000
FXUS62 KCHS 131409
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1009 AM EDT MON MAY 13 2013

.SYNOPSIS...
HIGH PRESSURE WILL EXTEND ACROSS THE REGION THIS WEEK. A WARMING
TREND WILL BEGIN MID WEEK WITH RAIN CHANCES INCREASING SLIGHTLY
BY LATE WEEK AS A MORE UNSETTLED PATTERN DEVELOPS.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
A HIGHLY UNUSUAL PATTERN FOR MID MAY IS SEEN ACROSS THE AREA
TODAY...WITH A PROGRESSIVE MID LATITUDE AND DEEP TROUGH OVER THE
EASTERN STATES THAT SWEEPS INTO THE ATLANTIC AFTER 18-21Z. ONE
LAST VORT LOBE EMBEDDED WITHIN THE TROUGH IS SHIFTING EAST AND SE
THIS MORNING AND IS GENERATING CONSIDERABLE HIGH LEVEL CLOUDINESS.
BUT THIS FEATURE WILL BE A FAST MOVER...SO CLOUD COVER WILL
DIMINISH DURING THE EARLY AND MID AFTERNOON...FOLLOWED BY
INCREASING BRIGHT SUNSHINE. WE HAVE ADJUSTED THE SKY COVER
FORECAST TO INDICATE PARTLY SUNNY SKIES BEFORE THE CLEARING TAKES
PLACE.

THE CLOUD COVER HAS BEEN OPAQUE ENOUGH WHERE IT HAS HELD THE
AMOUNT OF INSOLATION IN CHECK AND THAT ALONG WITH A COOL NORTHERLY
FLOW HAS SLOWED OUR RISE OF TEMPS. BUT ONCE CLOUD COVER CLEARS OUT
WE/LL SEE TEMPS RESPOND QUICKLY GIVEN THE HIGH SUN ANGLE. COOL
ADVECTION THIS MORNING WILL WANE BY AFTERNOON...AND WITH 850 MB
TEMPS FAR BELOW TYPICAL NORMS OUR MAX TEMPS TODAY WILL BE MORE
LIKE APRIL 13 RATHER THAN MAY 13.

WINDS WILL BE GUSTY AT TIMES INTO THIS AFTERNOON...BUT ON AVERAGE
10-15 MPH WINDS WILL PREVAIL.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY/...
TONIGHT...ELONGATED HIGH PRESSURE WILL GRADUALLY SHIFT EAST
TONIGHT AND BECOME CENTERED ACROSS CENTRAL GEORGIA/SOUTH CAROLINA
BY SUNRISE TUESDAY. THE BOUNDARY LAYER IS POISED TO DECOUPLE BY
MID-EVENING WITH THE LOSS OF INSOLATION. TEMPERATURES WILL DROP
QUICKLY AFTER SUNSET GIVEN THE LOW DEWPOINT REGIME THAT WILL BE IN
PLACE. SHOULD SEE SOLID RADIATIONAL CONDITIONS DOMINATE FOR MUCH
OF THE NIGHT AS WINDS TO CALM TO LIGHT. GENERALLY FAVORED THE
COOLER SIDE OF THE GUIDANCE ENVELOP WITH LOWS RANGING FROM THE
LOWER 40S INLAND TO THE UPPER 40S/LOWER 50S NEAR THE BEACHES. THE
RECORD LOW FOR SAVANNAH TUESDAY MORNING IS 49 DEGREES AND HAS A
GOOD CHANCE OF BEING EITHER TIED OR BROKEN. THE RECORDS FOR BOTH
THE CHARLESTON AIRPORT AND DOWNTOWN CHARLESTON LOOK SAFE ATTM. SEE
THE CLIMATE SECTION BELOW FOR MORE SPECIFIC CLIMATOLOGICAL
INFORMATION.

TUESDAY...SURFACE HIGH PRESSURE WILL QUICKLY MOVE OVER THE FORECAST
AREA THROUGH MIDDAY...BEFORE SLIPPING INTO THE ATLANTIC OVERNIGHT.
AT THE SAME TIME...UPPER LEVEL RIDGING WILL BE GRADUALLY SHIFTING
EAST BEHIND A DEPARTING TROUGH WELL OFF THE NEW ENGLAND COAST.
NORTHERLY WINDS AT SUNRISE WILL VEER THROUGHOUT THE DAY...BECOMING
EAST DURING THE AFTERNOON AND SOUTHEAST AFTER SUNSET. THE
COMBINATION OF RISING HEIGHTS ALOFT...DOWNSLOPE FLOW IN THE LOW
LEVELS AND ABUNDANT SUNSHINE WILL ALLOW TEMPERATURES TO PEAK A FEW
DEGREES HIGHER THAN THE PREVIOUS DAY. HOWEVER...ONSHORE SURFACE
WINDS WILL INITIALLY MITIGATE A MORE SUBSTANTIAL WARMING TREND. THUS
TEMPERATURES WILL STILL BE A FEW DEGREES BELOW SEASONAL
NORMALS...RISING TO THE MID 70S NORTH TO NEAR 80 DEGREES FARTHER
SOUTH. LOW TEMPERATURES IN THE 50 DEGREE RANGE WILL BE NEARLY 10
DEGREES WARMER THAN THE NIGHT BEFORE.

WEDNESDAY...THE UPPER RIDGE AXIS WILL BE DIRECTLY OVER THE EAST
COAST BY MID WEEK. AT THE SURFACE...HIGH PRESSURE WILL HAVE
SETTLED OVER THE ATLANTIC WHILE TROUGHING DEVELOPS JUST EAST OF
THE APPALACHIAN RANGE. WARM SOUTHERLY FLOW WILL INCREASE...AND
WHEN COMBINED WITH THE RIDGING ALOFT...WILL SUPPORT WARM AND DRY
CONDITIONS. HIGH TEMPERATURES WILL RANGE FROM THE LOW TO MID
80S...WITH A FEW LOCATIONS REACHING THE UPPER 80S MAINLY FAR
INLAND. LOW TEMPERATURES WILL ALSO BE MODERATING BACK TOWARD
SEASONAL NORMALS...COOLING INTO THE LOW 60S.

THURSDAY...A BIT MORE DISAGREEMENT IN MODEL SOLUTIONS IS EVIDENT
AS THE WEEK PROGRESSES. THE UPPER RIDGE WILL BREAK DOWN AS A BROAD
TROUGH WITH EMBEDDED SHORTWAVE ENERGY SHIFTS TOWARD THE MID
ATLANTIC AND SOUTHEAST STATES. GENERAL CONSENSUS IS THAT THIS
PATTERN CHANGE COULD ENHANCE THE INLAND SURFACE TROUGH AND SUPPORT
AN INCREASE IN DEEP MOISTURE. THE 00Z GFS SOLUTION SUGGESTS THAT
SHOWERS AND THUNDERSTORMS COULD DEVELOP BY THE AFTERNOON HOURS AND
SHIFT OFFSHORE DURING THE EVENING FOLLOWING THE STRONGEST
SHORTWAVE ENERGY. THE 00Z ECMWF IS MORE CONSERVATIVE WITH THE
STRENGTH OF UPPER LEVEL ENERGY AND ADVERTISES LITTLE TO NO
PRECIPITATION COVERAGE. PREFER TO KEEP RAIN CHANCES BELOW 15
PERCENT CONSIDERING THIS DISCREPANCY...AND INDICATE JUST A GENERAL
INCREASE IN SKY COVER. DESPITE THE BREAKDOWN OF THE UPPER
RIDGE...STRONG SOUTHERLY FLOW WILL MAINTAIN WARM CONDITIONS...WITH
TEMPERATURES RISING INTO THE MID TO UPPER 80S AWAY FROM THE
LOCALLY COOLER COASTLINE.

&&

.LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/...
THE UPPER LEVEL PATTERN WILL REMAIN RATHER WEAK AND ILL-DEFINED
THROUGH MUCH OF THE EXTENDED PERIOD...WHILE ATLANTIC HIGH PRESSURE
AND INLAND TROUGHING LINGER AT THE SURFACE. THERE DOES NOT APPEAR
TO BE ANY STRONG SYNOPTIC LEVEL FEATURES DRIVING SIGNIFICANT
WEATHER THROUGH THE WEEKEND. THUS THE LATEST THINKING IS THAT
SHOWER/THUNDERSTORM POTENTIAL WILL MAINLY BE A RESULT OF TYPICAL
DIURNAL HEATING/INSTABILITY AND SEABREEZE FORCING. HAVE THUS
INDICATED A SLIGHT CHANCE FOR THUNDERSTORMS DURING THE
CLIMATOLOGICALLY FAVORED AFTERNOON AND EARLY EVENING HOURS FRIDAY
THROUGH SUNDAY...KEEPING POPS BELOW 15 PERCENT ON MONDAY DUE TO
LONG RANGE PATTERN UNCERTAINTIES. HIGH TEMPERATURES EACH AFTERNOON
WILL BE QUITE WARM AND LIKELY A FEW DEGREES ABOVE SEASONAL
AVERAGES...GENERALLY REACHING THE MID TO UPPER 80S AWAY FROM THE
LOCALLY COOLER COASTLINE FRIDAY THROUGH MONDAY.

&&

.AVIATION /14Z MONDAY THROUGH FRIDAY/...
VFR. OCCASIONAL GUSTY NORTH AND NW WINDS INTO THIS AFTERNOON.

EXTENDED AVIATION OUTLOOK...THERE ARE NO CONCERNS AT THIS TIME.

&&

.MARINE...
TODAY...THE COASTAL WATERS WILL EXPERIENCE SOME PINCHING OF THE
GRADIENT BETWEEN A WAVE OF LOW PRESSURE EAST OF THE GULF STREAM
AND CONTINENTAL HIGH PRESSURE BUILDING FROM THE WEST. WHEN COOL
ADVECTION IS THROWN INTO THE MIX WE LOOK FOR NORTHERLY WINDS UP
NEAR 15 KT AND GUSTY THIS MORNING...BEFORE DROPPING OFF AND
BACKING MORE NW THIS AFTERNOON AS COOL ADVECTION ENDS AND THE
GRADIENT RELAXES SOME. SEAS WILL BE NO MORE THAN 2-4 FT GIVEN THE
RESTRICTIVE OFFSHORE FETCH.

TONIGHT...WINDS WILL REMAIN A BIT ELEVATED OVERNIGHT AS THE
VARIOUS PRESSURE AND THERMAL GRADIENTS TIGHTEN OVER THE COASTAL
WATERS. WINDS SHOULD ONLY INCREASE SLIGHTLY OVER THE COOLER
NEARSHORE WATERS...BUT MAY APPROACH 15-20 KT OVER THE GEORGIA
OFFSHORE WATERS...ESPECIALLY CLOSER TO THE WESTERN WALL OF THE
GULF STREAM. SEAS WILL AVERAGE 1-2 FT NEARSHORE WATERS AND 2-3 FT
OFFSHORE WATERS.

TUESDAY THROUGH FRIDAY...SURFACE HIGH PRESSURE WILL SHIFT OVER THE
ATLANTIC LATE TUESDAY AND LINGER OFFSHORE THROUGH MUCH OF THE
WEEK. THE MARINE ZONES WILL EVENTUALLY BECOME LOCATED BETWEEN
THIS ATLANTIC HIGH AND A DEVELOPING LOW PRESSURE TROUGH INLAND.
SOUTHERLY WINDS WILL PREVAIL...SURGING MID TO LATE WEEK AS THE
PRESSURE GRADIENT TIGHTENS ON THE PERIPHERY OF THE STRENGTHENING
INLAND TROUGH. AT THIS POINT...WINDS AND SEAS ARE EXPECTED TO
REMAIN BELOW ADVISORY CONDITIONS THROUGH THE PERIOD.

&&

.CLIMATE...
RECORD LOWS FOR 14 MAY.
CHARLESTON AIRPORT.... 42/1941
DOWNTOWN CHARLESTON... 51/1917
SAVANNAH AIRPORT...... 49/1997

&&

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

&&

$$

SYNOPSIS...
NEAR TERM...
SHORT TERM...ST/WMS
LONG TERM...WMS
AVIATION...
MARINE...
CLIMATE...