Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 301950
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
350 PM EDT SAT APR 30 2016

.SYNOPSIS...
HIGH PRESSURE WILL EXTEND ACROSS THE AREA TONIGHT AS A STATIONARY
FRONT TO THE NORTH TODAY LIFTS NORTH. LOW PRESSURE WILL PASS FAR
TO THE NORTH SUNDAY AND MONDAY. ANOTHER AREA OF LOW PRESSURE IS
EXPECTED TO DEVELOP OVER OR JUST NORTH OF THE AREA TUESDAY AND
WEDNESDAY. HIGH PRESSURE WILL BUILD BACK INTO THE AREA BY THE END
OF NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
INTO THIS EVENING...DEEP LAYERED LOW PRESSURE WILL SPIN IN THE
CENTRAL PLAINS WHILE DOWNSTREAM RIDGING WILL PREVAIL ACROSS MUCH
OF THE EAST AND SE...INCLUDING THE LOCAL CWFA. THIS DEFLECTS ANY
SHORT WAVES TO OUR NW AND NORTH AND KEEPS THE BULK OF DEVELOPING
CONVECTION OUTSIDE OUR AREA. THERE ARE NO LARGE SCALE FEATURES TO
INITIATE CONVECTION...BUT WITH SOME LOW LEVEL CONVERGENCE ALONG
A SHARP DIFFERENTIAL HEATING BOUNDARY FROM THE MORNING FOG/STRATUS
INTERACTING WITH THE SEA BREEZE AND THE PROXIMITY TO A DECAYING
FRONT TO THE NORTH...WE HAVE SMALL POPS MAINLY NEAR AND NORTH OF
I-26 IN CHARLESTON...BERKELEY AND DORCHESTER COUNTIES THIS
AFTERNOON. THERE IS ALSO A LOW LEVEL CONVERGENCE ZONE IN SOUTHERN
AND CENTRAL GA WHERE ADDITIONAL CONVECTION WILL CONTINUE
INITIATING. SOME OF THIS COULD SNEAK INTO EXTREME SW SECTIONS SW
OF STATESBORO BY NIGHTFALL. FOR THE VAST MAJORITY OF COMMUNITIES
HOWEVER IT/LL REMAIN RAINFREE INTO THIS EVENING. WHILE SEVERE
WEATHER LOOKS ALMOST NON- EXISTENT...GIVEN DCAPES OF 900-1200 J/KG
THERE COULD BE AN ISOLATED STRONG DOWNBURST IF UPDRAFTS ARE ABLE
TO OBTAIN ANY APPRECIABLE HEIGHT.

FOR TONIGHT...RIDGING ALOFT TRANSITIONS INTO THE ATLANTIC AS THE
CYCLONE IN THE CENTRAL STATES PUSHES AS LITTLE EASTWARD...NUDGED
BY ANOTHER LOW ORGANIZING IN THE DESERT SW. A DECENT MID LEVEL
PERTURBATION IN THE LOWER MS VALLEY LATE TODAY WILL PASS INTO THE
SE OVERNIGHT...AND REACHES THE ATLANTIC BY DAYBREAK SUNDAY. THIS
FEATURE WILL BE ACCOMPANIED BY A NOTED INCREASE IN MOISTURE AS
PWATS RISE FROM ABOUT AN INCH EARLY ON TO 1.5 INCHES OR MORE.
ALTHOUGH HEIGHT FALLS ARE RATHER SUBTLE AND THE MAIN PLUME OF LOW
LEVEL LEVEL WARM ADVECTION STAYS TO THE NW...THERE ARE
INDICATIONS OF A LATE NIGHT UPPER JET MAX TO AID IN SOME FORCING.
PLUS ISENTROPIC ASCENT...ALTHOUGH WEAK...IS ALSO EVIDENT ON THE
295-305K SURFACES.

THERE IS STILL A DISTINCT DISAGREEMENT BETWEEN VARIOUS
MODELS...WITH THE NAM AND SREF MEMBERS MORE IN LINE WITH THE
HIGH-RES MODELS IN KEEPING RAIN CHANCES DOWN TONIGHT. BUT THE
GLOBAL MODELS ARE FOCUSING ON A HIGHER PROBABILITY OF CONVECTION.
SOME OF THAT MAY BE DUE TO IT PICKING UP ON THE INCREASE IN
MOISTURE IN THE FORM OF OVERNIGHT LOW STRATUS AND DEBRIS CLOUDS
FROM UPSTREAM CONVECTION. WE/LL GO WITH A MORE CONSERVATIVE
FORECAST OF ONLY 20 POPS DURING THE LATE EVENING AND
OVERNIGHT. THIS MESHES WELL WITH OUR NEIGHBORS AND WE/LL MAKE
ADJUSTMENTS IF AND WHEN THEY BECOME NECESSARY.

ALTHOUGH DIURNAL CUMULUS WILL FADE THIS EVENING...HIGHER LEVEL
CLOUDS AND THE FORMATION OF STRATUS WILL CAUSE SKIES TO TRANSITION
FROM PARTLY CLOUDY EARLY TO MOSTLY CLOUDY OVERNIGHT. THAT ALONG
WITH WEAK WARM ADVECTION WILL LIMIT LOWS TO AN WARM 66-71F...OR
ABOUT 8-10F ABOVE NORMAL.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY/...
AN UNSETTLED PATTERN EXPECTED THROUGH THIS PERIOD. A BROAD...
POSITIVELY TILTED UPPER LEVEL TROUGH...WILL REMAIN OVER THE NORTH-
CENTRAL PORTION OF THE COUNTRY. THIS WILL KEEP OUR REGION ON THE
SOUTHEAST PERIPHERY OF THE UPPER TROUGH...WITH PERIODIC WEAK UPPER
IMPULSES EXPECTED TO MOVE ACROSS THE REGION SUNDAY AND MONDAY. GIVEN
THE WEAKNESS OF THE UPPER FEATURES...TIMING OF CONVECTION IS
CHALLENGING. FOR SUNDAY AND MONDAY...HAVE KEPT CHANCE POPS FOR MUCH
OF THE AREA. GIVEN UPPER FORCING IS WEAK THROUGH THIS PERIOD...FEEL
BEST CHANCES WILL BE DURING THE AFTERNOON COINCIDENT WITH MAXIMUM
HEATING. CAPE VALUES ARE MODERATE IN THE 1000-1500 J/KG RANGE...BUT
WEAK BULK SHEARS WILL MEAN ANY THUNDERSTORM ACTIVITY SHOULD REMAIN
BELOW SEVERE LIMITS AND LACK ORGANIZATION. ALTHOUGH GUIDANCE
MAINTAINS HIGHER POPS THAN TYPICAL DURING THE NIGH TIME
PERIODS...CONFIDENCE NOT VERY HIGH THAT THIS WILL OCCUR. NEVER THE
LESS...HAVE KEPT LOW END CHANCE DURING THE NIGHT TO REMAIN CLOSER TO
GUIDANCE AND COLLABORATE BETTER WITH SURROUNDING OFFICES.

TUESDAY WILL HAVE THE STRONGEST/BEST UPPER LEVEL SUPPORT AS THE
BROAD TROUGH SHARPENS AND MOVES E-NE TOWARD THE MID ATLANTIC. AT THE
SURFACE...A WEAK LOW PRESSURE SYSTEM IS PROGGED TO TRACK ACROSS
THE CAROLINAS AND MID ATLANTIC. THIS WILL KEEP THE AREA ON THE
WARM/UNSTABLE SIDE OF THE SYNOPTIC LOW. HAVE KEPT HIGH END CHANCE
POPS...BUT WOULD NOT BE SURPRISED IF LATER FORECASTS NUDGE INTO
LIKELY OR HIGHER POPS. GIVEN BETTER UPPER FORCING FROM THE
TROUGH...AS WELL AS BEING ON THE ENTRANCE SIDE OF AN UPPER
JET...WILL BE MONITORING THE POTENTIAL FOR SOME STORMS TO BE
STRONG OR POSSIBLY SEVERE. TOO SOON TO ADD MENTION DUE TO
UNCERTAINTY WITH TIMING OF THE UPPER FEATURES AND DEEP LAYER
MOISTURE...WHICH MAY BE DEPARTING THE AREA BY LATE MORNING/EARLY
AFTERNOON. IF THAT HAPPENS...CHANCES FOR ANY STRONG STORMS WILL BE
MUCH LOWER. HIGHS IN THE LOWER 80S AND LOWS IN THE MID TO UPPER
60S.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
THERE IS STILL A FAIR AMOUNT OF DISAGREEMENT WITH THE MODELS TUESDAY
NIGHT ONWARD. THE 00Z GFS HAS WEAK LOW PRESSURE HOVERING OVER OR
NEAR US TUESDAY NIGHT INTO WEDNESDAY...THEN MOVING TO THE NORTHEAST
WEDNESDAY NIGHT FOLLOWED BY BUILDING HIGH PRESSURE THURSDAY. THE 00Z
ECMWF HAS A MUCH STRONGER/STRENGTHENING LOW DURING THIS SAME TIMER
PERIOD. HOWEVER...WRAP AROUND SHOWERS WILL PERSIST INTO THURSDAY
BEFORE HIGH PRESSURE BUILDS THURSDAY NIGHT INTO FRIDAY. THE 00Z
CANADIAN SEEMS TO BE IN THE MIDDLE OF THESE TWO...EXCEPT IT BRINGS
THE HIGH PRESSURE IN WEDNESDAY NIGHT. GIVEN ALL THE DIFFERENT
SOLUTIONS AND A GENERAL TROUGH OVER THE EAST COAST...OPTED TO KEEP
CHANCE POPS TUESDAY NIGHT INTO WEDNESDAY...FOLLOWED BY POPS TRENDING
DOWNWARD TO SLIGHT CHANCE WEDNESDAY NIGHT INTO THURSDAY. BUILDING
HIGH PRESSURE WILL BRING DRY CONDITIONS ON FRIDAY WITH BELOW NORMAL
TEMPERATURES.

&&

.AVIATION /19Z SATURDAY THROUGH THURSDAY/...
VFR INTO EARLY TONIGHT...EXCEPT FOR A BRIEF PERIOD OF MVFR
CEILINGS AND A LOW END CHANCE OF A STRAY SHRA AT KCHS THIS
AFTERNOON. GUSTY SOUTH/SE WINDS AT BOTH SITES WILL DROP OFF WITH
SUNSET THIS EVENING.

CONDITIONS WILL DETERIORATE TO MVFR OR PERHAPS IFR AT BOTH
TERMINALS OVERNIGHT INTO SUNDAY MORNING...AS BOUNDARY LAYER
MOISTURE INCREASES WITHIN A SE/SOUTH FLOW AND THE NOCTURNAL
INVERSION DEVELOPS. WE HAVE SHOWN CEILINGS DEVELOPING AROUND 1500
FT BY 05-06Z AND LASTING THROUGH 13-14Z SUNDAY...BUT THE SREF DOES
SHOW 30-40 PERCENT PROBABILITIES OF IFR CONDITIONS. FOR NOW WE
HAVE A SCATTERED DECK AT 900 FT...JUST TO IMPLY THAT THE RISK OF
IFR COULD OCCUR. SURFACE VISIBILITIES SHOULD REMAIN 6SM OR GREATER
WITH TOO MUCH WIND WITHIN THE BOUNDARY LAYER...THUS LIMITING THE
FOG POTENTIAL.

WHILE THERE COULD BE A SHRA LATE TONIGHT INTO EARLY SUNDAY AT BOTH
TERMINALS DUE TO ENERGY MOVING IN ALOFT...ANY IMPACTS WOULD BE
FAIRLY BENIGN. THEN VFR WEATHER WILL RETURN AGAIN THE SECOND HALF
OF SUNDAY MORNING AND EARLY AFTERNOON.

EXTENDED AVIATION OUTLOOK...UNSETTLED CONDITIONS WILL RESULT IN
THE CHANCE FOR PERIODIC FLIGHT RESTRICTIONS WITHIN SCATTERED
SHOWERS/THUNDERSTORMS...MAINLY DURING THE AFTERNOON HOURS BOTH
KCHS AND KSAV THROUGH TUESDAY.

WEDNESDAY AND THURSDAY...LATEST MEDIUM RANGE GUIDANCE INDICATING
THE AREA WILL BE AT THE SOUTHERN END/BASE OF A LARGE...CLOSED UPPER
LOW OVER THE NE U.S./SE CANADA. WITH MUCH DRIER DEEP
LAYER MOISTURE...EXPECT THAT VFR WILL DOMINATE THIS PERIOD.

&&

.MARINE...
TONIGHT...A DECAYING STATIONARY FRONT NEAR THE NC/SC BORDER AND
EXTENDING EAST/SE INTO THE ATLANTIC AS A 1025 MB HUGGING THE COAST
OF NEW ENGLAND CONTINUES TO POKE SW ACROSS THE LOCAL WATERS. THIS
SUPPORTS A MODEST EAST/SE FLOW WITH SPEEDS AS HIGH AS 12-18 KT AND
SEAS BUILDING TO 2-4 FT...HIGHEST BEYOND 40 NM OFF THE GA COAST
AND THE NE PART OF AMZ350.

SUNDAY THROUGH THURSDAY...NO HIGHLIGHTS ARE EXPECTED THROUGH THE
PERIOD. IN GENERAL...THE WATERS WILL SIT BETWEEN ATLANTIC HIGH
PRESSURE WELL ENE OF THE AREA AND LOWER PRESSURE OVER THE MID
ATLANTIC AND CAROLINAS. THIS WILL RESULT IN SOUTH-SOUTHWEST WINDS
OF 15 KNOTS OR LESS AND SEAS 3 FEET OR LESS. UNSETTLE CONDITIONS
LIKELY WITH SCATTERED SHOWER AND THUNDERSTORMS...ESPECIALLY MONDAY
AND TUESDAY.

&&

.EQUIPMENT...
THE CHARLESTON HARBOR NOS TIDE GAUGE HAS STOPPED REPORTING ALL
METEOROLOGICAL AND TIDE DATA. THE NATIONAL OCEAN SERVICE IS
INVESTIGATING THE CAUSE OF THE OUTAGE. AN ESTIMATED TIME FOR DATA
RESTORATION IS UNKNOWN AT THIS TIME.

&&

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

&&

$$
SYNOPSIS...
NEAR TERM...
SHORT TERM...
LONG TERM...
AVIATION...
MARINE...
EQUIPMENT...



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