Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 010522
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1222 AM EST SUN FEB 1 2015

.SYNOPSIS...
HIGH PRESSURE WILL SHIFT INTO THE ATLANTIC TONIGHT AND SUNDAY...WHILE A
WEAK TROUGH OF LOW PRESSURE DEVELOPS OFFSHORE AND LIFTS NORTH AHEAD OF A
STRONG COLD FRONT PASSING OVER THE AREA MONDAY. HIGH PRESSURE WILL THEN
RETURN TO THE REGION BY TUESDAY...BEFORE SHIFTING OFFSHORE AHEAD OF
ANOTHER STORM SYSTEM APPROACHING FROM THE GULF OF MEXICO BY LATE IN THE
WEEK.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
DRY WEATHER WILL PREVAIL. CURRENT FORECAST LOOKS GOOD AND ONLY
MINOR ADJUSTMENTS WERE NEEDED FOR THE MIDNIGHT UPDATE.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH TUESDAY/...
SUNDAY...SURFACE HIGH PRESSURE AND ITS ASSOCIATED SHORT WAVE
RIDGING ALOFT WILL PULL INTO THE ATLANTIC IN ADVANCE OF AN
GRADUALLY AMPLIFYING SHORT WAVE AND IT/S CO-LOCATED SURFACE LOW
MOVING EAST THROUGH THE MID MISSISSIPPI VALLEY AND MIDWEST. AS
THIS TRANSITION OCCURS A VERY SUBTLE COASTAL TROUGH WILL FORM OUT
NEAR THE WESTERN WALL OF THE GULF STREAM ON THE WEST SIDE OF THE
ATLANTIC PROGRESSING ANTICYCLONE. WHILE A FEW SHOWERS WILL FORM IN
PROXIMITY TO THE COASTAL TROUGH...THEY LOOK TO REMAIN IN THE
OCEAN. DEEPER MOISTURE AND THE BEST FORCING WITH THE UPSTREAM
CYCLONE AND SHORT WAVE ALOFT WILL REMAIN WEST OF THE REGION
THROUGH THE DAY. THUS WE ARE SHOWING A RAIN FREE FORECAST.
ISENTROPIC LIFT WILL BE SUFFICIENT ENOUGH TO GENERATE AN INCREASE
IN MARINE- INDUCED STRATOCUMULUS CLOUDS WITHIN THE LOW LEVEL
SOUTHERLY FLOW...WHILE JET STREAM CIRRIFORM CLOUDS WILL PERSIST
FROM THE WEST. DESPITE THIS THERE IS CONSIDERABLE WARM ADVECTION
WHICH WILL SEND TEMPS FAR ABOVE NORMAL INTO THE MID AND UPPER 60S
INLAND...MAYBE EVEN HITTING 70 NEAR THE ALTAMAHA RIVER. SEA BREEZE
CIRCULATIONS WILL LIMIT COASTAL COMMUNITIES TO THE UPPER 50S AND
LOWER 60S. WHILE THESE TEMPS ARE NOT RECORDS...THEY DO SHOW A
TREMENDOUS DIURNAL RANGE IN TEMPS OF SOME 30-35 DEGREES IN MOST
SECTIONS.

SUNDAY NIGHT AND MONDAY...THIS LOOKS TO BE THE MOST ACTIVE PART OF
THE SHORT TERM PERIOD...WITH THE REGION TO BE IMPACTED BY A STRONG
COLD FRONT FROM THE WEST/NW. A POSITIVE TILTED SHORT WAVE ALOFT WILL
AMPLIFY FURTHER AS IT SWEEPS INTO THE OHIO/TENNESSEE VALLEYS BY
DAYBREAK MONDAY...THEN ALIGNS ITSELF MORE NEUTRALLY TILTED MONDAY AS
IT SWINGS BY TO THE NORTH MONDAY AFTERNOON. THIS PRONOUNCED FEATURE
ALOFT WILL SEND A STRONG AND FATS MOVING COLD FRONT OVER THE
APPALACHIANS BY 12Z MONDAY...INTO OUR NW TIER BY 15Z MONDAY...TO THE
COAST BY 18Z AND FURTHER OFFSHORE THEREAFTER. WE LOOK FOR A LOWERING
AND THICKENING OF CLOUD COVER SUNDAY EVENING...WITH SHOWERS TO
ARRIVE FROM THE WEST DURING THE LATE EVENING WEST AND OVERNIGHT
FURTHER EAST. THIS IS IN RESPONSE TO THE APPROACHING COLD FRONT...A
150 KT OR GREATER UPPER JET...A 50 KT OR STRONGER LOW LEVEL JET AND
PWATS THAT RISE TO 1.25 INCHES OR MORE. WHILE THERE IS STILL A
LITTLE UNCERTAINTY IN REGARDS TO TIMING...JUST ABOUT EVERYWHERE
BY SUNRISE MONDAY LOOKS TO BE WET. RAIN CHANCES WILL LINGERING
INTO MONDAY MORNING...THEN QUICKLY DROP OFF FROM WEST TO EAST FOR
THE LATE MORNING AND AFTERNOON IN WAKE OF THE COLD FRONT. WE HAVE
LIKELY TO CATEGORICAL POPS GOING FOR LATER SUNDAY NIGHT...WITH
CATEGORICAL ALL ZONES MONDAY MORNING. BY 18Z THE VAST MAJORITY OF
THE SHOWERS WILL BE OFFSHORE AND THE BULK OF AFTERNOON WILL BE
RAIN FREE. SINCE THERE ARE STILL SOME TIMING UNCERTAINTIES WE
HAVE NOT SHOWN ANYTHING HIGHER THAN 80 OR 90 PERCENT...BUT 100
POPS WILL BE NECESSARY AT SOME POINT ONCE THE EVENT GETS CLOSER.
QPF LOOKS TO ABOUT 1/4 TO 1/2 INCH ON AVERAGE GIVEN THE
PROGRESSIVE NATURE TO THE SHOWERS.

WHILE WE CANNOT ENTIRELY RULE OUT SOME ELEVATED CONVECTION...POOR
THERMODYNAMIC PROFILES SUGGEST THAT THE RISK FOR THUNDER IS LOW
ENOUGH TO OMIT FROM THE LATEST FORECAST.

THERE IS ALSO A SMALL WINDOW FOR POSSIBLE SEA FOG EARLY SUNDAY NIGHT
OVER THE COASTAL COUNTIES...BUT LATEST TRAJECTORY FORECASTS SUGGESTS
THAT IF IT IS ABLE TO FORM IT WOULD REMAIN MOSTLY IN THE NEARBY
ATLANTIC AS WINDS INCREASE.

WINDS WILL RISE CONSIDERABLY AFTER MIDNIGHT SUNDAY NIGHT IN RESPONSE
TO A POTENT LOW LEVEL JET PASSING THROUGH...WITH SW WINDS TO CLIMB
TO 15-25 AND GUSTY...GREATEST OVER COASTAL SC. THEN A PRONOUNCED
RISE/FALL COUPLET WILL DEVELOP MONDAY WITH THE PASSAGE OF THE COLD
FRONT AND THIS ALLOWS FOR WINDS TO VEER TO WEST/NW AND RISE TO 20-30
MPH WITH STRONGER GUSTS AREA WIDE. WE/LL NEED TO CAREFULLY
MONITOR FOR A POSSIBLE WIND ADVISORY OVER COASTAL SC LATE SUNDAY
NIGHT AND MAYBE OVER A LARGER AREA MONDAY. FOR NOW WE LOOK TO
REMAIN JUST BELOW THE WIND ADVISORY CRITERIA.

TEMPS WILL FALL ABOUT 5-10 DEGREES SUNDAY EVENING...THEN HOLD STEADY
OR EVEN RISE WITH INCREASED WARM ADVECTION AND INSULATING EFFECTS
OF THE OVERCAST SKIES. BY MONDAY MORNING EASTERN SECTIONS WILL BE
BACK INTO THE LOWER 60S. TEMPS WON/T BUDGE MUCH THE REST OF
MONDAY...MAYBE EVEN FALLING A FEW DEGREES AS COLD ADVECTION CRANKS
UP. DESPITE INCREASED SUNSHINE...MUCH OF THIS ENERGY WILL BE
UTILIZED EVAPORATING THE STANDING RAIN WATERS.

MONDAY NIGHT AND TUESDAY...COLD ADVECTION AND CLEAR SKIES WILL LEAD
TO A COLD NIGHT MONDAY NIGHT...WITH ANOTHER LARGE DIURNAL SWING IN
TEMPS TO OCCUR. AN ADVECTIVE FREEZE WILL MAKE IT TO NEAR THE US-17
INTRA-COASTAL...WITH ONLY THE BARRIER ISLANDS TO HOLD ABOVE
FREEZING. ALTHOUGH WINDS WILL DIMINISH WHEN COMPARED TO DURING THE
DAY MONDAY...WHEN COMBINED WITH THESE TEMPS WILL EQUATE TO WIND
CHILLS IN THE LOWER AND MIDDLE 20S BY TUESDAY MORNING. CANADIAN HIGH
PRESSURE WILL SETTLE ATOP THE LOCAL AREA TUESDAY WITH ZONAL FLOW
ALOFT...AND DESPITE PLENTIFUL INSOLATION THE LOW LEVEL THICKNESS
FORECAST SUPPORTS HIGHS ONLY IN THE UPPER 40S AND LOWER 50S AS THE
SYNOPTIC FLOW VEERS AROUND TO THE NE FROM OFF THE ATLANTIC.

LAKE WINDS...GUSTY WINDS WILL DEVELOP OVER LAKE MOULTRIE LATE SUNDAY
NIGHT WITH A ROBUST LOW LEVEL JET IN ADVANCE OF A STRONG COLD FRONT
THAT SHIFTS THROUGH MONDAY MORNING. COLD ADVECTION AND LARGE
ISALLOBARIC PRESSURE RISES WILL THEN TRANSPIRE IN WAKE OF THE FRONT
BEFORE FADING MONDAY NIGHT INTO TUESDAY. AS A RESULT WE/LL LIKELY
REQUIRE A LAKE WIND ADVISORY AT A LATER TIME FOR LAKE MOULTRIE.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
TRANSIENT SURFACE HIGH PRESSURE WILL MOVE INTO THE ATLANTIC TUESDAY
NIGHT. A COASTAL TROUGH WILL ONCE AGAIN DEVELOP ALONG THE PERIPHERY
OF THE ATLANTIC HIGH ON WEDNESDAY...WHILE A SOUTHERN STREAM
SHORTWAVE DEVELOPS FAR TO THE WEST ACROSS TEXAS AND SUPPORTS THE
DEVELOPMENT OF A SURFACE LOW IN THE GULF OF MEXICO. ALTHOUGH THE
INITIAL SHORTWAVE WILL DAMPEN LATE WEDNESDAY...THE SURFACE LOW WILL
CONTINUE TO TAKE SHAPE AND MOVE EAST ACROSS THE GULF. NUMERICAL
MODEL SOLUTIONS DIVERGE QUITE NOTABLY REGARDING THE STRENGTH OF THE
LOW PRESSURE WAVE AND THE PRESENCE OF ADDITIONAL SHORTWAVE ENERGY
DIVING INTO THE GULF COAST STATES OR SOUTHEAST LATE THURSDAY INTO
FRIDAY. AS A RESULT...CONFIDENCE IN FORECAST DETAILS BECOMES RATHER
LOW FOR THE LATE WEEK PERIOD.

AFTER A PERIOD OF DRY WEATHER EARLY IN THE WEEK...HAVE REINTRODUCED
RAIN CHANCES BY WEDNESDAY TO ACCOUNT FOR MARINE SHOWERS PROGRESSING
ONSHORE FROM THE COASTAL TROUGH. HAVE THEN INCREASED RAIN COVERAGE
WEDNESDAY NIGHT INTO THURSDAY...AS MEDIUM RANGE MODELS ARE IN
GENERAL AGREEMENT THAT SOME DEGREE OF RAIN WILL BE AFFECTING THE
FORECAST AREA DURING THIS TIME FRAME. MODEL SOLUTIONS THAT INDICATE
THE SECOND WAVE OF UPPER LEVEL ENERGY LATE THURSDAY INTO FRIDAY
MAINTAIN RAIN COVERAGE ACROSS THE REGION ACCORDINGLY...YET WILL CAP
RAIN POTENTIAL NO HIGHER THAN SLIGHT CHANCE THROUGH FRIDAY UNTIL
MODELS COME INTO BETTER AGREEMENT. HAVE INDICATED RAIN CHANCES
FALLING BELOW 10 PERCENT BY SATURDAY...WITH ANY COASTAL LOW SYSTEM
LIKELY LIFTING AWAY BY THE WEEKEND.

HIGH TEMPERATURES WILL BE IN THE UPPER 50S TO LOWER 60S WEDNESDAY
AND THURSDAY AFTERNOONS...BEFORE A NOTABLE COOLING TREND OCCURS ON
THE BACK SIDE OF THE LOW PRESSURE SYSTEM FRIDAY AND SATURDAY.

&&

.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
VFR.

EXTENDED AVIATION OUTLOOK...VFR CONDITIONS SHOULD WILL PREVAIL UNTIL
SUNDAY NIGHT INTO MONDAY MORNING...WHEN MVFR OR POSSIBLY LOWER
CONDITIONS WILL OCCUR IN SHRA AND LOWER CLOUD DECKS DUE TO A PASSING
COLD FRONT. BREEZY CONDITIONS AND/OR WIND SHEAR IS ALSO LIKELY
SUNDAY NIGHT/MONDAY. VFR CONDITIONS WILL THEN RETURN FOR THE BALANCE
OF MONDAY INTO THURSDAY.

&&

.MARINE...
OVERNIGHT...NO CHANGES.

SUNDAY...THE LOCAL WATERS WILL LIE WITHIN THE WESTERN
SIDE OF SURFACE HIGH PRESSURE MOVING FURTHER EAST INTO THE
ATLANTIC. A RELAXED GRADIENT INITIALLY WILL BEGIN TO TIGHTEN IN
ADVANCE OF A SLOWLY STRENGTHENING LOW AND TRAILING COLD FRONT
MOVING THROUGH THE MID/LOWER MISSISSIPPI VALLEY AND MIDWEST. WHEN
COMBINED WITH SEA BREEZE CIRCULATIONS WILL NOTICE AN INCREASE IN
WINDS AND SEAS DURING THE AFTERNOON...BUT STILL BELOW ANY ADVISORY
CONDITIONS.

SUNDAY NIGHT AND MONDAY...HAZARDOUS MARINE CONDITIONS WILL
EVENTUALLY DEVELOP AS THE AFOREMENTIONED LOW AND ASSOCIATED COLD
FRONT MOVES STEADILY EAST AND CROSS THE APPALACHIANS LATE SUNDAY
NIGHT...MOVING INTO AND THROUGH THE LOCAL MARINE DISTRICT BY LATE
MONDAY MORNING AND THE EARLY AFTERNOON. MIXING IS SOMEWHAT CURTAILED
BY THE WARM ADVECTION REGIME IN ADVANCE OF THE COLD FRONT SUNDAY
NIGHT...BUT SOLID SMALL CRAFT ADVISORIES SEEM LIKELY OVER MOST IF
NOT ALL WATERS. WE DID CONSIDER HOISTING A GALE WATCH FOR LATE
SUNDAY NIGHT...BUT AFTER COORDINATION WITH NEIGHBORING WFO/S JAX AND
ILM WE HAVE HELD OFF SINCE IT IS THE THIRD PERIOD OF THE FORECAST.
BUT INITIALLY GIVEN A 50 KT OR GREATER LOW LEVEL JET SUNDAY
NIGHT/EARLY MONDAY FOLLOWED BY A NOTABLE RISE/FALL COUPLET IN
PRESSURES WITH THE PASSAGE OF THE COLD FRONT...GALES SEEM LIKELY
ACROSS AT LEAST AMZ350-374.

MARINERS ARE ALSO ALERTED TO THE POSSIBILITY OF SEVERAL HOURS OF SEA
FOG...ESPECIALLY ON THE SOUTHERN AND CENTRAL SHELF WATERS SUNDAY
EVENING AS A WARMER AND MORE HUMID AIR MASS OVER-RIDES THE COOLER
NEARBY WATERS. BUT AS WINDS INCREASE AND TRAJECTORIES VEER TO THE SW
THROUGH THE NIGHT THE RISK FOR FOG LOOKS TO END BY 1-2 AM MONDAY.
ALSO...SOME STRONGER T-STORMS COULD FORM OUT NEAR THE GULF STREAM
LATE SUNDAY NIGHT INTO MONDAY MORNING PRIOR TO THE FRONTAL PASSAGE.

TUESDAY THROUGH THURSDAY...MUCH BETTER MARINE CONDITIONS WILL OCCUR
FOR MID WEEK UNDER THE INFLUENCE OF A TRANSIENT SURFACE
HIGH...BEFORE WINDS AND SEAS BUILD AGAIN THURSDAY IN ADVANCE OF
SYSTEM IN THE GULF OF MEXICO. WE/LL BE WELL BENEATH ANY ADVISORY
CONDITIONS TUESDAY AND WEDNESDAY...BUT HEADLINES MIGHT BE REQUIRED
AGAIN THURSDAY AS A STRONG HIGH PRESSURE WEDGE BEGINS TO FORM
INLAND AND A TIGHTER GRADIENT DEVELOPS BETWEEN THIS SYSTEM AND THE
GULF LOW.

&&

.TIDES/COASTAL FLOODING...
STRONG OFFSHORE WINDS WILL DEVELOP IN WAKE OF THE COLD FRONT
MONDAY AND WILL LIKELY LEAD TO THE DEVELOPMENT OF BLOW-OUT TIDES IN
THE AFTERNOON WITH THE LOW TIDE CYCLE. TIDES MIGHT BE AS MUCH AS 1
FT MLLW BELOW PREDICTED LEVELS DURING THAT TIME. NAVIGATE WITH
EXTREME CARE AS CURRENTS WILL BE STRONGER THAN NORMAL AND UNDERWATER
STRUCTURES AND SURFACES WILL BECOME EXPOSED THAT OTHERWISE MIGHT NOT
BE A PROBLEM DURING HIGHER TIDE LEVELS.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 1 AM MONDAY TO 1 AM EST TUESDAY FOR
     AMZ330-352.
     SMALL CRAFT ADVISORY FROM 1 AM MONDAY TO 5 AM EST TUESDAY FOR
     AMZ350.
     SMALL CRAFT ADVISORY FROM 7 PM THIS EVENING TO 5 AM EST
     TUESDAY FOR AMZ374.
     SMALL CRAFT ADVISORY FROM 4 AM MONDAY TO 1 AM EST TUESDAY FOR
     AMZ354.

&&

$$

ST



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