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Area Forecast Discussion

791
FXUS62 KCAE 291836
AFDCAE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE COLUMBIA SC
236 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 TONIGHT/...
TONIGHT...A STRONG MID AND UPPER LEVEL RIDGE WILL CONTINUE TO
EXTEND OVER THE REGION. AT THE SURFACE...A WEAK/DIFFUSE BOUNDARY WILL
REMAIN STALLED SOUTH OF THE AREA INITIALLY...THEN BEGIN TO LIFT
NORTHWARD ACROSS THE AREA FOLLOWING THE PASSAGE OF A WEAK MESO-
HIGH. MEANWHILE...A LARGE CONVECTIVE COMPLEX OVER THE LOWER MISSISSIPPI
VALLEY WILL CONTINUE TO PROGRESS TOWARD THE AREA...BUT MODELS ARE
CONSISTENT IN SHOWING IT WEAKENING AS IT ENCOUNTERS THE STRONG
UPPER LEVEL RIDGE. SO WHILE NO PRECIPITATION IS EXPECTED
TONIGHT...DO THINK THAT THE UPSTREAM HIGH LEVEL CLOUDS ASSOCIATED
WITH THE CONVECTIVE COMPLEX WILL BEGIN TO INCREASE/THICKEN OVER
THE AREA. SOME MODELS ARE HINTING AT THE POTENTIAL FOR PATCHY FOG
DEVELOPMENT OVER PARTS OF THE CSRA AND SOUTHERN MIDLANDS LATE
TONIGHT...BUT WILL NOT ADD MENTION TO THE FORECAST DUE TO
UNCERTAINTY IN WHAT ROLE THE HIGH CLOUDS WILL PLAY IN HINDERING
ITS FORMATION AND THE RELATIVELY LOW IMPACT IT WILL POSE IF IT
DOES FORM. LOW TEMPERATURES ARE FORECAST TO BE IN THE LOWER TO MID
60S ACROSS THE AREA.

&&

.SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/...
.SATURDAY...THE DAY WILL START OUT DRY WITH THE WEDGE FRONT STALLED
OVER THE NORTHERN CWA AND VERY WEAK SOUTHERLY FLOW IN PLACE. THERE
COULD BE SOME LOW CLOUDS NEAR THE FRONT NORTH OF A BISHOPVILLE TO
WINNSBORO LINE...BUT THEY SHOULD THIN OUT DURING THE MORNING WITH
DAYTIME HEATING. DESPITE THE LARGE CONVECTIVE COMPLEX HAPPENING THIS
AFTERNOON OVER THE LOWER MISSISSIPPI...THE MODELS ARE FAIRLY
INSISTENT THAT THICK CIRRUS SHIELD SHOULD THIN RAPIDLY AS IT MOVES
EAST OVERNIGHT. I AM NOT BETTING THE FARM ON THAT...SO I KEEP DECENT
CLOUD COVER IN THE GRIDS FOR THE NORTHEASTERN HALF OF THE CWA DURING
THE MORNING.

BY AFTERNOON...DAYTIME HEATING WILL BRING TEMPS INTO THE UPPER 80S
MOST EVERYWHERE...EXCEPT MAYBE A LITTLE COOLER FAR NORTH AS THE
MORNING HEATING WILL BE A LITTLE SLOWER DUE TO CLOUD COVER.
HOWEVER...THE WEDGE FRONT SHOULD RETREAT NORTHWARD BY
AFTERNOON...PLACING THE ENTIRE CWA IN WARM SOUTHERLY FLOW. DEW
POINTS WILL ALSO BE RISING INTO THE 60S...SO INSTABILITY WILL BE ON
THE INCREASE WITH CAPES RISING ABOVE 1000 J/KG IN THE WESTERN AND
NORTHERN CWA. THIS WILL SUPPORT SOME SCATTERED CONVECTIVE ACTIVITY.
SPC PUT THE NORTHWESTERN HALF OF THE CWA INTO A MARGINAL RISK
SATURDAY AFTERNOON AND EVENING...BUT THE THREAT SHOULD REMAIN
ISOLATED AS THERE IS NO DISTINCT FOCUSING MECHANISM IN PLAY TO
PROVIDE SIGNIFICANT LOW LEVEL LIFT.

.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 /SUNDAY THROUGH THURSDAY/...
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 /18Z FRIDAY THROUGH WEDNESDAY/...
HIGH LEVEL CLOUD COVER WILL EXPAND/THICKEN OVER THE AREA TONIGHT.
GUIDANCE IS INDICATING THE POTENTIAL FOR SOME REDUCED VISIBILITIES
IN PATCHY FOG AT THE TERMINALS LATE TONIGHT INTO SATURDAY MORNING...BUT
THERE IS SOME UNCERTAINTY IN WHAT IMPACT THE HIGH CLOUDS WILL
HAVE ON FOG FORMATION. FOR NOW...HAVE INDICATED MVFR CONDITIONS IN
PATCHY FOG AT KAGS/KOGB FROM 09-14Z...BUT WILL REFRAIN FROM DOING
SO AT THE OTHER TERMINALS UNTIL CONFIDENCE INCREASES.
OTHERWISE...VFR CONDITIONS WILL PREVAIL WITH RELATIVELY
LIGHT/VARIABLE WINDS THROUGH 18Z SATURDAY.

EXTENDED AVIATION OUTLOOK...SCATTERED AFTERNOON AND CONVECTION COULD
CAUSE SOME TEMPORARY ISSUES AT THE TERMINALS EACH AFTERNOON/EVENING
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.

&&

$$

NEAR TERM...JAQ
SHORT TERM...FWA
LONG TERM...FWA
AVIATION...JAQ/FWA



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