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Area Forecast Discussion

745
FXUS62 KCHS 060226
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1026 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 OVER THE CAROLINAS WILL SHIFT TOWARD THE MID
ATLANTIC OVERNIGHT...ALTHOUGH ADDITIONAL SHORTWAVE ENERGY WILL
MOVE SOUTH THROUGH THE SOUTHEAST U.S. ON THE BACKSIDE OF THE LOW.
THIS WILL HELP PRODUCE A FEW SHOWERS WHICH COULD ROTATE EAST
SOUTHEAST THROUGH THE LOCAL AREA ...MAINLY FOR THE NEXT SEVERAL
HOURS. ANY HEAVIER SHOWERS WILL BE CAPABLE OF PRODUCING GUSTY
WINDS UP TO AROUND 25 MPH DUE TO THE UNUSUALLY COLD AIR ALOFT.
THIS COLD AIR MASS WILL HELP PUSH TEMPERATURES TO NEAR RECORD
LOWS WITH UPPER 40S INLAND AND LOWER/MID 50S ALONG THE COAST BY
DAYBREAK. SOME INLAND SPOTS COULD EVEN REACH THE MID 40S...WHICH
COULD HARM SENSITIVE VEGETATION. SEE CLIMATE SECTION FOR DETAILS
REGARDING RECORD LOWS.

&&

.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 /02Z 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.

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

&&

.MARINE...
TONIGHT...SMALL CRAFT ADVISORIES WILL REMAIN IN EFFECT THROUGH
AROUND MIDNIGHT FOR ALL WATERS OUTSIDE CHS HARBOR. IMPROVING
CONDITIONS EXPECTED LATE AS THE CORE OF THE UPPER LOW PRESSURE
SYSTEM BEGINS TO MOVE AWAY.

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 2 AM EDT FRIDAY FOR AMZ350-352-354-
     374.

&&

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



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