Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 241124
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
724 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 IN TURN WILL CARVE 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 IS DEFINITELY NOT A
SUMMER-LIKE PATTERN...AND IT WILL SEND AN UNUSUAL LATE JULY 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 /12Z THURSDAY THROUGH MONDAY/...
SOLID VFR INTO MID AFTERNOON AT THE AIRFIELDS...WITH SW AND WEST
WINDS TO BECOME GUSTY AT TIMES WITHIN A WELL MIXED ATMOSPHERE.
ATTENTION THEN SHIFTS TO THE DEVELOPMENT OF SHRA/TSRA IN
ASSOCIATION WITH THE SEA BREEZE AND A NEARBY TROUGH OFF TO THE
WEST/NW. FLIGHT RESTRICTIONS ARE LIKELY FROM ABOUT 20Z-03Z...MOST
NOTABLY AT KCHS WHERE THE BEST INTERACTION OF BOUNDARIES WILL
OCCUR IN SYNC WITH THE PASSAGE OF ENERGY ALOFT. LOW-END CHANCE OF
SOME LATE NIGHT FOG AND/OR STRATUS IF WE GET SUFFICIENT RAIN AND
SKIES CLEAR OUT ENOUGH.

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...
SHORT TERM...
LONG TERM...
AVIATION...
MARINE...






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