Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 221048
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
548 AM EST SAT NOV 22 2014

...HEAVY RAINS WITH A RISK FOR SEVERE THUNDERSTORMS...

.SYNOPSIS...
HIGH PRESSURE WILL PREVAIL TODAY. A WARM FRONT WILL MOVE NORTH
THROUGH THE AREA SUNDAY. A COLD FRONT WILL THEN SHIFT TOWARD THE
COAST AND OFFSHORE BY MONDAY NIGHT...FOLLOWED BY HIGH PRESSURE INTO
THE MIDDLE OF NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
THE AREA WILL REMAIN PINNED BETWEEN AND AN INLAND WEDGE OF HIGH
PRESSURE AND A SHARPENING COASTAL TROUGH OFFSHORE. THIS
CONFIGURATION WILL SUPPORT BREEZY CONDITIONS ALONG THE COAST...
ESPECIALLY FROM HILTON SOUTH TO SAPELO ISLAND THROUGH THE DAY WITH
NORTHEAST WINDS 15-25 MPH WITH HIGHER GUSTS. MODELS SHOW SOME WEAK
ISENTROPIC ASSENT DEVELOPING ATOP THE WEDGE ACROSS SOUTHEAST
GEORGIA THIS AFTERNOON...BUT THE DRY MODIFIED ARCTIC AIRMASS AND
HIGH CONDENSATION PRESSURE DEFICITS SUGGEST IT WILL TAKE SOME
TIME FOR ANY MEASURABLE RAINFALL TO DEVELOP WITH MOST OF THE
290-295K ISENTROPIC UPGLIDE GOING TOWARDS CLOUD PRODUCTION. EXPECT
SUNNY SKIES TO DOMINATE THIS MORNING OUTSIDE OF A FEW MARINE
BASED STRATOCUMULUS MOVING ONSHORE...WITH THICKER CLOUD COVER
SPREADING IN FROM SOUTH TO NORTH FROM MID-LATE AFTERNOON.
AGAIN...THE COLUMN LOOKS TO DRY TO SUPPORT RAIN...SO GRIDDED POPS
WILL GENERALLY REMAIN LESS THAN 10 PERCENT ACROSS THE BOARD. HIGHS
WILL RANGE FROM THE LOWER TO MID 60S NORTH TO THE UPPER 60S ACROSS
THE SOUTH. THIS IS A SLIGHTLY ABOVE THE 22/00Z GUIDANCE MEAN AS
HIGHS HAVE BEEN RUNNING SEVERAL DEGREE HIGHER THAN EXPECTED OVER
THE PAST FEW DAYS.

FOR THE SUNRISE UPDATE...
* LOWERED TEMPERATURES INTO THE UPPER 20S ACROSS THE FAR NORTH AND
  RAISED THEM INTO THE LOWER 50S FAR SOUTH WHERE THE ONSHORE FLOW
  IS THE STRONGEST.
* ADJUSTED HOURLY TEMPERATURES AND DEWPOINTS BASED ON CURRENT TRENDS.
* LOWERED SKY COVER PERCENTAGES SLIGHTLY AS CLOUDS ARE SLOWER TO
  ARRIVE.
* INCREASED WINDS ALONG THE GEORGIA COAST SLIGHTLY PER COASTAL
  REPORTS.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH TUESDAY/...
TONIGHT...THE ATMOSPHERE WILL UNDERGO A SIGNIFICANT CHANGE TONIGHT
AS A STRONG LOW-LEVEL JET FORMS ACROSS THE DEEP SOUTH AHEAD OF A
DEVELOPING STORM SYSTEM WELL TO THE WEST. THE STRENGTHENING LOW-
LEVEL JET WILL ADVECT ANOMALOUSLY HIGH MOISTURE FROM OFF THE
ATLANTIC AND GULF OF MEXICO INTO THE AREA WITH PWATS SURGING TO
1.5-2 INCHES BY SUNRISE SUNDAY. WARM FRONTOGENESIS WILL INITIATE
ALONG THE GULF COAST AND NORTHERN FLORIDA THROUGH THE NIGHT...WHILE
THE INLAND WEDGE BEGINS TO BREAK DOWN AS THE PARENT HIGH SHIFTS
WELL OFFSHORE OF THE NORTH CAROLINA OUTER BANKS. THE COMBINATION
OF STRONG ISENTROPIC ASSENT ATOP THE DECAYING INLAND WEDGE AND
DEVELOPING WARM FRONT TO THE SOUTH WITH INCREASING 200-300 HPA
DIFLUENCE AHEAD OF STRONG SHORTWAVE MOVING ACROSS TEXAS WILL
SUPPORT A STEADILY EXPANDING AREA OF RAIN WITH EMBEDDED TSTMS
OVERNIGHT. THERE ARE STILL SOME DIFFERENCES NOTED IN THE VARIOUS
GUIDANCE ON THE EXACT TIMING OF WHEN MEASURABLE RAINFALL WILL MOVE
FROM NORTH TO SOUTH THROUGH THE FORECAST AREA...BUT ALL ARE IN
GENERAL AGREEMENT THAT WIDESPREAD RAINS WILL LIKELY BE IN PROGRESS
AS THE SUN RISES SUNDAY MORNING. HAVE UTILIZED 30/30/30 BLEND
APPROACH WITH THE VARIOUS MODELS TO CONSTRUCT HOURLY POPS...BUT
MAX POPS WILL RANGE FROM 70-80 PERCENT ACROSS THE CHARLESTON
COUNTY AREA TO 90-100 PERCENT ACROSS FAR SOUTHERN SOUTH CAROLINA
AND ALL OF SOUTHEAST GEORGIA. THE RAIN COULD BECOME LOCALLY HEAVY
AT TIMES AFTER MIDNIGHT...ESPECIALLY WITH THE POTENTIAL FOR SOME
EMBEDDED TSTMS. LOWS WILL RANGE FROM THE LOWER 50S WELL INLAND AND
FAR NORTH TO THE UPPER 50S TO LOWER 60S ACROSS THE SOUTH.

SUNDAY AND SUNDAY NIGHT...ROBUST SOUTHERN STREAM SHORTWAVE ENERGY
WILL RAPIDLY LIFT FROM THE WESTERN GULF OF MEXICO INTO THE EASTERN
TENNESSEE VALLEY DURING THE DAYTIME HOURS...PROVIDING THE ENERGY
TO DEEPEN A SURFACE LOW ACROSS THE MISSISSIPPI VALLEY. A PROMINENT
WARM FRONT DOWNSTREAM OF THE LOW SYSTEM WILL LIFT THROUGH THE
CAROLINAS SUNDAY AFTERNOON...WITH A DECENT TAP INTO ATLANTIC AND
GULF MOISTURE SUPPORTING A SURGE IN PRECIPITABLE WATER VALUES TO
NEARLY 2 INCHES. HEAVY RAINFALL IS EXPECTED ON SUNDAY AS A
RESULT...AND HAVE MAINTAINED RAIN CHANCES UP TO 100 PERCENT DURING
THE AFTERNOON TIME FRAME. RAIN ACCUMULATION COULD REACH 2 TO 3
INCHES...WITH EVEN SOME POSSIBLE 3 TO 4 INCHES BY THE NIGHTTIME
PERIOD. LATEST THINKING IS THAT THE MAIN FLOODING CONCERNS WILL BE
ASSOCIATED WITH HIGH TIDE ALONG THE COASTAL COUNTIES...AND WILL
NEED TO MONITOR THE TIMING OF HEAVIEST RAIN WITH ASTRONOMICAL HIGH
TIDES AROUND 8 TO 9 AM AND 8 TO 9 PM. WARM ADVECTION IN THE WAKE
OF THE LIFTING FRONT WILL ALLOW TEMPERATURES TO RISE INTO THE
UPPER 60S NORTH TO LOW 70S SOUTH OF THE SAVANNAH RIVER...WHILE
SOLID WARM SOUTHERLY FLOW AND THICK CLOUD COVER WILL SUPPORT VERY
MILD NIGHTTIME LOWS IN THE LOW TO MID 60S.

STORM PREDICTION CENTER HAS MAINTAINED A SLIGHT RISK ZONE ACROSS
THE FORECAST AREA FOR SUNDAY AND SUNDAY NIGHT. ALTHOUGH THERE IS A
SMALL CHANCE FOR ISOLATED SEVERE CONVECTION AS THE WARM FRONT
LIFTS THROUGH THE AREA SUNDAY AFTERNOON...MAINLY IN DAMAGING WIND
GUSTS OR AN ISOLATED TORNADO...THE EVENING TIME FRAME COULD BECOME
A LARGER CONCERN REGARDING SEVERE POTENTIAL. ONSHORE FLOW DURING
THE DAYTIME HOURS COULD ASSIST IN STABILIZING THE
ATMOSPHERE...WHILE THE DEVELOPMENT OF THE STRONGEST WIND FIELDS
COULD BE DELAYED UNTIL AT LEAST EARLY EVENING. MODEL SIMULATED
RADAR REFLECTIVITY SUGGESTS THERE COULD BE A BRIEF BREAK BETWEEN
THE WIDESPREAD RAIN ASSOCIATED WITH THE LIFTING WARM FRONT...AND A
SECONDARY BAND OF CONVECTION INITIATING JUST AHEAD OF THE DRY SLOT
AND ALONG A REGION OF ENHANCED VORTICITY WITHIN THE SOUTHERN
STREAM SHORTWAVE. A POSSIBLE PSEUDO SQUALL LINE COULD THEN
APPROACH AND BE BETTER TIMED WITH AN IMPRESSIVE 40 TO 50 KT LOW
LEVEL JET AND SUBSEQUENTLY INCREASING BULK SHEAR VALUES. ANY
CONVECTION WITH DEEPER UPDRAFTS COULD TAP INTO THESE STRONG WINDS
AND PRODUCE DAMAGING WINDS GUSTS AND PERHAPS SUPPORT ANOTHER SMALL
TORNADO THREAT.

RAIN CHANCES WILL DIMINISH FROM SOUTH TO NORTH LATE SUNDAY
NIGHT...AS THE MAIN SURFACE LOW TRACKS INTO THE GREAT LAKES REGION
AND THE FORECAST AREA FALLS WITHIN DRIER AIR BETWEEN THE WARM
FRONT AND AN APPROACHING COLD FRONT TO THE WEST. MODEL GUIDANCE
CONTINUES TO INDICATE THE POTENTIAL FOR FOG AND STRATUS
DEVELOPMENT AFTER MIDNIGHT...GIVEN THE WARM AIR AND ABUNDANT
RAINFALL FROM EARLIER IN THE DAY. WILL CONTINUE TO INDICATE PATCHY
FOG LATE SUNDAY NIGHT INTO EARLY MONDAY FOR THE LAND AREAS AND
NEARSHORE WATERS.

MONDAY AND MONDAY NIGHT...THE COLD FRONT TRAILING FROM THE STRONG
GREAT LAKES LOW PRESSURE WILL HAVE BECOME SOMEWHAT SEPARATED FROM
THE PARENT SYSTEM AND NEARLY PARALLEL TO THE FLOW ALONG THE
EASTERN PERIPHERY OF THE EXPANSIVE UPPER TROUGH AXIS. FRONTAL
PROGRESSION WILL BE SLOW AS A RESULT...LIKELY NOT OCCURRING UNTIL
THE NIGHTTIME HOURS. A RESIDUAL BAND OF DEEP MOISTURE AHEAD OF THE
FRONT COULD SUPPORT ISOLATED TO SCATTERED SHOWERS/THUNDERSTORMS
MONDAY AFTERNOON...AND WILL CONTINUE TO ADVERTISE RAIN CHANCES
ACCORDINGLY. TEMPERATURES WILL BE ABLE TO RISE WELL ABOVE SEASONAL
NORMALS...PEAKING IN THE UPPER 70S DUE TO A WARMER START TO THE
DAY AND WITHIN CONTINUED SOUTH/SOUTHWEST FLOW. HOWEVER EXPECT LOW
TEMPERATURES MONDAY NIGHT TO BE NOTABLY COOLER THAN THE PREVIOUS
NIGHT...RANGING FROM THE UPPER 40S INLAND TO THE LOW 50S CLOSER TO
THE COAST...STILL SEVERAL DEGREES ABOVE NORMAL.

TUESDAY...THE FRONT WILL LIKELY LINGER JUST OFFSHORE...AS WEAK
WAVES OF LOW PRESSURE DEVELOP ALONG THE SOUTHERN END OF THE
FEATURE. DEPENDING ON THE PROXIMITY OF THE FRONT AND ASSOCIATED
CONVERGENCE/FORCING...SCATTERED SHOWERS COULD STILL AFFECT THE AREA
THROUGH THE AFTERNOON...ESPECIALLY FOR COASTAL LOCATIONS CLOSER TO
THE MEANDERING FRONT. HIGH TEMPERATURES WILL BE AT LEAST 10
DEGREES COOLER THAN THE PREVIOUS DAY...ONLY REACHING THE MID 60S
IN THE WAKE OF THE COLD FRONT.

&&

.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
THE AXIS OF A ROBUST UPPER TROUGH WILL FINALLY SWEEP TOWARD THE
COAST WEDNESDAY...WITH ABUNDANT ENERGY HELPING TO DEEPEN THE
SURFACE WAVES OF LOW PRESSURE ALONG THE MEANDERING OFFSHORE FRONT.
THE RESULTING LOW SYSTEM WILL RAPIDLY LIFT NORTH/NORTHEAST AWAY
FROM THE AREA WEDNESDAY NIGHT. DRIER HIGH PRESSURE WILL THEN BUILD
INTO THE REGION FROM THE WEST. A NOTABLE COOLING TREND IS EXPECTED
WEDNESDAY THROUGH THE REMAINDER OF THE WEEK...WITH HIGH
TEMPERATURES SUPPRESSED IN THE UPPER 50S TO LOWER 60S...AND LOWS
FALLING INTO THE 30S.

&&

.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
VFR THROUGH EARLY THIS EVENING...THEN CLOUDS LOWER AFTER SUNSET
AS ISENTROPIC ASSENT BEGINS TO INCREASE. EXPECT PREVAILING MVFR
CIGS TO SPREAD SOUTH-NORTH OVERNIGHT...REACHING KSAV BY 04Z AND
KCHS BY 09Z. IFR CONDITIONS LIKELY AT KSAV AFTER 07Z AS HEAVIER
RAINS MOVE IN. AT KCHS...PRE-FRONTAL FOG/STRATUS WILL BE POSSIBLE
09-12Z. LIMITED CONDITIONS TO LOW-END MVFR FOR NOW WITH PREVAILING
4SM BR SCT004 BKN012.

EXTENDED AVIATION OUTLOOK...CONDITIONS WILL DETERIORATE SUNDAY...AS
A WARM FRONT LIFTS NORTH INTO THE AREA. THIS WILL RESULT IN MVFR
CONDITIONS IN RAIN...ISOLATED TSTMS AND LOCALLY HEAVY RAIN. THERE
IS AN ELEVATED POTENTIAL FOR IFR OR LOWER CONDITIONS BEHIND THE
WARM FRONT EARLY MONDAY. PERIODIC FLIGHT RESTRICTIONS ARE STILL
POSSIBLE EARLY NEXT WEEK UNTIL A COLD FRONT PULLS FARTHER OFFSHORE
BY MID WEEK. BREEZY CONDITIONS SUNDAY INTO MONDAY...WITH A RISK OF
WIND SHEAR SUNDAY NIGHT.

&&

.MARINE...
TODAY...PINCHED GRADIENT CONDITIONS BETWEEN INLAND HIGH PRESSURE
AND A SUBTLE COASTAL TROUGH OFFSHORE WILL SUPPORT GUSTY WINDS OVER
THE WATERS TODAY. WINDS WILL REMAIN 15-25 KT THROUGH THE
DAY WITH THE HIGHEST WINDS HOLDING OVER THE CENTRAL AND SOUTHERN
WATER WHERE THE SURFACE PRESSURE GRADIENT WILL REMAIN THE
TIGHTEST. WINDS MAY RELAX A BIT LATE THIS AFTERNOON...BUT CHOPPY
CONDITIONS WILL PERSIST. SEAS WILL AVERAGE 3-5 FT OVER THE
CHARLESTON COUNTY WATERS TO 5-7 FT OVER THE REMAINING AREAS. A
SMALL CRAFT ADVISORY REMAINS IN EFFECT FOR THE BEAUFORT WATERS
THROUGH LATE MORNING...AFTER WHICH SEAS WILL DROP BELOW 6 FT.
FLAGS WILL REMAIN IN FORCE FOR THE TWO GEORGIA MARINE LEGS THROUGH
THE DAY.

TONIGHT...WINDS WILL BEGIN TO VEER TO THE EAST OVERNIGHT AS THE
INLAND WEDGE BEGINS TO BREAK DOWN AND THE COASTAL FRONT EVENTUALLY
MERGES WITH A DEVELOPING WARM FRONT TO THE SOUTH. ELEVATED WINDS
AND SEAS WILL REMAIN IN PLACE...DESPITE LESS THAN PERFECT MIXING
PROFILES IN THE STRONG WARM AIR ADVECTION REGIME. WINDS LOOK TO
REMAIN 15-20 KT NEARSHORE WATERS WITH 20-25 KT OVER THE GEORGIA
OFFSHORE WATERS WHERE WARMER WATER TEMPERATURES WILL SUPPORT A BIT
MORE MIXING. SEAS WILL AVERAGE 4-7 FT NEARSHORE WATERS TO 6-8 FT
OFFSHORE WATERS.

SUNDAY AND SUNDAY NIGHT...A WARM FRONT WILL LIFT INTO AND THROUGH
THE COASTAL WATERS. WARM ADVECTION WILL LIMIT THE POTENTIAL FOR
IMPRESSIVE LOW LEVEL WINDS TO MIX TO THE OCEAN SURFACE...HOWEVER
WINDS JUST OFF THE SURFACE STILL LOOK STRONG ENOUGH TO SUPPORT THE
EVENTUAL EXPANSION/EXTENSION OF SMALL CRAFT ADVISORIES ACROSS ALL
WATERS. THE RISK FOR ANY MARGINAL GALES ACROSS THE NORTHERN SOUTH
CAROLINA WATERS AND THE OFFSHORE GEORGIA ZONES STILL APPEARS TOO LOW
TO SUPPORT A GALE WATCH AT THIS TIME. NUMEROUS TO WIDESPREAD SHOWERS
AND SCATTERED THUNDERSTORMS WILL IMPACT THE MARINE AREA...A FEW OF
WHICH COULD RESULT IN SPECIAL MARINE WARNINGS FOR DAMAGING WINDS AND
ISOLATED TORNADIC WATERSPOUTS. SINCE THE SHELF WATERS HAVE COOLED
CONSIDERABLY INTO THE 50S...AS THE WARM AND SATURATED AIR MASS
OVERSPREADS THE AREA...THERE COULD BE A CONCERN FOR LOW STRATUS
BUILD-DOWN AND/OR SEA FOG. WILL MAINTAIN MENTION OF PATCHY FOG TO
THE FORECAST FOR SUNDAY NIGHT.

MONDAY THROUGH WEDNESDAY...A SLOW MOVING COLD FRONT OVER THE
SOUTHEAST STATES ON MONDAY WILL MOVE INTO AND THROUGH THE WATERS
BY TUESDAY. LOW PRESSURE WILL THEN FORM ALONG THE LINGERING FRONT
JUST OUTSIDE OF THE MARINE AREA AND EVENTUALLY PULL THE FRONT
AWAY FROM THE REGION BY WEDNESDAY. DEPENDING UPON EXACTLY HOW
THIS PATTERN UNFOLDS...ADDITIONAL SMALL CRAFT ADVISORIES MAY BE
NEEDED DURING THIS TIME.

&&

.HYDROLOGY...
A WIDESPREAD HEAVY RAIN EVENT LATE TONIGHT INTO MONDAY IS
BECOMING MORE CERTAIN WITH EACH MODEL CYCLE. ANOMALOUSLY HIGH
PWATS OF 1.5-2 INCHES COUPLED WITH STRONG UPPER DYNAMICS WILL
SUPPORT WIDESPREAD HEAVY RAINS WITH EMBEDDED TSTMS ACROSS
SOUTHEAST SOUTH CAROLINA AND SOUTHEAST GEORGIA DURING THE PERIOD.
STORM TOTAL AMOUNTS OF 2-4 INCHES WITH LOCALLY HIGHER AMOUNTS CAN
BE EXPECTED WITH THE BULK OF THE HEAVIEST RAINS FALLING SUNDAY
INTO SUNDAY NIGHT. THE RISK FOR SIGNIFICANT FLASH FLOODING WILL
BE MAINLY CONFINED TO THE COASTAL COUNTIES WHERE THE COMBINATION
OF HEAVY RAIN AND ABOVE NORMAL HIGH TIDES WILL SUPPORT A HIGHER
RISK FOR FLASH FLOODING...ESPECIALLY IN THE DOWNTOWN CHARLESTON
AND SAVANNAH METRO AREAS. A FLASH FLOOD WATCH MAY EVENTUALLY BE
NEEDED FOR PARTS OF THE AREA...ESPECIALLY AT THE COAST.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 11 AM EST THIS MORNING FOR AMZ352.
     SMALL CRAFT ADVISORY UNTIL 5 AM EST TUESDAY FOR AMZ374.
     SMALL CRAFT ADVISORY UNTIL 5 PM EST MONDAY FOR AMZ354.

&&

$$

ST/WMS




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