DURING THE LATTER PART OF MAY TO EITHER
REPAIR THE SITE OR EXCHANGE FOR A NEW BUOY SYSTEM.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 7 PM EDT THIS EVENING FOR AMZ330.
     SMALL CRAFT ADVISORY UNTIL 11 PM EDT THIS EVENING FOR AMZ350-
     352-354.
     SMALL CRAFT ADVISORY UNTIL 2 AM EDT FRIDAY FOR AMZ374.

&&

$$
SYNOPSIS...
NEAR TERM...33/RJB
SHORT TERM...
LONG TERM...
AVIATION...33/RJB
MARINE...33/DPB
TIDES/COASTAL FLOODING...
CLIMATE...
EQUIPMENT...



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