Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 031651
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1251 PM EDT SUN MAY 3 2015

.SYNOPSIS...
HIGH PRESSURE OVER THE WATERS TODAY WILL SHIFT FURTHER OFFSHORE
TONIGHT AND PREVAIL THROUGH AT LEAST THE MIDDLE OF THIS WEEK. AN
AREA OF LOW PRESSURE IS EXPECTED TO DEVELOP NEAR THE BAHAMAS...AND
COULD MEANDER OFF THE SOUTHEAST COAST MID WEEK INTO NEXT WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
ANOTHER QUIET DAY AS SURFACE HIGH PRESSURE OVERHEAD MAINTAINS
CONTROL OF THE WEATHER PATTERN. THE HIGH WILL SHIFT EAST INTO THE
ATLANTIC THROUGH THE DAY...ALLOWING LIGHT ONSHORE FLOW TO DEVELOP.
STRONG SUBSIDENCE NOTED IN MODEL SOUNDINGS AND LACK OF MOISTURE
WILL KEEP A DRY FORECAST IN PLACE. SOME DIURNAL CU IS EXPECTED TO
DEVELOP THIS AFTERNOON WHICH WILL QUICKLY WANE AFTER SUNSET.
1000-850 MB THICKNESS VALUES FROM 12Z KCHS RAOB SUPPORTS HIGHS IN
THE LOW 80S AWAY FROM THE LOCALLY COOLER COASTLINE. WITH THIS
UPDATE...TRENDED DEW POINTS DOWN A COUPLE DEGREES BASED ON LATEST
OBS. OTHERWISE...ONGOING FORECAST WAS ON TRACK.

TONIGHT...SHORT WAVE RIDGING UPSTAIRS WILL GIVE WAY TO AN
APPROACHING MID LEVEL PERTURBATION CROSSING THE APPALACHIANS OF NC
LATE. THIS CAUSES THE SURFACE HIGH TO START TILTING INTO AN EAST/NE
TO WEST/SW ORIENTATION AS IT SLIDES FURTHER INTO THE ATLANTIC AND
EXTENDS BACK ACROSS THE LOCAL DISTRICT. DIURNAL CLOUDS WILL FADE
WITH SUNSET...BUT THERE IS A LITTLE ISENTROPIC LIFT ON THE 295K
SURFACE THAT MAY PRODUCE A FEW CLOUDS FROM OFF THE ATLANTIC
OVERNIGHT. AS DEW POINTS CONTINUE THEIR CLIMB IT WILL LEAD TO SOME
FOG POTENTIAL...BUT GIVEN LARGE CONDENSATION PRESSURE DEFICITS AND
TEMPS HAVE A DIFFICULT TIME ACHIEVING THEIR CROSS-OVER VALUES...WE
HAVE NO REASON TO ADD ANY FOG TO THE FORECAST. AT A MINIMUM THERE
WILL BE SOME GROUND FOG. THE HIGHER DEW POINTS AND SHALLOW ONSHORE
FLOW WILL PREVENT TEMPS FROM FALLING ANY LOWER THAN THE MID-UPPER
50S INLAND AND LOWER-MID 60S ON THE BARRIER ISLANDS.

&&

.SHORT TERM /MONDAY THROUGH WEDNESDAY/...
CANNOT RULE OUT AN ISOLATED DIURNAL SHOWER DURING ANY AFTERNOON
DURING THIS PERIOD DUE TO ONSHORE FLOW AND A POOL OF VORTICITY OVER
THE REGION...CUT-OFF WITHIN A BUILDING UPPER RIDGE. HOWEVER...GIVEN
DRY/CAPPED MODEL SOUNDINGS...MAINTAINED POPS BELOW 15 PERCENT AND A
RAIN-FREE FORECAST THROUGH MID WEEK. HIGHS IN THE LOWER 80S WILL BE
COMMON AWAY FROM THE IMMEDIATE COAST...AND MID 80S ARE ATTAINABLE
EACH DAY WELL INLAND. LOWS IN THE MID/UPPER 50S TO LOWER/MID 60S
WILL PREVAIL. ALSO OF NOTE...WHERE THE BOUNDARY LAYER DECOUPLES LOW-
LEVEL MOISTURE COULD SUPPORT PATCHY GROUND FOG EACH LATE NIGHT/EARLY
MORNING. HOWEVER...THE PROBABILITY AND POTENTIAL COVERAGE/IMPACTS DO
NOT JUSTIFY A MENTION OF FOG WITHIN PUBLIC FORECASTS.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
ATTENTION CONTINUES TO FOCUS ON LOW PRESSURE WHICH IS EXPECTED TO
DEVELOP OVER OR CLOSE TO THE BAHAMAS BY MID-WEEK. SINCE THE SURFACE
AND UPPER LOWS WILL RESIDE WITHIN A REX BLOCK PATTERN...BLOCKED BY
THE RIDGE TO THE NORTH...SLOW AND ERRATIC MOVEMENT OF THE SURFACE
LOW APPEARS LIKELY LATE WEEK THROUGH NEXT WEEKEND. IN FACT...LATEST
GUIDANCE EXHIBITS CONSIDERABLE SPREAD REGARDING THE STRENGTH...TRACK
AND RELATIVE TROPICAL/EXTRATROPICAL CHARACTERISTICS OF THE LOW...AND
THIS TRANSLATES TO A HIGH DEGREE OF FORECAST UNCERTAINTY LATE WEEK
INTO NEXT WEEKEND. REGARDLESS OF THE SOLUTION ONE CHOOSES...
DISCOUNTING THE 03/00 UTC CANADIAN SCENARIO A SIGNIFICANT/HIGH
IMPACT SYSTEM APPEARS UNLIKELY.

THE POTENTIAL FOR MOISTURE TO PUSH ONSHORE IS SUFFICIENT TO JUSTIFY
LOW POPS ESPECIALLY ALONG/EAST OF INTERSTATE 95 FRIDAY THROUGH
SUNDAY...BUT FORECAST CONFIDENCE REMAINS LOW EVEN REGARDING THE
POTENTIAL FOR ANY PRECIPITATION. THE ONGOING RAIN-FREE REGIME COULD
PERSIST THROUGH NEXT WEEKEND ESPECIALLY IF A WEAK LOW/TROUGH REMAINS
FARTHER OFFSHORE. OTHERWISE...HIGHS IN THE 80S AND LOWS IN THE 60S
SHOULD PREVAIL THROUGH THIS PERIOD.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
VFR CONDITIONS WILL PREVAIL AT KCHS AND KSAV THROUGH 18Z MONDAY.

EXTENDED AVIATION OUTLOOK...VFR CONDITIONS EXPECTED TO PREVAIL
THROUGH AT LEAST THE MIDDLE PART OF THE WEEK.

&&

.MARINE...
TODAY...DEEP BUT WEAKENING LOW PRESSURE WELL OUT IN THE ATLANTIC WILL
PULL FURTHER INTO THE OPEN OCEAN AND ALLOW FOR A HUGE REGION OF
HIGH PRESSURE TO BUILD ACROSS THE EASTERN STATES AND WESTERN
ATLANTIC. THIS WILL RESULT IN A SLACK PRESSURE GRADIENT ACROSS THE
LOCAL WATERS...AS GENTLE SEA BREEZE CIRCULATIONS FORM DURING THE
LATE MORNING AND AFTERNOON. MORE OF A CONCERN WILL COME FROM BACK
SWELL PROPAGATING FROM THE ATLANTIC LOW...PRODUCING 12-14 SECOND
PERIOD SWELLS OF 2-3 FT.

TONIGHT...HIGH PRESSURE PULLS A LITTLE FURTHER SEAWARD AS ITS
ASSOCIATED RIDGE AXIS SETS LIFTS NORTH OF THE MARINE COMMUNITY. THIS
WILL GENERATE SE WINDS OF 10 KT OR LESS THAT BACK MORE EASTERLY
LATE. SOME OF THE SWELL ENERGY WILL START TO DISSIPATE LATE...SO
SEAS WON/T BE MORE THAN 2 OR 3 FT.

MONDAY THROUGH FRIDAY...OFFSHORE HIGH PRESSURE WILL MAINTAIN
SYNOPTIC SCALE ONSHORE FLOW THROUGH THIS PERIOD. AS LOW PRESSURE
DEVELOPS OVER OR CLOSE TO THE BAHAMAS AND DRIFTS ERRATICALLY OFF THE
SOUTHEAST COAST MID TO LATE WEEK...A TIGHTENING PRESSURE GRADIENT
WILL TRANSLATE TO INCREASING WINDS...AND A BUILDING SWELL SHOULD
SPREAD INTO THE WATERS. 03/00 UTC WAVE WATCH GUIDANCE BASICALLY
DOUBLED SEAS OVER THE COASTAL WATERS LATE WEEK INTO NEXT WEEKEND.
GIVEN THE HIGH DEGREE OF UNCERTAINTY REGARDING THE STRENGTH AND
POSITION OF THE SURFACE LOW DURING THIS PERIOD...MAJOR ADJUSTMENTS
ARE NOT JUSTIFIED. EVEN SO... THE TIGHT GRADIENT AND INCREASING
FETCH BETWEEN THE SURFACE LOW/TROUGH AND HIGH PRESSURE TO THE NORTH
SHOULD PUSH SMALL CRAFT ADVISORY SEAS AND PERHAPS SCA WINDS INTO AT
LEAST PART OF THE COASTAL WATERS LATE WEEK.

RIP CURRENTS...WE/RE SHOWING A MODERATE RISK OF RIP CURRENTS AT AREA
BEACHES TODAY...THE RESULT OF SMALL BUT LONG PERIOD SWELLS...SEA
BREEZE CIRCULATIONS AND THE FULL MOON. ALWAYS SWIM NEAR A LIFE
GUARD.

FORECAST UNCERTAINTY REGARDING MANY ASPECTS OF OFFSHORE LOW
PRESSURE REMAINS HIGH. HOWEVER...ODDS STILL FAVOR A BUILDING SWELL
REACHING BEACHES AND INCREASING THE RIP CURRENT RISK MID/LATE WEEK
INTO NEXT WEEKEND. THUS...WILL CONTINUE TO HIGHLIGHT THE RIP
CURRENT POTENTIAL WITHIN THE HAZARDOUS WEATHER OUTLOOK.

&&

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

&&

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



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