Lake Wind Advisory 17, NWS Charleston, SC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
139 AM EST THU MAR 10 2011

.SYNOPSIS...
A COLD FRONT WILL MOVE OFF THE SOUTHEAST COAST THIS AFTERNOON...
WITH HIGH PRESSURE BUILDING IN FOR THE WEEKEND. A BACKDOOR COLD
FRONT WILL MOVE INTO THE REGION FROM THE NORTH SUNDAY NIGHT...WITH
A WEAK LOW PRESSURE SYSTEM POSSIBLY MOVING THROUGH MONDAY NIGHT OR
TUESDAY.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
THE AIR MASS ACROSS THE FORECAST AREA HAS BEEN WELL WORKED OVER
SINCE THE SQUALL LINE MOVED THROUGH EARLIER WEDNESDAY AFTERNOON
AND EVENING. LIGHT TO OCCASIONAL MODERATE RAINS WILL PERSIST
THROUGH 04-06Z...BEFORE THE STEADIEST RAINS MOVE INTO THE
ATLANTIC. WE WILL MAINTAIN 100 POPS EARLY TONIGHT...BUT WILL TREND
COVERAGE DOWN TO 60-70 POPS OVERNIGHT. THESE AMOUNTS MIGHT
ACTUALLY BE TOO LIBERAL...AND WE WILL ADJUST FURTHER IF
NECESSARY. WE HAVE ALREADY SEEN DECENT RAINS ACROSS THE
REGION...WITH DOPPLER RADAR ESTIMATES AS MUCH AS 1.5 TO 2 INCHES
HAVING FALLEN OVER PARTS OF INTERIOR SE GA. ADDITIONAL RAIN
AMOUNTS HOWEVER WILL BE NO MORE THAN ANOTHER 1/10 TO 1/4 INCH
TONIGHT..EXCEPT FOR SLIGHTLY HIGHER AMOUNTS OVER BERKELEY AND
CHARLESTON COUNTIES.

THE RISK OF THUNDERSTORMS IS PRETTY MUCH ZERO EARLY TONIGHT...BUT
AS SOME SURFACE BASED INSTABILITY TRIES TO MOVE IN LATE TONIGHT
AHEAD OF AN APPROACHING COLD FRONT...AND WE FALL INTO THE RIGHT
REAR QUAD OF THE 100 KT OR GREATER UPPER LEVEL JET WE MIGHT BE
ABLE TO SEE SOME ISOLATED CONVECTION FORM. WE WILL HOLD OFF ON
MENTION OF THUNDERSTORMS HOWEVER UNTIL AFTER 4 AM.

SKIES WILL REMAIN CLOUDY TONIGHT AND THAT ALONG WITH WARM
ADVECTION AHEAD OF THE COLD FRONT WILL KEEP TEMPS WELL ABOVE
SEASONAL NORMS. HOWEVER...WITH RAIN-COOLED CONDITIONS DROPPING
TEMPS DOWN TO NEAR OR AT THEIR DEW POINTS...LOWEST READINGS WILL
BE IN THE UPPER 50S AND LOWER 60S.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH SATURDAY/...
THURSDAY...THE COLD FRONT WILL BE JUST WEST OF THE FORECAST AREA
BY DAYBREAK THURSDAY...THEN TRACK STEADILY EASTWARD THROUGH THE
FORECAST AREA...PUSHING OFF THE GEORGIA AND SOUTH CAROLINA COAST
BY LATE MORNING OR EARLY AFTERNOON. WILL CARRY HIGH CHANCE/LIKELY
POPS IN THE MORNING ALL LOCALES...TRENDING TO SLIGHT CHANCE/CHANCE
POPS EARLY IN THE AFTERNOON. RAIN FREE WEATHER IS THEN EXPECTED
ACROSS MOST LOCALES BY LATE AFTERNOON. IMPRESSIVE DYNAMICS WILL BE
OVERSPREADING THE AREA DURING THE MORNING AND EARLY AFTERNOON
HOURS...WITH STRONG MID-UPPER LEVEL QG FORCING FOR ASCENT
ASSOCIATED WITH A ROBUST UPPER LEVEL TROUGH AND STRONG UPPER LEVEL
DIVERGENCE IN THE RIGHT REAR QUAD OF A 110+ KNOT H25 JET. IN
ADDITION TO THE DYNAMIC FORCING FOR ASCENT...MID-LEVEL LAPSE RATES
WILL BE STEEPENING TO AROUND 7 TO 7.5 C/KM. THAT SAID...WITH
ABUNDANT CLOUD COVER ANTICIPATED ACROSS THE REGION...SURFACE BASED
INSTABILITY SHOULD BE LIMITED TO AROUND 500 J/KG...THUS LIMITING
THE SEVERE WEATHER THREAT. NEVERTHELESS...WITH MOISTURE STRIPPING
OUT OF THE MID-LEVELS AND WET BULB ZERO HEIGHTS LOWERING TO
BETWEEN 8.5 AND 9.5 KFT...CAN/T ENTIRELY RULE OUT A FEW STORMS
BECOMING SEVERE. THE MAIN THREATS IF ANY SEVERE WEATHER
MATERIALIZES ARE EXPECTED TO BE DAMAGING STRAIGHT LINE WINDS AND
MARGINALLY SEVERE HAIL. MUCH WILL DEPEND ON WHETHER OR NOT ANY
BREAKS IN THE OVERCAST CAN DEVELOP PRIOR TO FRONTAL PASSAGE...AND
THIS IS DIFFICULT TO ASCERTAIN AT THIS TIME. NOT
IMPRESSED/CONFIDENT ENOUGH WITH THE POTENTIAL FOR SEVERE WEATHER
AT THIS TIME TO MENTION IN THE HAZARDOUS WEATHER OUTLOOK...BUT
WILL CONTINUE TO MONITOR TRENDS CLOSELY FOR ANY NEEDED CHANGES.
TEMPERATURES ARE EXPECTED TO TOP OUT GENERALLY IN THE MID-UPPER
60S.

THURSDAY NIGHT...STRONG COLD AIR ADVECTION WILL BE ONGOING ACROSS
THE FORECAST AREA BY THURSDAY EVENING AS THE COLD FRONT CONTINUES
TO PUSH EASTWARD THROUGH THE WESTERN ATLANTIC. STRONG DOWNSLOPE
FLOW IS EXPECTED TO GRADUALLY ERODE THE WRAP AROUND LOW LEVEL
CLOUD COVER...SO WILL LOOK FOR GENERALLY PARTLY CLOUDY SKIES
BECOMING MOSTLY CLEAR TOWARD DAYBREAK FRIDAY. MUCH COOLER
TEMPERATURES CAN BE EXPECTED...WITH LOWS BOTTOMING OUT IN THE MID
TO UPPER 30S INLAND AND AROUND 40 CLOSER TO THE COAST.

FRIDAY THROUGH SATURDAY...COLD AIR ADVECTION WILL CONTINUE
THROUGH THE FRIDAY AS HIGH PRESSURE BEGINS TO BUILD IN FROM THE
WEST. DOWNSLOPE FLOW WILL ALLOW FOR A GOOD BIT OF SUNSHINE...BUT
WITH THE UPPER LEVEL TROUGH PIVOTING ACROSS NORTHERN PORTIONS OF
THE FORECAST AREA...EXPECT SOME CUMULUS DEVELOPMENT.
OVERALL...WILL LOOK FOR PARTLY CLOUDY SKIES ACROSS NORTHERN ZONES
AND MOSTLY SUNNY CONDITIONS ACROSS THE SOUTH.

HIGH PRESSURE WILL THEN BUILD FROM THE NORTHERN GULF OF MEXICO
FRIDAY EVENING SLOWLY SOUTHEASTWARD INTO CENTRAL FLORIDA BY LATE
SATURDAY AFTERNOON. THIS WILL RESULT IN AIRMASS MODIFICATION ACROSS
THE REGION...WITH GENERALLY CLEAR CONDITIONS WITH PERHAPS A BIT OF
CIRRUS DRIFTING THROUGH FROM TIME TO TIME. 1000 MB GEOSTROPHIC WINDS
ARE FORECAST TO REMAIN AROUND 20 KNOTS THROUGH DAYBREAK
SATURDAY...SO DESPITE CLEAR SKIES WE DON/T ANTICIPATE IDEAL
RADIATIONAL COOLING CONDITIONS...AS WINDS WILL BE HARD PRESSED TO
COMPLETELY DECOUPLE FOR A LONG PERIOD OF TIME. OVERNIGHT LOWS SHOULD
BOTTOM OUT IN THE MID 30S INLAND AND IN THE UPPER 30S TO AROUND 40
CLOSER TO THE COAST. HIGHS ON SATURDAY ARE THEN EXPECTED TO REBOUND
CLOSER TO NORMAL...TOPPING OUT IN THE UPPER 60S TO AROUND 70
DEGREES.

LAKE WINDS...ANOTHER LAKE WIND ADVISORY MAY BE NEEDED ON LAKE
MOULTRIE THURSDAY INTO THURSDAY NIGHT OR EARLY FRIDAY...MAINLY
WITHIN THE COOL ADVECTION IN WAKE OF THE COLD FRONT AROUND MIDDAY
THURSDAY.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
HIGH PRESSURE WILL SINK SOUTH OVER CENTRAL FLORIDA SATURDAY NIGHT
AND SUNDAY BEFORE A BACKDOOR COLD FRONT DROPS INTO THE AREA FROM THE
NORTH SUNDAY NIGHT. THE MONDAY THROUGH WEDNESDAY TIME FRAME ARE
HIGHLY UNCERTAIN DUE TO LARGE MODEL SPREAD REGARDING AN APPROACHING
UPPER TROUGH AND POSSIBLE SURFACE LOW MOVING THROUGH. AT THIS
JUNCTURE WE HAVE MAINTAINED A DRY FORECAST BUT SHOW INCREASING
CLOUDS AND SLIGHTLY BELOW NORMAL TEMPERATURES.

&&

.AVIATION /06Z THURSDAY THROUGH MONDAY/...
A MESOSCALE LOW PRESSURE SYSTEM MOVED THROUGH AN HOUR OR TWO
AGO...SWITCHING WINDS ALL OVER THE PLACE. NOW THAT THE LOW HAS
DEPARTED...WINDS AT BOTH TERMINALS HAVE RETURNED TO SSE. GUIDANCE
INDICATES THE STRONGEST LOW-LEVEL JETTING IS SHIFTING OFF THE
SOUTHEAST COAST SO WE HAVE REMOVED WIND SHEAR FROM BOTH SITES.

PRIMARY CONCERN IS CEILINGS/VSBYS WITH A MARINE LAYER CONTINUALLY
REPLENISHING FROM THE SE AND A COOL STABLE LAYER IN PLACE AT THE
SURFACE JUST INLAND FROM THE TERMINALS. SO FAR THE IFR CEILINGS
HAVE REMAINED INLAND. THE STATISTICAL GUIDANCE IS REALLY HITTING
THE CEILINGS HARD THIS MORNING WITH PREVAILING IFR CONDITIONS.
HOWEVER IT IS NOT INITIALIZING TERRIBLY WELL EITHER. AT THIS
JUNCTURE WE FEEL PRETTY CONFIDENT THAT CIGS/VSBYS WILL DROP TO
MVFR CLOSER TO DAYBREAK BUT WE HAVE NOT INCLUDED ANY MENTION OF
IFR CONDITIONS. THE PRIMARY FRONT WILL MOVE THROUGH MID TO LATE
MORNING WITH WINDS BECOMING SW AND W BEHIND IT. SOME STRATIFORM
RAIN LEFTOVER FROM THE EARLIER SQUALL LINE SHOULD CLEAR CHS BY 08Z
BUT THERE ARE GOOD INDICATIONS THAT A PRETTY CONTIGUOUS BAND OF
SHOWERS AND POSSIBLY A STORM WILL MOVE THROUGH WITH THE FRONT
AFTER DAYBREAK. BEST FORCING IS UP IN SC SO WE ONLY INCLUDED
VICINITY SHOWERS AT SAV WITH PREVAILING SHRA AT CHS.

GUSTY WINDS WILL DEVELOP IN THE WAKE OF THE FRONT LATE THIS
MORNING AND CONTINUE THROUGH THE AFTERNOON. VFR CONDITIONS THIS
AFTERNOON/TONIGHT.

EXTENDED AVIATION OUTLOOK...VFR CONDITIONS THROUGH TUESDAY. GUSTY
SURFACE WINDS EXPECTED ON FRIDAY.

&&

.MARINE...
THE SOUTHERLY SYNOPTIC FLOW HAS BEEN TEMPORARILY INTERRUPTED BY THE
PASSAGE OF THE SQUALL LINE ACROSS THE COASTAL WATERS...BUT AS IT
SHIFTS EAST OF THE AREA BY MIDNIGHT THE SOUTHERLY FLOW WILL RE-
ESTABLISH ITSELF. WE LOOK FOR WINDS OF 15 OR 20 KT
OVERNIGHT...WITH GUSTS AS HIGH AS 25 KT ACROSS AMZ350. SEAS WILL
BE AS HIGH AS 6 OR 7 FT...WHICH IS ENOUGH TO MAINTAIN THE SCA/S
ACROSS ALL ATLANTIC WATERS. IN CHARLESTON HARBOR...THE AIR MASS
HAS STABILIZED ENOUGH WHERE WE DO NOT EXPECT ENOUGH OF THESE 40 KT
WINDS OFF THE SURFACE TO MIX DOWN WITHIN THE WARM ADVECTION. THUS
WE HAVE OPTED TO CANCEL THE SCA FOR AMZ330.

THURSDAY THROUGH MONDAY...A BRIEF LULL IN THE WINDS IS EXPECTED
THURSDAY MORNING AS THE CORE OF THE LOW-LEVEL JET SHIFTS EASTWARD
AND FURTHER OFFSHORE. THE COLD FRONT IS THEN EXPECTED TO PUSH
THROUGH THE COASTAL WATERS BY EARLY TO MID AFTERNOON...AND THIS
WILL ALLOW WINDS TO PICK BACK UP ONCE AGAIN AS STRONG COLD AIR
ADVECTION ENSUES THROUGH FRIDAY. SMALL CRAFT ADVISORIES WILL BE
NEEDED FOR MOST IF NOT ALL MARINE ZONES THURSDAY THROUGH FRIDAY
MORNING. COULD SEE SEAS LINGER AT SMALL CRAFT LEVELS ACROSS THE
OUTER GEORGIA WATERS THROUGH FRIDAY AFTERNOON. CONDITIONS WILL
GREATLY IMPROVE FRIDAY NIGHT AND OVER THE WEEKEND AS HIGH PRESSURE
BUILDS BACK IN AND THE GRADIENT WEAKENS...WITH WINDS AND SEAS
REMAINING BELOW SMALL CRAFT THRESHOLDS. A NORTHEAST FLOW DEVELOPS
SUNDAY NIGHT INTO MONDAY BEHIND A BACKDOOR COLD FRONT...BUT FOR
NOW CONDITIONS ARE EXPECTED TO REMAIN BELOW SMALL CRAFT LEVELS.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL NOON EST FRIDAY FOR AMZ350-352.
     SMALL CRAFT ADVISORY UNTIL 4 PM EST FRIDAY FOR AMZ374.
     SMALL CRAFT ADVISORY UNTIL 5 AM EST EARLY THIS MORNING FOR
     AMZ354.

&&

JRL

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE CHARLESTON SC
829 PM EST WED MAR 9 2011

SCZ045-101030-
INLAND BERKELEY-
829 PM EST WED MAR 9 2011

THIS HAZARDOUS WEATHER OUTLOOK IS FOR SOUTHEAST SOUTH CAROLINA.

.DAY ONE...TONIGHT.

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY.

LAKE WINDS...ANOTHER LAKE WIND ADVISORY MAY BE REQUIRED THURSDAY
AND THURSDAY NIGHT ACROSS LAKE MOULTRIE.

SEVERE WEATHER...SEVERE THUNDERSTORMS COULD BE ONGOING ACROSS
PARTS OF THE AREA AT DAYBREAK THURSDAY. THE STORMS ARE EXPECTED
TO RACE NORTHEAST THROUGH THE REGION PRIOR TO EARLY AFTERNOON
AHEAD OF A STRONG COLD FRONT. THE MAIN HAZARDS WITH THE STORMS
WILL BE DAMAGING WIND GUSTS AND ISOLATED TORNADOES.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME.

AMZ330-350-352-354-374-GAZ087-088-099>101-114>119-137>141-SCZ040-
042>044-047>052-101030-
CHARLESTON HARBOR-
WATERS FROM SOUTH SANTEE RIVER TO EDISTO BEACH SC OUT 20 NM-
WATERS FROM EDISTO BEACH SC TO SAVANNAH GA OUT 20 NM-
WATERS FROM SAVANNAH GA TO ALTAMAHA SOUND GA OUT 20 NM...INCLUDING
GRAYS REEF NATIONAL MARINE SANCTUARY-
WATERS FROM SAVANNAH GA TO ALTAMAHA SOUND GA EXTENDING FROM 20 TO
60 NM-JENKINS-SCREVEN-CANDLER-BULLOCH-EFFINGHAM-TATTNALL-EVANS-
INLAND BRYAN-COASTAL BRYAN-INLAND CHATHAM-COASTAL CHATHAM-LONG-
INLAND LIBERTY-COASTAL LIBERTY-INLAND MCINTOSH-COASTAL MCINTOSH-
ALLENDALE-HAMPTON-INLAND COLLETON-DORCHESTER-INLAND JASPER-BEAUFORT-
COASTAL COLLETON-CHARLESTON-COASTAL JASPER-TIDAL BERKELEY-
829 PM EST WED MAR 9 2011

THIS HAZARDOUS WEATHER OUTLOOK IS FOR ATLANTIC COASTAL
WATERS...SOUTHEAST GEORGIA AND SOUTHEAST SOUTH CAROLINA.

.DAY ONE...TONIGHT.

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY.

SEVERE WEATHER...SEVERE THUNDERSTORMS COULD BE ONGOING ACROSS
PARTS OF SOUTHEAST GEORGIA AND EASTERN SOUTH CAROLINA AT DAYBREAK
THURSDAY. THE STORMS ARE EXPECTED TO RACE NORTHEAST THROUGH THE
REGION PRIOR TO EARLY AFTERNOON AHEAD OF A STRONG COLD FRONT. THE
MAIN HAZARDS WITH THE STORMS WILL BE DAMAGING WIND GUSTS AND
ISOLATED TORNADOES.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME.

33