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Area Forecast Discussion

975
FXUS62 KCHS 150105
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
905 PM EDT SUN SEP 14 2014

.SYNOPSIS...
A STATIONARY FRONT ACROSS THE AREA THIS EVENING WILL WAVER SOUTH
OVERNIGHT. THE FRONT WILL GRADUALLY DISSIPATE MONDAY. A PRE-FRONTAL
TROUGH WILL MOVE IN TUESDAY....THEN A STRONGER COLD FRONT IS FORECAST
TO PUSH THROUGH THE REGION DURING THE MIDDLE OF THE WEEK. A STRONG
INLAND WEDGE OF HIGH PRESSURE WILL THEN PREVAIL IN WAKE OF THE
FRONT INTO NEXT WEEKEND.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
LATE SUNDAY EVENING...CONVECTION REMAINS FOCUSED ALONG COMPLEX
OUTFLOW BOUNDARIES IN THE VICINITY OF A STATIONARY FRONT WHICH
BISECTS THE FORECAST AREA. SLOW/ERRATIC CONVECTION PROPAGATION
WILL CONTINUE TO SUPPORT LOCALLY HEAVY RAINFALL...ESPECIALLY FROM
BULLOCH COUNTY EAST TO COASTAL COLLETON COUNTY. MAINTAINED THE
ONGOING FLASH FLOOD WATCH FOR THIS CORRIDOR. PER RECENT/ EXPECTED
RADAR TRENDS...DISCONTINUED THE PORTION OF THE WATCH WHICH
INCLUDED SAVANNAH AND CHARLESTON.

IN THE NEAR TERM...CATEGORICAL/LIKELY POPS REMAIN IN EFFECT CLOSE
TO THE STATIONARY FRONT...TAPERED THROUGH CHANCE TO SLIGHT CHANCE
NORTH AND SOUTH. EXPECT A GRADUAL DIMINISHING TREND IN CONVECTION
COVERAGE/INTENSITY OVERNIGHT...BUT AT LEAST SLIGHT CHANCE/CHANCE
POPS WILL PERSIST MOST AREAS THROUGH MOST/ALL OF THE NIGHT. LOCALLY
GREATER POPS COULD STILL BE REQUIRED OVERNIGHT...ESPECIALLY TOWARD
THE COAST...WILL CONTINUE TO ASSESS.

ALSO OF NOTE...LOWERING STRATUS COULD SUPPORT FOG ALONG/NORTH OF THE
FRONT OVERNIGHT.

LOWS LIKELY TO BE MODULATED BY THE RAIN BUT SHOULD GENERALLY
RANGE FROM THE UPPER 60S NORTH AND WEST TO LOWER TO MID 70S SOUTH
AND EAST...POSSIBLY SOME UPPER 70S ALONG THE GA COAST.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/...
MONDAY...THE LARGE SCALE PATTERN INDICATES THAT THE MID-LATITUDE
WESTERLIES WILL START TO IMPINGE ON THE FLAT RIDGING ALOFT OVER THE
LOCAL REGION...AS A SHORT WAVE TROUGH DROPS EAST/SE INTO THE GREAT
LAKES AND OHIO VALLEY. SIMULTANEOUSLY AT THE SURFACE THE INITIAL
COLD FRONT BECOMES LESS-DEFINED AND ESSENTIALLY WASHES OUT OVER OR
NEARBY AS THE SEA BREEZE CIRCULATION OVERSPREADS THE AREA AND
PROGRESSES INLAND FROM EAST TO WEST THROUGH THE DAY. MOISTURE IS
STILL PLENTIFUL WITH PWATS BETWEEN 1 AND 2 STANDARD DEVIATIONS ABOVE
NORMAL...PLUS THERE IS MODEST THERMODYNAMICS AND A UPPER JET STREAK
THAT SUGGESTS WE SHOULD EXPERIENCE SCATTERED TO NUMEROUS SHOWERS AND
T-STORMS AREAWIDE. COVERAGE DURING THE MORNING WILL BE GREATEST NEAR
THE REMNANT FRONT AND WHERE THE BEST LOW LEVEL CONVERGENCE IS
OBSERVED FROM CHARLESTON COUNTY TO NEAR THE SAVANNAH AREA. COVERAGE
EXPANDS INLAND DURING THE AFTERNOON AS MESO-SCALE BOUNDARY
INTERACTIONS OCCUR...WITH AT LEAST 50-60 PERCENT PROBABILITIES
INLAND FROM US-17. STORM MOTION IN THE ATMOSPHERE IS STILL
LIMITED...SO LOCALLY HEAVY RAINFALL IS CERTAINLY POSSIBLE. TEMPS
WILL TOP OUT IN THE 85-90 DEGREE RANGE PRIOR TO THE ONSET OF THE
CONVECTIVE RAINS. SCATTERED SHOWERS/TSTMS WILL BE ONGOING DURING THE
EARLY EVENING HOURS GIVEN BOUNDARY MERGERS/INTERACTIONS AND
SUFFICIENT MOISTURE. ACTIVITY WILL GRADUALLY WIND DOWN AS THE NIGHT
PROGRESSES...BUT WE/LL STILL HOLD ONTO SLIGHT CHANCE/CHANCE POPS
EVEN AFTER MIDNIGHT. STRATUS BUILD-DOWN AND CONDENSATION PRESSURE
DEFICITS UNDER 10-20 MB COULD LEAD TO SOME LATE NIGHT FOG CONCERNS.
TEMPS WILL AVERAGE A FEW DEGREES ABOVE NORMAL.

TUESDAY...A BROAD LARGE SCALE TROUGH WILL DOMINANT THE SCENARIO
ALOFT...WHILE A NE-SW ALIGNED SURFACE TROUGH APPROACHES FROM THE
WEST AND NW. EMBEDDED WITHIN THE TROUGH WE FIND A WEAKENING MID
LEVEL IMPULSE THAT ARRIVES LATE IN THE DAY. THE ADDITIONAL FORCING
ASSOCIATED WITH WITH THIS FEATURE PLUS THE RIGHT ENTRANCE REGION TO
THE NEARBY UPPER JET WILL TRIGGER WILL HAVE AMPLE MOISTURE TO WORK
WITH...THUS TRIGGERING SCATTERED TO NUMEROUS POPS. THERMODYNAMICS
ARE MORE FAVORABLE THAN RECENT DAYS...AND WITH A LITTLE MORE FLOW
ALOFT AND SEVERAL MESO-SCALE BOUNDARIES WE ANTICIPATE THAT A FEW OF
THE STORMS COULD BECOME STRONG OR EVEN MARGINALLY SEVERE. HOWEVER
THE RISK FOR ANY ORGANIZED SEVERE WEATHER IS GIVEN LIMITED DEEP
LAYER SHEAR AND ONLY MODEST INSTABILITY AT BEST. SOME COMPRESSIONAL
HEATING ADVANCE OF THE SURFACE TROUGH AND A DEEP DOWNSLOPE FETCH OFF
THE APPALACHIANS WILL BE ENOUGH TO NEGATE CONSIDERABLE CLOUD
COVER...AND SUPPORTS MAX TEMPS IN THE UPPER 80S TO NEAR 90.

WEDNESDAY...THE PRE-FRONTAL TROUGH USHERS IN THE APPROACH OF OUR
NEXT COLD FRONT...WHILE BROAD TROUGHINESS PREVAILS ALOFT. WHILE SOME
DRIER AIR DOES ARRIVE AS HIGH PRESSURE BUILDS SOUTH FROM THE
MID-ATLANTIC STATES AND OHIO VALLEY BY LATE IN THE DAY...THERE IS
STILL ADEQUATE MOISTURE AND FORCING UPSTAIRS FROM THE RIGHT REAR QUAD
OF THE UPPER JET AND ANOTHER SHORT WAVE TO ALLOW FOR CHANCE POPS.
HIGHEST PROBABILITIES WILL BE OVER COASTAL SE GA WHERE THE BEST LOW
LEVEL FORCING WILL OCCUR IN SYNC TO THE PROXIMITY TO SURFACE TROUGH
AND DEEPER MOISTURE PROFILES. THE PUSH OF THE NOTICEABLY COOLER AIR
MASS ISN/T UNTIL WEDNESDAY NIGHT...SO MID AND UPPER 80S WILL PREVAIL
PRIOR TO THEN.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
A STRONG WEDGE OF SURFACE HIGH PRESSURE WILL PREVAIL INLAND FOR
MUCH OF THE EXTENDED PERIOD...WHILE WAVES OF LOW PRESSURE DEVELOP
ALONG A LINGERING FRONT OFFSHORE THROUGH LATE WEEK. THE AXIS OF
THE UPPER TROUGH WILL REMAIN ALONG THE EAST COAST THROUGH
FRIDAY...THEN WEAKEN AND BECOME MUDDLED OVER THE WEEKEND. THE
BEST RAIN CHANCES WILL LIKELY BECOME INCREASINGLY CONFINED TO THE
IMMEDIATE COASTLINE AND MARINE ZONES WITHIN THIS PATTERN...AS
DEEPER MOISTURE AND FORCING REMAIN OFFSHORE ALONG THE FRONTAL ZONE
AND ASSOCIATED WAVES OF LOW PRESSURE. SOLID NORTHEAST FLOW...AS
WELL AS LOWER HEIGHTS ALOFT...WILL SUPPORT NOTABLY COOLER
CONDITIONS THROUGH THE PERIOD. HIGH TEMPERATURES WILL ONLY REACH
THE LOW 80S EACH AFTERNOON...WHILE LOW TEMPERATURES FALL INTO THE
LOW TO MID 60S AT LEAST THROUGH FRIDAY NIGHT...BEFORE POSSIBLY
MODERATING A FEW DEGREES SATURDAY AND SUNDAY NIGHTS.

&&

.AVIATION /01Z MONDAY THROUGH FRIDAY/...
AT KCHS...MVFR/IFR CEILINGS WILL PREVAIL THROUGH MONDAY. A PERIOD
OF LIFR CEILINGS ARE POSSIBLE LATE TONIGHT INTO MONDAY MORNING. AT
KSAV...VFR CONDITIONS SHOULD GIVE WAY TO MVFR/IFR CEILINGS LATER
TONIGHT...BUT TIMING REMAINS UNCERTAIN. ONCE SUB-VFR CEILINGS
DEVELOP THESE CONDITIONS WILL PREVAIL THROUGH MOST OF MONDAY WITH
ONLY BRIEF IMPROVEMENT TO VFR POSSIBLE MONDAY AFTERNOON. AT BOTH
SITES...00Z TAFS INDICATE VCSH UNTIL LATER TONIGHT. THEN...SHOWERS/
THUNDERSTORMS ARE LIKELY AT BOTH SITES ESPECIALLY MONDAY
AFTERNOON. HOWEVER...DUE TO UNCERTAINTY REGARDING WORST CONDITIONS
OPTED FOR PREVAILING -SHRA AND VCTS/CBS AT BOTH TERMINALS MONDAY
AFTERNOON.

EXTENDED AVIATION OUTLOOK...PERIODIC FLIGHT RESTRICTIONS POSSIBLE IN
OCCASIONAL SHRA AND/OR TSRA...AND MAINLY DURING THE AFTERNOON AND
EARLY NIGHT TIME PERIODS...AND IN LATE NIGHT/MORNING LOW STRATUS
AND/OR LIGHT FOG THROUGH THE WEEK.

&&

.MARINE...
TONIGHT...A STATIONARY FRONT WILL WAVER SLIGHTLY BETWEEN SC AND GA WATERS.
NORTH OF THE FRONT...NE WINDS 5-15 KT WILL PREVAIL...WHILE S/SE
WINDS AT SIMILAR SPEEDS WILL PREVAIL SOUTH OF THE FRONT. CLOSE TO
THE FRONT...VARIABLE WINDS WILL REMAIN LESS THAN 10 KT...AND
CONDITIONS WILL BE FAVORABLE FOR ISOLATED WATERSPOUTS. OUTSIDE ANY
THUNDERSTORMS...SEAS 1-3 FT WILL PREVAIL OVERNIGHT.

MONDAY THROUGH TUESDAY...A WEAK PRESSURE PATTERN WILL EXIST ACROSS
THE MARINE AREA DURING THIS TIME AS THE COLD FRONT BECOMES DIFFUSE
MONDAY AND DISSIPATES...BEFORE A PRE-FRONTAL TROUGH HEADS OUR WAY
TUESDAY. OUTSIDE OF ANY WATERSPOUTS AND ISOLATED TO SCATTERED
CONVECTION WINDS AND SEAS WILL BE NO MORE THAN 10 OR 12 KT AND 2 OR
3 FT...RESPECTIVELY. CONDITIONS APPEAR TO FAVOR POSSIBLE WATERSPOUTS
MONDAY AND TUESDAY MORNINGS...GIVEN A LIGHT WIND REGIME...ADEQUATE
INSTABILITY AND HIGH MOISTURE. WE/LL DEFER TO LATER SHIFTS TO
DETERMINE WHERE TO ISSUE ANY MARINE WEATHER STATEMENTS PENDING WHERE
THE BETTER DEFINED CONVERGENT BOUNDARIES FORM.

WEDNESDAY...A TRANSITION DAY ACROSS THE COASTAL WATERS AS A BACK
DOOR COLD FRONT ARRIVES FROM THE NORTH. THE PRESSURE GRADIENT SLOWLY
TIGHTENS...ESPECIALLY WEDNESDAY NIGHT...SO WINDS AND SEAS WILL
REMAIN WELL BELOW ANY SMALL CRAFT CRITERIA. HOWEVER...SOME LONGER
PERIOD SWELL FROM DISTANT TC EDOUARD WILL BEGIN TO IMPACT THE
COASTAL WATERS MAKING FOR SOME PROBLEMS IN NAVIGATION.

THURSDAY THROUGH SATURDAY...CONDITIONS WILL HAVE DETERIORATED AS A
SOLID NE PINCHING EVENT UNFOLDS BETWEEN THE STALLED FRONT TO OUR
SOUTH AND A STRENGTHENING WEDGE INLAND. THE COMBINATION OF THE
TIGHTER GRADIENT AND A MIX OF LINGERING SWELLS FROM FAR OFF TC
EDOUARD AND THE LONG ONSHORE FETCH SUPPORTS THE POTENTIAL FOR SMALL
CRAFT ADVISORIES.

RIP CURRENTS...LONG PERIOD SWELL FROM TC EDOUARD WILL ARRIVE AT THE
BEACHES LATER WEDNESDAY INTO THURSDAY...BEFORE STRONGER ONSHORE
WINDS IMPACT THE COASTAL SECTIONS FRIDAY THROUGH SUNDAY. THESE
CONDITIONS WILL LIKELY LEAD TO AN ENHANCED RISK OF RIP CURRENTS
DURING THE SECOND HALF OF THE WEEK. SINCE THIS IS MY FIRST GOOD LOOK
AT THE SITUATION I/LL HOLD OFF ADDING TO THE HAZARDOUS WEATHER
OUTLOOK AT THIS STAGE PENDING MORE CONTINUITY.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...FLASH FLOOD WATCH UNTIL MIDNIGHT EDT TONIGHT FOR GAZ099>101-
     114-115.
SC...FLASH FLOOD WATCH UNTIL MIDNIGHT EDT TONIGHT FOR SCZ047>049-
     051.
MARINE...NONE.

&&

$$

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






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