Area Forecast Discussion
Issued by NWS Columbia, SC

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000
FXUS62 KCAE 302041
AFDCAE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE COLUMBIA SC
441 PM EDT SAT APR 30 2016

.SYNOPSIS...
A STATIONARY FRONT NEAR THE NORTH AND SOUTH CAROLINA BORDER TODAY
WILL LIFT NORTH AS A WARM FRONT TONIGHT. A MOIST SOUTHERLY FLOW
WILL OCCUR OVER THE FORECAST AREA THROUGH SUNDAY. A SLOW MOVING
COLD FRONT WILL MOVE NEAR THE REGION MONDAY. AN AREA OF LOW
PRESSURE WILL LIKELY DEVELOP ALONG THE FRONT NEAR THE FORECAST
AREA TUESDAY.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
MORNING STRATUS HAS BEEN REPLACED WITH DIURNALLY INDUCED CUMULUS
WITH SOME CONVECTION ALREADY DEVELOPING ACROSS CENTRAL GEORGIA
ALONG AN AXIS OF SURFACE CONVERGENCE AND NEAR 500MB DIFFLUENT
ZONE. DIFFUSE SURFACE BOUNDARY REMAINS SITUATED ACROSS THE
NORTHERN MIDLANDS INTO THE UPSTATE AND COULD BECOME A FOCUS FOR
CONVECTION LATER THIS AFTERNOON. CURRENT MESOANALYSIS DATA
INDICATES LIFTED INDEX VALUES AROUND -4C TO -5C ALTHOUGH MIXED
LAYER CAPE IS IN THE 500-1000 J/KG RANGE. SOUNDINGS INDICATE MOST
OF THE MOISTURE IN THE LOWER LEVELS WITH DRY AIR ALOFT AND
PRECIPITABLE WATER VALUES AROUND 1.3 INCHES. WILL CONTINUE TO
FOCUS HIGHEST POPS ALONG THE BOUNDARY TO THE NORTH AND IN THE
UPPER CSRA AND WESTERN MIDLANDS THIS AFTERNOON...THOUGH ALL STILL
IN THE CHANCE RANGE...WITH ONLY SLIGHT CHANCE POPS IN THE
SOUTHEASTERN MIDLANDS CLOSER TO THE UPPER RIDGE AXIS AND AWAY FROM
SURFACE CONVERGENCE BOUNDARIES. SEVERE THREAT REMAINS MINIMAL AND
SPC HAS SHIFTED THE MARGINAL RISK BACK FURTHER TO THE NORTHWEST.

SHOULD SEE A GENERAL DECLINE IN THE ACTIVITY THIS EVENING WITH THE
LOSS OF HEATING BUT SOME MODEL GUIDANCE SUGGESTS ANOTHER ROUND OF
SHOWERS OR CONVECTION OVERNIGHT DURING THE 04Z-12Z TIME FRAME AS A
SHORTWAVE CURRENTLY ALONG THE WESTERN GULF COAST TRACKS EAST
ACROSS THE REGION. WILL KEEP CHANCE POPS THROUGH THE OVERNIGHT
HOURS TO ACCOUNT FOR THIS. LOWS OVERNIGHT WILL BE IN THE 60S.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY/...
.SUNDAY...SUNDAY WILL BE CHARACTERIZED BY CONSIDERABLE CLOUDINESS
ONCE AGAIN WITH PWS IN THE 1.5 INCH RANGE AND CONTINUED UPPER LEVEL
MOISTURE TRANSPORT FROM THE WEST AND SOUTHWEST. THERE REMAINS
SIGNIFICANT SPREAD IN THE GUIDANCE IN TERMS OF POPS/QPF/TIMING...SO
I LEANED MORE ON THE PROXIMITY TO THE UPPER LEVEL JET MORE THAN
ANYTHING ELSE WITH LITTLE IN THE WAY OF FOCUSING SURFACE CONVERGENCE
ON THE SYNOPTIC SCALE. THEREFORE...POPS ARE HIGHEST IN THE
NORTHWESTERN PORTION OF THE CWA...CLOSER TO THE AGEOSTROPHIC LIFT
BEING INDUCED BY UPPER DIVERGENCE NEAR A JET STREAK THAT SHOULD PASS
OVER TENNESSEE DURING THE DAY. DUE TO THE CLOUD COVER...TEMPS WILL
BE A TOUCH COOLER THAN NORMAL IN THE AFTERNOON...RANGING FROM NEAR
80 NEAR THE NC BORDER TO THE MID 80S IN THE CSRA.

.SUNDAY NIGHT...NOT MUCH CHANGE IN THE PATTERN. THE STRONGEST MID TO
UPPER LEVEL FLOW WILL REMAIN NORTH OF THE AREA...BUT SMALL
DISTURBANCES IN THE FLOW WILL ALLOW FOR THE CHANCE OF SOME
SHOWERS...AND MAYBE A THUNDERSTORM IN THE EVENING. OVERNIGHT TEMPS
WILL BE ABOVE NORMAL...IN THE MID TO UPPER 60S...AS CONSIDERABLE
CLOUDINESS AND PERSISTENT LOW LEVEL SOUTHERLY FLOW WILL RETARD THE
USUAL DIURNAL TEMPERATURE DROP OVERNIGHT.

.MONDAY...MID LEVEL HEIGHTS FALL JUST A LITTLE BIT ON MONDAY...BUT
THE MAIN JET ENERGY WILL SPEND YET ANOTHER DAY NORTH OF THE CWA OVER
THE OHIO VALLEY. SURFACE FRONT WILL REMAIN TO THE NORTH AS
WELL...AND WITH UPPER LEVEL MOISTURE DECREASING A BIT WE MAY GET
SOME MORE SUNSHINE AND SEE TEMPS CREEP BACK UP TO THE MID 80S
EVERYWHERE. THE WARMER SURFACE TEMPS AND THE SLIGHT DIP IN HEIGHTS
ALOFT WILL LOAD TO A LITTLE BETTER AFTERNOON
INSTABILITY...HOWEVER...SO THE CHANCE OF THUNDERSTORMS WILL REMAIN
IN THE FORECAST. THIS TIME AROUND...THE CHANCES MAY BE A LITTLE
BETTER OVER THE SOUTHERN HALF OF THE FA WHERE THE INSTABILITY
BECOMES THE GREATEST.

.MONDAY NIGHT...HEIGHTS WILL LOWER FURTHER MONDAY NIGHT AS THE FIRST
SIGNS OF A DEVELOPING DEEP TROF/UPPER LOW BEGIN TO APPEAR. THIS WILL
SUPPORT THE MAINTENANCE OF CONVECTION THAT DEVELOPS DURING THE
AFTERNOON WELL INTO THE EVENING HOURS...WITH AGAIN A CHANCE OF
THUNDERSTORMS EVERYWHERE. THE ACTIVITY SHOULD GRADUALLY WIND DOWN
OVERNIGHT WITH THE LOSS OF INSTABILITY...BUT IT COULD LINGER FOR A
WHILE IN THE NORTHERN HALF OF THE CWA WITH MORE UPPER JET SUPPORT.

.TUESDAY...THIS SHOULD BE THE MOST LIKELY DAY FOR RAIN ACROSS THE
CWA. THE ONLY REAL QUESTION IS TIMING AND PLACEMENT. THE GFS IS
FASTER WITH THE UPPER FLOW AND HAS MOST OF THE RAIN IN THE
SOUTHEASTERN HALF OF THE CWA...WHILE THE ECMWF IS SLOWER AS IT HAS A
DEEPER DISTURBANCE DEVELOPING...PUTTING THE ENTIRE CWA IN THE
CROSSHAIRS OF THE BETS RAIN CHANCES. FOR NOW...DUE TO THE
UNCERTAINTY...I TOOK A MODEL BLEND APPROACH...BUT IT WOULD NOT
SURPRISE ME TO SEE AN INCREASE TO LIKELY POPS MOST AREAS ON TUESDAY
IF CURRENT TRENDS CONTINUE. ONCE AGAIN...CLOUD COVER WILL KEEP MAX
TEMPS DOWN A LITTLE BELOW NORMAL.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
THERE IS A DECENT AMOUNT OF UNCERTAINTY DURING THE MIDDLE OF THE
WEEK DUE TO SIGNIFICANT DIFFERENCES. FOR EXAMPLE...COMPARING THE 12Z
RUNS OF THE ECMWF AND GFS...THE EC HAS A MUCH SHARPER TROF OVER
NORTHERN GEORGIA...STARTING TO GO NEGATIVE TILT...WHILE THE GFS HAS
A MUCH MORE ROUNDED SHAPE...IMPLYING MUCH LESS SYNOPTIC SUPPORT FOR
CONVECTION. THEREFORE...THE GFS IS MUCH DRIER THAN THE EC FOR
WEDNESDAY. THE AGREEMENT GETS A LITTLE BETTER AT MID LEVELS FOR
THURSDAY AS THEY BOTH SHOW AN ANOMALOUS UPPER LOW DEVELOPING IN THE
NORTHEASTERN QUARTER OF THE COUNTRY...BUT THE SURFACE DETAILS ARE
DIVERSE WITH THE GFS SHOWING A MUCH WEAKER SURFACE LOW. THEY BOTH
HINT AT A FEW SHOWERS POSSIBLE IN THE AFTERNOON UNDER THE CYCLONIC
FLOW ALOFT...SO I HAVE SLIGHT CHANCE TO LOW END CHANCE POPS IN FOR
MOST OF THE CWA ON THURSDAY. FRIDAY BOTH MODELS SHOW SOME VERY
UNSEASONABLY COOL TEMPS ON THE BACK SIDE OF THE UPPER
LOW....MODIFYING ONLY A LITTLE BY SATURDAY.

&&

.AVIATION /21Z SATURDAY THROUGH THURSDAY/...
CUMULUS FIELD ACROSS THE AREA WITH BASES 5000 TO 6000 FEET...AND
HIGH LEVEL CLOUDS ABOVE. SCATTERED CONVECTION ONGOING ACROSS CENTRAL
GEORGIA INTO THE UPSTATE OF SOUTH CAROLINA AND THIS SHOULD CONTINUE
OVER THE NEXT FEW HOURS. THE STATIONARY SURFACE BOUNDARY ALONG THE
SC/NC BORDER MAY BECOME A FOCUS FOR CONVECTION AS WELL. IT APPEARS
CONVECTION WILL AVOID THE TERMINALS AND THEREFORE DID NOT INCLUDE
ANY MENTION IN THE FORECAST. WILL AMEND AS NEEDED IF STORMS APPROACH
ANY TERMINAL. PERSISTENT SOUTH TO SOUTHEASTERLY WIND EXPECTED
THROUGH THE AFTERNOON AND OVERNIGHT HOURS BEFORE BECOMING MORE SOUTH
TO SOUTHWESTERLY AFTER 14Z ON SUNDAY.

SOME MODEL GUIDANCE SUGGESTING SOME OVERNIGHT PRECIPITATION
ASSOCIATED WITH A PASSING UPPER DISTURBANCE BUT CONFIDENCE IS NOT
HIGH ENOUGH TO INCLUDE IN THE FORECAST THIS FAR OUT. BUT THERE IS A
POSSIBILITY OF SOME OVERNIGHT SHOWERS DURING THE 04Z-12Z TIME FRAME.
REASONABLE CONFIDENCE THAT LOW STRATUS WILL DEVELOP AGAIN TONIGHT
WITH A STRONG 30-35 KNOT LOW LEVEL JET SO WILL CONTINUE MVFR/IFR
CIGS AFTER 04Z-06Z THROUGH AROUND 14Z.

EXTENDED AVIATION OUTLOOK...WE COULD SEE SOME LOW CLOUDS CREATING
PROBLEMS FOR A FEW HOURS AT THE TERMINALS MONDAY THROUGH
WEDNESDAY MORNINGS AS THE LOW LEVEL MOISTURE RETAINS ITS HOLD ON
THE AREA. OTHERWISE...SCATTERED CONVECTION MAY CAUSE SOME BRIEF
MVFR/IFR CONDITIONS EACH AFTERNOON/EVENING THROUGH WEDNESDAY.

&&

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

&&

$$



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