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Area Forecast Discussion

128
FXUS62 KCHS 301921
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
321 PM EDT TUE SEP 30 2014

.SYNOPSIS...
HIGH PRESSURE WILL BUILD INTO THE REGION FROM THE NORTH THROUGH
THURSDAY...BEFORE A STRONG COLD FRONT MOVES THROUGH LATE FRIDAY
AND FRIDAY NIGHT. HIGH PRESSURE WILL THEN BUILD OVER THE REGION
THROUGH EARLY NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
THE LAST OF CLOUDS WILL DISSIPATE NEAR THE ALTAMAHA RIVER OVER THE
NEXT FEW HOURS AS SUNSET APPROACHES. HIGH PRESSURE WILL EXTEND
CROSS THE AREA TONIGHT. CLEAR SKIES...LOW DEWPOINTS AND CALM WINDS
WILL ALLOW FOR EXCELLENT RADIATIONAL CONDITIONS. GENERALLY FAVORED
THE LOWER SIDE OF GUIDANCE TO CONSTRUCT TONIGHT/S LOWS AS A
RESULT. LOWS WILL RANGE FROM THE LOWER 60S INLAND TO THE MID-
UPPER 60S AT THE COAST. A FEW UPPER 50S ARE LIKELY IN
CLIMATOLOGICALLY COLDER SITES SUCH AS ALLENDALE...JAMESTOWN...
WITHERBEE AND RIDGEVILLE.

FOG COULD BECOME A PROBLEM EARLY WEDNESDAY MORNING AS TEMPERATURES
APPROACH CROSS-OVER TEMPERATURES. MODEL DERIVED CLOUD PRODUCTS
SUGGEST SOME THIN CIRRUS WILL BE PASSING OVERHEAD 09-12Z...WHICH
MAY LIMIT THE FOG SOMEWHAT. GUIDANCE IS NOT HITTING THE FOG
PROSPECTS ALL THAT HARD...BUT ITS HARD TO IGNORE THE WIDESPREAD
DENSE FOG THAT WAS PRESENT OVER MUCH OF NORTHERN SOUTH CAROLINA
AND THE PIEDMONT/FOOTHILLS OF NORTH CAROLINA THIS MORNING. AREAS
OF FOG WILL BE HIGHLIGHTED WEST OF THE I-95 CORRIDOR WITH PATCHY
FOG EAST OF THERE TO THE COAST. THE FOG COULD BECOME LOCALLY DENSE
AT TIMES...ESPECIALLY NEAR LOW-LYING AREAS SUCH AS MARSHES...
SWAMPS...RIVERS AND LARGE DITCHES.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY/...
WEDNESDAY AND THURSDAY...SURFACE HIGH PRESSURE WILL BUILD FROM
THE NORTH DURING THE MID WEEK PERIOD. AT THE SAME TIME...UPPER
LEVEL RIDGING WILL AMPLIFY ALONG THE EAST COAST DOWNSTREAM OF A
POTENT SHORTWAVE TROUGH. PRECIPITABLE WATER VALUES REMAIN BELOW
ONE INCH...INDICATIVE OF THE DRY AIR MASS IN PLACE. DRY AIR AND
SUBSIDENCE UNDER THE DEEP LAYER RIDGE WILL CONFINE ANY ISOLATED
SHOWER POTENTIAL SOUTH OF THE FORECAST AREA...CLOSER TO DEEPER
MOISTURE AND SOME CONVERGENCE ASSOCIATED WITH RETURN FLOW ALONG
THE PERIPHERY OF THE SURFACE HIGH. INLAND TEMPERATURES WILL
REBOUND INTO THE MID TO UPPER 80S UNDER MOSTLY CLEAR TO PARTLY
CLOUDY SKIES EACH AFTERNOON...SEVERAL DEGREES ABOVE SEASONAL
NORMALS. AS WIND DIRECTIONS STEADILY VEER MORE SOLID ONSHORE MID
WEEK...EXPECT A DECENT TEMPERATURE GRADIENT BETWEEN THE COASTAL
COUNTIES AND INLAND LOCATIONS...AS WELL AS MILDER NIGHTTIME
MINIMUMS IN THE LOW TO MID 60S.

THURSDAY NIGHT INTO FRIDAY...A HIGHLY AMPLIFIED UPPER LEVEL TROUGH
WILL SHIFT THROUGH THE MISSISSIPPI VALLEY THURSDAY NIGHT...THEN
BECOME NEGATIVELY TILTED WHILE SWINGING TOWARD THE EAST COAST ON
FRIDAY. THE UPPER RIDGE AND SURFACE HIGH OVER THE FORECAST AREA
WILL BE PUSHED INTO THE ATLANTIC AS A RESULT...ALLOWING THE
PREDOMINANTLY EAST FLOW TO CONTINUE VEERING TO THE SOUTH LATE
WEEK. NUMERICAL MODEL SOLUTIONS CONTINUE TO SLOW THE PROGRESS OF
THE STRONG COLD FRONT AHEAD OF THE UPPER LEVEL SYSTEM...POSSIBLY
DELAYING ITS PASSAGE THROUGH THE FORECAST AREA UNTIL FRIDAY
EVENING. INITIAL ISOLATED PRECIPITATION COULD OCCUR ALONG THE FAR
SOUTHERN EDGE OF THE FORECAST AREA AS EARLY AS THURSDAY
NIGHT...MAINLY DUE TO THE AFOREMENTIONED RETURN FLOW AND PERHAPS A
SUBTLE WARM FRONT LIFTING THROUGH THE REGION. SHOWER AND
THUNDERSTORM CHANCES WILL THEN INCREASE FROM WEST TO EAST THROUGH
FRIDAY AFTERNOON...WITH BEST CHANCES LATER INTO THE DAY TOWARD THE
EVENING TIME FRAME. CONSIDERING THE TREND IN DELAYING THE FRONTAL
PASSAGE UNTIL LATE DAY OR AFTER SUNSET...THE POTENTIAL FOR THE
BULK OF THE CONVECTION TO OCCUR DURING THE HIGHER INSTABILITY OF
THE AFTERNOON IS DIMINISHING. ALTHOUGH BULK SHEAR VALUES WILL
INCREASE TO 30 TO 40 KT...THERE IS SOME UNCERTAINTY AS TO WHETHER
INSTABILITY WILL BE SUFFICIENT TO SUPPORT STRONG TO SEVERE
THUNDERSTORMS. PREFER TO KEEP MENTION OF ANY ORGANIZED STRONG TO
SEVERE WEATHER OUT OF THE FORECAST AND HAZARDOUS WEATHER OUTLOOK
DUE TO THESE TIMING ISSUES.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
MEDIUM RANGE GUIDANCE IS IN VERY GOOD AGREEMENT WITH THE OVERALL
SYNOPTIC PATTERN...LEADING TO HIGHER THAN NORMAL CONFIDENCE IN THE
FORECAST FOR THE LONG TERM PERIOD. A DEEP UPPER LEVEL TROUGH WILL
LIFT OUT TO THE NORTHEAST OVER THE WEEKEND AND GET REPLACED BY A
MORE BROAD UPPER LEVEL TROUGH WHICH WILL ENCOMPASS MUCH OF THE
EASTERN UNITED STATES THROUGH EARLY NEXT WEEK. MEANWHILE AT THE
SURFACE...A STRONG COLD FRONT WILL MOVE ACROSS THE AREA FRIDAY
NIGHT...WITH HIGH PRESSURE THEN BUILDING OVER THE SOUTHEAST STATES
INTO EARLY NEXT WEEK.

AS FOR EXPECTED WEATHER...SCATTERED SHOWERS AND THUNDERSTORMS WILL
ACCOMPANY THE PASSAGE OF THE COLD FRONT FRIDAY NIGHT...WITH
RAIN-FREE CONDITIONS AND SIGNIFICANTLY COOLER TEMPERATURES THEN
EXPECTED THROUGH EARLY NEXT WEEK.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
VFR. SHALLOW GROUND FOG POSSIBLE AT BOTH TERMINAL EARLY WEDNESDAY
MORNING. WILL LIMIT VISIBILITIES TO MVFR FOR NOW...ALTHOUGH LOWER
CONDITIONS ARE POSSIBLE...ESPECIALLY AT KSAV.

EXTENDED AVIATION OUTLOOK...VFR CONDITIONS ARE EXPECTED TO PREVAIL
THROUGH MUCH OF FRIDAY OUTSIDE OF ANY LATE NIGHT/EARLY MORNING
PATCHY FOG AND/OR STRATUS. FLIGHT RESTRICTIONS WILL BE POSSIBLE
FRIDAY NIGHT INTO EARLY SATURDAY WITHIN SCATTERED SHOWERS AND
THUNDERSTORMS ASSOCIATED WITH A PASSING COLD FRONT.

&&

.MARINE...
TONIGHT...QUIET CONDITIONS. WINDS AND SEAS WILL SUBSIDE OVERNIGHT
AS LOW PRESSURE MOVES FARTHER AWAY AND THE RESULTING PRESSURE
GRADIENT LOOSENS. EXPECT WINDS

WEDNESDAY THROUGH SUNDAY...WINDS/SEAS WILL REMAIN WELL BELOW SMALL
CRAFT ADVISORY LEVELS AS HIGH PRESSURE BUILDS FROM THE NORTH THROUGH
MID WEEK. IN GENERAL...ONSHORE WINDS WILL REMAIN LESS THAN 15 KT
WITH SEAS NO HIGHER THAN 1 TO 3 FT. SOUTHERLY FLOW WILL THEN
STRENGTHEN ON FRIDAY AHEAD OF A COLD FRONT THAT PUSHES OFFSHORE
FRIDAY NIGHT...HOWEVER CONDITIONS STILL LOOK TO REMAIN BELOW
ADVISORY CRITERIA. OFFSHORE FLOW WILL THEN PREVAIL ON
SATURDAY...WITH A SLIGHT NORTHEAST SURGE POSSIBLE SUNDAY BEHIND A
WEAK REINFORCING COLD FRONT.

&&

.EQUIPMENT...
REPAIRS TO THE DOWNTOWN CHARLESTON WEATHER SENSOR AT WATERFRONT
PARK /KCXM/ ARE COMPLETE. HOURLY OBSERVATIONS ARE ONCE AGAIN
AVAILABLE. DAILY CLIMATE PRODUCTS WILL RESUME WEDNESDAY AFTERNOON.

&&

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

&&

$$






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