772
FXUS62 KCAE 200901
AFDCAE
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE COLUMBIA SC
401 AM EST FRI DEC 20 2024
SYNOPSIS
A STRONG COLD FRONT CLEARS SKIES OUT TODAY AND TONIGHT. BREEZY
CONDITIONS ARE EXPECTED THIS AFTERNOON THROUGH THIS EVENING.
THIS WILL BE FOLLOWED BY SEVERAL DAYS OF COLD WEATHER WITH
SUBFREEZING TEMPERATURES AT NIGHT. A WARMING TREND IS EXPECTED
TOWARDS CHRISTMAS ALONG WITH THE NEXT CHANCE OF RAIN.
NEAR TERM /THROUGH TONIGHT/
KEY MESSAGE(S):
- A SHARP SHORTWAVE AND STRONG SURFACE FRONT WILL PUSH THROUGH
THE AREA THIS AFTERNOON-EVENING.
A SHARP 500MB SHORTWAVE IS CURRENTLY DIVING TOWARDS THE REGION
FROM THE NORTHWEST, WITH OUR AREA STILL UNDER SOUTHWESTERLY FLOW
ALOFT AHEAD OF THIS TROUGH. SOME WEAK LOW LEVEL MOISTURE
CONVERGENCE AND ISENTROPIC LIFT THROUGHOUT THURSDAY, NOW COUPLED
WITH SUBSTANTIAL DRY AIR ALOFT, AS ALLOWED SOME WIDESPREAD
LOW STRATUS TO DEVELOP. THIS STRATUS IS STEADILY ERODING FROM
THE WEST AS THE SHORTWAVE AND SURFACE FRONT APPROACH, BUT
STRATUS WILL LINGER FOR OUR AREA INTO FRIDAY MORNING.
WINDS WILL QUICKLY SHIFT OUT OF THE WEST AS THE INITIAL SURFACE
FRONT MOVES THROUGH LATE THIS MORNING, WITH NOTICEABLE DRY
ADVECTION DROPPING DEW POINTS 5-10 DEGREES BY EARLY AFTERNOON. A
REINFORCING SHOT OF DRY, COLD ADVECTION WITH THE PRIMARY COLD
FRONT IS THEN EXPECTED AS WINDS SHIFT NORTHWESTERLY THIS
EVENING. GUSTY WINDS OVER 30 MPH ARE LIKELY ACROSS THE AREA AS
THIS PRIMARY FRONT MOVES THROUGH AND IMMEDIATELY PROCEEDING IT
AS 850-700MB WINDS RAMP UP OVER 40 KNOTS; A LAKE WIND ADVISORY
IS IN EFFECT FROM 4PM THROUGH 11PM. THIS FORECAST IS ON THE
HIGHER END OF GUIDANCE (~90TH PERCENTILE FROM THE HREF-NBM).
CLIMATOLOGICALLY, THIS SHARP OF TROUGH AND SURFACE FRONT TENDS
TOWARDS THE EXTREMES OF GUIDANCE WITH STRONG, UNIDIRECTIONAL,
NORTHWESTERLY FLOW THROUGHOUT THE DRY ADIABATIC MIXED BOUNDARY
LAYER BELOW 700MB.
THE OTHER FEATURE OF NOTE TODAY IS THE POTENTIAL FOR SHOWERS AS
THE TROUGH AXIS IMPINGES ON THE AREA THIS AFTERNOON-EVENING. ALL
GUIDANCE IS HIGHLIGHTING SOME ISOLATED-SCATTERED SHOWERS ACROSS
THE NORTHERN MIDLANDS AND PEE DEE THIS AFTERNOON AS THE STRONG
VORT ADVECTION AND HEIGHT FALLS OVERRUN SOME RELATIVELY WARM
SURFACE TEMPS AND RESIDUAL LOW LEVEL MOISTURE. SOME GRAUPEL
SHOWERS ARE POSSIBLE ACROSS THESE AREAS WITH THE EXTREME SURFACE
TO 700MB LAPSE RATES PRODUCING 50-200 J/KG OF MU CAPE BETWEEN 0
AND MINUS 10 C. COMBINE THAT WITH AN EXTREMELY WELL MIXED LAYER
BELOW THE ICE-SNOW PRODUCING CLOUD BASE AND WET BULB ZERO TEMPS
IN THE 30'S, AND ITS A PRETTY GOOD SETUP. SO DESPITE SURFACE
TEMPS IN THE UPPER 40'S, WE COULD SEE SOME BRIEF GRAUPEL,
PRIMARILY IN THE PEE DEE.
SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/
KEY MESSAGE(S):
- NOTICEABLY COOLER AND DRIER THIS WEEKEND WITH SUBFREEZING
OVERNIGHT TEMPERATURES.
- A COLD WEATHER ADVISORY MAY BE NEEDED FOR SUNDAY NIGHT INTO MONDAY
MORNING.
THE REGION WILL BE UNDER THE INFLUENCE OF LONGWAVE RIDGING THIS
WEEKEND AS A FEW MOISTURE-STARVED SHORTWAVES MOVE MAINLY NORTH OF
THE FORECAST AREA. SURFACE HIGH PRESSURE WILL EXTEND FROM THE
CANADIAN BORDER SOUTH TO THE GOMEX AND ADVECT EASTWARD WHILE
DEEPENING OVER NEW ENGLAND BY SUNDAY. THIS WILL BRING MUCH COOLER
AND DRIER CONDITIONS TO THE AREA, WITH HIGH TEMPERATURES SATURDAY 5-
8 DEGREES BELOW NORMAL (LOW 50S) AND 8-12 DEGREES BELOW NORMAL BY
SUNDAY (LOW TO MID 40S). PWATS WILL BE AROUND 0.3" WITH DEWPOINTS IN
THE 20S, OR PERHAPS THE TEENS SUNDAY INTO SUNDAY NIGHT.
FAVORABLE RADIATIONAL COOLING CONDITIONS ARE EXPECTED SATURDAY NIGHT
UNDER CLEAR SKIES AND A WEAKENING PRESSURE GRADIENT. THIS SHOULD JET
OVERNIGHT LOWS INTO THE LOW TO MID 20S. HOWEVER, EVEN COLDER
TEMPERATURES ARE EXPECTED SUNDAY NIGHT WITH THE SURFACE HIGH PASSING
MORE TO OUR NORTHEAST, ALLOWING CAA TO DROP VALUES INTO THE UPPER
TEENS TO LOW 20S. COMBINED WITH SOME WEAK BOUNDARY LAYER WINDS,
THERE REMAINS THE POSSIBILITY FOR WIND CHILL VALUES TO DIP INTO THE
MID-TEENS. COLD WEATHER ADVISORY CRITERIA FOR US RANGES FROM 10
DEGREES ALONG THE SC/NC BORDER TO 15 DEGREES ACROSS THE REMAINDER OF
THE MIDLANDS AND CSRA. CURRENT LREF PROBABILITIES OF APPARENT TEMPS
<16 DEGREES F RANGE FROM ABOUT 45 PERCENT ACROSS THE PEE DEE TO
ABOUT 25% IN THE COLUMBIA AREA SOUTHWEST TO AUGUSTA. SO, WHILE THESE
PROBABILITIES ARE STILL LOW, THEY BEAR WATCHING OVER THE NEXT 24
HOURS TO DETERMINE IF A HEADLINE WILL BE NEEDED.
LONG TERM /MONDAY THROUGH THURSDAY/
KEY MESSAGE(S):
- A VERY GRADUAL WARMING TREND STARTS MONDAY, THOUGH TEMPERATURES
WILL BE BELOW NORMAL THROUGH MIDWEEK.
- THE NEXT STORM SYSTEM ARRIVES AROUND CHRISTMAS DAY.
MONDAY STARTS OFF DOWNRIGHT COLD, BUT WEAK UPPER RIDGING WILL START
TO PHASE ACROSS THE REGION. TEMPERATURES RISE A FEW DEGREES FROM
SUNDAY, KICKING OFF A SLOW WARMING TREND THROUGH MID-WEEK.
ADDITIONAL TEMPERATURE AND MOISTURE ADVECTION OCCURS TUESDAY AND
WEDNESDAY AS THE THE SURFACE HIGH PULLS AWAY AND UPPER LEVEL
SOUTHWEST FLOW STRENGTHENS AHEAD OF A DISTURBANCE MOVING ACROSS THE
DEEP SOUTH. CONFIDENCE IS INCREASING THAT THIS SYSTEM WILL BRING THE
NEXT THREAT FOR WIDESPREAD RAIN ACROSS THE REGION FOR PERHAPS
WEDNESDAY AND THURSDAY, THOUGH THE DETAILS HAVE YET TO BE WORKED
OUT. STILL, PWAT VALUES WILL RISE CLOSE TO 1" AND TEMPERATURES WILL
RISE INTO THE 50S ON TUESDAY TO THE LOW 60S BY WEDNESDAY AND
THURSDAY. LOWS WILL FOLLOW SUIT, STARTING OUT IN THE 20S MONDAY
NIGHT, RISING INTO THE 30S TUESDAY NIGHT AND THE 40S BY WEDNESDAY
AND THURSDAY NIGHTS.
AVIATION /09Z FRIDAY THROUGH TUESDAY/
MIX OF LIFR AND IFR CIGS AND SOME VSBY RESTRICTIONS EXPECTED
UNTIL MID- MORNING WITH WIDESPREAD STRATUS-FOG IN PLACE.
A DENSE DECK OF STRATUS REMAINS IN PLACE ACROSS THE AREA AND
WILL LINGER INTO FRIDAY MORNING. THE STRATUS DECK IS STEADILY
BECOMING MORE HYBRID FOG EARLY THIS MORNING WITH A MIX OF LIFR
AND IFR VSBY AND CIGS FOR OGB, CAE, AND DNL; AGS AND CUB HAVE
SAT AT LOW MVFR AND IFR MUCH OF THE NIGHT WITH LITTLE-NO VSBY
RESTRICTIONS. THIS TYPE OF PATTERN IS EXPECTED TO LAST INTO
MID-FRIDAY MORNING WITH AT LEAST IFR RESTRICTIONS AT ALL TAF
SITES THROUGH 14Z. AN APPROACHING FRONT WILL EVENTUALLY ERODE
THE STRATUS FROM THE WEST, BUT NOT UNTIL LATE THIS MORNING.
WINDS WILL SHIFT OUT OF THE WEST BY LATE THIS MORNING, WITH SOME
GUSTS TO AROUND 20 MPH LIKELY INTO THE AFTERNOON. A SECONDARY
STRONGER FRONT IS EXPECTED TO MOVE THROUGH AFTER 20Z, WITH GUSTS
OVER 30 MPH POSSIBLE OUT OF THE NORTHWEST. SOME PRECIP IS
POSSIBLE ACROSS NE SOUTH CAROLINA THIS EVENING WITH THE SECOND
FRONT, BUT NO SHOWERS ARE EXPECTED AT ANY TAF SITE AT THIS TIME.
EXTENDED AVIATION OUTLOOK...NO SIGNIFICANT IMPACTS TO AVIATION.
CAE WATCHES/WARNINGS/ADVISORIES
SC...LAKE WIND ADVISORY FROM 4 PM THIS AFTERNOON TO 11 PM EST THIS
EVENING FOR SCZ016-018-020>022-025>031-035-037-038-041-
115-116-135>137.
GA...LAKE WIND ADVISORY FROM 4 PM THIS AFTERNOON TO 11 PM EST THIS
EVENING FOR GAZ040-063>065-077.
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