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Area Forecast Discussion

292
FXUS62 KCHS 010813
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
413 AM EDT SUN MAY 1 2016

.SYNOPSIS...
LOW PRESSURE WILL PASS FAR TO THE NORTH TODAY AND MONDAY. ANOTHER
AREA OF LOW PRESSURE IS EXPECTED TO DEVELOP JUST NORTH OF THE AREA
TUESDAY AND WEDNESDAY. HIGH PRESSURE WILL BUILD INTO THE REGION BY
THE END OF THE WEEK.

&&

.NEAR TERM /THROUGH TODAY/...
THROUGH SUNRISE...APPROACHING SHORTWAVE ENERGY HAS BEEN ABLE TO
SPARK OFF ISOLATED TO SCATTERED SHOWERS AND TSTMS ACROSS PARTS OF
SOUTHEAST GEORGIA THIS MORNING. INSTABILITY IS MODEST FOR EARLY
MORNING HOURS PER RAP SOUNDINGS AND MSAS INSTABILITY FIELDS, SO
THE RISK FOR TSTMS WILL CONTINUE. ISOLATED TO PERHAPS SCATTERED
CONVECTION WILL GRADUALLY SPREAD NORTHEAST THROUGH DAYBREAK AS
SHORTWAVE ENERGY TRAVERSES THE AREA. WILL SHOW AN AREA OF 20-30
GRIDDED POPS MOVING NORTHEAST ACROSS ALL OF SOUTHERN SOUTH
CAROLINA AND SOUTHEAST GEORGIA COINCIDENT WITH THE SHORTWAVE FOR
THE NEXT SEVERAL HOURS. THE RISK FOR MEASURABLE RAINFALL SHOULD
END BY SUNRISE AS SUBSIDENCE DEVELOPS AS THE SHORTWAVE EXITS TO
THE NORTHEAST.

TODAY...UPPER RIDGING WILL CONTINUE TO ERODE AND SHIFT FARTHER
OFFSHORE TODAY IN RESPONSE TO A STRONG SHORTWAVE KICKING OUT OF
THE CENTRAL PLAINS AND ANOTHER LOW CUTTING OFF OVER THE FOUR
CORNERS REGION. AFTER SEVERAL DAYS OF DRY WEATHER, TODAY IS
LOOKING INCREASINGLY ACTIVE FOR SHOWERS/TSTMS AS ANOTHER POTENT
SOUTHERN STREAM SHORTWAVE APPROACHES AND INTERACTS WITH MODERATE
INSTABILITY ACROSS THE SOUTHEAST STATES. MOST OF THE MORNING LOOKS
DRY AS SUBSIDENCE DOMINATES IN THE WAKE OF EXITING SHORTWAVE
ENERGY, BUT THIS WILL CHANGE BY EARLY AFTERNOON AS INFERRED
CYCLONIC VORTICITY ADVECTION AHEAD OF THE DOWNSTREAM SHORTWAVE AND
UPPER DIVERGENCE ASSOCIATED WITH THE LEFT EXIT REGION OF AN
APPROACHING SUBTROPICAL JET STREAM SPREAD IN FROM THE SOUTHWEST.
THE MOST FAVORABLE ALIGNMENT OF LOW-LEVEL CONVERGENCE, UPPER
FORCING AND INSTABILITY LOOKS TO SETTLE INTO THE AREA NORTH OF
I-16 AND WEST OF I-95 BY EARLY-MID AFTERNOON. POPS WILL BE
INCREASED TO 50 PERCENT IN THIS REGION WITH 20-40 PERCENT POPS
ELSEWHERE--LOWEST ALONG THE BEACHES.

WATER VAPOR IMAGERY SHOWS A DRY SLOT QUICKLY APPROACHING FROM THE
WEST WHICH IS ON TARGET TO OVERSPREAD THE AREA LATER THIS
MORNING. THIS WILL SUPPORT MODERATE BREAKS IN THE CLOUD CANOPY, SO
TEMPERATURES WILL ONCE AGAIN WARM INTO THE MID-UPPER 80S WITH A
FEW ISOLATED INSTANCES OF 90 OCCURRING ACROSS INTERIOR SOUTHEAST
GEORGIA WHERE THE BREAKS WILL BE THE MOST PREVALENT THIS MORNING.
SIMILAR TO SATURDAY, A STRONGER ONSHORE FLOW ACROSS THE CENTRAL
SOUTH CAROLINA COAST WILL SUPPORT COOLER/MORE STABLE CONDITIONS
ACROSS MUCH OF CHARLESTON COUNTY WHERE HIGHS WILL ONLY WARM INTO
THE LOWER 80S AWAY FROM THE BEACHES.

MODIFIED SOUNDINGS DEPICT MODERATE INSTABILITY BY EARLY AFTERNOON
WITH SBCAPE REACHING AS HIGH AS 2500 J/KG INLAND AND LIFTED
INDICES AS LOW AS -6C. THERE IS QUITE A BIT OF 0-3KM CAPE NOTED
WEST OF THE I-95 CORRIDOR WHICH SUGGESTS STORMS COULD GO UP WITH
SOME FEROCITY ONCE INITIATION OCCURS. THE APPROACHING DRY SLOT
WILL SUPPORT A RISK FOR DAMAGING WINDS WITH DCAPE VALUES REACHING
AS HIGH AS 900-1200 J/KG. HIGH CAPE VALUES IN THE -10 TO -30C
LAYER AND WBZ HEIGHTS JUST ABOVE 10 KFT WILL ALSO SUPPORT A RISK
FOR MARGINALLY SEVERE HAIL. DESPITE STRONG INSTABILITY, WEAK SHEAR
PROFILES OF 15-25 KT SUGGEST THE FORMATION OF ANY ORGANIZED SEVERE
WEATHER IS LOW. HOWEVER, ISOLATED SEVERE THUNDERSTORMS WILL BE
POSSIBLE, ESPECIALLY WHERE LOW-LEVEL FORCING IS SUPPLEMENTED BY
MESOSCALE BOUNDARY COLLISIONS. THE RISK FOR SEVERE THUNDERSTORMS
WILL BE THE GREATEST NORTH OF I-16 AND WEST OF I-95 AND WILL BE
HIGHLIGHTED IN THE HAZARDOUS WEATHER OUTLOOK.

&&

.SHORT TERM /TONIGHT THROUGH WEDNESDAY/...
TONIGHT...CONVECTION WILL GRADUALLY WIND DOWN DURING THE EARLY
EVENING AS INSTABILITY WANES AND SHORTWAVE ENERGY PUSHES OFF TO
THE NORTHEAST AWAY FROM THE AREA. COULD SEE AN ISOLATED SHOWER
BRUSH THE CENTRAL/UPPER CHARLESTON COUNTY COAST EARLY MONDAY
MORNING AS NOCTURNAL SHOWER/TSTM ACTIVITY DEVELOPS OVER THE
COASTAL WATERS, BUT CONFIDENCE IN THIS SCENARIO IS STILL RATHER
LOW. IT WILL BE ANOTHER WARM/HUMID NIGHT WITH LOWS ONLY DROPPING
INTO THE UPPER 60S INLAND TO THE LOWER 70S AT THE COAST.

MONDAY...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
MONDAY. GIVEN THE WEAKNESS OF THE UPPER FEATURES...TIMING OF
CONVECTION IS CHALLENGING. MONDAY STARTS OUT DRY WITH POPS
INCREASING TO CHANCE FROM WEST TO EAST AS THE DAY PROGRESSES. THE
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. THE
MODELS STILL INDICATE HIGH POPS MONDAY NIGHT. THIS SEEMS TO BE A
LITTLE OVERDONE GIVEN THE LOCATION OF THE SYNOPTIC FEATURES. KEPT
CHANCE POPS...BUT HAVE THEM TRENDING DOWNWARD AS THE NIGHT
PROGRESSES.

TUESDAY...THE TROUGH REMAINS OVER THE EAST COAST WHILE A SHORT WAVE
ROUNDS THE BASE OF THE TROUGH DURING THE DAY...MOVING INTO THE
MIDDLE MISSISSIPPI VALLEY. AT THE SURFACE...A BROAD AREA OF WEAK LOW
PRESSURE WILL BE SPREAD ACROSS THE MID-ATLANTIC STATES WITH A COLD
FRONT STRETCHED DOWN NEAR THE FLORIDA PANHANDLE. OUR AREA WILL BE IN
THE WARM/UNSTABLE SECTOR OF THE SYNOPTIC PATTERN.
PLENTIFUL MOISTURE ACROSS THE AREA...PWATS EXCEEDING 1.5
INCHES...COMBINED WITH GOOD LIFT DUE TO THE TROUGH AND THE
APPROACHING COLD FRONT WILL LEAD TO SHOWERS AND THUNDERSTORMS.
RAISED POPS TO ACCOUNT FOR THIS. THE INGREDIENTS ARE COMING TOGETHER
FOR SOME OF THESE STORMS TO BE STRONG OR MAYBE SEVERE.
ALONG WITH THE AFOREMENTIONED LIFT AND MOISTURE THERE WILL BE A JET
STREAK APPROACHING FROM THE WEST. THERE WILL ALSO BE PLENTY OF
INSTABILITY AT THE SURFACE. THE QUESTION IS DO ALL OF THE
INGREDIENTS COME TOGETHER AT THE RIGHT TIME? IF THEY DO THEN THE
GREATEST THREAT WOULD BE DAMAGING WINDS AND HAIL. GIVEN THERE IS
STILL SOME UNCERTAINTY IN THE FEATURES COMING TOGETHER AT THE RIGHT
TIME...ESPECIALLY THE COLD FRONT WHICH MAY CROSS THROUGH THE AREA
TUESDAY NIGHT. WE STILL DO NOT HAVE SEVERE IN THE FORECAST AND ARE
HIGHLIGHTING IT IN THE HWO. THIS WILL BE UPDATED IN THE UPCOMING
FORECAST PACKAGES.

WEDNESDAY...THE TROUGH IS STILL OVER THE EAST COAST WHILE THE SHORT
WAVE ROUNDS THE EASTERN PERIPHERY OF IT...MOVING INTO THE MID-
ATLANTIC STATES. AT THE SURFACE A COLD FRONT WILL BE JUST OFFSHORE
IN THE MORNING...MOVING AWAY DURING THE DAY. SOME REMNANT LIGHT
SHOWERS ARE POSSIBLE...ESPECIALLY IN THE MORNING. POPS WILL
GRADUALLY DECREASE DURING THE DAY AS HIGH PRESSURE BUILDS INTO THE
REGION...ALLOWING FOR DRYING CONDITIONS. HIGH WILL BE A FEW DEGREES
BELOW NORMAL...IN THE UPPER 70S.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
MODELS ARE NOW IN FAIRLY GOOD AGREEMENT SHOWING WEAK HIGH PRESSURE
OVER THE AREA WEDNESDAY NIGHT WHILE A STORM SYSTEM IMPACTS THE
NORTHEASTERN STATES. A DRY COLD FRONT IS FORECAST TO MOVE THROUGH ON
THURSDAY...BRINGING COOLER TEMPERATURES FOR FRIDAY. DESPITE A TROUGH
REMAINING OVER THE EAST COAST DURING THIS ENTIRE TIME PERIOD...POPS
ARE LOW BECAUSE HIGH PRESSURE WILL BE SPREAD ACROSS OR NEAR THE
SOUTHEAST STATES FRIDAY AND SATURDAY.

&&

.AVIATION /07Z SUNDAY THROUGH THURSDAY/...
BEST CHANCES FOR MVFR CIGS PRIOR TO SUNRISE WILL BE AT KCHS. RIGHT
NOW...CONDITIONS DO NOT FAVOR SIGNIFICANT STRATUS BUILD DOWN SO
CIGS ARE NOT EXPECTED TO DROP TO IFR THERE. WILL CARRY PREVAILING
MVFR CIGS 08-12Z. AT KSAV...EXPECT MAINLY VFR NEXT FEW HOURS WITH
MARGINAL MVFR CIGS POSSIBLE JUST BEFORE SUNRISE. WILL GO A TEMPO
GROUP FROM 09-12Z TO COVER THIS. OTHERWISE...VFR TODAY. BEST
CHANCES FOR SHOWERS/TSTMS WILL REMAIN WEST OF THE TERMINALS. WILL
NOT CARRY A MENTION OF TSRA OR SHRA FOR THE 06Z TAF CYCLE.

EXTENDED AVIATION OUTLOOK...PERIODIC FLIGHT RESTRICTIONS WITHIN
SCATTERED SHOWERS/THUNDERSTORMS...MONDAY THROUGH TUESDAY NIGHT.

&&

.MARINE...
TODAY AND TONIGHT...A SOUTHERLY FLOW WILL PERSIST TODAY AS HIGH
PRESSURE REMAINS WELL OFFSHORE. WINDS WILL REMAIN AROUND 10 KT
WITH SEAS 2-4 FT THROUGH THE PERIOD.

MONDAY 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
ARE 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.

&&

$$

ST/MS



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