Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 021041
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
641 AM EDT MON MAY 2 2016

.SYNOPSIS...
SEVERAL AREAS OF LOW PRESSURE WILL GRADUALLY PUSH A COLD FRONT
TOWARD THE REGION TODAY THROUGH TUESDAY...PRODUCING UNSETTLED
CONDITIONS. THE COLD FRONT WILL PASS THROUGH THE REGION TUESDAY
NIGHT...FOLLOWED BY ANOTHER COLD FRONT ON THURSDAY. HIGH PRESSURE
WILL THEN EXPAND INTO THE REGION OVER THE WEEKEND.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
LOOKS LIKE A BIT MORE SUN WILL OCCUR THIS MORNING THAN WHAT WAS
EXPECTED EARLIER. HAVE RAISED HIGHS ABOUT 1-2 DEGREES FROM THE
PREVIOUS FORECAST FOR MOST AREAS.

TODAY...ANOTHER CONVECTIVELY ACTIVE AFTERNOON IS EXPECTED ACROSS
MUCH OF SOUTHEAST SOUTH CAROLINA AND SOUTHEAST GEORGIA AS SOUTHERN
STREAM SHORTWAVE ENERGY APPROACHES FROM THE WEST. MODEST
INSTABILITY...DEEP MOISTURE AND INCREASING FORCING INDUCED BY
DIFFERENTIAL CYCLONIC VORTICITY ADVECTION WILL SUPPORT ANOTHER
ROUND OF SCATTERED TO NUMEROUS SHOWERS AND TSTMS. MOST OF THE HIGH
RESOLUTION MODELS ARE KEYING IN INTERIOR SOUTHEAST GEORGIA FOR THE
GREATEST COVERAGE OF CONVECTION DURING THE MID-LATE AFTERNOON AS
THIS REGION APPEARS TO HAVE THE BEST JUXTAPOSITION OF LOW-LEVEL
CONVERGENCE AND SURFACE BASED INSTABILITY. CONVECTION WILL BE
FURTHER ENHANCED BY INCREASING DIFLUENCE ALOFT INDUCED BY
DIVERGING BRANCHES OF THE POLAR AND SUBTROPICAL JET STREAMS.

ACCURATELY PINNING DOWN THE CONVECTIVE PATTERN THIS FAR OUT IS
EXTREMELY DIFFICULT DUE TO LIKELY MESOSCALE INTERACTIONS...THUS
POPS ACROSS THE INTERIOR WILL BE CAPPED AT 50-60 PERCENT FOR NOW.
HIGHER POPS WILL LIKELY BE NEEDED AT SOME POINT...BUT FURTHER
EVALUATION OF THE MESOSCALE ENVIRONMENT WILL BE NEEDED LATER THIS
MORNING. HIGHS WILL SIMILAR TO SUNDAY...RANGING FROM THE MID 70S
AT THE BEACHES TO THE UPPER 80S ACROSS INTERIOR SOUTHEAST GEORGIA.
ONCE AGAIN...A FEW INSTANCES OF 90 DEGREES CAN NOT BE RULED OUT
ACROSS INTERIOR SOUTHEAST GEORGIA...ESPECIALLY SOUTH OF THE I-16
CORRIDOR.

NO ORGANIZED SEVERE WEATHER IS EXPECTED THIS AFTERNOON IN THE
ABSENCE OF ANY MEANINGFUL SHEAR...HOWEVER DCAPES NEAR 1200 J/KG
COUPLED WITH MODEST HCAPE WITHIN THE -10 TO -30C LAYER WILL
SUPPORT A RISK FOR ISOLATED SEVERE TSTMS...ESPECIALLY WHERE
UPDRAFTS ARE AUGMENTED BY MESOSCALE BOUNDARY COLLISIONS. THE
PRIMARY HAZARDS WILL BE DAMAGING WINDS...MARGINALLY SEVERE HAIL
AND LOCALLY HEAVY RAINFALL.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY/...
TONIGHT...NUMEROUS SHOWERS/TSTMS WILL LIKELY BE ONGOING ACROSS
INLAND AREAS AT SUNSET. THERE REMAINS MUCH UNCERTAINTY HOW THE
CONVECTIVE PATTERN WILL EVOLVE OVERNIGHT WITH THE BULK OF UPPER
FORCING PROGGED TO BE DISPLACED ACROSS THE MIDLANDS AS SHORTWAVE
ENERGY PASSES TO THE NORTH WHILE INSTABILITY WANES. IN FACT..THERE
IS QUITE A BIT OF ANTICYCLONIC VORTICITY ADVECTION /AVA/ AND
SUBSIDENCE PROGGED TO OVERSPREAD MUCH OF THE FORECAST AREA AFTER
MIDNIGHT WITH AN AVA MAXIMUM SETTING UP NEAR AUGUSTA BY SUNRISE
TUESDAY. THIS WOULD SUGGEST LOW CHANCES FOR MEASURABLE RAINFALL
OVERNIGHT. HOWEVER...THE VARIOUS NAM/GFS/ECMWF MOS NUMBERS ALL
SHOW HIGH CHANCE TO LIKELY POPS FOR MUCH OF THE NIGHT WHICH IS
CURIOUS. IT COULD BE THAT THE MODELS ARE HAVING A HARD TIME
RESOLVING POSSIBLE LOW STRATUS DEVELOPMENT IN THE WARM/MOIST FLOW
AHEAD OF THE APPROACHING COLD FRONT...BUT THIS IS UNCLEAR. THE
LATEST SREF MEAN CERTAINLY DOES NOT SUPPORT MOS POP NUMBERS NEARLY
THAT HIGH...WHICH INCREASES THE UNCERTAINTY EVEN MORE. PLAN TO
TAPPER DOWN POPS INTO THE 20-30 PERCENT RANGE FROM LATE EVENING
ON...BUT THERE IS CERTAINLY A BIG BUST POTENTIAL HERE. LOWS WILL
RANGE FROM THE UPPER 60S INLAND TO THE LOWER 70S AT THE COAST.

TUESDAY AND TUESDAY NIGHT...A TROUGH WILL BE OVER THE EAST COAST
WHILE SEVERAL SHORTWAVES ROUND THE BASE OF THE TROUGH...CROSSING
THROUGH THE REGION. MESOSCALE BOUNDARIES CREATED BY EARLIER/ONGOING
CONVECTION NEAR OUR AREA WILL COMBINE WITH PLENTY OF DEEP-LAYERED
MOISTURE IN PLACE...PWATS RANGING FROM 1.5-1.75 INCHES...TO GENERATE
SHOWERS AND THUNDERSTORMS. ADDITIONALLY...A COLD FRONT WILL BE
APPROACHING FROM THE WEST WHICH WILL INCREASE FORCING. THIS
FAVORABLE THERMODYNAMIC/KINEMATIC ENVIRONMENT WILL PRODUCE STRONG
THUNDERSTORMS. A FEW OF THESE STORMS COULD BECOME
SEVERE...ESPECIALLY IN THE AFTERNOON AND EVENING. DAMAGING
WINDS...LOCALLY HEAVY RAINFALL...AND HAIL WILL BE THE GREATEST
THREATS. THERE IS STILL SOME UNCERTAINTY WHERE THE BEST COVERAGE
WILL BE AS THIS WILL DEPEND ON THE ANTECEDENT/DEVELOPING MESOSCALE
ENVIRONMENT. ELEVATED POPS REMAIN IN FORECAST WITH THE HIGHEST POPS
INITIALLY ACROSS THE INLAND COUNTIES IN THE MORNING THEN EXPANDING
INTO MUCH OF THE AREA BY THE AFTERNOON. THE HEAVIEST PRECIPITATION
WILL SHIFT OFFSHORE IN THE EVENING. THE FRONT SHOULD CROSS THROUGH
THE AREA LATE TUESDAY NIGHT AND POPS WILL RAPIDLY DIMINISH FOLLOWING
ITS PASSAGE. HIGH TEMPERATURES WILL GENERALLY BE IN THE LOWER 80S.
THOUGH BREAKS IN THE CLOUDS COULD CAUSE THEM TO RISE MUCH HIGHER.
LOWS SHOULD BE IN THE 60S.

WEDNESDAY AND WEDNESDAY NIGHT...THE COLD FRONT SHOULD CROSS THROUGH
OUR AREA AROUND DAYBREAK. REMNANT SHOWERS AND THUNDERSTORMS...MAINLY
LIMITED TO THE COASTAL COUNTIES...WILL QUICKLY BE PUSHED OFFSHORE
WITH THE FRONT. THE REST OF THE MORNING INTO THE AFTERNOON WILL BE
DRY WITH CLEARING SKIES. DEW POINTS WILL FALL INTO THE 50S WHILE
HIGHS WILL BE IN THE UPPER 70S TO NEAR 80 DEGREES. ANOTHER COLD
FRONT WILL PUSH THROUGH THE AREA WEDNESDAY NIGHT. THIS FRONT IS
LACKING MOISTURE...SO AT MOST WE CAN EXPECT SOME CLOUDS...BUT NO
SHOWERS OR THUNDERSTORMS. LOWS WILL BE IN THE UPPER 50S TO NEAR 60
DEGREES.

THURSDAY...A TROUGH WILL REMAIN OVER THE EAST COAST. AT THE SURFACE
A STORM SYSTEM WILL BE SPREAD ACROSS THE NORTHEASTERN STATES WHILE
BROAD HIGH PRESSURE WILL BE SPREAD ACROSS THE CENTRAL PLAINS. THIS
SYNOPTIC FLOW WILL LEAD TO WEST WINDS AT THE SURFACE AND NORTHWEST
FLOW ALOFT. DESPITE PLENTY OF SUNSHINE...HIGHS WILL BE SEVERAL
DEGREES BELOW NORMAL...IN THE MID 70S.

&&

.LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/...
MODELS ARE IN GOOD AGREEMENT SHIFTING THE TROUGH AXIS FROM OVER THE
EAST COAST THURSDAY NIGHT TO FAR OFFSHORE BY SUNDAY.
REPLACING THE TROUGH WILL BE A BUILDING RIDGE...ORIGINATING FROM THE
CENTRAL U.S. EXPECT DRY CONDITIONS THROUGH THIS PERIOD WITH
TEMPERATURES TRENDING UPWARD EACH DAY.

&&

.AVIATION /12Z MONDAY THROUGH FRIDAY/...
VFR. TSTM PROBABILITIES APPEAR TO BE INCREASING FOR KSAV SO A
TEMPO GROUP FOR MARGINAL MVFR VSBYS IN TSRA WILL BE INCLUDED FROM
20-23Z. TSTMS LOOK TO REMAIN WEST OF KCHS TODAY.

EXTENDED AVIATION OUTLOOK...PERIODIC FLIGHT RESTRICTIONS WITHIN
SCATTERED SHOWERS/THUNDERSTORMS MONDAY NIGHT THROUGH TUESDAY
NIGHT.

&&

.MARINE...
TODAY...A SOUTHERLY WIND REGIME WILL HOLD FIRM WITH WINDS 10-15
KT WITH SEAS 2-4 FT.

TONIGHT...NOCTURNAL SURGING WILL OCCUR AHEAD OF AN APPROACHING
COLD FRONT. WINDS LOOK TO MAX OUT AT 15-20 KT...HIGHEST ACROSS THE
GEORGIA OFFSHORE AND CHARLESTON COUNTY WATERS. FREQUENT GUSTS LOOK
TO REMAIN BELOW 25 KT FOR NOW...SO A SMALL CRAFT ADVISORY IS NOT
NEEDED ATTM. SEAS WILL BUILD 3-5 FT GEORGIA OFFSHORE AND
CHARLESTON COUNTY WATERS WITH 2-4 FT REMAINING COASTAL LEGS.

TUESDAY THROUGH FRIDAY...A COLD FRONT WILL PASS THROUGH THE AREA
TUESDAY NIGHT/WEDNESDAY MORNING...FOLLOWED BY ANOTHER COLD FRONT
WEDNESDAY NIGHT/THURSDAY MORNING. OFFSHORE WINDS WILL PREVAIL
THROUGH LATE WEEK. THE PRESSURE GRADIENT IS EXPECTED TO STRENGTHEN
LATE WEDNESDAY NIGHT INTO EARLY FRIDAY MORNING. SMALL CRAFT
ADVISORIES MAY BE NEEDED FOR WINDS GUSTS...ESPECIALLY FOR THE
OUTER GEORGIA WATERS. CONDITIONS IMPROVE ON FRIDAY AS THE GRADIENT
WEAKENS.

&&

.EQUIPMENT...
THE CHARLESTON HARBOR NOS TIDE GAUGE HAS STOPPED REPORTING ALL
METEOROLOGICAL AND TIDE DATA. THE NATIONAL OCEAN SERVICE IS
INVESTIGATING THE CAUSE OF THE OUTAGE. AN ESTIMATED TIME FOR DATA
RESTORATION IS UNKNOWN AT THIS TIME.

&&

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

&&

$$

ST/MS


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