Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 301957
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
357 PM EDT WED JUL 30 2014

.SYNOPSIS...
A COASTAL TROUGH WILL SETTLE OVER THE AREA THROUGH LATE THIS WEEK
AND WILL PERSIST INTO THE MIDDLE OF NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
WITHIN THE ONGOING DEEP LAYERED CYCLONIC FLOW REGIME...BROAD LOW-
LEVEL MOISTURE CONVERGENCE AND VARIOUS MESOSCALE BOUNDARIES WILL
CONTINUE TO SUPPORT ISOLATED/SCATTERED SHOWERS INTO THIS
EVENING...ESPECIALLY BUT NOT LIMITED TO LOCATIONS ALONG/WEST OF
I-95. A MARKED SUBSIDENCE INVERSION BASED WITHIN THE 800-700 MB
LAYER WILL LIMIT UPDRAFT DEPTH AND THE POTENTIAL FOR LIGHTNING.
NEVERTHELESS...A SLIGHT CHANCE FOR THUNDER IS JUSTIFIED.

THE POTENTIAL FOR SEVERE WEATHER REMAINS VERY LOW THROUGH THE
EVENING...ALTHOUGH ELEVATED DOWNDRAFT CAPES COULD CONTRIBUTE TO
GUSTY WINDS WITHIN ANY THUNDERSTORMS/HEAVY SHOWERS.

AFTER DARK...COVERAGE OF SHOWERS SHOULD DIMINISH AS THE BOUNDARY
LAYER STABILIZES. HOWEVER...TO VARYING DEGREES GUIDANCE DEPICTS
ADDITIONAL SHOWER DEVELOPMENT WELL INTO THE NIGHT AS DEEP LAYERED
CYCLONIC FLOW AND LOW-LEVEL MOISTURE CONVERGENCE PERSIST. WHILE A
SHOWER CANNOT BE RULED OUT JUST ABOUT ANYWHERE...MAINTAINED SLIGHT
CHANCE POPS OVERNIGHT ROUGHLY ALONG THE I-95 CORRIDOR...ESPECIALLY
NEAR THE COAST. FORECAST CONFIDENCE IN THIS OVERNIGHT POPS
FORECAST IS NOT HIGH...AND ADJUSTMENTS COULD BE REQUIRED WITHIN
SUBSEQUENT FORECAST UPDATE PACKAGES.

OTHERWISE...TEMPERATURES WILL BOTTOM OUT IN THE UPPER 60S WELL
INLAND AND IN THE 70S MOST OTHER AREAS...NOT MUCH BELOW 80F GIVEN
ONSHORE FLOW AT THE BEACHES.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/...
SHORTWAVE ENERGY DROPPING INTO THE LONGWAVE UPPER TROUGH ON THURSDAY
WILL CAUSE IT TO DIG TOWARD THE CENTRAL GULF COAST. AS A RESULT MID
AND UPPER LEVEL WINDS WILL BACK TO SOUTHWESTERLY...ELIMINATING THE
CAP AND INCREASING PWATS. EXTENSIVE CLOUDINESS AND THE LACK OF
LOW-LEVEL RIDGING WILL KEEP HIGH TEMPS FROM CLIMBING MUCH HIGHER
THAN 90 DEGREES IN MOST LOCATIONS. THIS IN TURN WILL LIMIT
INSTABILITY PARAMETERS WITH MIXED LAYER CAPE AROUND 1000 J/KG IN THE
AFTERNOON. THE COASTAL TROUGH WILL BEGIN SHIFTING TOWARD THE COAST
DURING THE DAY...AND A SEA BREEZE WILL SETUP BY AFTERNOON.
CONVERGENCE ASSOCIATED WITH THESE TWO FEATURES SHOULD HELP TRIGGER
ISOLATED SHOWERS AND TSTMS.

FRIDAY INTO SATURDAY WE EXPECT A SIGNIFICANT INCREASE IN SHOWER AND
TSTM COVERAGE. THE UPPER TROUGH WILL DEEPEN AND A SERIES OF
SHORTWAVES WILL MOVE INTO CENTRAL SC. PWATS INCREASE ABOVE 2 INCHES
WHILE THE SURFACE TROUGH STRENGTHENS AND MOVES INLAND. ADDITIONALLY
A 90 KT JET STREAK DEVELOPING ACROSS NEW ENGLAND WILL BE LOCATED
SUCH THAT SOME UPPER LEVEL DIVERGENCE WILL OVERSPREAD THE SOUTHEAST
UNITED STATES. WE ARE SHOWING HIGH END CHANCE POPS FRIDAY THROUGH
SATURDAY THOUGH AT SOME POINT LIKELY POPS MAY BE JUSTIFIED FOR
SATURDAY. HEAVY RAINFALL WITH SOME LOCALIZED FLOODING WILL BE THE
MAIN HAZARD DUE TO SUCH A MOIST AIRMASS COMBINED WITH AMPLE FORCING
AND STEERING FLOW AROUND 10 KT. HIGHS WILL BE IN THE UPPER 80S.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
THE UNSETTLED PATTERN WILL CONTINUE FOR THE LATTER HALF OF THE
WEEKEND AND AT LEAST INTO EARLY NEXT WEEK. THE TROUGH WILL REMAIN IN
THE VICINITY OF THE FORECAST AREA WITH A TROUGH ALOFT AND PWATS IN
EXCESS OF 2 INCHES. ALL THESE FACTORS ADD UP TO AN ACTIVE PERIOD
WITH RELATIVELY HIGH RAIN CHANCES. GIVEN THE TIME RANGE POPS HAVE
BEEN KEPT IN THE HIGH CHANCE RANGE...BUT IF THE MODELS CONTINUE
THEIR CURRENT TRENDS IT IS LIKELY THAT HIGHER POPS WILL EVENTUALLY
BE WARRANTED. LOCALLY HEAVY RAINFALL WILL REMAIN A CONCERN THROUGH
EARLY NEXT WEEK WITH ROUNDS OF CONVECTION ANTICIPATED. TEMPERATURES
WILL BE BELOW NORMAL...RUNNING ABOUT 3-5 DEGREES BELOW NORMAL FOR
HIGHS INTO THE MID WEEK TIME PERIOD.

&&

.AVIATION /20Z WEDNESDAY THROUGH MONDAY/...
SHOWERS AND ASSOCIATED BRIEF FLIGHT RESTRICTIONS COULD CONTINUE
INTO THE EVENING AT KSAV. SHOWERS COULD PERSIST AROUND KSAV WELL
INTO THE NIGHT...WILL CONTINUE TO ASSESS. THUNDER CANNOT BE RULED
OUT...BUT DUE TO THE LOW PROBABILITY 18Z TAFS DO NOT INDICATE
VCTS/CBS. ASSUMING A BREAK IN PRECIPITATION OVERNIGHT...SHOWERS
SHOULD REDEVELOP IN THE VICINITY OF THE KSAV AND KCHS THURSDAY
MORNING. OUTSIDE SHOWERS...MAINLY VFR CONDITIONS SHOULD PREVAIL
THROUGH THURSDAY.

WILL AMEND TAFS AS DICTATED BY NEAR TERM CONVECTIVE TRENDS THIS
AFTERNOON.

EXTENDED AVIATION...A SURFACE TROUGH WILL DRIFT INTO THE AREA LATE
THIS WEEK AND THROUGH THE WEEKEND. AN ACTIVE PERIOD IS EXPECTED
AND OCCASIONAL FLIGHT RESTRICTIONS ARE POSSIBLE DURING THIS TIME.

&&

.MARINE...
A CYCLONIC PRESSURE GRADIENT SOMEWHAT ENHANCED BETWEEN HIGH
PRESSURE TO THE NORTH AND LOW PRESSURE TO THE SOUTH WILL SUPPORT
EAST WINDS 10-15 KT WITH A FEW GUSTS AS HIGH AS 20 KT TONIGHT.
SEAS OF 2-3 FT WILL PREVAIL...ALTHOUGH SEAS COULD BUILD TO AS HIGH
AS 4 FT BEYOND 20 NM LATE.

THURSDAY THROUGH SUNDAY...A COASTAL TROUGH WILL DRIFT OVER THE
WATERS AND EVENTUALLY INLAND BY EARLY NEXT WEEK. E TO SE WINDS WILL
PREVAIL THURSDAY INTO FRIDAY...SWINGING AROUND TO SOUTHERLY ON
SATURDAY ONCE THE TROUGH SHIFTS INLAND. THE GRADIENT MAY TIGHTEN AT
TIMES THOUGH WINDS/SEAS WILL REMAIN BELOW ADVISORY THRESHOLDS.

&&

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

&&

$$

NEAR TERM...SPR
SHORT TERM...JRL
LONG TERM...BSH
AVIATION...JRL/SPR
MARINE...JRL/SPR





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