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Area Forecast Discussion

870
FXUS62 KCHS 292333
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
733 PM EDT SUN MAR 29 2015

.SYNOPSIS...
HIGH PRESSURE WILL MOVE SOUTH OF THE AREA TONIGHT. WEAK COLD FRONTS
WILL PUSH INTO THE REGION MONDAY AND AGAIN WEDNESDAY...AND BOTH
FRONTS SHOULD DISSIPATE OVER OR CLOSE TO THE AREA. WARMER ATLANTIC
HIGH PRESSURE WILL THEN BUILD OVER THE REGION THROUGH LATE WEEK.
A STRONGER COLD FRONT WILL ARRIVE FROM THE NORTHWEST NEXT WEEKEND.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
THE CENTER OF SURFACE HIGH PRESSURE CURRENTLY IN THE PROCESS OF
TRANSLATING OFF THE COAST. TEMPS SHOULD BEGIN A FREE-FALL AFTER
SUNSET BUT THEN STEADY OUT LATER TONIGHT. DETAILS REGARDING
TEMP TRENDS AND FROST POTENTIAL WILL BE STRONGLY DEPENDENT ON THE
TIMING AND STRENGTH OF AN INCREASING RETURN FLOW ATOP THE STABLE
SURFACE LAYER OVERNIGHT.

MODEL GUIDANCE IS IN GOOD AGREEMENT INDICATING THAT TEMPERATURES
WILL LIKELY REACH MINIMUMS RIGHT AROUND MIDNIGHT...THEN BEGIN A
SLOW WARMING TREND DURING THE PRE DAWN HOURS...AS SOUTHERLY FLOW
INCREASES AND THE PRESSURE GRADIENT TIGHTENS. THERE IS A SMALL
WINDOW OF OPPORTUNITY WHEN TEMPERATURES FALL TO AROUND 37 DEGREES
ACROSS PORTIONS OF INLAND BERKELEY...DORCHESTER...AND COLLETON
COUNTIES IN SOUTH CAROLINA THAT PATCHY FROST COULD DEVELOP.
HOWEVER...LATEST THINKING IS THAT THE INTRODUCTION OF A LOW LEVEL
JET TO THE WEST AND THE BRIEF DURATION OF TEMPERATURES IN THE
IDEAL RANGE WILL PREVENT SCATTERED TO WIDESPREAD COVERAGE. TRENDS
WILL BE CLOSELY MONITORED DURING THE EVENING TIME FRAME...AS MORE
RAPID COOLING OR A MORE PERSISTENTLY WEAK GRADIENT COULD SUPPORT
BETTER FROST COVERAGE AND NECESSITATE THE ISSUANCE OF A FROST
ADVISORY.

LOW TEMPERATURES WILL RANGE FROM THE UPPER 30S INLAND CHARLESTON
TRI COUNTY REGION TO THE LOW 40S ELSEWHERE...WITH MINIMUMS
REACHED AROUND MIDNIGHT BEFORE CLOUDS AND WINDS INCREASE AHEAD OF
A COLD FRONT TO THE WEST.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/...
MONDAY...THINKING ON GENERAL SCENARIO FOR MONDAY REMAINS LITTLE
CHANGED. WEAK BAND OF CONVERGENCE ASSOCIATED WITH A COLD FRONT WILL
MOVE THROUGH THE REGION FROM NORTHWEST TO SOUTHEAST THROUGH THE DAY.
UPPER SUPPORT DURING THE MORNING WILL COME FROM THE RIGHT ENTRANCE
REGION OF A WEAK JET MOVING THROUGH THE MID ATLANTIC. THIS SHOULD
CREATE ENOUGH UPPER LEVEL DIVERGENCE TO ALLOW FOR MODEST UPWARD
MOTION...SUPPORTING A LINE OF SHOWERS. WITH DEW POINTS NO HIGHER
THAN THE 40S...IT WILL BE TOUGH TO SQUEEZE MUCH QPF OUT DURING THE
MORNING AS THE LINE MOVES QUICKLY FROM THE UPSTATE INTO THE NORTHERN
HALF OF OUR CWA BY EARLY AFTERNOON. THE UPPER SUPPORT DIMINISHES
DURING THE AFTERNOON AS THE BOUNDARY MOVES THROUGH THE REMAINDER OF
THE CWA...BUT TEMPERATURES IN THE SOUTH WILL NOTICEABLY WARMER AS
THERE WILL BE SEVERAL MORE HOURS OF LOW LEVEL WARM/MOIST
ADVECTION...AS WELL AS MORE OF A CHANCE FOR SOME BROKEN SUNSHINE
EARLY IN THE DAY. THEREFORE...WHILE THE POPS ACTUALLY DECREASE A BIT
LATER IN THE DAY...SOME SURFACE BASED INSTABILITY MAY DEVELOP...SO I
HAVE KEPT THE MENTION OF THUNDER FOR THE SOUTHERN HALF OF THE AREA.

HIGH TEMPS WILL RANGE FROM THE MID 60S NORTH TO MID 70S SOUTH...WITH
THE COOLEST TEMPS DUE TO EARLIER CLOUD COVER AND RAIN MORE THAN
ANYTHING ELSE.

MONDAY NIGHT...THE LINGERING LOW CHANCES OF RAIN IN THE SOUTH SHOULD
COME TO AN END BY MIDNIGHT WITH CLOUDS DIMINISHING. AIR MASS BEHIND
THE FRONT CAN BE TRACED BACK TO THE PACIFIC RATHER THAN POLAR
REGIONS...SO LOWS WILL BE SEASONABLE WITH MID 40S INLAND TO NEAR 50
AT THE COAST.

TUESDAY...AS ANOTHER JET PASSES THROUGH THE NORTHERN GULF AND
FLORIDA...SOME HIGHER CLOUDS WILL MOVE IN FROM THE WEST OVER
GEORGIA. THE NAM HITS THAT THERE COULD SOME SOME ISOLATED
SHOWERS...OR MAYBE EVEN A THUNDERSTORM AS TEMPS WARM WELL INTO THE
70S SOUTH OF INTERSTATE 16...BUT MY CURRENT BELIEF IS THAT THIS WILL
HOLD OFF TO THE WEST AND THE DAY WILL BE DRY.

TUESDAY NIGHT...ANOTHER WEAK FRONT WILL PASS THROUGH THE AREA LATE
TUESDAY NIGHT. THIS FRONT WILL HAVE PALTRY MOISTURE TO WORK
WITH...ESPECIALLY OVER THE NORTHERN THIRD OF THE CWA...AND ANOTHER
UNINSPIRING JET MAX...SO I HAVE GONE A LITTLE BELOW MOS GUIDANCE AND
CAPPED THE POPS AT 20 PERCENT. WITH MORE CLOUDS AROUND...OVERNIGHT
MINS SHOULD BE MILDER...HOLDING IN THE 50S THROUGHOUT THE CWA.

WEDNESDAY...THE FRONT SHOULD STALL TO THE SOUTH AND WEST OF THE CWA
AS HIGH PRESSURE MOVES THROUGH THE MID ATLANTIC STATES. CALLING THE
HIGH A WEAK WEDGE MIGHT BE GIVING IT TOO MUCH CREDIT...BUT IT WILL
ACT TO ALLOW THE WINDS TO TURN ONSHORE FOR WEDNESDAY...KEEPING HIGH
TEMPS DOWN INTO THE 60S NEAR THE COAST. INLAND...THE LOW LEVELS WILL
BE WARMING WITH 925 MB TEMPS RUNNING 16 TO 18 C BY AFTERNOON IN THE
GEORGIA COUNTIES. NORMAL MIXING DOWN BRINGS TEMPS INTO THE MID TO
POSSIBLY UPPER 70S. WITH THE UNCERTAINTY THIS FAR OUT IN THE EXACT
FINAL RESTING PLACE OF THE FRONT...I HAVE LEFT IN A SLIGHT CHANCE OF
SHOWERS SOUTH OF INTERSTATE 16.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
THROUGH LATE WEEK...ABOVE NORMAL TEMPERATURES WILL PREVAIL
THEN...NORMAL TO BELOW-NORMAL TEMPERATURES SHOULD RETURN NEXT
WEEKEND.

AS AN UPPER SHORTWAVE TROUGH EJECTS EAST/NORTHEAST ACROSS THE
REGION...AT LEAST CHANCE POPS FOR SHOWERS AND THUNDERSTORMS ARE
JUSTIFIED ESPECIALLY THURSDAY. BETWEEN THE DEPARTING SHORTWAVE AND
AN APPROACHING COLD FRONT...FRIDAY COULD TURN OUT TO BE A VERY WARM
DAY WITH HIGHS IN THE 80S AND POPS BELOW 15 PERCENT WITH NO MENTION
OF PRECIPITATION. A STRONGER COLD FRONT WILL ARRIVE FRIDAY NIGHT OR
SATURDAY. TIMING REMAINS UNCERTAIN...BUT CHANCE POPS AND A MENTION
THUNDERSTORMS ARE CENTERED ON SATURDAY. DRIER AND COOLER CONDITIONS
ARE THEN EXPECTED SUNDAY.

&&

.AVIATION /23Z SUNDAY THROUGH FRIDAY/...
VFR AT KCHS AND KSAV THROUGH 00Z TUESDAY. MINIMAL CHANCES FOR A
BRIEF SHOWER EITHER SIDE OF MIDDAY ON MONDAY. SURFACE WINDS SHOULD
BECOME GUSTY FROM MID MORNING TO LATE AFTERNOON. WSW TO SW FLOW
COULD BRIEFLY EXCEED 15G25KT BY A FEW KNOTS DURING THE TIME WHEN
THE AXIS OF THE STRONGEST LOW LEVEL JET MOVING ACROSS THE COASTAL
CORRIDOR.

EXTENDED AVIATION OUTLOOK...MAINLY VFR.

&&

.MARINE...
OVERNIGHT...WINDS ARE EXPECTED TO STEADILY VEER FROM NORTHEAST
LATE THIS AFTERNOON TO SOUTHWEST DURING THE PRE DAWN HOURS...AS
SURFACE HIGH PRESSURE STEADILY SLIPS DIRECTLY OVER THE MARINE
ZONES AND PROGRESSES FARTHER OFFSHORE. A DECENT NOCTURNAL LOW
LEVEL JET AFTER MIDNIGHT WILL SUPPORT SOUTH/SOUTHWEST FLOW
INCREASING TO 10 TO 15 KT ACROSS A MAJORITY OF THE MARINE ZONES
OUTSIDE OF THE CHARLESTON HARBOR.

MONDAY THROUGH FRIDAY...WINDS WILL INCREASE OUT OF THE SOUTHWEST
AHEAD OF THE FRONT MONDAY. AT THIS TIME...IT LOOKS LIKE WE WILL HAVE
A FEW HOURS JUST BELOW SCA WINDS IN THE NEARSHORE CHARLESTON COUNTY
AND THE OFFSHORE GEORGIA WATERS...ROUGHLY BETWEEN 10 AM AND 6
PM...SO THIS WILL NEED TO BE WATCHED CLOSELY BY FUTURE SHIFTS. ANY
INCREASES IN WINDS WOULD CAUSE THE NEED OF AN SCA.

WINDS WILL COME DOWN FAIRLY QUICKLY MONDAY NIGHT AS FRONT MOVES AWAY
AND A WEAK SURFACE RIDGE MOVES IN BEHIND...CAUSING THE PRESSURE
GRADIENT TO COLLAPSE.

ANOTHER WEAK FRONT WILL MOVE THROUGH THE WATERS LATE TUESDAY
NIGHT...BUT CURRENTLY I THINK WINDS WILL BE 15 KNOTS OR LESS WITH
THAT FRONT.

ON WEDNESDAY...WEAK HIGH PRESSURE WILL BUILD OVER THE MID
ATLANTIC...CAUSING MARINE WINDS TO VEER TO THE EAST...THEN
EVENTUALLY SOUTHEAST BY THURSDAY AND SOUTH OR SOUTHWEST ON FRIDAY AS
THE SURFACE HIGH MOVES INTO THE WESTERN ATLANTIC. AGAIN WINDS SHOULD
BE 15 KNOTS OR LESS.

&&

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

&&

$$
SYNOPSIS...
NEAR TERM...
SHORT TERM...FWA
LONG TERM...SPR
AVIATION...
MARINE...
CLIMATE...



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