Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 022205
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
605 PM EDT MON MAY 2 2016

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

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
THROUGH THIS EVENING...WHILE THERE IS STILL AN ISOLATED SEVERE
RISK IT IS NOW CONFINED TO ONLY ALLENDALE AND HAMPTON COUNTIES IN
SE AND FROM JENKINS AND SCREVEN COUNTIES TO TATTNALL AND EVANS IN
GA. LAPSE RATES ARE BECOMING LESS FAVORABLE AND EVEN INSTABILITY
IS NOT AS IMPRESSIVE AS IT WAS EARLIER IN THE DAY. HOWEVER...WITH
DCAPES STILL 800-900 J/KG THERE IS STILL A RISK FOR ISOLATED
DAMAGING WINDS. PLUS THE CAPE IN THE HAIL GROWTH LAYER OF 400-500
J/KG COULD YET RESULT IN MARGINALLY SEVERE HAIL. THE CHANCES FOR
SEVERE WEATHER WILL COME TO AN END BY 8 PM WITH SUNSET.

IN ADDITION THERE HAS BEEN SLOW MOVEMENT TO STORMS NEAR THE US-301
CORRIDOR AND WITH CELLS ALIGNED IN TANDEM WITH THE MEAN FLOW THERE
REMAINS THE POTENTIAL FOR ADDITIONAL TRAINING/BACK-BUILDING TO
LEAD TO AT LEAST MINOR FLOODING CONCERNS. THERE IS HOWEVER A SMALL RISK
FOR MORE SIGNIFICANT FLOODING AND POSSIBLE FLASH FLOODING
CONCERNS...MAINLY IN ALLENDALE AND BULLOCH COUNTIES.

THE TEMP CURVE HAS SEEN FURTHER REFINEMENTS TO ACCOUNT FOR THE
RAIN COOLED CONDITIONS AND EXTENSIVE CLOUD COVER.

FOR TONIGHT...CONVECTION WILL STEADILY FADE WITH THE LOSS OF HEATING
AND TYPICAL NOCTURNAL STABILIZING INFLUENCES. HOWEVER...THERE IS
STILL DECENT FORCING THAT OCCURS WITH A SHORT WAVE ALONG THE
NORTHERN GULF COAST THIS EVENING TO PASS INTO THE AREA OVERNIGHT AND
INTO THE ATLANTIC AROUND DAYBREAK. IN ADDITION THERE IS DIFLUENCE
ALOFT WITH DIVERGING BRANCHES OF THE POLAR JET TO THE NORTH/NW AND
SUB-TROPICAL JET TO THE SOUTH/SW. ALTHOUGH OUR CONFIDENCE IS
MODERATE AT BEST...THIS DOES SUPPORT AT LEAST SLIGHT CHANCE AND
CHANCE POPS AFTER DIURNAL CONVECTION DWINDLES FAR INLAND AFTER 9-10
PM. THIS IS MORE IN LINE WITH THE HIGH-RES MODELS AND THE
SREF...RATHER THAN THE GLOBAL MODELS WHICH HAVE HAD A DIFFICULT TIME
OF LATE WITH NOCTURNAL CONVECTION. INSTEAD THEY SEEM TO BE FOCUSING
MORE ON LOW STRATUS THAT SHOULD OCCUR. THERE IS LIKELY TOO MUCH
MIXING OF THE PLANETARY BOUNDARY LAYER WITH GEOSTROPHIC WINDS OF 15
KT OR GREATER TO PERSIST...SO OTHER THAN A LITTLE GROUND FOG WHERE
RAINS OCCURRED...THERE ARE NO SIGNIFICANT FOG CONCERNS.

THE FORMATION OF AT LEAST PATCHY LOW STRATUS...DEBRIS CLOUDS FROM
EARLIER CONVECTION AND THE ELEVATED DEW POINTS WON/T ALLOW FOR MIN
TEMPS ANY LOWER THAN THE UPPER 60S TO NEAR 70. DOWNTOWN CHARLESTON
HAS A CHANCE OF A POSSIBLE RECORD HIGH MINIMUM FOR MAY 2ND /72F
SET IN 2010/ IF THEY DON/T RECEIVE TOO MUCH RAIN PRIOR TO THE END
OF THE CALENDAR DAY.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/...
TUESDAY...A BROAD...POSITIVELY TILTED UPPER TROUGH WILL BE OVER THE
CENTRAL U.S. WITH A TRAILING COLD FRONT RUNNING FROM THE MID
ATLANTIC...SOUTHWEST ACROSS THE SOUTHEAST U.S....APPROACHING OUR
REGION. THE COMPLICATING FACTOR FOR FIGURING OUT THE THUNDERSTORM AND
SEVERE POTENTIAL IS THE AMOUNT OF CONVECTION THAT MIGHT BE PRESENT IN
THE MORNING. ALL MODELS INDICATE THAT AT LEAST SCATTERED SHOWERS AND
ISOLATED THUNDERSTORMS WILL BE AROUND BETWEEN 06Z AND 15Z...THEN
RAPIDLY MOVES EAST. THE NAM THEN INDICATES THAT DEEP LAYER MOISTURE
WILL DROP THROUGH THE DAY...LIMITING CONVECTIVE COVERAGE...WHILE THE
GLOBAL MODELS KEEP SUFFICIENT DEEP LAYER MOISTURE IN PLACE. GOING
WITH THE MAJORITY AND KEEPING SOME CONSISTENCY WITH PREVIOUS
FORECASTS...HAVE KEPT HIGH END CHANCE/LIKELY POPS REDEVELOPING LATER
IN THE MORNING AND THROUGH THE AFTERNOON. WILL HAVE A SIMILAR AMOUNT
OF INSTABILITY AS PREVIOUS DAYS...GENERALLY SURFACE BASED CAPES OF
1000-2000 J/KG IN PLACE. IN ADDITION...WEAK VORT LOBES WILL
MOVE ACROSS THE AREA IN THE SOUTHWEST UPPER FLOW THROUGH THE
DAY. AT THIS POINT...IT IS VERY DIFFICULT TO TIME ANY ONE
IMPULSE. GIVEN THESE CONDITIONS...FEEL THERE IS STILL A LOW/MARGINAL
RISK FOR ISOLATED SEVERE STORMS DURING THE AFTERNOON. THE MAIN
THREAT WILL BE STRONG/DAMAGING WINDS WITH DOWNDRAFT CAPES IN THE 500-
700 J/KG RANGE. SMALL HAIL WILL ALSO BE POSSIBLE. DEEP
SOUTHWEST/UNIDIRECTIONAL FLOW MAY ALSO LEAD TO THE POTENTIAL FOR
TRAINING OF CELLS...WHICH COULD RESULT IN LOCALLY HEAVY RAINFALL.
HIGHS IN THE LOWER 80S.

THE BULK OF THE CONVECTION IS EXPECTED TO END BY MIDNIGHT AS THE
SURFACE FRONT MOVES THROUGH THE AREA AND DEEP LEVEL DRYING MOVES IN.
LOWS IN THE LOWER 60S. KEPT THE TREND OF LOWER POPS FROM WEST TO
EAST THROUGH THE NIGHT...WITH MOST POPS LESS THAN 15% OVER LAND BY
MORNING.

WEDNESDAY...COOLER AND DRIER CONDITIONS ARE EXPECTED AS THE LARGE
SCALE PATTERN TRANSITIONS TO THE BLOCK...WITH A DEEP UPPER LOW OVER
THE OH RIVER VALLEY AND RIDGE OVER THE ROCKIES. A WEST-NORTHWEST
LOW LEVEL FLOW...MOSTLY SUNNY SKIES AND HIGHS IN THE UPPER 70S
AROUND 80. THIS IS CLOSE TO NORMAL. PERIODIC UPPER VORT LOBES WILL
MOVE ACROSS THE AREA ON THE BASE OF THE UPPER/BLOCKING TROUGH.
HOWEVER...OTHER THAN BRIEF INCREASES IN CLOUDS...NO MEASURABLE
PRECIP. IS EXPECTED. BY WEDNESDAY NIGHT...A RE-REINFORCING COLD FRONT
WILL MOVE THROUGH...BUT IS EXPECTED TO COME THROUGH DRY. WINDS WILL
STAY UP ALL NIGHT FROM THE WEST-NORTHWEST...WITH LOWS DROPPING TO
THE MID 50S INLAND TO AROUND 60 COAST...CLOSER TO NORMAL.

THURSDAY...THE AREA WILL REMAIN ON THE SOUTHERN END OF THE BLOCKING
UPPER LOW...WHICH WILL DRIFT INTO THE NORTHEAST AND MID ATLANTIC
REGION. EVEN WITH SUNNY SKIES...NORTHWEST FLOW AND WEAK COLD
ADVECTION WILL KEEP HIGHS IN THE MID 70S...ABOUT 3-5 DEGREES BELOW
NORMAL.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
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 /22Z MONDAY THROUGH SATURDAY/...
MOST OF THE VALID 18Z TAF CYCLE WILL BE VFR.

ALTHOUGH EITHER SITE COULD STILL EXPERIENCE A SHRA THIS
EVENING...NO SIGNIFICANT IMPACTS WILL OCCUR.

CONVECTION WILL LIKELY FADE IN COVERAGE THIS EVENING...BUT WITH
THE APPROACH OF ENERGY ALOFT OVERNIGHT THERE CERTAINLY COULD BE A
RISK OF SHRA/TSRA AT KCHS AGAIN. BUT PROBABILITIES ARE TOO LOW TO
INCLUDE AT THIS TIME.

THERE IS LIKELY TOO MUCH WIND TONIGHT TO CAUSE ANY FOG
CONCERNS...BUT AREAS OF LOW STRATUS MAY OCCUR LATE TONIGHT INTO
THE MIDDLE OF TUESDAY MORNING.

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

EXTENDED AVIATION OUTLOOK...FOR TUESDAY...PERIODIC FLIGHT
RESTRICTIONS POSSIBLE IN SCATTERED SHOWERS/THUNDERSTORMS...ESPECIALLY
DURING THE AFTERNOON...AT BOTH KCHS AND KSAV. WEDNESDAY THROUGH
SATURDAY...VFR WILL PREVAIL BOTH SITES.

&&

.MARINE...
TONIGHT...THE PRESSURE PATTERN WILL TIGHTEN BETWEEN STRONG HIGH
PRESSURE TO THE DISTANT EAST/NE OF BERMUDA AND LOW PRESSURE REACHING
FROM NORTHERN VIRGINIA TO SOUTHERN NEW JERSEY BY MORNING. A TRAILING
COLD FRONT FROM THE LOW WILL CROSS THE APPALACHIANS EARLY TONIGHT
AND INTO THE SC UPSTATE AND CENTRAL SAVANNAH RIVER VALLEY LATE.
ALTHOUGH WARM ADVECTION WILL LIMIT HOW MUCH MIXING OF A 25-35 KT LOW
LEVEL JET WILL OCCUR...SOUTH/SW WINDS OVER THE LOCAL WATERS WILL
STILL REACH AS HIGH AS 15 OR 20 KT. A FEW INFREQUENT GUSTS TO 25 KT
WILL OCCUR...ESPECIALLY OVER AMZ350-374...BUT NOT ENOUGH TO HOIST A
SMALL CRAFT ADVISORY. SEAS ARE ABLE TO BUILD TO AS HIGH AS 3-5
FT...HIGHEST ACROSS THE OUTER GA WATERS BEYOND 40 NM OFF THE
COAST. MARINE INTEREST SHOULD REMAIN ALERT DUE TO ISOLATED TO
SCATTERED SHOWERS/T-STORMS WILL OCCUR.

TUESDAY AND WEDNESDAY...CONDITIONS ARE EXPECTED TO REMAIN BELOW
SMALL CRAFT ADVISORY LEVELS. A COLD FRONT WILL BE APPROACHING THE
REGION ON TUESDAY...THE MOVE THROUGH THE WATERS ON WEDNESDAY. WINDS
COULD PERIODICALLY GET AS HIGH AS 15-20 KNOTS FROM THE SOUTHWEST
THROUGH WEDNESDAY MORNING AHEAD OF THE FRONT...BUT GENERALLY 15
KNOTS OR LESS EXPECTED TO PREVAIL. WINDS WILL SHIFT TO WEST-
NORTHWEST WEDNESDAY AFTERNOON BEHIND THE FRONT...BUT EXPECTED TO
REMAIN 15-20 KNOTS OR LESS WITH BUILDING SEAS TO 4 FEET
OFFSHORE/BEYOND 20 NM.

WEDNESDAY NIGHT AND THURSDAY...WINDS INCREASING BACK TO 15-20 KNOTS
FROM THE WEST-NORTHWEST AS A REINFORCING COLD FRONT MOVES THROUGH
AND STRONGER HIGH PRESSURE BUILDS FROM THE WEST. SEAS BUILDING TO 4-5
FEET BEYOND 20 NM.

FRIDAY AND SATURDAY...THE PRESSURE GRADIENT GRADUALLY DECREASES AS
HIGH PRESSURE CONTINUES MOVING IN FROM THE WEST. EXPECT WINDS OF 15
KNOTS OR LESS AND SEAS DECREASING TO 3 TO 4 FEET.

&&

.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.

&&

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



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