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Area Forecast Discussion

373
FXUS62 KCHS 222338
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
738 PM EDT TUE APR 22 2014

.SYNOPSIS...
A COLD FRONT WILL CROSS THE AREA LATE TONIGHT. HIGH PRESSURE WILL
BUILD INTO THE REGION ON WEDNESDAY AND THEN PREVAIL THROUGH THE
END OF THE WEEK. A COLD FRONT MAY DRIFT IN FROM THE NORTH THIS
WEEKEND BEFORE WARMER CONDITIONS RETURN EARLY NEXT WEEK AHEAD OF A
STRONGER COLD FRONT TO THE WEST.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
TUESDAY EVENING...SCATTERED/NUMEROUS SHOWERS AND ISOLATED
THUNDERSTORMS CONTINUED TO ADVANCE TOWARD THE E/SE...DEEPER INTO
THE FORECAST AREA AND HEADED FOR THE COAST. LIGHTNING WAS
PRIMARILY CONFINED TO MULTICELL CONVECTION ALONG THE I-16
CORRIDOR WHERE A POOL OF SURFACE BASED CAPES AROUND 500 J/KG AND
LIFTED INDICES -2 TO -3C EXISTED ALONG/SOUTH OF OUTFLOW
BOUNDARIES PUSHING INTO THIS REGION FROM THE N/W. LOW LEVEL
INVERTED-V PROFILES MARKED BY 0-3 KM LAPSE RATES 7-8 C/KM AND
DOWNDRAFT CAPES 500-700 J/KG SUGGEST THE POTENTIAL FOR WIND GUSTS
30-40 MPH MAINLY ALONG THE I-16 CORRIDOR BUT EVEN NE ALONG THE SC
COAST WHERE SHOWERS OCCUR. RADAR TRENDS AND LATEST HIGH
RESOLUTION MODEL GUIDANCE SUGGEST POPS TAPERED FROM CHANCE/LIKELY
UNTIL LATER THIS EVENING TO SLIGHT CHANCE THEN LESS THEN 15
PERCENT OVERNIGHT.

ONCE THE PRE-FRONTAL TROUGH SHIFTS OFFSHORE LATE THIS EVENING OR
DURING THE EARLY OVERNIGHT HOURS...A WESTERLY FLOW DEVELOPS AND
WILL LIMIT THE MOISTURE AVAILABLE AHEAD OF THE PRIMARY
FRONT. THEREFORE...EXPECT MAINLY RAIN-FREE CONDITIONS OVERNIGHT.
THERE IS SOME INDICATION THAT THERE COULD BE SUFFICIENT BOUNDARY
LAYER MOISTURE TO SUPPORT SOME PATCHY FOG OR LOW CLOUDS JUST AHEAD
OF THE PRIMARY FRONT...AND THE FORECAST MAY NEED TO TREND MORE IN
THIS DIRECTION WITH LATER UPDATES. LOWS TONIGHT SHOULD BE IN THE
MID TO UPPER 50S..WITH SOME LOWER 60S ALONG THE IMMEDIATE COAST.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/...
WEDNESDAY AND WEDNESDAY NIGHT...WE WILL START THE DAY IN NORTHWEST
FLOW ALOFT AHEAD OF THE DEEP RIDGE BUILDING IN FROM THE WEST. AT THE
SURFACE...HIGH PRESSURE CENTERED OVER THE GREAT LAKES WILL BUILD IN
ACROSS THE FORECAST AREA THROUGH THE OVERNIGHT. VERY DRY AIR IN THE
MID/UPPER LEVELS COMBINED WITH THE LACK OF FORCING AND STRONG
SUBSIDENCE INVERSION WILL KEEP THE FORECAST DRY. TEMPERATURES WILL
BE COOLER THAN TUESDAY BEHIND THE FRONT...THOUGH THEY WILL STILL TOP
OUT AROUND NORMAL. LOOK FOR HIGHS IN THE UPPER 70S TO AROUND 80.
OVERNIGHT LOWS ARE EXPECTED TO FALL INTO THE LOW TO MID 50S IN MOST
AREAS.

THURSDAY THROUGH FRIDAY...THE INFLUENCE OF THE UPPER RIDGE WILL
REACH ITS MAX INFLUENCE ON THURSDAY AS THE AXIS OF THE FEATURE MOVES
ACROSS THE EASTERN CONUS. THEN BY FRIDAY...A MORE ZONAL FLOW WILL
MOVE IN ALOFT IN RESPONSE TO A CLOSED LOW PROGRESSING INTO THE GREAT
LAKES REGION. SURFACE HIGH PRESSURE WILL SLIDE EAST OF THE FORECAST
AREA THURSDAY AFTERNOON AND WILL REMAIN OFFSHORE THROUGH FRIDAY. A
FAST MOVING COLD FRONT WILL APPROACH FROM THE NORTH AND WEST FRIDAY
AFTERNOON...AND MAY HELP TO SPARK A FEW SHOWERS AND THUNDERSTORMS.
THURSDAY WILL BE DRY AS THE SUBSIDENCE INVERSION REMAINS IN PLACE
PER MODEL SOUNDINGS. BUT BY FRIDAY...THE INVERSION WEAKENS ENOUGH TO
ALLOW FOR 500-1000 J/KG WITHIN A BROAD CONVERGENCE ZONE BETWEEN THE
APPROACHING COLD FRONT AND THE AFTERNOON SEA BREEZE. POPS HAVE BEEN
KEPT IN THE SLIGHT CHANCE RANGE. TEMPERATURES FOR THURSDAY WILL BE
ONCE AGAIN RIGHT AROUND NORMAL FOR LATE APRIL...HELD DOWN A BIT BY
THE ONSHORE FLOW. FRIDAY WILL THEN SEE VALUES IN THE 80S THANKS TO
THE SOUTHWEST FLOW ASSOCIATED WITH THE COLD FRONT.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
CONDITIONS SHOULD REMAIN FAIRLY DRY THIS WEEKEND ALONG THE WESTERN
EDGE OF ATLANTIC HIGH PRESSURE AT THE SFC AND A ZONAL FLOW ALOFT.
HOWEVER...A WEAK COLD FRONT COULD APPROACH FROM THE NORTH LATE
SATURDAY INTO EARLY SUNDAY...LEADING TO THE POSSIBILITY OF A SHOWER
AND/OR THUNDERSTORM. AT THIS TIME...THE FRONT LOOKS TO STALL NORTH
OF THE AREA...THUS HAVE MAINTAINED A RAIN-FREE FORECAST. OVERALL
HIGH TEMPS WILL BE WARMER THAN PREVIOUS DAYS...IN THE LOW/MID 80S
EACH DAY. CHANCES OF PRECIP WILL THEN INCREASE MONDAY INTO TUESDAY
AS SOUTHERLY FLOW PERSISTS BETWEEN ATLANTIC HIGH PRESSURE AND A LOW
PRESSURE SYSTEM TRACKING EAST OVER THE CENTRAL UNITED STATES. A
SLIGHT CHANCE OF SHOWERS AND THUNDERSTORMS HAVE BEEN INCLUDED IN THE
LATEST FORECAST AS INSTABILITY INCREASES WITH OVERALL HIGH TEMPS IN
THE MID 80S AWAY FROM THE COAST. GREATEST CHANCES OF PRECIP SHOULD
OCCUR ON TUESDAY AS A COLD FRONT ASSOCIATED WITH THE LOW PRESSURE
SYSTEM APPROACHES THE SOUTHEAST DURING MIDWEEK.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
GUSTY SHOWERS WILL IMPACT KCHS THIS EVENING...WHILE GUSTY
THUNDERSTORMS ARE EXPECTED AT KSAV. THEN...SHOWERS WILL PUSH
OFFSHORE AND VFR CONDITIONS SHOULD PREVAIL FOR THE REMAINDER OF
THE 00Z TAF PERIOD. LOW LEVEL MOISTURE POOLED WITHIN THE COLD
FRONTAL TROUGH COULD SUPPORT FLIGHT RESTRICTIONS BETWEEN 06Z-09Z
AND 12Z-14Z...ESPECIALLY AT KSAV. HOWEVER...FORECAST CONFIDENCE
REMAINS INSUFFICIENT TO INCLUDE MVFR OR LOWER CONDITIONS DURING
THIS TIME.

EXTENDED AVIATION OUTLOOK...VFR CONDITIONS ARE EXPECTED TO
PREVAIL.

&&

.MARINE...
TONIGHT...WEAK LOW LEVEL JETTING IN THE WARM AIR ADVECTION REGIME
AHEAD OF A PRE-FRONTAL TROUGH APPROACHING FROM THE WEST WILL KEEP
SOUTHWEST TO WEST WINDS ELEVATED UPWARDS OF AROUND 15 KT MUCH OF
THIS EVENING. ONCE THE PRE-FRONTAL TROUGH SHIFTS OFFSHORE LATE
THIS EVENING OR DURING THE EARLY OVERNIGHT HOURS...THE FLOW WILL
SHIFT WESTERLY AND DIMINISH TO 10 TO 15 KT. A COLD FRONT WILL THEN
MOVE OFFSHORE LATE TONIGHT/EARLY WEDNESDAY MORNING. SEAS WILL
REMAIN 2-3 FT ACROSS THE NEAR SHORE WATERS AND 3-4 FT ACROSS THE
OUTER GA WATERS.

WEDNESDAY THROUGH SUNDAY...GENERALLY QUIET CONDITIONS ARE EXPECTED
TO PREVAIL THROUGH THE WEEKEND WITH NO SMALL CRAFT ADVISORY
CONDITIONS EXPECTED. HIGH PRESSURE WILL BUILD INTO THE AREA
WEDNESDAY AND THEN SLIDE BY TO THE EAST THURSDAY. WEDNESDAY WILL
START OFF WITH NORTHERLY FLOW WHICH WILL VEER AROUND TO MORE
SOUTHERLY BY THURSDAY AFTERNOON. ANOTHER FAST MOVING COLD FRONT WILL
MOVE THROUGH OVER THE WEEKEND WITH MORE HIGH PRESSURE BY SUNDAY.
WINDS WILL BE 15 KT OR LESS...WITH SEAS 2-4 FT WEDNESDAY THEN 1-3 FT
THEREAFTER.

&&

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

&&

$$

SYNOPSIS...
NEAR TERM...SPR
SHORT TERM...BSH
LONG TERM...DPB
AVIATION...BSH/SPR
MARINE...BSH/JAQ/SPR






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