National Weather Service Weather Forecast Office

Area Forecast Discussion

626
FXUS62 KCHS 180206
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1006 PM EDT FRI MAY 17 2013

.SYNOPSIS...
AN UPPER DISTURBANCE WILL MOVE NORTH OF THE AREA THROUGH THE WEEKEND
AS ATLANTIC HIGH PRESSURE BUILDS ACROSS THE REGION. HIGH PRESSURE
WILL BE THE DOMINANT FEATURE THROUGH MUCH OF NEXT WEEK BEFORE A COLD
FRONT POSSIBLY APPROACHES ON FRIDAY.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
ATLANTIC HIGH PRESSURE AT THE SURFACE WILL PREVAIL TONIGHT...AS A
SHORT WAVE TROUGH APPROACHES FROM THE WEST. MID AND HIGH LEVEL
CLOUDS WILL INCREASE IN COVERAGE AND THICKEN SOME OVERNIGHT AS THE
TROUGH NEARS. THE INCREASE IN CLOUDS AND A LIGHT SOUTHERLY FLOW
WILL KEEP LOW TEMPERATURES MAINLY IN THE MID 60S TONIGHT...WITH
UPPER 60S NEAR THE IMMEDIATE COAST.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/...
SATURDAY AND SATURDAY NIGHT...A DEEP AND EXPANSIVE LONGWAVE UPPER
RIDGE WILL ENCOMPASS MUCH OF THE EASTERN HALF OF THE COUNTRY WITH AN
EMBEDDED SHORTWAVE TROUGH POSITIONED NEAR THE OHIO VALLEY. THIS
BAGGY TROUGH CAUGHT WITHIN THE LARGER SCALE RIDGE WILL SLOWLY
MEANDER ACROSS THE APPALACHIANS AND TOWARDS THE EAST COAST. PIECES
OF VORT ENERGY ASSOCIATED WITH THIS FEATURE WILL CROSS THE FORECAST
AREA WITH SOME LOWERING OF HEIGHTS. AT THE SURFACE...THE FORECAST
AREA WILL BE IN THE SOUTHERLY FLOW REGIME AROUND HIGH PRESSURE OVER
THE ATLANTIC. MODEL SOUNDINGS SHOW THE ATMOSPHERE BECOME MORE
CONDUCIVE TO CONVECTIVE DEVELOPMENT IN THE AFTERNOON COMPARED TO
PREVIOUS DAYS...ESPECIALLY ALONG AND WEST OF I-95. AREAS EAST OF
I-95 ARE PROGGED TO SEE WARMER 850 MB TEMPS AND A CAP THAT WILL
LIKELY KEEP DEVELOPMENT ISOLATED AT BEST. FURTHER WEST...THE CAP
ERODES AND WITH COOLING/MOISTENING PROFILES...SCATTERED
SHOWERS/THUNDERSTORMS ARE EXPECTED. THE EXPECTATION IS THAT THIS
WILL BE JUST GARDEN VARIETY SHOWERS/STORMS AS NONE OF THE SEVERE
WEATHER PARAMETERS ARE PARTICULARLY IMPRESSIVE. HIGHS WILL CONTINUE
A FEW DEGREES ABOVE NORMAL REACHING THE MID/UPPER 80S.
OVERNIGHT...ONGOING CONVECTION SHOULD BECOME INCREASINGLY CONFINED
FURTHER WEST AND NORTH AS THE SEABREEZE PUSHES INLAND. I HAVE
MAINTAINED A SMALL AREA OF SLIGHT CHANCES THROUGH THE NIGHT CLOSER
TO THE TROUGH AND BETTER MOISTURE. LOWS WILL BE MILD AND IN THE
MID/UPPER 60S.

SUNDAY THROUGH MONDAY...THIS WILL BE THE MOST ACTIVE TIME PERIOD
WITH THE BEST COVERAGE OF SHOWERS/STORMS. THE BAGGY SHORTWAVE TROUGH
AND ASSOCIATED PASSING VORT MAXES WILL LINGER OVERHEAD WHILE A MOIST
S/SE FLOW IN THE LOW LEVELS CONTINUES. THE MODELS CONTINUE TO DEPICT
AN INCREASINGLY MOIST ATMOSPHERE WITH PWATS RISING INTO THE 1.7-1.8
INCH RANGE AT TIMES...WHICH IS NEAR THE 99TH PERCENTILE AND 2
STANDARD DEVIATIONS ABOVE NORMAL FOR MID/LATE MAY. THE RESULT IS A
QUITE MOIST AND UNCAPPED SCENARIO WHERE SHOWERS/STORMS COULD DEVELOP
AT JUST ABOUT ANY TIME. IN FACT IT WOULDN/T BE SURPRISING IF AT TIME
THE COVERAGE OF PRECIP BECOMES NUMEROUS. THIS WILL LIKELY BE MORE
CLOSELY TIMED WITH THE PASSING OF EMBEDDED ENERGY ALOFT WHICH HAS A
LOW CONFIDENCE AT THIS TIME. POPS HAVE BEEN INCREASED MORE INTO THE
MID/HIGH CHANCE RANGE FOR THE DAYTIME HOURS...WITH EVEN LOW CHANCES
GOING OVERNIGHT. WITH CONSIDERABLE CLOUD COVER AROUND INSOLATION
WILL BE A BIT LIMITED KEEPING HIGHS DOWN A FEW DEGREES...BUT STILL
NEAR OR SLIGHTLY ABOVE NORMAL.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
THE UPPER SHORTWAVE NORTH OF THE AREA ON MONDAY WILL ESSENTIALLY
DISSOLVE ACROSS THE EASTERN CAROLINAS ON TUESDAY LEAVING A VERY WEAK
RIDGE PATTERN IN PLACE. ATLANTIC HIGH PRESSURE WILL PRODUCE AN
ONSHORE FLOW WITH SEA BREEZES DEVELOPING EACH AFTERNOON. SURFACE
DEWPOINTS WILL PERSIST IN THE MIDDLE 60S WITH HIGHS CLIMBING WELL
INTO THE 80S EACH DAY. ALTHOUGH THERE ARE NO STRONG FORCING
MECHANISMS...WE KEPT ISOLATED SHOWERS AND THUNDERSTORMS IN THE
FORECAST EACH AFTERNOON/EVENING. A COLD FRONT COULD MOVE INTO THE
AREA ON FRIDAY.

&&

.AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
VFR CONDITIONS WILL PREVAIL AT KCHS AND KSAV THROUGH 00Z SUNDAY.
ISOLATED/SCATTERED CONVECTION COULD DEVELOP IN THE AFTERNOON
SATURDAY MAINLY ALONG AND WEST OF THE I-95 CORRIDOR...BUT
PROBABILITIES OF ANY CONVECTION IMPACTING THE TERMINALS ARE TOO LOW
TO INCLUDE IN THE FORECAST AT THIS TIME.

EXTENDED AVIATION OUTLOOK...PRIMARILY VFR. LOW CHANCES OF DIRECT IMPACTS
FROM ISOLATED TO SCATTERED MAINLY AFTERNOON SHOWERS/THUNDERSTORMS
THROUGH EARLY NEXT WEEK.

&&

.MARINE...
TONIGHT...QUIET MARINE CONDITIONS WILL PREVAIL AS SURFACE HIGH
PRESSURE EAST OF THE WATERS REMAINS THE DOMINANT WEATHER FEATURE.
GENERALLY EXPECT SOUTH WINDS LESS THAN 15 KTS WITH SEAS 2-3
FEET...HIGHEST IN THE OUTER WATERS.

THROUGH EARLY NEXT WEEK...ATLANTIC HIGH PRESSURE WILL BE THE PRIMARY
MARINE INFLUENCE WITH SOUTHERLY FLOW PREVAILING. WIND SPEEDS WILL
PERSIST IN THE 10-15 KT RANGE WITH SEAS 4 FT OR LESS.

&&

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

&&

$$

SYNOPSIS...
NEAR TERM...JAQ
SHORT TERM...BSH
LONG TERM...JAQ
AVIATION...ECT
MARINE...ECT/BSH