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000
FXUS62 KCHS 171956
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
356 PM EDT MON JUN 17 2013

.SYNOPSIS...
HIGH PRESSURE WILL CONTINUE TO RETREAT FARTHER INTO THE ATLANTIC
EARLY THIS WEEK. A COLD FRONT WILL APPROACH FROM THE NORTHWEST
TUESDAY...THEN SLOWLY PROGRESS THROUGH THE AREA WEDNESDAY AND
THURSDAY. HIGH PRESSURE WILL THEN BUILD FROM THE NORTH INTO THE WEEKEND.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
AS OF MID AFTERNOON...SHOWERS AND THUNDERSTORMS ARE EXPANDING IN
COVERAGE...MOSTLY INLAND...BUT ALSO CLOSER TO THE COAST ALONG THE
SEA BREEZE. EXPECT DECENT COVERAGE OF CONVECTION THROUGH THIS
EVENING DUE TO DEEP MOISTURE...SHORTWAVE ENERGY ALOFT...AND
SEVERAL BOUNDARIES SUCH AS THE SEA BREEZE AND CONVECTIVE OUTFLOWS.
COVERAGE SHOULD WANE TOWARD MIDNIGHT AS INSTABILITY
DIMINISHES...LIKELY TRANSITIONING OVER THE COASTAL WATERS WITH THE
BETTER INSTABILITY. THERE COULD BE A FEW SEVERE STORMS WITH
DAMAGING WINDS AND/OR LARGE HAIL THROUGH EARLY EVENING...MAINLY
WHERE BOUNDARY COLLISIONS OCCUR. IT WILL BE MILD WITH LOWS CLOSE
TO 70 INLAND RANGING TO THE MID 70S ALONG THE COAST.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/...
MONDAY...AN IMMENSE MID AND UPPER LEVEL TROUGH WILL BE FOUND OVER SE
CANADA...WHILE A FLAT AND STRETCHED OUT RIDGE IS LOCATED FROM THE SW
ATLANTIC ACROSS THE GULF AND NORTHERN OLD MEXICO INTO THE SE
PACIFIC. THE LOCAL REGIME WILL LIE NEAR THE SOUTHERN EXTENSION OF A
SLIGHTLY CYCLONIC FLOW ALOFT...WITH WEAK ENTRENCHED SHORT WAVES
FOUND WITHIN THE SOUTHERN STREAM OF THE JET. ONE OF THESE FEATURES
WILL TRIGGER THE DEVELOPMENT OF A VERY WEAK WARM FRONT OR TROUGH
ACROSS SOUTHERN GA IN THE AFTERNOON...AS THE LAST OF THE BERMUDA
SURFACE HIGH STRIVES TO HANG ON. THE MOST NOTICEABLE CHANGES IN THE
AIR MASS WILL BE THE RETURN OF HIGHER DEW POINTS...MUCH GREATER
MOISTURE AS PWATS TOP OUT NEAR 1.8 TO 1.9 INCHES AND WARMER TEMPS.
ALL THIS IS COURTESY OF THE RETURN FLOW AROUND THE ATLANTIC RIDGE.
INSTABILITY AND ESPECIALLY CAPE WILL BE AT HIGHER VALUES...THE
PERSISTENT SUBSIDENCE CAP WILL HAVE ERODED WHILE CINH WANES
THROUGHOUT THE DAY...AND THERE IS A LITTLE COOLER CONDITIONS IN THE
MID LEVELS. THE COMBINED INFLUENCES WILL ALLOW FOR THE RESUMPTION OF
OUR TYPICAL WARM SEASON CONVECTION...TRIGGERED BY THE SEA
BREEZE...THE SOUTHERN GA TOUGH OR WARM FRONT AND UPSTREAM BOUNDARIES
THAT COULD DRIFT IN WITH THE WESTERLY FLOW. DUE TO A SLOW STORM
MOTION OF NO MORE THAN ABOUT 10 KT AND THE ELEVATED PWATS...LOCALLY
HEAVY RAINS CAN OCCUR IN SOME OF THE MORE PERSISTENT STORMS.
CONVECTION WILL HOLD OFF UNTIL LATE MORNING OR EARLY AFTERNOON WHEN
WE REACH OUR TRIGGER TEMPS...WITH HIGHEST AFTERNOON COVERAGE MAINLY
IN THE SCATTERED RANGE...FROM 30 POPS NEAR THE COAST TO 50 POPS FAR
INLAND. DESPITE PARTLY TO MOSTLY CLOUDY SKY CONDITIONS...WARM
ADVECTION AND A STRETCHING OF THE LOW LEVEL THICKNESS WILL GENERATE
MAX TEMPS WITHIN A DEGREE OR TWO EITHER SIDE OF 90 INLAND FROM THE
INTRA-COASTAL WATERS.

MONDAY NIGHT...ALTHOUGH THERE IS A RETURN TO THE CINH AS PER
SOUNDINGS...GIVEN THAT THE SURF ACE TROUGH OR WARM FRONT WILL LIFT
THROUGH THE FORECAST AREA AND THERE IS SOME SHORT WAVE ENERGY
ALOFT...WE FEEL THAT SLIGHT CHANCE AND CHANCE POPS ARE JUSTIFIED
DESPITE THE NOCTURNAL ENVIRONMENT. OUR GRIDS WILL SHOW THE GREATEST
POPS ALONG THE NW RANGE OF THE CWFA DURING THE EVENING...THEN
TRANSITIONING TO OVER THE CHARLESTON TRI-COUNTY ZONES LATE AT NIGHT
IN PROXIMITY TO THE SURFACE FEATURE. MINIMUM TEMPS WILL BE NEAR OR
SLIGHTLY ABOVE NORMAL.

TUESDAY THROUGH WEDNESDAY...THE LARGE SCALE PATTERN ACROSS THE NORTH
AMERICAN CONTINENT WILL BE HIGHLY AMPLIFIED AND SOMEWHAT PROGRESSIVE
THROUGH THE PERIOD. LOCALLY WE WILL LIE NEAR THE SOUTHERN REACHES OF
CYCLONIC FLOW OVER THE EASTERN UNITED STATES...WITH PERIODIC MID
LEVEL PERTURBATIONS TO PASS ON THROUGH. SIMULTANEOUSLY AT THE
SURFACE WE WILL FIND A COLD FRONT FROM NEW ENGLAND TO THE TENNESSEE
VALLEY ON TUESDAY THAT STRUGGLES TO PUSH SE THROUGH WEDNESDAY. THE
FRONT BECOMES ORIENTED MORE PARALLEL TO THE FLOW ALOFT...WHILE AT
THE SAME TIME WAVES OF LOW PRESSURE PREVENT THE FRONT FROM SHIFTING
SOUTH AND SE AT MORE THAN A CRAWL. PRESENTLY IT LOOKS LIKE WE WILL
REMAIN IN THE WARM SECTOR SOUTH OF THE FRONT THROUGH THE MIDDLE OF
THE WEEK...AWAITING THE FORMATION OF ONE LAST WAVE THAT CLOSES INTO
A LOW OFF THE NC COAST LATE WEDNESDAY OR WEDNESDAY NIGHT. THERE IS
AMPLE INSTABILITY AND MOISTURE TO PRODUCE AT LEAST SCATTERED
CONVECTION. THERMODYNAMICS ARE NOT OVERLY IMPRESSIVE IN REGARDS TO
SEVERE WEATHER...BUT AT THIS TIME OF YEAR THERE IS ALWAYS AT
LEAST AN ISOLATED RISK SHOULD ANY BOUNDARY INTERACTIONS RESULT IN
STRONGER UPDRAFTS. COMPRESSIONAL HEATING IN ADVANCE OF THE COLD
FRONT FRONT...AIDED BY A DEEP WESTERLY FLOW OFF THE APPALACHIANS
WILL ALLOW FOR MANY LOCATIONS TO PEAK AT OR ABOVE 90 EACH AFTERNOON.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
THE CENTER OF UPPER LEVEL RIDGING WILL REMAIN WEST OF THE
REGION...ALLOWING THE PATTERN ALOFT FOR THE SOUTHEAST STATES TO
BE SOMEWHAT WEAK AND PROGRESSIVE THROUGH MUCH OF THE EXTENDED
PERIOD. THE LINGERING FRONT NEAR THE SOUTHERN PERIPHERY OF THE
FORECAST AREA LOOKS TO REMAIN GENERALLY IN PLACE...EVENTUALLY
TRANSITIONING INTO A COASTAL FRONT/COASTAL TROUGH FEATURE AS HIGH
PRESSURE BUILDS FROM THE NORTH. MEDIUM RANGE MODEL SOLUTIONS STILL
DIVERGE ON DETAILS FOR THE LATE WEEK AND WEEKEND PERIOD...AND HAVE
DECIDED TO MAINTAIN A RATHER GENERIC 30 PERCENT POP DURING THE
DAYTIME HOURS FRIDAY THROUGH AT LEAST SUNDAY. IF THE COASTAL
TROUGH PATTERN DOES INDEED TAKE SHAPE...THEN EXPECT BEST
CONVECTIVE COVERAGE TO TRANSITION OFFSHORE EACH NIGHT. HIGH
TEMPERATURES WILL VARY LITTLE EACH AFTERNOON...REACHING THE UPPER
80S TO AROUND 90 DEGREES AWAY FROM THE LOCALLY COOLER COASTLINE.

&&

.AVIATION /19Z MONDAY THROUGH SATURDAY/...
GENERALLY VFR. RISK FOR SHOWERS/TSTMS WILL INCREASE THIS AFTERNOON
INTO EARLY EVENING AS DEEP MOISTURE MOVE INTO THE AREA IN
ASSOCIATION WITH UPPER-LEVEL SHORTWAVE ENERGY AND SEVERAL
LOW-LEVEL BOUNDARIES INCLUDING THE SEA BREEZE...DIFFERENTIAL
HEATING AND CONVECTIVE OUTFLOWS. MAINTAINED THE TEMPO GROUP FOR
TSRA AT KCHS AS SHRA ARE ALREADY DEVELOPING IN THE VICINITY.
AMENDMENTS WILL MOST CERTAINLY BE NEEDED THROUGHOUT THE REST OF
THE AFTERNOON...ESPECIALLY AT KSAV...AS MESOSCALE AND SHORT-TERM
RADAR TRENDS BECOME MORE APPARENT. THERE WILL BE AT LEAST A SMALL
RISK FOR SHRA/TSRA THE REST OF THE TAF PERIOD BEYOND THIS
EVENING...ESPECIALLY AT KCHS WHERE DEEPER MOISTURE IS
EXPECTED...BUT CONFIDENCE IS TOO LOW TO MENTION ATTM.

EXTENDED AVIATION...PERIODIC FLIGHT RESTRICTIONS POSSIBLE LATER
MONDAY THROUGH THURSDAY IN ASSOCIATION WITH SCATTERED TO NUMEROUS
SHRA/TSRA.

&&

.MARINE...
TONIGHT...WINDS WILL INCREASE SLIGHTLY AHEAD OF AN APPROACHING
COLD FRONT. SPEEDS COULD REACH AS HIGH AS 15-20 KT AT TIMES WITH
SEAS 2-4 FT...HIGHEST E.

MONDAY AND MONDAY NIGHT...THE LOCAL DOMAIN WILL BE PLACED WITHIN THE
WEST AND NW PORTION OF THE SUB-TROPICAL ATLANTIC RIDGE MONDAY THAT
GRADUALLY GIVES WAY TO A WEAK WARM FRONT OR SURFACE TROUGH THAT
PROGRESSES THROUGH MONDAY NIGHT. WHILE THERE WILL BE SOME INCREASE
IN WINDS WITH THE SEA BREEZE CIRCULATION MONDAY AFTERNOON AND WITH
NOCTURNAL LOW LEVEL JETTING MONDAY NIGHT...SOUTH AND SW WINDS WILL
GENERALLY HOLD UNDER 15-17 KT. SEAS AROUND 2-3 FEET MONDAY WILL RISE
ABOUT ANOTHER FOOT MONDAY NIGHT. ISOLATED TO SCATTERED CONVECTION
WILL FINALLY MAKE A RETURN TO THE COASTAL WATERS DURING THIS TIME.

TUESDAY THROUGH WEDNESDAY...THE QUASI-WARM FRONT OR SURFACE TROUGH
WILL LIFT NORTH OF THE MARINE COMMUNITY EARLY IN THE PERIOD...WHILE
WE FIND THE ATLANTIC RIDGE SUBDUED TO THE SOUTH. MEANWHILE...AN
UPSTREAM COLD FRONT WILL RELUCTANTLY MAKE A SE PUSH TOWARD THE
WATERS TUESDAY NIGHT AND WEDNESDAY. STILL TOO MUCH UNCERTAINTY AS TO
HOW FAR THE FRONT WILL BE ABLE TO PENETRATE...AS THE OCEANIC RIDGE
TO THE SOUTH AND SE ATTEMPTS TO HOLD FIRM. WE DO FEEL CONFIDENT THAT
WINDS AND SEAS WILL ASCEND TUESDAY AND TUESDAY NIGHT...WITH A
TIGHTENING OF THE PRESSURE GRADIENT BETWEEN THE UPSTREAM COLD FRONT
AND THE ATLANTIC HIGH. EVEN SO...ODDS AT THIS STAGE ARE AGAINST ANY
SMALL CRAFT ADVISORY CONDITIONS. WIND AND SEA CONDITIONS WILL THEN
BE DETERMINED BY WHERE THE FRONT ALIGNS ITSELF ON WEDNESDAY...BUT NO
MATTER WHERE IT IS LOCATED...ADVISORY HEADLINES ARE NOT ANTICIPATED.
MARINERS ARE ADVISED THAT AT LEAST SCATTERED CONVECTION WILL
OCCUR...AND WE/LL MAINTAIN A WEATHER WATCH FOR THE POSSIBLE
ORGANIZATION OF STRONGER STORMS MOVING OFF THE COAST IN ADVANCE OF
THE COLD FRONT.

THURSDAY THROUGH FRIDAY...THE FRONT LOOKS TO BECOME MORE DIFFUSE
NEAR OR JUST SE OF THE LOCAL WATERS...AS HIGH PRESSURE BUILDS OVER
NEW ENGLAND AND THE MID ATLANTIC REGION. WINDS AND SEAS WILL BE WELL
BELOW ANY CRITERIA FOR SMALL CRAFT ADVISORIES.

&&

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

&&

$$

SYNOPSIS...
NEAR TERM...RJB
SHORT TERM...DPB
LONG TERM...WMS
AVIATION...RJB/DPB
MARINE...RJB/DPB