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Area Forecast Discussion

375
FXUS62 KCHS 281747
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
147 PM EDT TUE JUL 28 2015

.SYNOPSIS...
THE REGION WILL REMAIN SITUATED BETWEEN WEAK HIGH PRESSURE TO THE
NORTH AND LOW PRESSURE TO THE SOUTH UNTIL LATE THIS WEEK.
THEN...BROAD LOW PRESSURE WILL DEVELOP AND WILL PERSIST OVER THE
REGION LATE THIS WEEK INTO EARLY NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
THIS AFTERNOON...A LARGE MID LVL RIDGE OF HIGH PRESSURE WILL PERSIST
OVER THE CENTRAL UNITED STATES WHILE A MID LVL TROUGH OF LOW
PRESSURE REMAINS POSITIONED DOWNSTREAM OFF THE NORTHEAST COAST. AT
THE SFC...A SERIES OF LOW PRESSURE WAVES WILL CONTINUE TO DEVELOP
ALONG/NEAR A BOUNDARY POSITIONED OVER FLORIDA AND OFF THE SOUTHEAST
COAST...THEN SLOWLY LIFT NORTH/NORTHEAST OFFSHORE. THESE WEAK AREAS
OF LOW PRESSURE WILL BE THE PRIMARY DRIVER OF LIGHT EAST/NORTHEAST
FLOW OCCURRING ALONG COASTAL AREAS INTO THE AFTERNOON. FURTHER
INLAND...MOISTURE LEVELS CHARACTERIZED BY PWATS NEAR 1.8 TO 2.0
INCHES SHOULD SUPPORT A FEW SHOWERS AND/OR THUNDERSTORMS DURING PEAK
HEATING AHEAD OF A WEAK H5 SHORTWAVE THAT BEGINS TO ROUND THE
NORTHEAST PERIPHERY OF HIGH PRESSURE CENTERED TO OUR WEST. LATEST
RADAR TRENDS AND MESOSCALE ANALYSIS INDICATE SHOWER AND THUNDERSTORM
DEVELOP REMAIN ON TRACK EARLY THIS AFTERNOON. THE BULK OF H5
SHORTWAVE ACTIVITY SHOULD REMAIN UPSTREAM THROUGH TONIGHT...THUS
PRECIP CHANCES WILL REMAIN CAPPED AT 20 PERCENT WITH COVERAGE MAINLY
WEST OF INTERSTATE 95.

OVERALL TEMPS WILL BE QUITE WARM THIS AFTERNOON...BUT SHOULD BE
LIMITED A DEGREE OR TWO DUE TO CIRRUS CLOUDS ALOFT. EXPECT MAX TEMPS
IN THE UPPER 80S/LOWER 90S NEAR COASTAL LOCATIONS AND MID/UPPER
90S INLAND. HEAT INDICES WILL APPROACH 103-106 IN A FEW LOCATIONS
THIS AFTERNOON.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY/...
TONIGHT...CUMULUS WILL DISSIPATE QUICKLY AFTER SUNSET WITH ONLY
CIRRUS EXPECTED TO TRAVERSE THE SKY THROUGH THE NIGHT. SOME
STRATOCUMULUS WILL LIKELY LINGER OVER THE COAST WITH THE ONSHORE
FLOW. SOME FOG AND STRATUS IS LIKELY FORM AGAIN EARLY WEDNESDAY
MORNING...BUT ITS POTENTIAL SEVERITY IS A BIT UNKNOWN THIS FAR
OUT...ESPECIALLY GIVEN THE MODELS HAVE BEEN PERFORMING WELL BELOW
AVERAGE ON CAPTURE FOG TRENDS. LOWS WILL RANGE FROM THE LOWER 70S
INLAND TO THE MID 70S AT THE COAST WITH UPPER 70S/NEAR 80 AT THE
BEACHES AND DOWNTOWN CHARLESTON.

WEDNESDAY MORNING...ANY FOG/STRATUS WILL GIVE WAY TO PARTLY SUNNY
CONDITIONS. THEN...ISOLATED/SCATTERED DIURNAL THUNDERSTORMS ARE
EXPECTED TO DEVELOP DURING THE AFTERNOON AS A CHANNEL OF
VORTICITY/DEFORMATION ON THE EASTERN PERIPHERY OF AN INLAND UPPER
RIDGE INTERACTS WITH THE SEA BREEZE. POPS ARE GRADUATED FROM SLIGHT
CHANCE NEAR THE COAST TO CHANCE ALONG/WEST OF I-95 WHERE HIGHER
PWATS WILL RESIDE. OTHERWISE...EXPECT HIGH TEMPERATURES IN THE
LOWER/MID 90S INLAND AND 80S ALONG THE IMMEDIATE COAST.

WEDNESDAY NIGHT...DIURNAL CONVECTION SHOULD DISSIPATE OVER
LAND...ALTHOUGH THE GFS MAINTAINS CONVECTION NEAR THE COAST INTO THE
OVERNIGHT HOURS. MEANWHILE...MODEL SOUNDINGS AND THE 28/00Z NAM PROG
OF 1000 MB PRESSURE CONDENSATION DEFICITS SUGGESTS THAT FOG/STRATUS
COULD DEVELOP. TEMPERATURES SHOULD BOTTOM OUT IN THE LOWER TO MID
70S INLAND AND 75-80F CLOSE TO THE COAST.

EXPECT A SIMILAR REGIME THURSDAY. ANY MORNING FOG/STRATUS WILL GIVE
WAY TO PARTLY SUNNY SKIES...AND ISOLATED/SCATTERED DIURNAL
SHOWERS/THUNDERSTORMS SHOULD AGAIN DEVELOP ESPECIALLY DURING THE
AFTERNOON/EARLY EVENING. ACCOUNTING FOR THE EAST/WEST MOISTURE
GRADIENT WHICH SHOULD PERSIST ACROSS THE REGION...POPS ARE TAPERED
FROM SLIGHT CHANCE ALONG THE COAST TO CHANCE INLAND. OTHERWISE...
EXPECT HIGH TEMPS IN THE LOWER/MID 90S INLAND AND 80S ON THE
BEACHES.

THE POTENTIAL FOR STRATUS/FOG COULD DIMINISH THURSDAY NIGHT.
OTHERWISE...DIURNAL/EVENING CONVECTION SHOULD GRADUALLY DISSIPATE.
DESPITE THE 28/00Z GFS DEPICTION OF PERSISTENT CONVECTION
OVERNIGHT...LOWERED POPS BELOW 15 PERCENT WITH NO MENTION OF
PRECIPITATION OVER LAND AFTER MIDNIGHT.

PER LATEST MODEL TRENDS...FRIDAY SHOULD PROVE TO BE THE MOST
CONVECTIVELY ACTIVE DAY OF THIS FORECAST PERIOD. A TROUGH AT THE
SURFACE AND ALOFT WILL BEGIN TO TAKE SHAPE OVER THE REGION...AND A
PLUME OF DEEP MOISTURE FEATURING PWATS WELL OVER 2 INCHES/1 TO 2
STANDARD DEVIATIONS ABOVE NORMAL WILL SAG INTO THE REGION FROM THE
NORTH. THIS REGIME SHOULD READILY SUPPORT AT LEAST SCATTERED/
NUMEROUS SHOWERS/THUNDERSTORMS FRIDAY AFTERNOON. IN GENERAL...LATEST
GUIDANCE POINTS TO HIGHEST POPS ACROSS INTERIOR/NORTHERN
COUNTIES...THUS INTRODUCED LIKELY POPS THERE FRIDAY AFTERNOON.
HOWEVER...THIS SCENARIO WILL LIKELY CHANGE OVER THE NEXT FEW DAYS.
MEANWHILE...FRIDAY TEMPERATURES ARE TRICKY DUE TO UNCERTAINTY
REGARDING THE TIMING OF CONVECTION INITIATION. THUS...DID NOT MAKE
SIGNIFICANT CHANGES TO ONGOING TEMPERATURES IN THE LOWER/MID 90S
INLAND AND 80S ALONG THE COAST...BUT CONVECTION/ASSOCIATED CLOUD
COVER COULD GREATLY ALTER MIDDAY/AFTERNOON TEMPERATURES.

THE POTENTIAL FOR SEVERE WEATHER/LOCALLY HEAVY RAINFALL APPEARS
LIMITED WITHIN DIURNAL CONVECTION WEDNESDAY AND THURSDAY.
FRIDAY...THE POTENTIAL FOR SEVERE WEATHER SHOULD INCREASE...ALTHOUGH
FORECAST INSTABILITY IS NOT OVERLY IMPRESSIVE. OF GREATER
CONCERN...HIGH PWATS AND WEAK TROPOSPHERIC FLOW COULD PROMOTE
LOCALLY EXCESSIVE RAINFALL BEGINNING FRIDAY. IN PARTICULAR...
IF HEAVY RAIN FALLS ALONG THE COAST DURING ELEVATED HIGH TIDES...
THE POTENTIAL FOR LOCALIZED FLOODING COULD BE ENHANCED.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
AN UNSETTLED REGIME FEATURING ABOVE NORMAL POPS AND BELOW NORMAL
HIGH TEMPERATURES WILL PREVAIL THROUGH THIS PERIOD AS A DEEP TROUGH
OF LOW PRESSURE/AN ASSOCIATED PLUME OF ENHANCED MOISTURE/HIGH PWATS
RESIDES OVER THE REGION. SEVERAL FACTORS REDUCE CONFIDENCE REGARDING
FORECAST DETAILS...MAINLY RELATED TO THE STRENGTH OF THE BERMUDA
HIGH AND THE INTERACTION OF THE ATLANTIC RIDGE WITH THE TROUGH OVER
THE SOUTHEAST. IF THE ATLANTIC RIDGE DOES NOT STRENGTHEN...THE
TROUGH AND DEEPEST MOISTURE REMAIN OVER THE REGION OR EVEN PUSH
SLIGHTLY OFFSHORE AS DEPICTED BY THE 28/00Z OPERATIONAL EUROPEAN. ON
THE OTHER HAND...IF THE BERMUDA HIGH EXPANDS...THE TROUGH AND DEEPER
MOISTURE COULD BE SHUNTED INLAND...SUPPORTING A SUBTLE
WARMING/DRYING TREND ESPECIALLY EARLY NEXT WEEK. DUE TO UNCERTAINTY
REGARDING THE SYNOPTIC SCENARIO AND THE USUAL MESOSCALE UNCERTAINTY
REGARDING CONVECTION EVOLUTION...CONTINUED TO CAP MAXIMUM POPS
AROUND 50 PERCENT THIS WEEKEND INTO EARLY NEXT WEEK. EVENTUALLY...
PERIODS OF HIGHER POPS WILL LIKELY BE REQUIRED FOR SOME OR ALL OF
THE FORECAST AREA.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
VFR CONDITIONS WILL PREVAIL AT THE CHS AND SAV TERMINALS THIS
AFTERNOON AND EARLY TONIGHT. MVFR CONDITIONS ARE LIKELY AT BOTH
TERMINALS LATE TONIGHT INTO EARLY WEDNESDAY MORNING...MAINLY DUE
TO FOG. HAVE MAINTAINED 4SM BR BETWEEN 08Z-13Z AT BOTH TERMINALS.
THERE IS ALSO A LOW TO MODERATE CHANCE OF TEMPO IFR CONDITIONS
OCCURRING BETWEEN 09Z-13Z...WITH THE GREATEST CHANCE OCCURRING AT
THE SAV TERMINAL. VFR CONDITIONS SHOULD QUICKLY RETURN AT BOTH
TERMINALS BETWEEN 13-14Z WEDNESDAY AND PERSIST INTO THE AFTERNOON.

EXTENDED AVIATION OUTLOOK...FLIGHT RESTRICTIONS WILL BE POSSIBLE IN
STRATUS/FOG WEDNESDAY MORNING. A LOW PROBABILITY FOR FLIGHT
RESTRICTIONS EXISTS WITHIN AFTERNOON THUNDERSTORMS WEDNESDAY AND
THURSDAY. THE PROBABILITY FOR THUNDERSTORMS/ASSOCIATED FLIGHT
RESTRICTIONS WILL INCREASE FRIDAY AND SATURDAY.

&&

.MARINE...
THIS AFTERNOON...WINDS/SEAS ARE EXPECTED TO REMAIN WELL BELOW SMALL
CRAFT ADVISORY LEVELS AS LOW PRESSURE PASSES WELL OFFSHORE AND A
SEABREEZE DEVELOPS ALONG THE COAST. IN GENERAL...WINDS WILL BECOME
MORE EASTERLY THIS AFTERNOON AND REMAIN AT OR BELOW 10-15 KTS. SEAS
SHOULD BE NO HIGHER THAN 2-3 FT...HIGHEST BEYOND 20 NM FROM THE
COAST.

TONIGHT...EAST WINDS WILL TIP BACK TO THE NORTHEAST OVERNIGHT WITH
SPEEDS AROUND 5 KT. SEAS WILL AVERAGE 2-3 FT...EXCEPT 1-2 FT OVER
THE GEORGIA NEARSHORE WATERS.

WEDNESDAY THROUGH SUNDAY...ONSHORE WINDS WILL PERSIST WEDNESDAY
THROUGH THURSDAY...WITH SOME ENHANCEMENT OCCURRING DURING
AFTERNOON SEABREEZE CIRCULATIONS. IN GENERAL...WINDS WILL REMAIN
AT OR BELOW 15 KTS WITH SEAS NO HIGHER THAN 2-4 FT...HIGHEST
BEYOND 20 NM. AFTER A TRANSITION THROUGH A WEAK PRESSURE PATTERN
THURSDAY NIGHT AND FRIDAY...WINDS SHOULD BECOME SOUTH/SOUTHWEST BY
THIS WEEKEND...PERHAPS INCREASING TO 15-20 KT IN SOME AREAS WITH
THE AFTERNOON SEABREEZE AND WITH NOCTURNAL SURGES. SEAS SHOULD
REMAIN BETWEEN 2-4 FT NEARSHORE AND 4-5 FT BEYOND 20 NM THIS
WEEKEND. THUNDERSTORMS COULD PRODUCE LOCAL HAZARDS AND COULD
GREATLY ALTER SYNOPTIC WINDS ESPECIALLY LATE WEEK THROUGH THIS
WEEKEND.

&&

.TIDES/COASTAL FLOODING...
CURRENT EXTRATROPICAL SURGE GUIDANCE TAKES TIDE LEVELS NEAR
7.0 FT MLLW IN THE CHARLESTON HARBOR FOR HIGH TIDE THIS
EVENING...WHICH IS THE THRESHOLD FOR SHALLOW COASTAL FLOODING FOR
THE LOWER SOUTH CAROLINA COAST. A COASTAL FLOOD ADVISORY COULD BE
NEEDED FOR PARTS OF THE LOWER SOUTH CAROLINA COAST IF THIS TREND
CONTINUES...BUT THE EVENT LOOKS MARGINAL AT BEST. EVEN IF TIDE
LEVELS DO NOT REACH 7.0 FT MLLW IN THE CHARLESTON HARBOR...SOME
VERY MINOR SALT WATER INUNDATION IS LIKELY TO OCCUR IN SOME OF THE
NORMALLY FLOOD PRONE AREAS OF DOWNTOWN CHARLESTON...ASSUMING
LEVELS SURPASS 6.8 FT MLLW. THERE ARE NO CONCERNS FOR SHALLOW
COASTAL FLOODING ALONG THE GEORGIA COAST WITH THIS EVENING/S HIGH
TIDE CYCLE.

ELEVATED HIGH TIDE LEVELS WILL PREVAIL THROUGH THIS WEEKEND/INTO
EARLY NEXT WEEK DUE TO THE UPCOMING JULY 31 FULL MOON/AUGUST 2
PERIGEE AND PERSISTENT ONSHORE WINDS. EXTRATROPICAL SURGE GUIDANCE
CONTINUES TO FORECAST A SERIES OF SHALLOW SALT WATER FLOODING
EVENTS...ESPECIALLY AROUND THE TIMES OF THE EVENING HIGH TIDES.
EVENING HIGH TIDES COULD ATTAIN COASTAL FLOOD ADVISORY LEVELS ALONG
THE SOUTH CAROLINA COAST WEDNESDAY INTO EARLY NEXT WEEK AND ALONG
THE GEORGIA COAST WEDNESDAY OR THURSDAY THROUGH AT LEAST THIS
WEEKEND. WILL CONTINUE TO HIGHLIGHT THE POTENTIAL FOR SHALLOW SALT
WATER FLOODING/COASTAL FLOOD ADVISORIES WITHIN THE HAZARDOUS WEATHER
OUTLOOK.

&&

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

&&

$$
SYNOPSIS...
NEAR TERM...DPB
SHORT TERM...SPR
LONG TERM...SPR
AVIATION...DPB/SPR
MARINE...DPB/SPR
TIDES/COASTAL FLOODING...



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