Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 211423
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1023 AM EDT TUE APR 21 2015

.SYNOPSIS...
HIGH PRESSURE WILL BUILD IN TODAY THROUGH WEDNESDAY. A WEAK COLD FRONT
WILL DROP THROUGH THE AREA THURSDAY NIGHT...THEN STALL TO THE SOUTH.
A STORM SYSTEM WILL AFFECT THE REGION FRIDAY NIGHT THROUGH SATURDAY
NIGHT. HIGH PRESSURE WILL BUILD IN FROM THE NORTHWEST SUNDAY INTO
MONDAY. A COLD FRONT MAY AFFECT THE AREA NEXT TUESDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
THE COLD FRONT IS NOW WELL OFFSHORE...WITH SURFACE HIGH PRESSURE
OVER THE GULF COAST STATES EXPANDING EASTWARD IN ITS WAKE. THE DAY
WILL BE DRY WITH NO MORE THAN SOME PASSING CIRRUS CLOUDS ASSOCIATED
WITH THE UPPER JET. DOWNSLOPE FLOW WILL HELP OFFSET THE WEAK COLD
ADVECTION BEHIND THE DEPARTING COLD FRONT. LOW LEVEL THICKNESS
VALUES FROM 12Z KCHS RAOB SUPPORT HIGHS IN THE UPPER 70S/NEAR 80
WHICH LOOKS REASONABLE. OVERALL...VERY LITTLE CHANGE WAS MADE WITH
THIS UPDATE.

TONIGHT...PERHAPS SOME HIGH CLOUDS WILL INCREASE LATE TONIGHT.
A SETUP FOR DECENT RADIATIONAL COOLING WITH NEAR CALM WINDS AND
DRY AIR IN THE LOWEST LAYERS. A FEW OF OUR NORMALLY COOLER
LOCATIONS SUCH AS ALLENDALE COULD SEE READINGS DIP TO THE UPPER
40S WITH LOWS IN THE LOWER TO MID 50S MANY AREAS WEST OF U.S. 17.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY/...
DRY HIGH PRESSURE WILL SLIDE OFF THE EAST COAST ON WEDNESDAY WHILE A
ZONAL FLOW PERSISTS ALOFT. ASIDE FROM SOME INCREASING LATE DAY
CIRRUS WE EXPECT SUNNY SKIES. LOW-LEVEL FLOW WILL BACK TO A MORE
SOUTHERLY TRAJECTORY LATE IN THE DAY...ALLOWING SURFACE DEWPOINTS TO
RISE INTO THE MID/UPPER 50S. TEMPERATURES WILL TOP OUT IN THE LOWER
80S.

WEDNESDAY NIGHT INTO THURSDAY...SOME INCREASE IN UPPER SHORTWAVE
ENERGY WILL HELP PUSH A BACK DOOR COLD FRONT TOWARD THE AREA. THERE
ARE SOME DIFFERENCES IN MODEL TIMING OF THE FRONTAL PASSAGE. THE GFS
HAS CONTINUED TO BE FASTER AND ALSO WETTER WITH THE FRONT...SHOWING
STRONGER SHORTWAVE ENERGY AND BETTER MOISTURE ADVECTION AHEAD OF IT.
HOWEVER THE GFS REMAINS THE OUTLIER WITH THE REMAINDER OF THE MODEL
SUITE ONLY SHOWING ISOLATED SHOWERS OR TSTMS DROPPING INTO THE AREA
ON THURSDAY...DISSIPATING AS IT MOVES SOUTH. WE THEREFORE ARE ONLY
SHOWING 20 POPS OVER OUR NORTHERN TWO-THIRDS AND DRY FARTHER SOUTH.
SIGNIFICANT CLOUD COVER AND SOME LATE-DAY COLD ADVECTION IN NORTHERN
AREAS WILL GIVE A RANGE IN HIGH TEMPS OF LOW/MID 80S NEAR THE
ALTAMAHA RIVER AND MIDDLE 70S FAR NORTH.

SHORTWAVE RIDGING ON FRIDAY WILL SUPPORT DRY HIGH PRESSURE AT THE
SURFACE...THOUGH MID-LEVEL MOISTURE WILL BE ON THE INCREASE SO CLOUD
COVER WILL INCREASE DURING THE DAY. WEAK COLD ADVECTION AND
INCREASING CLOUDINESS WILL KEEP HIGHS IN THE MID/UPPER 70S.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
A POTENT SHORTWAVE WILL MOVE THROUGH THE AREA FRIDAY NIGHT AND
SATURDAY...OFF THE COAST SATURDAY NIGHT. A WARM FRONT WILL DEVELOP
OVER THE AREA AND SLOWLY LIFT NORTH DURING THE DAY SATURDAY. BACKING
LOW-LEVEL FLOW AHEAD OF THE SHORTWAVE WILL SUPPORT OVERRUNNING
PRECIPITATION FRIDAY NIGHT AND SATURDAY MORNING...THEN SOME
CONVECTIVE RAINS POSSIBLE SATURDAY AFTERNOON AND EVENING AS THE
FRONT LIFTS NORTH. THERE IS INCREASING MODEL CONSISTENCY WITH THIS
SCENARIO SO WE BUMPED POPS UP TO 50% ON SATURDAY.

DRY HIGH PRESSURE BUILDS IN FROM THE NORTH SUNDAY INTO MONDAY WITH
TEMPS SLIGHTLY BELOW NORMAL. THERE ARE SOME HINTS THAT ANOTHER
SYSTEM WILL AFFECT THE AREA NEXT TUESDAY BUT DUE TO LARGE MODEL
DIFFERENCES WE MAINTAINED A DRY FORECAST AND PERSISTENCE TEMPS.

&&

.AVIATION /14Z TUESDAY THROUGH SATURDAY/...
VFR CONDITIONS WILL PREVAIL AT KCHS/KSAV THROUGH 12Z WEDNESDAY.

EXTENDED AVIATION OUTLOOK...LOW STRATUS OR FOG POSSIBLE THURSDAY
NIGHT INTO FRIDAY MORNING AS A FRONT DROPS THROUGH. CEILING AND/OR
VISIBILITY RESTRICTIONS POSSIBLE ON SATURDAY WITH SHOWERS AND TSTMS.

&&

.MARINE...
THE PRESSURE GRADIENT IS BEGINNING TO RELAX AS THE COLD FRONT
PUSHES FURTHER EAST AND SURFACE HIGH PRESSURE EXPANDS OVER THE
AREA. WEST/NORTHWEST WINDS 10-15 KT WILL BECOME MORE SOUTHWEST 5-10
KT THIS AFTERNOON WITH SEAS 2-3 FEET ON AVERAGE. SEAS WITHIN 20 NM
WILL SUBSIDE TO 1-2 FT TONIGHT.

FAIRLY QUIET CONDITIONS WILL PERSIST WEDNESDAY THROUGH THE WEEKEND.
SOUTHERLY FLOW STRENGTHENS WEDNESDAY AND WEDNESDAY NIGHT AHEAD OF A
COLD FRONT...THEN TURNS TO THE NNE BRIEFLY LATE THURSDAY NIGHT INTO
FRIDAY BEHIND THE FRONT. INCREASING WESTERLY FLOW ANTICIPATED NEXT
WEEKEND AS A STORM SYSTEM PASSES THROUGH...DURING WHICH ADVISORIES
ARE POSSIBLE.

&&

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

&&

$$
SYNOPSIS...
NEAR TERM...ECT
SHORT TERM...JRL
LONG TERM...JRL
AVIATION...
MARINE...JRL



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