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Area Forecast Discussion

986
FXUS62 KCAE 300234
AFDCAE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE COLUMBIA SC
1034 PM EDT FRI APR 29 2016

.SYNOPSIS...
A WEAK SURFACE TROUGH WILL BE IN THE FORECAST AREA THROUGH THE
WEEKEND. DRY UPPER RIDGING OVER THE AREA TODAY AND TONIGHT WILL
BEGIN TO SHIFT EAST OF THE REGION SATURDAY ALLOWING A MOISTURE
INCREASE.

&&

.NEAR TERM /THROUGH SATURDAY/...
AN UPPER LEVEL RIDGE WILL REMAIN OVER THE REGION PREVENTING
PRECIPITATION OVERNIGHT. A LARGE CONVECTIVE COMPLEX TO THE WEST
WILL WEAKEN AS IT MOVES UNDER THE UPPER RIDGE AND INTO SYNOPTIC
SCALE SUBSIDENCE. HIGH CLOUDS FROM THE UPSTREAM CONVECTION WILL
STREAM INTO THE FORECAST AREA OVERNIGHT. THE HRRR INDICATES THE
POTENTIAL FOR FOG IN THE EASTERN MIDLANDS WHERE THERE MAY BE LESS
CLOUD COVERAGE AND INCREASING MOISTURE IN LIGHT SOUTHERLY FLOW.
HOWEVER CLOUD COVERAGE IN THE HRRR MAY BE UNDERDONE WHICH WOULD
LIMIT FOG POTENTIAL. IN ADDITION A 20 KT LLJ WILL PROMOTE SOME
LOWER LEVEL MIXING. LOW TEMPERATURES ARE FORECAST TO BE IN THE
LOWER TO MID 60S ACROSS THE AREA.

SATURDAY...HIGH PRESSURE WILL RIDGE INTO THE MID-ATLANTIC STATES
REINFORCING A BOUNDARY JUST NORTH OF THE FORECAST AREA. WARM
ADVECTION AND SOUTHERLY FLOW WILL LEAD TO INCREASED MOISTURE
ACROSS THE REGION AND OROGRAPHIC LIFT IN THE UPSTATE. A NUMBER OF
HI RESOLUTION MODELS INDICATE CONVECTION DEVELOPING ALONG THE
HIGHER TERRAIN IN THE UPSTATE AS WELL AS ALONG THE BOUNDARY IN
NC. THIS SUGGESTS A CHANCE OF SHOWERS AND THUNDERSTORMS DEVELOPING
IN THE NORTHERN AND EXTREME WESTERN PORTIONS OF THE FORECAST AREA
SATURDAY AFTERNOON. THE CONVECTION WOULD TEND TO MOVE E/NE IN THE
STEERING FLOW BRINGING THE CHANCE FOR PRECIPITATION FURTHER INTO
THE CENTRAL AND NORTHERN MIDLANDS DURING THE LATE AFTERNOON. THE
REMNANTS OF THE CONVECTIVE COMPLEX MAY ALSO PLAY A ROLE IN THE
LOCATION OF CONVECTIVE INITIATION WHICH INCREASES UNCERTAINTY.

TEMPERATURES...TEMPERATURES WILL BE IN THE UPPER 80S MOST
EVERYWHERE...POSSIBLY A LITTLE COOLER FAR NORTH AS THE MORNING
HEATING WILL BE A LITTLE SLOWER DUE TO CLOUD COVER.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
.SATURDAY NIGHT...WITH THE MEAN FLOW AT MID LEVELS BEING WEST
SOUTHWESTERLY...THE CONVECTION THAT DEVELOPS NORTH AND WEST OF THE
AREA SATURDAY AFTERNOON AND EVENING SHOULD DRIFT OVER THE CWA
OVERNIGHT...KEEPING CLOUDS AND SPOTTY SHOWERS/TSTORMS A THREAT ALL
NIGHT. PWS WILL BE INCREASING TO >1.5 INCHES...BUT THE MAIN JET AT
UPPER LEVELS REMAINS WELL TO THE NORTH OF THE CWA AND SURFACE
CONVERGENCE WILL BE MAINLY INDUCED BE EARLIER CONVECTION...SO I
HAVE NOT GONE AS HIGH AS THE GFS WOULD SUGGEST FOR POPS SATURDAY
NIGHT. MIN TEMPS WILL REMAIN ABOVE NORMAL IN THE MID 60S WITH
CLOUDS SUPPRESSING THE DIURNAL TEMP DROP.

.SUNDAY...SIMILAR TO SATURDAY NIGHT...PLENTIFUL MOISTURE WILL BE IN
PLACE TO ALLOW FOR SIGNIFICANT CLOUDINESS. HOWEVER...A CLEAR
FOCUSING MECHANISM FOR CONVECTION WILL BE LACKING OVER THE CWA...AND
THE CLOUDS WILL KEEP MAX TEMPS SEVERAL DEGREES LOWER THAN
SATURDAY...LIMITING THE INSTABILITY. I HAVE KEPT A CHANCE OF SHOWERS
AND THUNDERSTORMS...BUT AGAIN AM LEANING TOWARD LOWER GUIDANCE
VALUES.

.SUNDAY NIGHT AND MONDAY...NOT MUCH CHANGE TO THE PATTERN. THERE
MAYBE A SLIGHT INCREASE IN SOUTHWESTERLY WINDS AS ANOTHER FRONT
TRIES TO APPROACH FROM THE NORTHWEST...BUT IT SHOULD REMAIN NORTH OF
THE CWA THROUGH MONDAY. PWS MAY ALSO DROP A BIT...BUT THAT MEANS A
LITTLE BIT WARMER TEMPERATURES AGAIN...PRODUCING SOME MODEST LOW
LEVEL INSTABILITY BY AFTERNOON. CHANCE OF THUNDERSTORMS LOOKS
APPROPRIATE.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
THE BEST CHANCE OF WIDESPREAD RAIN LOOK TO BE TUESDAY AS THE UPPER
JET WHICH WILL BE HELD OFF TO THE NORTH OVER THE WEEKEND INTO MONDAY
FINALLY STARTS TO DIVE SOUTHEASTWARD AS A MORE SIGNIFICANT TROUGH
DEVELOPS IN EASTERN NORTH AMERICA. THERE IS SOME GLOBAL MODEL TIMING
DIFFERENCES WITH HOW FAST THE UPPER DISTURBANCE DEVELOPS A SURFACE
LOW WHICH DRAGS A COLD FRONT THROUGH THE CWA. THE 12Z GFS QUICKLY
RACES THE SYSTEM THROUGH AND BRINGS COOLER AND DRIER WEATHER IN FOR
WEDNESDAY...WHILE THE SLOWER 00Z ECMWF DOES NOT BRING THE POLAR AIR
MASS IN UNTIL THURSDAY. THEREFORE...I HAVE KEPT SCATTERED CONVECTION
IN THE FORECAST THROUGH WEDNESDAY IN DEFERENCE TO THE ECMWF. IN
EITHER CASE...A MODIFIED POLAR AIR MASS SHOULD MOVE IN FOR THE END
OF THE WEEK.

&&

.AVIATION /03Z SATURDAY THROUGH WEDNESDAY/...
HIGH CONFIDENCE FOR VFR CONDITIONS THROUGH 06Z.

HIGH LEVEL CLOUDS OVER THE REGION. GUIDANCE IS INDICATING THE
POTENTIAL FOR IFR VSBYS/CIGS IN FOG ACROSS THE MIDLANDS TAF SITES
EARLY SATURDAY MORNING...BUT THERE IS SOME UNCERTAINTY IN WHAT
IMPACT THE HIGH CLOUDS WILL HAVE ON FOG FORMATION. HAVE INDICATED
MVFR CONDITIONS IN PATCHY FOG AT KAGS/KOGB FROM 09-14Z. OTHERWISE...
VFR CONDITIONS FORECAST. ISOLATED TO SCATTERED CONVECTION TO
DEVELOP SATURDAY AFTERNOON...BUT CONFIDENCE IS TOO LOW TO INCLUDE
IN TAFS AT THIS TIME.

EXTENDED AVIATION OUTLOOK...SCATTERED AFTERNOON/EVENING CONVECTION
COULD CAUSE SOME TEMPORARY RESTRICTIONS THROUGH MONDAY. EARLY
MORNING LOW CIGS LOOK POSSIBLE AT ALL THE TERMINALS SUNDAY/MONDAY
MORNING WITH MOISTURE INCREASING AND LOW LEVEL WINDS REMAINING
LIGHT. BETTER CHANCES FOR CONVECTIVELY INDUCED MVFR/IFR CONDITIONS
SEEM TO BE IN LINE FOR TUESDAY. WEDNESDAY IT BECOMES MORE UNCERTAIN
DUE TO DIFFERENCES BETWEEN THE MODELS.

&&

.CAE WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.

&&

$$



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