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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KCHS 160508
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
108 AM EDT SUN JUN 16 2013

.SYNOPSIS...
HIGH PRESSURE WILL CONTINUE TO SHIFT INTO THE ATLANTIC OVERNIGHT
THROUGH SUNDAY...THEN WILL WEAKEN MONDAY. A COLD FRONT WILL
APPROACH FROM THE NORTHWEST BY THE MIDDLE OF NEXT WEEK. THIS FRONT
WILL LIKELY STALL OVER THE REGION THROUGH LATE NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
-- Changed Discussion --
ONLY MINOR CHANGES WERE MADE FOR THE EARLY MORNING UPDATE.
-- End Changed Discussion --

&&

.SHORT TERM /6 AM THIS MORNING THROUGH TUESDAY/...
SUNDAY...A LARGE AND ELONGATED GULF OF MEXICO RIDGE IN THE MID AND
UPPER ATMOSPHERE WILL FLATTEN IN RESPONSE TO A SHORT WAVE THAT IS
FOUND IN THE CENTRAL STATES SATURDAY THAT WILL PROGRESS INTO THE
TENNESSEE VALLEY BY LATE IN THE DAY. BUT SIMULTANEOUSLY THE
PERSISTENT BERMUDA HIGH AT THE SURFACE AND IN THE LOWER TROPOSPHERE
WILL EXTEND WEST ACROSS THE LOCAL AREA. GIVEN THE LACK OF
INSTABILITY...MINIMAL MOISTURE AND A PERSISTENT AND WELL PRONOUNCED
CAP AROUND 800-900 MILLIBARS THE RISK FOR CONVECTION IS ONCE AGAIN
UNUSUALLY ABSENT FROM THE FORECAST. WHILE WE CAN/T ENTIRELY RULE OUT
AN ISOLATED SHOWER OR T-STORM SNEAKING IN FROM THE SOUTH ALONG THE
SEA BREEZE...RAIN CHANCES ARE ONCE AGAIN OMITTED FROM THE FORECAST.
WE STAYED CLOSE TO THE LOW LEVEL THICKNESS FORECAST WHICH SUPPORTS
MAX TEMPS IN THE UPPER 80S TO NEAR 90...EXCEPT FOR LOWER AND MIDDLE
80S CLOSE TO THE SHORELINE.

SUNDAY NIGHT...THE SHEARED OUT VORT UPSTREAM WILL SHIFT THROUGH SC
AND GA...CAUSING AN ILL DEFINED SURFACE BASED TROUGH TO FORM IN AN
MOSTLY EAST-WEST ORIENTATION ACROSS OUR SOUTHERN CWFA. THE
ASSOCIATED PVA ALOFT COMBINED WITH A SMALL BUT NOTICEABLE INCREASE
IN ISENTROPIC LIFT COULD TRIGGER A FEW LATE NIGHT SHOWERS.
HOWEVER...MOISTURE PROFILES REMAIN SHALLOW...SO RAIN CHANCES ARE
NOTHING MORE THAN ISOLATED POPS OVER COASTAL SE GA LATE WHERE BEST
CONVERGENCE AND MOISTURE WILL BE PRESENT. MINIMUM TEMPS WILL BE NEAR
OR A TAD BELOW SEASONAL NORMALS GIVEN A LIGHT WIND REGIME AND
MINIMAL MOISTURE.

MONDAY...WHILE THERE IS SOME AMPLIFICATION TO THE PATTERN ALOFT OVER
THE WESTERN STATES...MUCH OF THE EASTERN STATES WILL BE WITHIN A
WESTERLY FLOW TO THE NORTH OF A FLAT AND SUPPRESSED RIDGE IN THE
GULF AND ACROSS FLORIDA. EMBEDDED IMPULSES LOOK TO MOVE OVERHEAD
WITHIN THE MOSTLY ZONAL FLOW ALOFT. THAT ALONG WITH THE REMNANTS
OF THE POORLY DEFINED SURFACE TROUGH WILL FORCE THE SINKING MOTION
ASSOCIATED WITH THE SUB-TROPICAL ATLANTIC RIDGE TO RELAX ITS
GRIP...AS THE HIGH STARTS TO PULL OFF TO THE EAST AND SE. THIS IN
TURN ALLOWS FOR THE RETURN OF MOISTURE AS PWATS CLIMB TO VALUES NEAR
OR EVEN ABOVE MID JUNE LEVELS. THIS COMBINED WITH HIGHER
INSTABILITY...CONVECTIVE AVAILABLE POTENTIAL ENERGY AND COOLER 500
MILLIBAR TEMPS WILL ALLOW FOR REAPPEARANCE OF SHOWERS AND T-STORMS.
GIVEN SOME INCREASE IN MID LEVEL WIND FIELDS THERE MIGHT BE A COUPLE
OF STRONG OR MARGINALLY SEVERE PULSE-TYPE CELLS THAT POP. PLUS THERE
IS A SLOW STORM MOTION THAT SUPPORTS LOCALLY HEAVY RAINFALL IN A FEW
STORMS AS WELL. HIGHEST CHANCES WILL BE IN THE SCATTERED RANGE
ACROSS INLAND SECTIONS ALONG THE SEA BREEZE AND OTHER MESO-SCALE
BOUNDARIES FROM UPSTREAM. A CONTINUED EXPANSION OF THE LOW LEVEL
THICKNESS WILL ALLOW FOR TEMPS TO CLIMB A COUPLE OF DEGREES HIGHER
THAN ON SUNDAY.

TUESDAY...A MORE AMPLIFIED DESIGN WILL BE FOUND ACROSS NORTH
AMERICA...WITH A RIDGE IN THE ROCKIES AND PLAINS AND A BROAD TROUGH
OVER SE CANADA AND MUCH OF THE EASTERN STATES. LOCALLY THE FLOW
ALOFT BECOMES MORE CYCLONIC...WITH YET AGAIN MID LEVEL PERTURBATIONS
TO PROGRESS OVER OR NEARBY. ONE OF THESE WILL CAUSE A WAVE OF LOW
PRESSURE TO FORM AT THE SURFACE ALONG A COLD FRONT OVER EXTREME SE
VIRGINIA AND/OR EXTREME NE NORTH CAROLINA BY LATE IN THE DAY. STORMS
WILL LIKELY TRY AND ORGANIZE UPSTREAM IN ADVANCE OF THE COLD FRONT
AND ITS PRE-FRONTAL TROUGH AND DRIVEN BY A DEEP AND QUICKER WEST AND
NW FLOW WILL MAKE A RUN FOR OUR NORTHERN AND WESTERN ZONES BY LATE
IN THE DAY. IF COLD POOLING DEVELOPS TO DRIVE THE CONVECTION IN FAST
ENOUGH THIS COULD SUPPORT A RISK FOR SEVERE WEATHER. HOWEVER...THE
THERMODYNAMICS AT THE TIME ARE NOT OVERLY IMPRESSIVE...LAPSE RATES
AREN/T THAT SUBSTANTIAL AND DCAPES ARE NOT FORECAST MORE THAN
600-800 J/KG. FOR THESE REASONS WE HAVE CHOSEN NOT TO ADD MENTION TO
THE HAZARDOUS WEATHER OUTLOOK. COMPRESSIONAL HEATING AHEAD OF THE
FRONT COMBINED WITH SOME DOWNSLOPE FLOW OFF THE MOUNTAINS WILL MORE
THAN NEGATE THE GREATER AMOUNT OF CLOUD COVER...AS TEMPS REACH THE
LOWER 90S MANY LOCALES BEFORE ANY RAINS ARRIVE. A TIGHTER PRESSURE
GRADIENT SETS IN BETWEEN THE MID ATLANTIC LOW AND RIDGE TO THE
SE...AND WHEN ENHANCED BY THE RESULTANT SEA BREEZE CIRCULATION IT
WILL BECOME BREEZY OVER THE COASTAL SC ZONES IN THE AFTERNOON.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
ONCE THE MAIN WAVE OF LOW PRESSURE PULLS NORTHEAST OF THE REGION
TUESDAY NIGHT INTO WEDNESDAY...THE WEAK COLD FRONT WILL BECOME
PARALLEL TO THE FLOW ALOFT AND LIKELY STALL OVER THE FORECAST
AREA. WITH A BROAD UPPER TROUGH IN PLACE FOR MUCH OF THE REMAINING
EXTENDED PERIOD...THE FRONT COULD LINGER ALONG THE SOUTHEAST
COASTLINE INTO AT LEAST LATE WEEK. ALTHOUGH DETAILS ARE STILL
UNCERTAIN THIS FAR IN ADVANCE...HAVE MAINTAINED SOLID THUNDERSTORM
CHANCES DURING THE DAYLIGHT HOURS EACH AFTERNOON...WITH SOME
REDUCTION IN COVERAGE DURING THE CLIMATOLOGICALLY UNFAVORED
NOCTURNAL PERIODS. HIGH TEMPERATURES EACH DAY ARE EXPECTED TO
REMAIN WITHIN A DEGREE OR TWO OF SEASONAL NORMALS...REACHING THE
UPPER 80S TO AROUND 90 DEGREES AWAY FROM THE LOCALLY COOLER
COASTLINE.

&&

.AVIATION /05Z SUNDAY THROUGH THURSDAY/...
-- Changed Discussion --
VFR.

EXTENDED AVIATION...NO CONCERNS INTO EARLY MONDAY. PERIODIC
FLIGHT RESTRICTIONS POSSIBLE LATER MONDAY THROUGH WEDNESDAY IN
ASSOCIATION WITH THE RETURN OF CONVECTION.
-- End Changed Discussion --

&&

.MARINE...
-- Changed Discussion --
OVERNIGHT...HIGH PRESSURE WILL CONTINUE TO SHIFT OFFSHORE...SUPPORTING
E/SE WINDS 5-15 KT VEERING TOWARD THE S/SE. SEAS DOMINATED BY A
8-9 SECOND EASTERLY SWELL WILL REMAIN 2-3 FT...POSSIBLY UP TO 4
FT OVER THE FAR EASTERN PORTIONS OF THE GA OFFSHORE WATERS.

SUNDAY...THE COASTAL WATERS WILL BE SITUATED UNDER THE INFLUENCE OF
THE SUB-TROPICAL ATLANTIC RIDGE...GENERATING GENTLE TO MODERATE SE
AND SOUTH BREEZES AS PER THE BEAUFORT WIND SCALE.

SUNDAY NIGHT AND MONDAY...FOR THE MOST PART THE LOCAL REGIME WILL
REMAIN WITHIN THE ANTICYCLONIC FLOW AROUND THE ATLANTIC
RIDGE...INTERRUPTED ONLY BY THE SUBTLE CYCLONIC EFFECTS OF A WEAK
TROUGH THAT DEVELOPS OVER OR NEARBY. THIS WILL ALLOW FOR THE
RESUMPTION OF ISOLATED TO SCATTERED CONVECTION...BUT OUTSIDE OF ANY
SHOWERS/T-STORMS THERE ARE NO CONCERNS IN REGARDS TO THE SYNOPTIC
WINDS AND PREVAILING SEAS.

MONDAY NIGHT AND TUESDAY...THE PATTERN WILL CHANGE AS THE OCEANIC
HIGH GIVES WAY TO THE APPROACH OF AN UPSTREAM COLD FRONT AND ITS
PRE-FRONTAL TROUGH. THE PRESSURE GRADIENT WILL TIGHTEN AS A
RESULT...AND MARINERS CAN EXPECT AN INCREASE IN BOTH WINDS AND SEAS
TO OCCUR. PROBABLY NOT QUITE TO THE THRESHOLDS OF A REQUIRED
SCA...BUT WINDS WILL BE UP AS HIGH AS 15-20 KT AND SEAS WILL CLIMB
TO 4 OR 5 FT. IN ADDITION...ISOLATED TO SCATTERED CONVECTION WILL
IMPACT THE AREA...WITH THE POTENTIAL FOR SOME ORGANIZATION OF STRONG
OR SEVERE STORMS POSSIBLE VERY LATE TUESDAY OR TUESDAY NIGHT.

A MORE BENIGN PRESSURE PATTERN WILL UNFOLD FOR WEDNESDAY AS THE
FRONT STALLS OVER THE SOUTHEAST COASTLINE...ALLOWING FOR MUCH
LIGHTER WIND FIELDS AND A REDUCTION IN SEA CONDITIONS.
-- End Changed Discussion --

&&

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

&&

$$

ST