Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 240800
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
400 AM EDT THU JUL 24 2014

.SYNOPSIS...
AN ATLANTIC RIDGE OF HIGH PRESSURE WILL REMAIN SOUTH OF THE AREA
INTO EARLY NEXT WEEK...WITH A WEAK TROUGH OF LOW PRESSURE TO PREVAIL
INLAND. A COLD FRONT WILL APPROACH LATE MONDAY AND WILL BECOME
STATIONARY SOUTH AND SOUTHEAST OF THE AREA DURING THE MIDDLE OF
NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
TODAY...A BIT MORE UNSETTLED TODAY COMPARED TO WEDNESDAY AS A
LOW AND MID-LEVEL TROUGH APPROACHES FROM THE NORTHWEST ALONG WITH
SOME DEEPER MOISTURE. DECENT WEST TO SOUTHWEST LOW-LEVEL FLOW WILL
HELP KEEP THE SEA BREEZE PINNED NEAR THE COAST AND THUS IT MAY
TAKE UNTIL EARLY-MID AFTERNOON TO GET CONVECTION GOING
LOCALLY...ALTHOUGH THERE WILL BE SHOWERS AND STORMS FIRING UP TO
THE WEST NEAR THE TROUGH AND THESE WILL BE PROGRESSING EASTWARD AS
WELL. ALL OF THE CONVECTION WILL THEN CONTINUE TO SHIFT TOWARD THE
COAST THROUGH THE AFTERNOON. INSTABILITY APPEARS MODERATE BUT DEEP
LAYER FLOW WILL BE A BIT STRONGER AND THUS CANNOT RULE OUT A FEW SEVERE
STORMS...WITH DAMAGING WINDS THE MAIN HAZARD GIVEN SOME DRIER AIR
ALOFT. IT WILL BE A BIT BREEZY GIVEN THE INCREASING BOUNDARY LAYER
WINDS...WITH SOME GUSTS NEAR 25 MPH A GOOD BET. HIGHS SHOULD TOP
OUT IN THE MID 90S INLAND AND PROBABLY EVEN CLOSE TO 90 AT THE
COAST GIVEN THE STRONGER OFFSHORE FLOW/PINNED SEA BREEZE.

TONIGHT...THE SURFACE TROUGH WILL APPROACH THE AREA BEFORE
STALLING OUT AS IT RUNS OUT OF STEAM FROM ITS WEAKENING PARENT
TROUGH ALOFT. EVENING CONVECTION WILL DISSIPATE AS
INSTABILITY/CONVERGENCE WEAKEN...ALTHOUGH COULD SEE A FEW SHOWERS
LINGER WELL INTO THE EVENING MOSTLY OVER SOUTH CAROLINA WHICH WILL
BE CLOSER TO THE DYING TROUGH. LOWS SHOULD RANGE FROM THE LOWER
TO MID 70S INLAND TO UPPER 70S AT THE COAST.

&&

.SHORT TERM /FRIDAY THROUGH SUNDAY/...
FRIDAY...THE LOCAL REGION WILL BE POSITIONED NEAR THE SOUTHERN APEX
OF A LONG WAVE TROUGH COVERING THE EAST/SE STATES...SNUGGLED IN
BETWEEN ONE ANTICYCLONE OVER THE NW BAHAMAS AND ANOTHER COVERING
MUCH OF THE SOUTHERN TIER OF THE NATION. AT THE SAME TIME AT THE
SURFACE...THE EAST/NE TO WEST/SW ALIGNED TROUGH WILL BECOME MORE
ILL-DEFINED OVER OR JUST INLAND FROM THE CWFA...KEEPING AMPLE
MOISTURE AND INSTABILITY IN PLACE. LAPSE RATES ARE POOR
OVERALL...BUT THERE IS SOME FORCING FOR ASCENT IN ASSOCIATION WITH
THE RIGHT ENTRANCE REGION TO THE UPPER JET AND A POTENTIAL
PERTURBATION THAT MOVES IN ALOFT DURING PEAK HEATING. THESE FEATURES
ALONG WITH THE SEA BREEZE AND SURFACE TROUGH WILL TRIGGER SCATTERED
SHOWERS/T-STORMS. A WARM WEST/SW SYNOPTIC FLOW WILL NEGATE SOME OF
THE 50-70 PERCENT CLOUD COVER...BOOSTING TEMPS INTO THE LOWER 90S
BEFORE RAIN-COOLED CONVECTION SETS IN.

SATURDAY THROUGH SUNDAY...THE LONG WAVE TROUGH LIFTS OUT LATER
SATURDAY AND IN ITS PLACE THERE IS A MERGER OF THE THE TWO
ANTICYCLONES BY SUNDAY...WITH RIDGING TO ENCOMPASS THE AREA FROM THE
BAHAMAS TO THE SOUTHERN PLAINS AND MUCH OF THE ROCKIES. THERE ARE
STILL HINTS OF THE REMNANTS OF THE SURFACE TROUGH WHICH APPEARS TO
MORPH INTO THE TYPICAL PIEDMONT TROUGH. THERE DOES APPEAR TO BE A
SUBTLE SHORT WAVE THAT MOVES THROUGH SATURDAY...BUT NONE ARE
APPARENT AT THIS JUNCTURE FOR SUNDAY. WITH LESS AVAILABILITY OF
MOISTURE GIVEN THAT PWATS FALL TO BETWEEN THE 25TH AND 50TH
PERCENTILE OVER THE WEEKEND OUR RAIN CHANCES WOULD BE NO MORE THAN
ISOLATED TO SCATTERED COVERAGE SATURDAY AND ISOLATED COVERAGE
SUNDAY. WITH LESS COVERAGE OF SHOWERS/T-STORMS AND AN EXPANSION OF
LOW LEVEL THICKNESS OUR MAX TEMPS WILL CLIMB INTO THE LOWER AND
MIDDLE 90S AWAY FROM THE BEACHES. WHILE HEAT INDICES WON/T BE
ANYWHERE NEAR THE HEAT ADVISORY CRITERIA OF 110 DEGREES OR
GREATER...BY SUNDAY SOME PLACES WILL EXPERIENCE A HEAT INDEX OF
ABOUT 104-108 DEGREES. WE MENTION THIS BECAUSE WE HAVE ONLY ISSUED
ONE HEAT ADVISORY SO FAR THIS YEAR AND VALUES SUCH AS THESE HAVE BE
UNCOMMON OF LATE.

&&

.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
A DEEP LAYERED GYRE OVER OR NEAR SOUTHERN HUDSON BAY IN CANADA WILL
CIRCULATE OCCASIONAL SHORT WAVES THROUGH THE GREAT LAKES AND OHIO
VALLEY WHICH CARVES OUT A BROAD AND FAIRLY WELL AMPLIFIED TROUGH
ACROSS THE EASTERN HALF OF THE COUNTRY DURING THE EARLY AND MIDDLE
PARTS OF NEXT WEEK. THIS SENDS AN UNUSUAL MID SUMMER COLD FRONT INTO
THE AREA FROM THE NW LATER MONDAY AND EARLY TUESDAY. SURPRISINGLY IT
LOOKS LIKE THERE IS ENOUGH NW PUSH BEHIND THE FRONT TO SEND IT
THROUGH THE AREA...BEFORE IT STALLS OUT NOT FAR TO THE SE AND SOUTH
FOR THE MIDDLE OF THE WEEK. RAIN CHANCES WILL CLIMB MONDAY AND
TUESDAY IN CONJUNCTION WITH THE FRONT...MAINLY IN THE 20-40 PERCENT
RANGE. PROVIDED THE FRONT CLEARS THE AREA RAIN CHANCES ARE NO MORE
THAN 20 PERCENT WEDNESDAY...THEN 20-30 PERCENT NEXT THURSDAY AS THE
FRONT STARTS TO TREK BACK NORTH. COMPRESSIONAL HEATING OUT AHEAD OF
THE FRONT ALLOWS FOR ABOVE NORMAL TEMPS MONDAY...WITH ONLY VERY
MINIMAL COOL ADVECTION TO DROP READINGS SLIGHTLY BELOW NORMAL
TUESDAY THROUGH THURSDAY.

&&

.AVIATION /08Z THURSDAY THROUGH MONDAY/...
VFR CONDITIONS LIKELY. AN INLAND SURFACE TROUGH AND THE SEA BREEZE
WILL YIELD SCATTERED CONVECTION TODAY...MAINLY THIS
AFTERNOON...PERSISTING INTO THE EVENING...ESPECIALLY AT KCHS. WE
MAINTAINED VCTS FOR NOW.

EXTENDED AVIATION OUTLOOK...MOST OF THE TIME THROUGH SUNDAY WILL BE
VFR...WITH ONLY SMALL PROBABILITIES OF BRIEF FLIGHT RESTRICTIONS IN
ISOLATED TO SCATTERED AFTERNOON/EVENING CONVECTION. BETTER CHANCES
FOR SUB-VFR WEATHER MONDAY IN ADVANCE OF A COLD FRONT.

&&

.MARINE...
TODAY AND TONIGHT...A TROUGH OF LOW PRESSURE INLAND WILL PROGRESS
TOWARD THE COAST THIS EVENING AND STALL OUT. SOUTH TO SOUTHWEST
WINDS WILL BE BREEZY TODAY AHEAD OF THE TROUGH BEFORE LESSENING
AND SHIFTING WEST LATE TONIGHT. WE MAINTAINED WINDS NO MORE THAN
20 KT...JUST BELOW ADVISORY LEVELS...BUT THERE COULD BE A FEW
GUSTS NEAR 25 KT...MAINLY ALONG THE CHARLESTON COUNTY COAST AND
OFFSHORE WATERS. SEAS SHOULD PEAK NEAR 4 FT...HIGHEST EAST.

FRIDAY THROUGH SATURDAY...NOTHING OUT OF THE ORDINARY IN REGARDS TO
SUMMERTIME MARINE CONDITIONS...WITH A WEST AND SW FLOW AT LESS THAN
15 KT AS THE COASTAL WATERS WILL LIE BETWEEN A POORLY DEFINED INLAND
TROUGH AND THE BERMUDA-AZORES HIGH ACROSS FLORIDA.

SUNDAY THROUGH TUESDAY...LOW PRESSURE MOVING THROUGH THE NE QUAD
OF THE COUNTRY EARLY NEXT WEEK WHILE SIMULTANEOUSLY THE SUB-
TROPICAL ATLANTIC RIDGE IS SHUNTED A LITTLE FURTHER SOUTH. THIS
ALLOWS FOR A COLD FRONT TO APPROACH EARLY IN THE WEEK...PROBABLY
STALLING OUT OVER OR NEAR THE COASTAL WATERS LATE IN THE FORECAST
PERIOD. THERE IS A FAIRLY DECENT TIGHTENING OF THE GRADIENT THAT
OCCURS...A GOOD 2-3 MB SPREAD FROM NORTH TO SOUTH OVER THE LOCAL
MARINE ZONES. IT DOESN/T LOOK TO BE STRONG ENOUGH FOR SMALL CRAFT
ADVISORY CONDITIONS...BUT WE COULD BE PUSHING 20 KT AT TIMES AND
SEAS WILL BE BUILDING TO 4 OR 5 FT. WE/LL ALSO NEED TO REMAIN
ALERT FOR ORGANIZED T-STORMS IN ASSOCIATION WITH THE COLD
FRONT...MAINLY LATE MONDAY INTO TUESDAY.

&&

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

&&

$$

NEAR TERM...RJB
SHORT TERM...33
LONG TERM...33
AVIATION...33/RJB
MARINE...33/RJB





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