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Area Forecast Discussion

325
FXUS62 KCHS 260830
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
430 AM EDT SAT JUL 26 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 PREVAILING
INLAND. A COLD FRONT WILL APPROACH AND CROSS THE REGION LATE MONDAY
AND BECOME STATIONARY SOUTH AND SOUTHEAST OF THE AREA THROUGH THE
MIDDLE OF NEXT WEEK. THE FRONT WILL THEN SLOWLY DISSIPATE OFF THE
SOUTHEAST COAST THROUGH LATE NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
EARLY THIS MORNING...DUE TO THE WET GROUNDS FROM DECENT RAINFALL
IN THE PAST 12-18 HOURS...PLUS CLEARING SKIES AND LITTLE TO NO
WINDS...WE ARE STARTING TO SEE SOME FOG AND STRATUS FORM NEAR OUR
NW TIER. THIS TREND WILL CONTINUE THROUGH 12Z...LEADING TO AT
LEAST PATCHY FOG OVER MUCH OF SC INLAND FROM THE US-17 CORRIDOR
AND NORTH OF I-16 IN SE GA THROUGH 8 OR 9 AM. IN ADDITION...DUE TO
LINGERING BOUNDARY INTERACTIONS THERE WILL BE A FEW SHOWERS OR
T-STORMS OVER CHARLESTON AND SOUTHERN BERKELEY COUNTIES.

TODAY...THE LONG WAVE TROUGH IN THE EAST BEGINS TO SLOWLY PULL
INTO THE ATLANTIC ALLOWING FOR THE PLAINS RIDGE TO EXPAND EAST.
SUBTLE HEIGHT RISES ALOFT WILL ENSUE LOCALLY. THERE IS STILL
EVIDENCE OF THE WEAK INLAND TROUGH AS IT MORPHS INTO THE LEE-SIDE
PIEDMONT TROUGH...PLUS BOUNDARIES FROM THE RECENT CONVECTION.
WE DO REMAIN CAPPED THIS MORNING AND THERE IS CONSIDERABLE DRY AIR
ABOVE 700 MB AND PWATS ARE DOWN BETWEEN THE 25TH AND 50 THE
PERCENTILE. THESE CONDITIONS WILL RESTRICT OUR COVERAGE OF
SHOWERS/T-STORMS...ESPECIALLY WHEN COMPARED TO YESTERDAY. BUT
GIVEN SOME MESO-SCALE BOUNDARIES...A RESULTANT SEA BREEZE AND
ADEQUATE LOW LEVEL MOISTURE WE WILL CARRY SLIGHT CHANCE POPS FROM
ABOUT 1-8 PM WITH AN INFLUX OF SOME HIGHER THETA-E AIR.

ANOTHER CONCERN FOR TODAY WILL BE TEMPS AND THE RESULTING HEAT
INDEX. GIVEN A DEEP WESTERLY FLOW THROUGHOUT MUCH OF THE
TROPOSPHERE...WE HAVEN/T STRAYED TOO FAR FROM THE LOW LEVEL
THICKNESS FORECAST...WHICH YIELDS MID 90S ACROSS MUCH OF THE
REGION AWAY FROM THE IMMEDIATE SHORELINE. WHEN COMBINED WITH DEW
POINTS IN THE LOWER AND MIDDLE 70S THE RESULTING HEAT INDICES WILL
PEAK AT 102-105 DEGREES. NOT ENOUGH FOR A HEAT ADVISORY THIS LATE
INTO THE SUMMER...BUT HIGH ENOUGH WHERE CAUTION IS ADVISED IF YOU
MUST BE OUTSIDE DURING THE MAXIMUM AFTERNOON HEATING.

TONIGHT...IN THE ABSENCE OF ANY SUPPORT ALOFT...LINGERING CONVECTION
THIS EVENING WILL TAPER OFF BY AROUND SUNSET. EVEN DRIER AIR ABOVE
THE BOUNDARY LAYER WORKS ITS WAY IN AND SKIES WILL BECOME MOSTLY
CLEAR. SINCE THERE IS A BUILD UP OF HEAT DURING THE DAYTIME OUR
NIGHT TIME MINS WON/T BE ANY LOWER THAN THE LOWER OR MIDDLE 70S
INLAND...WITH UPPER 70S ALONG THE BARRIER ISLAND COMMUNITIES.

&&

.SHORT TERM /SUNDAY THROUGH TUESDAY/...
SUNDAY AND SUNDAY NIGHT...THE FORECAST AREA WILL BE POSITIONED UNDER
THE EASTERN PERIPHERY OF AN EXPANSIVE UPPER LEVEL RIDGE THAT IS
CENTERED ACROSS THE CENTRAL PLAINS AND THE FOUR CORNERS REGION. AT
THE SURFACE....THE REGION WILL BE CAUGHT BETWEEN HIGH PRESSURE TO
THE EAST AND AN INLAND TROUGH OF LOW PRESSURE. MODEL SOUNDINGS SHOW
A NOTABLE CAP AND SUBSIDENCE INVERSION AROUND 800 MB WHICH IS
EXPECTED TO KEEP THINGS QUIET. IN FACT...GIVEN THE LACK OF
CONVECTIVE ACTIVITY IN THE MODELS...A DRY FORECAST IS IN PLACE. THE
BIGGEST FORECAST CONCERN WILL BE RISING TEMPERATURES. WITHIN THE
INLAND SURFACE TROUGH...WINDS WILL TAKE ON MORE OF A WESTERLY
COMPONENT. THIS WILL ALLOW HIGHS TO REACH THE MID TO UPPER 90S. WHEN
COMBINED WITH DEWPOINTS IN THE LOW TO MID 70S...HEAT INDEX VALUES
WILL REACH INTO THE 105-110 RANGE IN THE AFTERNOON WHICH IS JUST
BELOW HEAT ADVISORY THRESHOLDS. THE DRY FORECAST THEN CONTINUES
OVERNIGHT AHEAD OF AN APPROACHING COLD FRONT. LOWS WILL ONLY FALL
INTO THE UPPER 70S IN MOST AREAS.

MONDAY THROUGH TUESDAY...EARLY IN THE WEEK THE MID/UPPER LEVEL
PATTERN ACROSS THE EASTERN CONUS WILL AMPLIFY SIGNIFICANTLY AS A
SERIES OF SHORTWAVES ROTATE ACROSS THE GREAT LAKES REGION. THIS WILL
SUPPRESS THE WEEKEND UPPER RIDGE FURTHER SOUTH AND ALLOW FOR A DEEP
TROUGH WITH FALLING HEIGHTS. THE MOST NOTABLE FEATURE EARLY IN THE
WEEK IS THE COLD FRONT THAT IS PROGGED TO APPROACH THE AREA AND
CROSS MONDAY NIGHT. THIS IS A STRONG COLD FRONT FOR LATE JULY DRIVEN
BY AN INCREASINGLY ANOMALOUSLY DEEP TROUGH. IN FACT...BY MONDAY
EVENING HEIGHTS IN THE CORE OF THE TROUGH TO THE NORTH WILL BE ON
THE ORDER OF 3 TO 4 STANDARD DEVIATIONS BELOW NORMAL. A TROUGH THIS
DEEP DRIVING A STRONG COLD FRONT IS ALMOST SURE TO BRING ABOUT AN
ACTIVE ROUND OF THUNDERSTORMS LATE MONDAY. MID LEVEL FLOW INCREASES
INTO THE 40-50 KNOT RANGE WHICH RESULTS IN DEEP LAYER SHEAR VALUES
OF AROUND 30-35 KNOTS RIGHT ALONG THE FRONT. MODEL SOUNDINGS SHOW AN
ATMOSPHERE THAT WOULD BE SUPPORTIVE OF AN ENVIRONMENT CAPABLE OF
PRODUCING DISCRETE CELLS WITH SUPER-CELL STRUCTURES PRODUCING LARGE
HAIL AND DAMAGING WINDS. THERE WILL BE NO SHORTAGE OF SURFACE BASED
INSTABILITY WITH TREMENDOUS SURFACE HEATING AND COMPRESSIONAL
HEATING LEADING TO HIGHS IN THE UPPER 90S IN MANY AREAS. IN
FACT...WE COULD SEE HEAT INDEX VALUES OF 110 FOR A FEW HOURS AND A
HEAT ADVISORY MAY BE NEEDED FOR PARTS OF THE AREA. THE SHEAR IS
UNIDIRECTIONAL BUT THE VARIOUS THERMODYNAMIC INDICES POINT TO AN
INCREASING THREAT OF A SEVERE WEATHER EVENT MONDAY EVENING. NOT
SURPRISINGLY...MUCH OF THE FORECAST AREA IS IN THE DAY 3 SLIGHT RISK
FROM SPC. WE WILL ADD A MENTION TO THE HWO WITH THIS PACKAGE. THE
FRONT AND ASSOCIATED THUNDERSTORM ACTIVITY WILL PUSH THROUGH AND
OFFSHORE THROUGH TUESDAY. THICKNESSES DROP OFF CONSIDERABLY UNDER
THE TROUGH ALOFT AND A MUCH COOLER DAY IS EXPECTED. TUESDAY HIGHS
WILL LIKELY REMAIN IN THE UPPER 80S FOR MOST AREAS.

&&

.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
THE PATTERN IN THE LONG TERM WILL BE DOMINATED BY THE ANOMALOUSLY
DEEP MID/UPPER LEVEL TROUGH ACROSS THE EASTERN CONUS. THE LOWERING
HEIGHTS AND THICKNESS VALUES WILL RESULT IN A MUCH COOLER PERIOD
WITH BELOW NORMAL TEMPERATURES THROUGH THE END OF THE WEEK. WEAK
HIGH PRESSURE WILL BE POSITIONED TO THE NORTHEAST WHICH WILL RESULT
IN AN EASTERLY ONSHORE FLOW THROUGH MUCH OF THE PERIOD. CHANCES FOR
CONVECTION WILL START OFF LOWER WEDNESDAY...BUT WILL INCREASE SLOWLY
THROUGH THE END OF THE FORECAST WITH A DEVELOPING COASTAL TROUGH IN
THE VICINITY.

&&

.AVIATION /09Z SATURDAY THROUGH WEDNESDAY/...
CONVECTIVE DEBRIS CLOUD COVER WILL CONTINUE TO DIMINISH EARLY THIS
MORNING...ENOUGH FOR SOME MVFR OR LOWER CONDITIONS IN FOG AND
POSSIBLE STRATUS AT KCHS CLOSER TO DAYBREAK DUE TO THE WET
GROUNDS FROM RECENT RAINFALL. WE CAN/T RULE OUT A BRIEF SHRA AT
KCHS EARLY THIS MORNING DUE TO LINGERING BOUNDARIES FROM EARLIER
CONVECTION. BUT FLIGHT RESTRICTIONS ARE UNLIKELY.

COVERAGE OF SHRA/TSRA LATER TODAY WILL BE ISOLATED...SO ANY
DIRECT IMPACTS ON EITHER OR BOTH TERMINALS IS TOO LIMITED TO
INCLUDE WITH THE 06Z TAFS.

ASIDE FROM THE EARLY MORNING FOG AT KCHS AND MAYBE IN ISOLATED
AFTERNOON CONVECTION...VFR WEATHER WILL BE THE RULE AT BOTH AIRFIELDS.

EXTENDED AVIATION OUTLOOK...PRIMARILY VFR. A COLD FRONT IS EXPECTED TO
MOVE THROUGH THE AREA LATE MONDAY. BRIEF CEILING AND VISIBILITY
REDUCTIONS WILL BE POSSIBLE WITH THUNDERSTORMS THAT DEVELOP IN THE
EVENING HOURS.

&&

.MARINE...
TODAY...THE LOCAL WATERS WILL LIE NEAR THE NW PERIPHERY OF THE
SUB-TROPICAL ATLANTIC RIDGE THAT EXTENDS ACROSS SOUTHERN FLORIDA.
AT THE SAME TIME A WEAK TROUGH WILL AGAIN BE FOUND INLAND OVER THE
MID-ATLANTIC AND SE STATES. THIS RESULTS IN GENTLE TO MODERATE WEST/SW
WINDS BACKING AROUND MORE TO THE SOUTH/SW WITH THE SEA BREEZE
CIRCULATIONS THIS AFTERNOON. THE WAVE SPECTRUM IS MAINLY FROM WIND
DRIVEN WAVES OF 2-3 FT...BUT ALSO A LITTLE SMALL 8 SECOND SWELL
FROM THE SE.

TONIGHT...THERE IS LITTLE CHANGE IN THE OVERALL SYNOPTIC
PATTERN...ALTHOUGH THE INLAND TROUGH DOES BECOME A LITTLE BETTER
DEFINED. WINDS WILL CLOCK BACK AROUND TO THE SW/WEST THROUGH THE
NIGHT WITH AT MOST ONLY A SMALL NOCTURNAL SURGE. SEAS WILL PRETTY
MUCH HOLD IN A STEADY STATE...AVERAGING 2-3 FT.

SUNDAY THROUGH WEDNESDAY...EARLY IN THE PERIOD THE SETUP WILL
FEATURE A TIGHTENING SOUTHWEST GRADIENT ACROSS THE WATERS AS A COLD
FRONT APPROACHES FROM THE NORTHWEST. THE STRONG COLD FRONT WILL
CROSS THE WATERS MONDAY NIGHT...LIKELY ACCOMPANIED STRONG
THUNDERSTORMS. DURING THIS SUNDAY/MONDAY TIME PERIOD...THE GRADIENT
WILL SUPPORT SOUTHWEST WINDS IN THE 15-20 KT RANGE AT TIMES.
MARGINAL SMALL CRAFT ADVISORY CONDITIONS WILL BE POSSIBLE
PERIODICALLY...ESPECIALLY FOR THE OUTER GEORGIA WATERS. THEN FOR THE
LATTER PART OF THE FORECAST PERIOD...THE GRADIENT WILL SLACKEN AND
WINDS WILL BECOME MORE NORTHEASTERLY WITH TIME. WINDS AND SEAS ARE
EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY THRESHOLDS TUESDAY AND
WEDNESDAY.

&&

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

&&

$$

NEAR TERM...
SHORT TERM...BSH
LONG TERM...BSH
AVIATION...
MARINE...






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