Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 030525
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
125 AM EDT TUE MAY 3 2016

.SYNOPSIS...
MULTIPLE AREAS OF LOW PRESSURE WILL GRADUALLY PUSH A COLD FRONT
TOWARD THE REGION OVERNIGHT THROUGH TUESDAY...PRODUCING UNSETTLED
CONDITIONS. THE COLD FRONT WILL PASS THROUGH THE REGION TUESDAY
NIGHT...FOLLOWED BY A REINFORCING COLD FRONT ON THURSDAY. HIGH
PRESSURE WILL THEN EXPAND INTO THE REGION FROM THE WEST THROUGH
THE WEEKEND.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
ONE CONCENTRATED AREA OF SHOWER/TSTMS WILL PASS ALONG THE
CHARLESTON COUNTY COAST THROUGH 3 AM. EXPECT DRY CONDITIONS MOST
AREAS FOR THE NEXT SEVERAL HOURS. EXPECT ISOLATED TO SCATTERED
SHOWERS/TSTMS TO DEVELOPING INLAND AND POSSIBLY MOVING INTO THE
CHARLESTON TRI-COUNTY AREA 3AM-SUNRISE. MAINTAINED ELEVATED POPS
AROUND 30 PERCENT IN THIS AREA TO COVER. NUDGED OVERNIGHT LOWS UP
A DEGREE OR SO PER GOING TRENDS. REST OF THE FORECAST IS FINE.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH THURSDAY/...
TUESDAY...A BROAD...POSITIVELY TILTED UPPER TROUGH WILL BE OVER THE
CENTRAL U.S. WITH A TRAILING COLD FRONT RUNNING FROM THE MID
ATLANTIC...SOUTHWEST ACROSS THE SOUTHEAST U.S....APPROACHING
OUR REGION DURING THE AFTERNOON. THE COMPLICATING FACTOR FOR
FIGURING OUT THE THUNDERSTORM AND SEVERE POTENTIAL IS THE AMOUNT
OF CONVECTION THAT MIGHT BE PRESENT IN THE MORNING. ALL MODELS
INDICATE THAT AT LEAST SCATTERED SHOWERS AND ISOLATED
THUNDERSTORMS WILL BE AROUND BETWEEN 06Z AND 15Z...THEN RAPIDLY
MOVES EAST. THE NAM THEN INDICATES THAT DEEP LAYER MOISTURE WILL
DROP THROUGH THE DAY...LIMITING CONVECTIVE COVERAGE...WHILE THE
GLOBAL MODELS KEEP SUFFICIENT DEEP LAYER MOISTURE IN PLACE. GOING
WITH THE MAJORITY AND KEEPING SOME CONSISTENCY WITH PREVIOUS
FORECASTS...HAVE KEPT HIGH END CHANCE/LIKELY POPS REDEVELOPING
LATER IN THE MORNING AND THROUGH THE AFTERNOON. WILL HAVE A
SIMILAR AMOUNT OF INSTABILITY AS PREVIOUS DAYS...GENERALLY SURFACE
BASED CAPES OF 1000-2000 J/KG IN PLACE. IN ADDITION...WEAK VORT
LOBES WILL MOVE ACROSS THE AREA IN THE SOUTHWEST UPPER FLOW THROUGH
THE DAY. AT THIS POINT...IT IS VERY DIFFICULT TO TIME ANY ONE
IMPULSE. GIVEN THESE CONDITIONS...FEEL THERE IS STILL A
LOW/MARGINAL RISK FOR ISOLATED SEVERE STORMS DURING THE AFTERNOON.
THE MAIN THREAT WILL BE STRONG/DAMAGING WINDS WITH DOWNDRAFT CAPES
IN THE 500- 700 J/KG RANGE. SMALL HAIL WILL ALSO BE POSSIBLE. DEEP
SOUTHWEST/UNIDIRECTIONAL FLOW MAY ALSO LEAD TO THE POTENTIAL FOR
TRAINING OF CELLS...WHICH COULD RESULT IN LOCALLY HEAVY RAINFALL.
HIGHS IN THE LOWER 80S.

THE BULK OF THE CONVECTION IS EXPECTED TO END BY MIDNIGHT AS THE
SURFACE FRONT MOVES THROUGH THE AREA AND DEEP LEVEL DRYING MOVES IN.
LOWS IN THE LOWER 60S. KEPT THE TREND OF LOWER POPS FROM WEST TO
EAST THROUGH THE NIGHT...WITH MOST POPS LESS THAN 15% OVER LAND BY
MORNING.

WEDNESDAY...COOLER AND DRIER CONDITIONS ARE EXPECTED AS THE LARGE
SCALE PATTERN TRANSITIONS TO THE BLOCK...WITH A DEEP UPPER LOW
OVER THE OH RIVER VALLEY AND RIDGE OVER THE ROCKIES. A WEST-
NORTHWEST LOW LEVEL FLOW...MOSTLY SUNNY SKIES AND HIGHS IN THE
UPPER 70S AROUND 80. THIS IS CLOSE TO NORMAL. PERIODIC UPPER VORT
LOBES WILL MOVE ACROSS THE AREA ON THE BASE OF THE UPPER/BLOCKING
TROUGH. HOWEVER...OTHER THAN BRIEF INCREASES IN CLOUDS...NO
MEASURABLE PRECIP. IS EXPECTED. BY WEDNESDAY NIGHT...A RE-
REINFORCING COLD FRONT WILL MOVE THROUGH...BUT IS EXPECTED TO COME
THROUGH DRY. WINDS WILL STAY UP ALL NIGHT FROM THE WEST-
NORTHWEST...WITH LOWS DROPPING TO THE MID 50S INLAND TO AROUND 60
COAST...CLOSER TO NORMAL.

THURSDAY...THE AREA WILL REMAIN ON THE SOUTHERN END OF THE BLOCKING
UPPER LOW...WHICH WILL DRIFT INTO THE NORTHEAST AND MID ATLANTIC
REGION. EVEN WITH SUNNY SKIES...NORTHWEST FLOW AND WEAK COLD
ADVECTION WILL KEEP HIGHS IN THE MID 70S...ABOUT 3-5 DEGREES BELOW
NORMAL.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
MODELS ARE IN GOOD AGREEMENT SHIFTING THE TROUGH AXIS FROM OVER THE
EAST COAST THURSDAY NIGHT TO FAR OFFSHORE BY SUNDAY.
REPLACING THE TROUGH WILL BE A BUILDING RIDGE...ORIGINATING FROM THE
CENTRAL U.S. EXPECT DRY CONDITIONS THROUGH THIS PERIOD WITH
TEMPERATURES TRENDING UPWARD EACH DAY.

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
TSTMS WILL PASS SOUTH OF THE KCHS THROUGH 07Z. WATCHING FOR
POSSIBLE REDEVELOPMENT WELL INLAND AFTER 09Z...WHICH COULD IMPACT
KCHS PRIOR TO SUNRISE. WILL CARRY VCTS TO ACCOUNT FOR THIS...BUT
NOT INCLUDE PREVAILING OR TEMPO GROUPS FOR TSRA JUST YET. KSAV
LOOKS TO REMAIN DRY...ALTHOUGH WOULD NOT BE SURPRISED TO SEE A
LITTLE SHALLOW GROUND FOG DEVELOP THERE PRIOR TO DAYBREAK. NO
IMPACTS ARE ANTICIPATED. ATTN SHIFTS TO THIS AFTERNOON WHEN
ANOTHER ROUND OF SHRA/TSRA WILL IMPACT THE REGION. TIMING/COVERAGE
IS STILL QUITE UNCERTAIN THIS FAR OUT...BUT MOST GUIDANCE SUGGESTS
ANY IMPACTS TO THE TERMINALS WILL BE AFTER 20-21Z. WILL THEREFORE
NOT INCLUDE ANY MENTION OF TSRA THIS FAR OUT FOR THE 06Z TAF
CYCLE. THIS WILL BE REEVALUATED FOR THE 12Z TAF CYCLE ONCE THE 06Z
MODEL DATA ARE RECEIVED.

EXTENDED AVIATION OUTLOOK...FOR TUESDAY...PERIODIC FLIGHT
RESTRICTIONS POSSIBLE IN SCATTERED SHOWERS/THUNDERSTORMS...ESPECIALLY
TUESDAY NIGHT...AT BOTH KCHS AND KSAV. WEDNESDAY THROUGH
SATURDAY...VFR WILL PREVAIL BOTH SITES.

&&

.MARINE...
OVERNIGHT...A WEAK GRADIENT SUPPORTING S WINDS MAINLY 10 KT OR
LESS WILL TRANSITION TO A TIGHTENING PRESSURE GRADIENT/INCREASING
LOW-LEVEL WINDS. AS A RESULT...S/SW WINDS SHOULD INCREASE TO 15-20
KT...AND SEAS SHOULD BUILD FROM 2-3 FT TO 3-5 FT MOST
AREAS...HIGHEST BEYOND 20 NM. SCA CONDITIONS ARE NOT ANTICIPATED.
ALSO OF NOTE...THUNDERSTORM COVERAGE IS EXPECTED TO INCREASE
ACROSS COASTAL WATERS OVERNIGHT...AND LOCALIZED HAZARDOUS/SPECIAL
MARINE WARNING CONDITIONS ARE POSSIBLE.

TUESDAY AND WEDNESDAY...CONDITIONS ARE EXPECTED TO REMAIN BELOW
SMALL CRAFT ADVISORY LEVELS. A COLD FRONT WILL BE APPROACHING THE
REGION ON TUESDAY...THE MOVE THROUGH THE WATERS ON WEDNESDAY. WINDS
COULD PERIODICALLY GET AS HIGH AS 15-20 KNOTS FROM THE SOUTHWEST
THROUGH WEDNESDAY MORNING AHEAD OF THE FRONT...BUT GENERALLY 15
KNOTS OR LESS EXPECTED TO PREVAIL. WINDS WILL SHIFT TO WEST-
NORTHWEST WEDNESDAY AFTERNOON BEHIND THE FRONT...BUT EXPECTED TO
REMAIN 15-20 KNOTS OR LESS WITH BUILDING SEAS TO 4 FEET
OFFSHORE/BEYOND 20 NM.

WEDNESDAY NIGHT AND THURSDAY...WINDS INCREASING BACK TO 15-20 KNOTS
FROM THE WEST-NORTHWEST AS A REINFORCING COLD FRONT MOVES THROUGH
AND STRONGER HIGH PRESSURE BUILDS FROM THE WEST. SEAS BUILDING TO 4-5
FEET BEYOND 20 NM.

FRIDAY AND SATURDAY...THE PRESSURE GRADIENT GRADUALLY DECREASES AS
HIGH PRESSURE CONTINUES MOVING IN FROM THE WEST. EXPECT WINDS OF 15
KNOTS OR LESS AND SEAS DECREASING TO 3 TO 4 FEET.

&&

.EQUIPMENT...
THE CHARLESTON HARBOR NOS TIDE GAUGE HAS STOPPED REPORTING ALL
METEOROLOGICAL AND TIDE DATA. THE NATIONAL OCEAN SERVICE IS
INVESTIGATING THE CAUSE OF THE OUTAGE. AN ESTIMATED TIME FOR DATA
RESTORATION IS UNKNOWN AT THIS TIME.

&&

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

&&

$$

ST



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