Area Forecast Discussion
Issued by NWS Charleston, SC

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS62 KCHS 270944
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
544 AM EDT FRI MAR 27 2015

.SYNOPSIS...
A STRONG COLD FRONT WILL APPROACH FROM THE WEST AND NORTHWEST THIS
MORNING...PASSING THROUGH THE AREA THIS AFTERNOON. UNSEASONABLY COLD
HIGH PRESSURE WILL PREVAIL THIS WEEKEND. FROST AND AN INLAND FREEZE
COULD OCCUR LATE SATURDAY NIGHT INTO EARLY SUNDAY. HIGH PRESSURE
WILL SHIFT SOUTH OF THE REGION MONDAY...THEN A COLD FRONT WILL
MOVE THROUGH LATE MONDAY INTO EARLY TUESDAY. THE COLD FRONT WILL
STALL THEN WILL LIFT NORTH AS A WARM FRONT AS WARMER HIGH PRESSURE
BUILDS OVER THE REGION THROUGH THE MIDDLE OF NEXT WEEK. ANOTHER
COLD FRONT COULD APPROACH FRIDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
FOR TODAY...A DEEPENING AND AMPLIFYING LONG WAVE TROUGH WILL
PREVAIL OVER THE EASTERN STATES...WITH A SHORT WAVE OVER THE LOWER
MS VALLEY THAT PASSES INTO THE SE STATES BY LATE...WHILE A SECOND
AND STRONGER SHORT WAVE WILL DIVE FROM THE MID MS VALLEY INTO THE
TN VALLEY IN THE AFTERNOON. THIS TRANSITION WILL CAUSE HEIGHTS
ALOFT TO STEADILY FALL AND WILL SHOVE A STRONG COLD FRONT INTO THE
NW TIER DURING THE LATE MORNING...TOWARD OUR COASTAL CORRIDOR BY
EARLY OR MID AFTERNOON...AND INTO THE ATLANTIC THEREAFTER. SHOWERS
ARE ORGANIZING IN GEORGIA AND ALABAMA AND WILL DEVELOP INTO A
SWATH OF SHOWERS THAT WILL ADVANCE AHEAD OF THE COLD FRONT AND
ENTER OUR WEST/NW SECTIONS BY AROUND 8 OR 9 AM...SWEEPING RATHER
QUICKLY EASTWARD AND PROVIDING EVERYONE WITH A FEW HOURS OF RAIN
TODAY.

LARGE SCALE FORCING FOR ASCENT ASSOCIATED WITH A 150 KT OR GREATER
UPPER JET WILL HAVE PLENTY OF MOISTURE TO WORK WITH AS PWATS ARE
BETWEEN 1 AND 2 STANDARD DEVIATIONS ABOVE NORMAL. AS A RESULT WE
ARE SHOWING 80 POPS IN ALL COUNTIES...BUT ONCE RADAR TRENDS ARE
BETTER ILLUSTRATED WE MIGHT BE ABLE TO CARRY 100 POPS FOR A GOOD
CHUNK OF THE CWFA. RAIN CHANCES WILL DROP OFF CONSIDERABLY BEHIND
THE FRONT AS DRIER AIR PUNCHES IN FROM THE SW DURING THE MID AND
LATE AFTERNOON HOURS. GIVEN A STEERING MOTION TOWARD THE EAST/NE
AT 40-50 MPH THE AMOUNT OF RAIN ON AVERAGE LOOKS TO BE LESS THAN
1/4 OR 1/3 INCH.

WITH CONSIDERABLE CLOUD COVER IN PLACE THE THERMODYNAMIC PROFILE
IS FAR FROM IMPRESSIVE. BUT GIVEN SOME NEGATIVE LIFTED
INDICES...MUCAPES AS MUCH AS 300-500 J/KG AND O-6 KM BULK SHEAR OF
75 KT OR SO WE FELT COMPELLED TO CARRY A SLIGHT CHANCE OF
THUNDERSTORMS.

DEEPER MIXING WILL DEVELOP ACROSS SE GA DURING THE MID AND LATE
AFTERNOON AS THE DRIER AIR WORKS IT/S WAY IN AND PRESSURES START
TO CLIMB WE ANTICIPATE GUSTY WEST/NW WINDS TO RISE INTO THE 15-25
MPH RANGE. FURTHER NORTH IN SC THE CONDITIONS ARE NOT QUITE AS
FAVORABLE...BUT STILL WINDS WILL PEAK AT 10-20 MPH.

TEMPS ARE OFF TO A WARM START BY LATE MARCH STANDARDS AND WITH
SEVERAL HOURS OF WARM ADVECTION THIS WILL HELP IN NEGATING THE
EXTENSIVE CLOUD COVER AND LACK OF INSOLATION. THIS SHOULD BUMP US
INTO THE UPPER 60S AND LOWER 70S MOST COMMUNITIES...ALTHOUGH A FEW
MID 70S MIGHT BE ACHIEVED SOUTH OF SAVANNAH.

TONIGHT...ALTHOUGH THE DEEP MOISTURE WILL HAVE PULLED EAST WITH
THE COLD FRONT...THERE IS STILL SOME LINGERING LOW LEVEL MOISTURE
WITHIN THE FIRST COUPLE OF MILES OFF THE DECK. A POTENT SHORT WAVE
EMBEDDED WITHIN THE LONG WAVE TROUGH ALOFT WILL MOVE DIRECTLY
THROUGH THE CWFA AROUND 05-10Z. THIS WILL SUPPORT 20-30 POPS AND
MAINLY ACROSS THE CHARLESTON TRI-COUNTY REGION WHERE THE BEST
MOISTURE WILL REMAIN. ALTHOUGH COLDER AIR WILL ARRIVE BEHIND THIS
FEATURE IT WON/T GET HERE SOON ENOUGH TO PRODUCE ANYTHING MORE
THAN ISOLATED TO SCATTERED SHOWERS. HOWEVER...STEEP MID LEVEL
LAPSE RATES WITH 500 MB TEMPS AROUND -26 OR -27C COULD ALLOW FOR
SOME SOFT HAIL OR GRAUPEL TO OCCUR IN A FEW OF THE SHOWERS AS THE
SHORT WAVE SWINGS THROUGH. 850 MB TEMPS FALL TO AN ANOMOUSLY COLD
-1C SOUTH AND -4C NORTH AND WILL ALLOW FOR TEMPS TO PLUNGE DOWN
INTO THE UPPER 30S AND LOWER 40S BY DAYBREAK SATURDAY. THIS WILL
BE ABOUT 20-25F COLDER THAN THIS MORNING.

&&

.SHORT TERM /SATURDAY THROUGH MONDAY/...
SATURDAY MORNING...A STRONG SHORTWAVE EMBEDDED WITHIN A LONGWAVE
TROUGH ALOFT 2 TO 3 STANDARD DEVIATIONS DEEPER THAN NORMAL FOR LATE
MARCH WILL PUSH THROUGH THE REGION. MODEL SOUNDINGS SUGGEST A WINDOW
OF OPPORTUNITY FOR CONVECTION SUPPORTED BY VERY COLD AIR
ALOFT/STEEPENING MID-LEVEL LAPSE RATES...BEFORE A SUBSIDENCE
INVERSION DEVELOPS SATURDAY AFTERNOON. HOWEVER...THE PROBABILITY FOR
ANY MEASURABLE PRECIPITATION IN THE FORM OF RAIN SHOWERS AND EVEN
ISOLATED GRAUPEL/LIGHTNING REMAINS TOO LOW...BELOW 15 PERCENT...TO
JUSTIFY A MENTION WITHIN PUBLIC FORECASTS. WILL CONTINUE TO ASSESS.

OTHERWISE...THE MAIN STORY THIS WEEKEND WILL CENTER ON UNSEASONABLY
COOL TEMPERATURES...STRUGGLING TO REACH 60F MOST AREAS EACH
DAY...EXCEPT IN THE LOWER/MID 60S NEAR THE ALTAMAHA RIVER. THESE
HIGH TEMPERATURES WILL AVERAGE 10-14F BELOW NORMAL.

OF GREATEST IMPORT...COLD HIGH PRESSURE WILL SHIFT SOUTHWARD/TOWARD
THE REGION SATURDAY NIGHT/EARLY SUNDAY. THE POTENTIAL FOR BOUNDARY
LAYER DECOUPLING/EFFICIENT RADIATIONAL COOLING WILL INCREASE...AND
TEMPERATURES ARE EXPECTED TO FALL INTO THE 30S AWAY FROM THE
IMMEDIATE COAST. IN FACT...A COUPLE OF HOURS OF SUBFREEZING
TEMPERATURES COULD OCCUR WELL INLAND ESPECIALLY IF WINDS BECOME
CALM. PER COLLABORATION WITH WFOS CAE AND ILM OPTED NOT TO ISSUE
LATE 4TH PERIOD/EARLY 5TH PERIOD FREEZE WATCHES. HOWEVER...ADDED A
MENTION OF FROST AWAY FROM THE COAST...AND FREEZE WATCHES/WARNINGS
AND/OR FROST ADVISORIES COULD EVENTUALLY BE REQUIRED.

MONDAY...THE NEXT COLD FRONT WILL APPROACH THE REGION. AHEAD OF THIS
FEATURE...TEMPERATURES SHOULD RECOVER INTO THE UPPER 60S/LOWER 70S.
ALSO...AT LEAST SLIGHT CHANCE/CHANCE POPS AS AN AXIS OF FORCING FOR
ASCENT/AN ASSOCIATED BAND OF ENHANCED MOISTURE ADVANCES INTO THE
REGION FROM THE NORTHWEST. ISOLATED THUNDERSTORMS CANNOT BE RULED
OUT...BUT INSTABILITY APPEARS MARGINAL THUS OPTED NOT TO ADD A
MENTION OF THUNDER WITHIN THE FRIDAY MORNING FORECAST.

&&

.LONG TERM /MONDAY NIGHT THROUGH THURSDAY/...
THE LATE MONDAY/EARLY TUESDAY COLD FRONT WILL WEAKEN...STALL THEN
WILL EITHER DISSIPATE OR PUSH NORTH AS A WARM FRONT. THUS...A
WARMING TREND IS EXPECTED WITH TEMPERATURES NEAR NORMAL TUESDAY
THEN ABOVE NORMAL...AT LEAST IN THE MID/UPPER 70S WEDNESDAY
THROUGH LATE WEEK. MORE SUNSHINE THAN EXPECTED WEDNESDAY WILL
SUPPORT HIGHS AROUND 80F. THE NEXT OPPORTUNITY FOR SIGNIFICANT
PRECIPITATION WILL OCCUR AFTER WEDNESDAY AS A SOUTHERN SHORTWAVE
TROUGH PUSHES THROUGH THE REGION. TIMING REMAINS UNCERTAIN...POPS
COULD INCREASE AS EARLY AS LATER WEDNESDAY OR WEDNESDAY NIGHT AND
COULD LINGER INTO FRIDAY AS ANOTHER WEAK COLD FRONT ADVANCES INTO
THE REGION...BUT HIGHEST POPS...CAPPED AT CHANCE FOR NOW...ARE IN
ORDER THURSDAY INTO THURSDAY NIGHT. ALSO...MODELS DEPICT
SUFFICIENT INSTABILITY FOR JUSTIFY A MENTION OF THUNDER THURSDAY
AND FRIDAY.

&&

.AVIATION /10Z FRIDAY THROUGH TUESDAY/...
KCHS...VFR CONDITIONS WILL ONLY BE TEMPORARY THIS MORNING AS
FLIGHT RESTRICTIONS WILL RESULT FROM DEVELOPING STRATUS CLOUDS
THAT DROP US INTO THE MVFR RANGE BY DAYBREAK. ADDITIONAL SUB-VFR
CONDITIONS ALONG WITH SHOWERS AND MAYBE AN ISOLATED T-STORM WILL
ACCOMPANY A COLD FRONT...AS IT MOVES TOWARD AND THROUGH THE
AIRFIELD DURING THE LATE MORNING AND AFTERNOON. WEST AND NW WINDS
WILL BE GUSTY AT TIMES...PEAKING AROUND 20 KT...BEFORE FADING WITH
SUNSET. VFR CONDITIONS WILL RETURN TONIGHT BEHIND THE EXITING COLD
FRONT...ALTHOUGH A FEW SHOWERS ARE STILL POSSIBLE AS STRONG ENERGY
ALOFT SWINGS THROUGH.

KSAV...THE AIRPORT WILL TEETER BACK AND FORTH FROM VFR TO MVFR
THIS MORNING...ALTHOUGH EVENTUALLY MVFR WILL PREVAIL. AFTER 15Z
SHOWERS AND MAYBE A T-STORM MOVE THROUGH IN ASSOCIATION WITH A
STRONG COLD FRONT...BEFORE VFR WEATHER FINALLY RETURNS LATE
TODAY AND PERSISTS INTO TONIGHT BEHIND THE COLD FRONT. GUSTY
WESTERLY WINDS WILL PREVAIL DURING MUCH OF THE DAYLIGHT
HOURS...PEAKING AT 20-25 KT IN THE AFTERNOON IN WAKE OF THE COLD
FRONT.

EXTENDED AVIATION OUTLOOK...FLIGHT RESTRICTIONS POSSIBLE IN SHOWERS
MONDAY. OTHERWISE...MAINLY VFR.

&&

.MARINE...
TODAY...A STRONG COLD FRONT WILL HEAD THROUGH THE SE STATES THIS
MORNING...REACHING THE COASTAL WATERS THIS AFTERNOON...PASSING TO
THE EAST/SE AFTER 2 OR 3 PM. DESPITE SOME MARINE LAYERING EFFECTS
WITHIN THE WARM ADVECTION...A FAIRLY DECENT CYCLONIC PRESSURE
GRADIENT WILL ASSIST IN BUMPING SW WINDS UP INTO THE 15 TO 20 KT
RANGE. THERE WILL EVEN BE FREQUENT GUSTS TO NEAR 25 KT ON THE
OUTER GA WATERS AND INFREQUENT GUSTS TO 25 KT ON THE CHARLESTON
COUNTY ATLANTIC WATERS. THIS WILL BE ENOUGH TO CAUSE SEAS TO BUILD
TO 6 FT ON THESE AFOREMENTIONED MARINE ZONES...AND IT IS HERE
WHERE WE HAVE OUR SMALL CRAFT ADVISORIES. THE OTHER WATERS WILL
STAY JUST BELOW ANY ADVISORY CONDITIONS THROUGH THE DAY.
MEANWHILE...SEA FOG IS STILL EVIDENT BASED ON GOES-E SATELLITE
PRODUCTS AND WILL PERSIST INTO THE AFTERNOON UNTIL WINDS VEER TO
WEST AND SCOUR OUT THE FOG. COVERAGE THOUGH DOESN`T APPEAR TO BE
ENOUGH TO JUSTIFY A DENSE FOG ADVISORY. INSTEAD THERE IS A MARINE
WEATHER STATEMENT IN EFFECT. MARINERS ARE ALSO ADVISED THAT A FEW
T-STORMS WILL MOVE THROUGH DURING THE LATE MORNING AND AFTERNOON
HOURS.

TONIGHT...STEADY ISALLOBARIC PRESSURE RISES WILL DEVELOP BEHIND
THE DEPARTING COLD FRONT...KEEPING NW WINDS ELEVATED. AS A RESULT
WE HAVE HOISTED ANOTHER SMALL CRAFT ADVISORY ON THE AMZ354 WHERE
FREQUENT GUSTS TO 25 KT ARE ANTICIPATED WITHIN THE COLD
ADVECTION. THIS WILL GO ALONG WITH AN ALREADY PRE-EXISTING
ADVISORY ON THE OUTER GA WATERS FOR SEAS OF 6 FT AND GUSTS OF 25
OR 30 KT. WE/LL BE CLOSE TO ADVISORY CONDITIONS ON THE SC
ATLANTIC WATERS...AND WE STILL MAY NEED TO RAISE THE FLAGS AT A
LATER TIME.

SATURDAY THROUGH WEDNESDAY...ELEVATED OFFSHORE WINDS AND ASSOCIATED
SMALL CRAFT ADVISORY CONDITIONS SHOULD RELAX AS HIGH PRESSURE SHIFTS
TOWARD THE WATERS SATURDAY AFTERNOON THROUGH SATURDAY EVENING.
HOWEVER...LATE SATURDAY NIGHT INTO SUNDAY GUIDANCE DEPICTS A SURGE
OF NORTHEAST WINDS WHICH COULD PRODUCE A FEW HOURS OF LOCALIZED
SMALL CRAFT ADVISORY CONDITIONS. THEN...AS HIGH PRESSURE SHIFTS
SOUTH OF THE WATERS SUNDAY NIGHT INTO MONDAY...ONSHORE WINDS 10 KT
OR LESS SHOULD VEER TOWARD THE SOUTHWEST AND INCREASE IN
SPEED...ESPECIALLY MONDAY AHEAD OF AN APPROACHING COLD FRONT.

AFTER A WEAKENING COLD FRONT PASSES THEN STALLS MONDAY NIGHT OR
EARLY TUESDAY...WINDS AND SEAS WILL REMAIN WELL BELOW SCA LEVELS
THROUGH MID WEEK.

SEAS WILL CHANGE DURING VIRTUALLY EACH PERIOD OF THIS FORECAST. SEAS
WILL BEGIN SATURDAY AT 2-4 FT WITHIN NEARSHORE WATERS AND 4-6 FT
BEYOND 20 NM WILL SUBSIDE TO 1-3 FT BY SATURDAY EVENING...THEN WILL
BUILD TO 2-4 FT AND PERHAPS AS HIGH AS 5 FT BEYOND 20 NM LATE
SATURDAY NIGHT THROUGH SUNDAY MORNING. SUNDAY NIGHT...SEAS SHOULD
SUBSIDE TO 1-2 FT...THEN INCREASING WINDS WILL SUPPORT SEAS BUILDING
TO AT LEAST 3-5 FT MONDAY. SEAS SHOULD THEN SUBSIDE TO 1-2 FT AGAIN
BY MID WEEK.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 11 PM THIS EVENING TO 11 AM EDT
     SATURDAY FOR AMZ352.
     SMALL CRAFT ADVISORY UNTIL 1 PM EDT SATURDAY FOR AMZ374.
     SMALL CRAFT ADVISORY FROM 11 AM THIS MORNING TO 11 PM EDT THIS
     EVENING FOR AMZ350.

&&

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



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.