Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 181447
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1047 AM EDT SAT APR 18 2015

.SYNOPSIS...
A WEAK PRESSURE PATTERN WILL BLANKET THE REGION TODAY. A WARM
FRONT WILL DEVELOP AND LIFT NORTH OF THE AREA TONIGHT. AN UPPER
LEVEL DISTURBANCE WILL MOVE THROUGH ON SUNDAY...THEN A COLD FRONT
WILL CROSS THE AREA MONDAY NIGHT. HIGH PRESSURE WILL PREVAIL
TUESDAY THROUGH THURSDAY...THEN A COLD FRONT WILL SWEEP THROUGH
THURSDAY NIGHT OR FRIDAY. ANOTHER STORM SYSTEM MAY AFFECT THE
SOUTHEAST UNITED STATES NEXT WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
LATE THIS MORNING...A BROKEN BAND OF SHOWERS CONTINUES TO WORK ITS
WAY NORTHEAST OF THE SAVANNAH RIVER AND WILL IMPACT MUCH OF
SOUTHEAST SOUTH CAROLINA OVER THE NEXT FEW HOURS. THIS INCLUDES
COASTAL LOCATIONS FROM AROUND EDISTO TO FOLLY BEACH AND EVENTUALLY
TOWARDS SULLIVANS ISLAND AND ISLE OF PALMS. THIS AREA OF RAIN
LOOKS TO BE FORCED MAINLY BY SUBTLE EMBEDDED SHORTWAVE ENERGY
ALOFT THAT WILL FINALLY PUSH EAST OF THE AREA THIS AFTERNOON.
SHORTWAVE RIDGING WILL BRIEFLY BUILD IN THROUGH THE EVENING AS
WELL. FOR THE AFTERNOON...THE RATHER DIFFUSE AND ILL DEFINED
SURFACE PATTERN WILL NOT PROVIDE ANY SIGNIFICANT FEATURES TO HANG
OUR HATS ON. INSTEAD...IT APPEARS THE BEST CHANCES FOR
PRECIPITATION WILL OCCUR IN AREAS THAT SEE SOME SCATTERING OF THE
OVERCAST AND PERIODS OF INSOLATION. THE BEST CHANCE FOR THIS TO
OCCUR WILL BE SOUTHEAST GEORGIA...AND THAT IS WHERE THE HIGHEST
CHANCE POPS ARE FOR THE AFTERNOON. EVEN STILL...IT LOOKS LIKE
MAINLY JUST SHOWERS WITH ONLY A SLIGHT CHANCE FOR THUNDERSTORMS.
THE MID LEVELS ARE QUITE WARM AND REGARDLESS OF THE SURFACE
HEATING THE POTENTIAL FOR SURFACE DESTABILIZATION ISN/T GREAT. AS
IS EXPECTED...TEMPERATURES ARE QUITE TRICKY TODAY AND WILL LARGELY
BE DETERMINED BY BREAKS IN THE CLOUDS AND BRIEF PERIODS OF SUN.
THE INHERITED HIGH TEMPERATURE FORECAST STILL LOOKS GOOD AND NO
CHANGES WERE MADE.

TONIGHT...A DEVELOPING WARM FRONT WITH SOME CLASSIC LOOKING MODEL
FEATURES TAKES SHAPE AND SHOWERY WEATHER WILL REDEVELOP OVERNIGHT
AS HIGHER PWATS SHIFT IN FROM THE GULF AND MID AND UPPER FLOW
BACKS SIGNIFICANTLY TO OUR W AS AN AMPLIFIED UPPER TROUGH EJECTS
INTO THE PLAINS STATES. POPS ARE TRICKY GIVEN TIMING UNCERTAINTIES
AND VARYING MODEL QPF DEPICTIONS BUT THE HIGHEST RAIN CHANCES WILL
OCCUR AFTER MIDNIGHT AND ESPECIALLY NEARING DAYBREAK ON SUNDAY.
MID LEVEL INSTABILITY ALSO INCREASES LATE AND THERE COULD BE A FEW
TSTMS THAT DEVELOP ACROSS SE GEORGIA LATE. VERY WARM AND MOIST
CONDITIONS OVERNIGHT MAY LEAD TO SOME FOG FORMATION BUT MORE
DEFINITELY VERY LOW STRATUS CLOUDS.

&&

.SHORT TERM /SUNDAY THROUGH TUESDAY/...
A LONGWAVE TROUGH OVER THE CENTRAL UNITED STATES WILL DEEPEN AS IT
SHIFTS TO THE EAST ON SUNDAY...EJECTING SEVERAL PRONOUNCED
SHORTWAVES INTO THE LOCAL AREA. A WARM FRONT WILL BE LIFTING NORTH
DURING THE MORNING...WITH DEEPENING AND STRENGTHENING SOUTHERLY FLOW
ADVECTING PWATS IN EXCESS OF 1.90" INTO SOUTHEAST GA/SC. IN THE
MORNING THE PRECIP WILL BE PRIMARILY DRIVEN BY OVERRUNNING AS WARM
CONVEYOR BELT MOISTURE PUSHES ACROSS THE HIGH PRESSURE WEDGE OVER
INLAND SC. LATER IN THE DAY THE MODE WILL SWITCH TO A MORE
CONVECTIVE REGIME AS THE ENTIRE FORECAST AREA RESIDES IN THE WARM
SECTOR AND MODERATE SURFACE-BASED INSTABILITY /1000-1500 J/KG CAPE/
DEVELOPS. GIVEN THE EXTENSIVE CLOUD COVER AND WEAK LAPSE RATES...
SEVERE WEATHER DOES NOT LOOK LIKE A SIGNIFICANT CONCERN ON SUNDAY.
HOWEVER WE MAINTAINED CATEGORICAL POPS FOR THE DAY...WITH POPS
TRENDING DOWN FROM WEST TO EAST SUNDAY NIGHT AS THE BEST DYNAMICAL
FORCING SHIFTS EAST.

MONDAY LOOKS INTERESTING...MAINLY IN REGARD TO THUNDERSTORM
POTENTIAL. THE LONGWAVE TROUGH AXIS REMAINS TO OUR WEST WITH ANOTHER
SERIES OF WEAK SHORTWAVES LIFTING NORTHEAST INTO THE AREA. THE MAIN
CHANGE FROM SUNDAY WILL BE SIGNIFICANTLY DRIER AIR MOVING IN BETWEEN
400 AND 850 MB. THIS MID-LEVEL DRY ADVECTION WILL ALLOW FOR
PRODIGIOUS BREAKS IN THE CLOUDS...HELPING PUSH TEMPS INTO THE MIDDLE
80S. DESPITE THE MID-LEVEL DRY AIR...THE BOUNDARY LAYER WILL REMAIN
QUITE MOIST DUE TO CONTINUED SOUTHERLY FLOW. WITH SFC DEWPOINTS
REMAINING IN THE MIDDLE 60S...SURFACE-BASED CAPES ARE EXPECTED TO
INCREASE TO AT LEAST 1500-2000 J/KG DURING THE AFTERNOON WITH LIFTED
INDICES RANGING FROM -6 TO -9C. LOW AND MID-LEVEL LAPSE RATES ARE
ALSO PRETTY IMPRESSIVE AND 0-6 KM BULK SHEAR INCREASES TO 40-50 KT
DURING THE AFTERNOON. THE LATEST MODEL CONSENSUS HAS THE MAIN COLD
FRONT MOVING THROUGH MONDAY EVENING THOUGH A PRE-FRONTAL TROUGH WILL
LIKELY TRIGGER INITIAL CONVECTION DURING THE DAY. ALTHOUGH SHEAR
VALUES WILL BE QUITE HIGH...THE UNIDIRECTIONAL NATURE OF THE WIND
FIELDS SUGGEST THE POTENTIAL FOR MULTI-CELL THUNDERSTORMS THOUGH
SOME SUPERCELLS CANNOT BE RULED OUT. THE ADVENT OF THE DRY AIR ALOFT
WILL YIELD PRIMARILY A DAMAGING WIND THREAT THOUGH THE LAPSE RATES
WILL ALSO SUPPORT SOME HAIL POTENTIAL. IT IS NOT SURPRISING THAT THE
LATEST DAY 3 OUTLOOK FROM THE STORM PREDICTION CENTER PLACES OUR
ENTIRE FORECAST AREA IN THE SLIGHT RISK. WE PLAN TO INCLUDE MENTION
OF SEVERE WEATHER POTENTIAL IN OUR LOCAL HAZARDOUS WEATHER OUTLOOK.

THE FRONT SHOULD BE OFFSHORE BY LATE MONDAY NIGHT WITH MUCH DRIER
LOW-LEVEL AIR FILTERING IN. ON TUESDAY WE EXPECT MOSTLY SUNNY SKIES
AND DEWPOINTS DROPPING INTO THE LOW/MID 50S. A DOWNSLOPE WIND
COMPONENT WILL HELP OFFSET THE COLD AIR ADVECTION AND PRODUCE HIGH
TEMPS OF 79-82F.

&&

.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
A RELATIVELY DRY AND SEASONABLE PATTERN WILL BE IN PLACE TUESDAY
NIGHT THROUGH THURSDAY WITH ZONAL FLOW ALOFT AND WEAK HIGH PRESSURE
AT THE SURFACE. HIGHS WILL CLIMB INTO THE LOWER 80S WITH LOWS IN THE
50S/60S. A WEAK COLD FRONT WILL DROP THROUGH THURSDAY NIGHT OR
FRIDAY...POTENTIALLY PRODUCING SCATTERED SHOWERS. THEN SATURDAY A
PROGRESSIVE UPPER SHORTWAVE WILL PUSH THROUGH THE AREA...BRINGING
BETTER RAIN CHANCES AND INCREASING CLOUD COVER.

&&

.AVIATION /15Z SATURDAY THROUGH WEDNESDAY/...
KSAV...CEILINGS ARE STARTING TO LIFT TO MVFR AND MAY EVEN GO VFR
AT SOME POINT THIS AFTERNOON AS SOME PARTIAL SCATTERING OCCURS.
SHOWERS MAY DEVELOP IN THE VICINITY...BUT CONFIDENCE IS TOO LOW TO
INCLUDE ANYTHING DIRECTLY IMPACTING THE TERMINAL. TONIGHT...CONFIDENCE
IS LOW WITH INCREASING POTENTIAL FOR LOW CLOUDS AND FOG...THEN A
CHANCE OF RAIN.

KCHS...ANOTHER ROUND OF SHOWERS IS POISED TO IMPACT THE TERMINAL
LATE THIS MORNING EVEN AS CEILINGS ARE LIFTING TO MVFR. THIS
SHOULD BE RELATIVELY SHORT-LIVED HOWEVER AND LITTLE TO NO ACTIVITY
IS ANTICIPATED THIS AFTERNOON. TONIGHT...DETERIORATING CONDITIONS
ONCE AGAIN WITH A WARM FRONT DEVELOPING TO THE SOUTH...DEEP
MOISTURE...RAIN CHANCES AND INCREASING POTENTIAL FOR IFR CIGS
AFTER MIDNIGHT.

EXTENDED AVIATION OUTLOOK...MVFR CEILINGS AND/OR VISIBILITIES EXPECTED
SUNDAY AND SUNDAY NIGHT WITH SHOWERS AND ISOLATED TSTMS ASSOCIATED
WITH AN UPPER DISTURBANCE. OCCASIONAL IFR CONDITIONS POSSIBLE. MAINLY
VFR MONDAY AND MONDAY NIGHT...EXCEPT FOR OCCASIONAL REDUCTIONS IN
CEILING AND VISIBILITY WITH SCATTERED SHOWERS/STORMS WITH A COLD
FRONT. VFR THEN EXPECTED TUESDAY INTO WEDNESDAY.

&&

.MARINE...
NO SIGNIFICANT CONCERNS WITH WINDS AND SEAS THROUGH TONIGHT AS A
WEAK PRES PATTERN GIVES WAY TO MOSTLY LIGHT ONSHORE FLOW BY TONIGHT.
SEAS 2 TO 3 FT ON AVERAGE. VSBY PROBLEMS ARE NOT EXPECTED THIS
MORNING BUT WILL HAVE TO WATCH FOR LOW CIGS CAUSING SOME VSBY
OBSCURATIONS IN SOME LOCAL INTRA-COASTAL WATERWAYS LATER TONIGHT.

A WARM FRONT LIFTS NORTH OF THE WATERS SUNDAY WITH AN INCREASING
SOUTHERLY FLOW UNTIL A COLD FRONT SWEEPS THROUGH MONDAY NIGHT. WINDS
WILL APPROACH 20 KT LATE IN THE DAY MONDAY AS A LOW-LEVEL JET MOVES
THROUGH AHEAD OF THE COLD FRONT. A QUIETER PATTERN DEVELOPS TUESDAY
THROUGH LATE WEEK AS HIGH PRESSURE PREVAILS.

&&

.TIDES/COASTAL FLOODING...
ALTHOUGH WE ARE IN A RELATIVELY HIGH TIDE CYCLE...SURFACE WINDS NOW
SHIFTING TO THE SOUTH DO NOT SUPPORT MUCH IN THE WAY OF POSITIVE
TIDAL ANOMALY. SINCE TIDES DID NOT REACH 7.0 FT MLLW AT CHARLESTON
ON FRIDAY EVENING...THE CHANCES FOR TIDAL FLOODING THIS EVENING
IS RELATIVELY LOW.

&&

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

&&

$$

NEAR TERM...BSH
SHORT TERM...JRL
LONG TERM...JRL
AVIATION...BSH
MARINE...JRL
TIDES/COASTAL FLOODING...



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