440
FXUS62 KCHS 272020
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
420 PM EDT WED OCT 27 2021
SYNOPSIS
A LOW PRESSURE SYSTEM WILL IMPACT THE REGION THURSDAY THROUGH
THE END OF THE WEEK. HIGH PRESSURE WILL RETURN EARLY NEXT WEEK.
NEAR TERM /UNTIL 6 AM THURSDAY MORNING/
THE MID-LEVELS WILL CONSIST OF A NARROW RIDGE, WITH ITS AXIS
STRETCHING FROM APPROXIMATELY THE GREAT LAKES REGION DOWN INTO
THE SOUTHEAST THIS EVENING. THE RIDGE WILL GRADUALLY SHIFT TO
THE ENE WITH TIME. AT THE SURFACE, WEAK HIGH PRESSURE WILL MOVE
OFFSHORE THIS EVENING AND OVERNIGHT. MEANWHILE, A WARM FRONT
WILL APPROACH FROM THE SOUTHWEST OVERNIGHT. THOUGH, THE FRONT IS
NOT EXPECTED TO REACH OUR AREA BY DAYBREAK THURSDAY. THE HIGH
WILL CONTINUE TO BRING OUR AREA DRY CONDITIONS FOR MOST OF THE
NIGHT. HOWEVER, MOISTURE WILL BE INCREASING ACROSS OUR AREA, IN
ADVANCE OF THE FRONT. SOME OF THE MODELS INDICATE A FEW SHOWERS
COULD REACH THE ALTAMAHA RIVER AND VICINITY JUST BEFORE DAYBREAK
THURSDAY. THEREFORE, WE HAVE SLIGHT CHANCE POPS THERE.
EVERYWHERE ELSE IS EXPECTED TO REMAIN DRY. OTHERWISE, HIGH
CLOUDS WILL GRADUALLY INCREASE ACROSS OUR AREA OVERNIGHT, MOST
NOTABLY ACROSS OUR GA COUNTIES. TEMPERATURES WILL GENERALLY BE
IN THE UPPER 40S FAR INLAND. BUT THEY'LL BE WARMER (GENERALLY
THE 50S) ALONG THE IMMEDIATE COAST DUE TO THE WINDS EVENTUALLY
COMING OFF THE WARMER OCEAN, AND CLOSER TO THE ALTAMAHA RIVER
AND VICINITY WHERE THERE WILL BE MORE CLOUDS.
SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/
THURSDAY: AN ANOMALOUSLY DEEP MID LVL TROUGH/LOW AND ASSOCIATED SFC
REFLECTION WILL TRACK ACROSS THE MISSISSIPPI RIVER VALLEY TO THE
TENNESSEE AND OHIO RIVER VALLEYS DURING THE AFTERNOON/EVENING. AS
THIS OCCURS, A WARM FRONT WILL SHIFT NORTH ACROSS THE LOCAL AREA BY
LATE DAY, FOLLOWED BY A COLD FRONT SWEEPING THROUGH THE REGION
OVERNIGHT. WITHIN THE WARM SECTOR AHEAD OF THE COLD FRONT, A 40-50
KT LOW-LVL JET WILL HELP ADVECT DEEP MOISTURE INTO THE LOCAL AREA
WITH PWATS AROUND 2 INCHES DURING THE AFTERNOON INTO EARLY EVENING.
INSTABILITY SHOULD REMAIN MARGINAL GIVEN A FAIR AMOUNT OF CLOUD
COVER ASSOCIATED WITH ISENTROPIC LIFT AND ESPECIALLY IF ONGOING
CONVECTION FROM THE PREVIOUS NIGHT PROLONGS SOME STABILIZATION
ACROSS THE LOCAL AREA DURING THE DAY. HOWEVER, LATEST GUIDANCE DOES
SUGGEST SBCAPE INCREASING TO AROUND 1000-1500 J/KG WITHIN THE WARM-
SECTOR LATE AFTERNOON INTO EARLY EVENING WHEN IMPRESSIVE
FORCING/SHEAR ALSO COINCIDE ACROSS THE LOCAL AREA. BULK SHEAR (0-
6KM) AROUND 50-55 KT AND HELICITY (0-1 KM) BETWEEN 300-500 M2/S2 IN
COMBINATION WITH FORCING ASSOCIATED WITH AN ADVANCING H5 SHORTWAVE,
UPPER LVL DIVERGENCE WITH AN H25 JET, AND THE APPROACHING COLD FRONT
SUGGEST THE POTENTIAL FOR SOME THUNDERSTORMS TO BE STRONG AND/OR
SEVERE WITH DAMAGING STRAIGHT LINE WINDS AND PERHAPS AN ISOLATED
TORNADO OR TWO ACROSS PARTS OF SOUTHEAST GEORGIA AND SOUTHEAST SOUTH
CAROLINA, ALTHOUGH THE BEST POTENTIAL FOR A TORNADO APPEARS TO BE
ACROSS THE QUAD COUNTY AREA WHERE SFC WINDS ARE SLIGHTLY MORE BACKED
CLOSER TO A FRONT DURING EARLY EVENING HOURS. GIVEN COLD TEMPS (-20
C) ASSOCIATED WITH THE LARGE H5 LOW CENTERED FAR NORTHWEST OF THE
REGION, POOR MID-LVL LAPSE RATES ACROSS THE LOCAL AREA, AND EXPECTED
CONVECTIVE MODE (LINEAR OR CLUSTERS OF THUNDERSTORMS), LARGE HAIL
WILL BE A CONSIDERABLY LESS THREAT. THE PROGRESSIVE NATURE OF THE
EVENT SHOULD ALSO LIMIT OVERALL FLOODING POTENTIAL, BUT ISOLATED
POCKETS OF HEAVY RAINFALL COULD PRODUCE MINOR FLOODING ALONG LOW-
LYING AREAS AND ROADWAYS.
THE GREATEST POTENTIAL FOR SEVERE WEATHER SHOULD OCCUR ALONG AND
EAST OF THE I-95 CORRIDOR (CURRENTLY OUTLOOKED WITH A SLIGHT RISK BY
SPC) LATE AFTERNOON/EVENING (4-10 PM), STARTING ACROSS SOUTHEAST
GEORGIA FIRST, THEN ADVANCING INTO SOUTHEAST SOUTH CAROLINA. FURTHER
INLAND, A MARGINAL RISK FOR SEVERE WEATHER REMAINS ACROSS THE AREA
AS WELL, BUT THE POTENTIAL SHOULD REMAIN SOMEWHAT MORE LIMITED GIVEN
LESS INSTABILITY AND THE POTENTIAL OF ONGOING CONVECTION FROM THE
PREVIOUS NIGHT STABILIZING THE ATMOSPHERE DURING THE DAY.
OUTSIDE THE POTENTIAL OF STRONG/SEVERE THUNDERSTORMS, ATMOSPHERIC
CONDITIONS WILL STILL FAVOR BREEZY WINDS ACROSS THE REGION MID-LATE
AFTERNOON THROUGH THE EVENING. HIGHS SHOULD PEAK IN THE LOW/MID 70S,
WARMEST ALONG THE COAST. CHANCES OF PRECIP WILL DECREASE WITH COLD
FROPA OVERNIGHT, BUT SOME LINGERING SHOWERS ARE POSSIBLE LATE NIGHT
GIVEN LINGERING MOISTURE AND THE LARGE MID-UPPER LVL LOW POSITIONED
TO THE WEST-NORTHWEST. LOWS SHOULD DIP INTO THE MID 50S INLAND TO
UPPER 50S/LOWER 60S AT THE BEACHES.
FRIDAY AND SATURDAY: AN EXPANSIVE MID-UPPER LVL LOW COVERING MUCH OF
THE EAST CONUS WILL SLOWLY SHIFT TOWARD THE EASTERN SEABOARD THIS
WEEKEND. A FEW SHOWERS WILL BE POSSIBLE WITH LINGERING MOISTURE AND
COOLER MID-LVL TEMPS ON FRIDAY, BUT MOISTURE IN THE MID-UPPER LVLS
WILL LIKELY EXIT THE AREA SATURDAY, FAVORING DRIER CONDITIONS. TEMPS
WILL BE COOLER THAN NORMAL, WITH HIGHS GENERALLY RANGING IN THE MID
60S INLAND TO UPPER 60S/AROUND 70 NEAR THE COAST EACH DAY. LOW TEMPS
SHOULD RANGE IN THE UPPER 40S INLAND TO MID-UPPER 50S CLOSER TO THE
COAST FRIDAY NIGHT.
LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/
MODELS ARE IN GOOD AGREEMENT THAT A LARGE MID-UPPER LVL LOW AS WELL
AS SFC LOW PRESSURE WILL SLOWLY ADVANCE OFF THE MID-ATLANTIC AND
NORTHEAST COASTS LATE WEEKEND AND INTO EARLY NEXT WEEK, WHILE HIGH
PRESSURE BUILDS INTO THE LOCAL AREA FROM THE WEST, EVENTUALLY
BECOMING CENTERED ACROSS THE SOUTHEAST UNITED STATES EARLY NEXT
WEEK. DRIER AIR AND A LACK OF SIGNIFICANT FORCING MECHANISMS WILL
SUPPORT A RAIN-FREE FORECAST THROUGH THE MIDDLE OF NEXT WEEK. TEMPS
THROUGH THE PERIOD WILL MOSTLY BE BELOW NORMAL, ALTHOUGH WILL BE
MODERATING WITH TIME EARLY NEXT WEEK. IN GENERAL HIGHS SHOULD PEAK
IN THE LOWER 70S WHILE A FEW MIDDLE 70S ARE POSSIBLE ACROSS
SOUTHEAST GEORGIA. LOWS SHOULD GENERALLY RANGE IN THE MID-UPPER 40S
WELL INLAND TO UPPER 50S/AROUND 60 NEAR THE COAST.
AVIATION /20Z WEDNESDAY THROUGH MONDAY/
18Z TAFS:
VFR THROUGH TONIGHT. A STORM SYSTEM WILL BRING IMPACTS TO THE
AREA TOWARDS THE END OF THE TAF TIME PERIOD, FIRST TO SAV, THEN
TO CHS/JZI. FOR CHS/JZI, WE INTRODUCED MVFR VIA A PROB30 AFTER
15Z. FOR SAV, WE HAVE MVFR VIA A PROB30 AFTER 13Z. WE THEN, HAVE
PREVAILING IMPACTS AFTER 16Z ALONG WITH GUSTY WINDS. THOUGH,
MORE ADJUSTMENTS TO THE TIMING/IMPACTS ARE EXPECTED.
EXTENDED AVIATION OUTLOOK: A STORM SYSTEM WILL BRING FLIGHT
RESTRICTIONS WITHIN SHOWERS/THUNDERSTORMS AND GUSTY WINDS AT
SAV/CHS/JZI TERMINALS ON THURSDAY, ESPECIALLY DURING THE AFTERNOON
INTO EARLY EVENING HOURS. GUSTY WINDS SHOULD PERSIST FRIDAY, BUT
CONDITIONS ARE EXPECTED TO BE VFR DURING THE WEEKEND AND INTO EARLY
NEXT WEEK AT ALL TERMINALS.
MARINE
TONIGHT: WEAK HIGH PRESSURE WILL MOVE OFFSHORE THIS EVENING AND
OVERNIGHT. MEANWHILE, A WARM FRONT WILL APPROACH FROM THE
SOUTHWEST OVERNIGHT. THOUGH, THE FRONT IS NOT EXPECTED TO REACH
OUR AREA BY DAYBREAK THURSDAY. THESE SYNOPTIC FEATURES WILL
CAUSE WINDS TO BE LIGHT AND VARIABLE THIS EVENING, THEN SHIFTING
TO THE ESE AND INCREASING TO 5-10 KT BY DAYBREAK THURSDAY. SEAS
WILL BE 1-2 FT WITHIN 20 NM AND 2-3 FT FOR THE GA WATERS BEYOND
20 NM.
THURSDAY THROUGH MONDAY: CONDITIONS WILL DETERIORATE ACROSS COASTAL
WATERS THURSDAY AS A STRONG LOW PRESSURE SYSTEM TRACKS ACROSS THE
REGION. OUTSIDE SHOWERS AND THUNDERSTORMS, SOME OF WHICH COULD BE
SEVERE WITH DAMAGING WINDS AND WATERSPOUTS THURSDAY AFTERNOON INTO
THURSDAY EVENING, AN ENHANCED PRESSURE GRADIENT WILL SUPPORT SMALL
CRAFT ADVISORIES, STARTING ACROSS GEORGIA WATERS THURSDAY AFTERNOON,
THEN FOR THE REMAINDER OF COASTAL WATERS OUTSIDE THE CHS HARBOR LATE
THURSDAY AFTERNOON. THERE IS A POTENTIAL FOR SMALL CRAFT ADVISORY
LEVEL CONDITIONS IN THE CHS HARBOR THURSDAY NIGHT, BEFORE CONDITIONS
SLOWLY IMPROVE HEADING INTO DAYBREAK FRIDAY. ELEVATED WINDS/SEAS
WILL THEN PERSIST ACROSS ALL OTHER WATERS FOR MUCH OF FRIDAY BEFORE
ADDITIONAL IMPROVEMENT OCCURS FRIDAY NIGHT INTO SATURDAY, WHEN THE
LAST OF SMALL CRAFT ADVISORIES COMES TO AN END. CONDITIONS ARE THEN
EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY LEVELS SUNDAY AND
MONDAY AS HIGH PRESSURE EXPANDS ACROSS THE AREA.
CHS WATCHES/WARNINGS/ADVISORIES
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 5 PM THURSDAY TO 8 PM EDT FRIDAY FOR
AMZ352.
SMALL CRAFT ADVISORY FROM 2 PM THURSDAY TO 8 AM EDT SATURDAY
FOR AMZ374.
SMALL CRAFT ADVISORY FROM 5 PM THURSDAY TO 8 AM EDT SATURDAY
FOR AMZ350.
SMALL CRAFT ADVISORY FROM 2 PM THURSDAY TO 8 PM EDT FRIDAY FOR
AMZ354.
NEAR TERM...
SHORT TERM...
LONG TERM...
AVIATION...
MARINE...
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