799
FXUS62 KCAE 170715
AFDCAE
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE COLUMBIA SC
215 AM EST TUE DEC 17 2024
SYNOPSIS
WARM AND DRY CONDITIONS ARE EXPECTED AS MID-LEVEL RIDGING
DEVELOPS ACROSS THE SOUTHEAST. A FRONT WITH SOME SCATTERED
SHOWERS IS EXPECTED ON WEDNESDAY, WITH A STEADY COOL DOWN
EXPECTED FOLLOWING THIS FRONT INTO THE WEEKEND. WELL BELOW
AVERAGE TEMPS ARE LIKELY SUNDAY AND INTO EARLY NEXT WEEK.
NEAR TERM /THROUGH TONIGHT/
KEY MESSAGE(S):
- DENSE FOG ADVISORY IN EFFECT FOR THE WESTERN MIDLANDS AND
NORTHERN CSRA
- DENSE FOG POSSIBLE TONIGHT ACROSS THE REMAINDER OF THE CWA
- CLEARING THROUGH THE MORNING WITH CLOUDS AND A FEW SHOWERS
POSSIBLE TONIGHT
FOG CONTINUES TO EXPAND AND BECOME INCREASINGLY DENSE IN THE
WESTERN PORTIONS OF THE FORECAST AREA AS WELL AS ALONG THE
COAST. THROUGH DAYBREAK EXPECT THE FOG TO CONTINUE EXPANDING AND
BLANKET THE ENTIRE FORECAST AREA WITH DENSE FOG ACROSS THE
WESTERN MIDLANDS AND NORTHERN CSRA WITH POTENTIAL FOR DENSE
CONDITIONS ELSEWHERE. THE DENSE FOG ADVISORY REMAINS IN EFFECT
THROUGH 8 AM FOR FAIRFIELD COUNTY SOUTH/SOUTHWEST INTO THE
NORTHERN CSRA COUNTIES. ADDITIONAL COUNTIES MAY NEED TO BE
ADDED. TEMPERATURES WILL HOLD NEARLY STEADY OR RISE SLIGHTLY AS
THE FOG BECOMES DENSE WITH OVERNIGHT LOWS GENERALLY IN THE MID
TO UPPER 40S.
WITH LIGHT WINDS EXPECTED TODAY THE FOG WILL TAKE SOME TIME TO
ERODE HOWEVER SKIES WILL BECOME PARTLY TO MOSTLY SUNNY BY LATE
MORNING. MID LEVEL RIDGING WILL AGAIN BE OVER THE REGION WITH A
COLD FRONT APPROACHING LATE TOADY AND TONIGHT. AFTERNOON HIGH
TEMPERATURES WILL RANGE FROM THE UPPER 60S IN THE WESTERN
MIDLANDS AND NORTHERN CSRA TO THE MID 70S IN THE FAR EASTERN
MIDLANDS. WITH THE FRONT NORTH OF THE FORECAST AREA TONIGHT A
FEW LIGHT SHOWERS WILL BE POSSIBLE AFTER MIDNIGHT. LOW
TEMPERATURES WILL BE IN THE LOW TO MID 50S.
SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/
KEY MESSAGE(S):
- AN APPROACHING FRONT WILL DEVELOP SOME SHOWERS FOR WEDNESDAY.
A QUICKLY DIVING 500MB SHORTWAVE WILL DRIVE A BROAD COLD FRONT
INTO THE EASTERN US AS WE MOVE INTO WEDNESDAY. THE ASSOCIATED
STRENGTHENING FLOW AHEAD OF THE FRONT WILL INCREASE MOISTURE
CONVERGENCE AND PWAT'S WILL PUSH BACK TO AROUND 1.0" BY
WEDNESDAY MORNING. THERE IS NOT A LARGE RESERVOIR OF MOISTURE
AVAILABLE TO THE SOUTHWEST HOWEVER, HENCE WHY PWAT'S ONLY RISE
TO AROUND 1.0" FOR MOST OF THE AREA. THE DETERMINISTIC GUIDANCE
HAS COME INTO MUCH BETTER AGREEMENT WITH THE PRECIP DEPICTION
FOR THIS SYSTEM, WITH DEVELOPING PREFRONTAL, ISENTROPICALLY
FORCED SHOWERS THROUGHOUT THE DAY BUT THEN VERY LITTLE, IF ANY,
PRECIP FROM THE FRONTAL FORCING ITSELF LATER WEDNESDAY
AFTERNOON; THIS IS AGAIN PRIMARILY A RESULT OF THE RELATIVELY
WEAK MOISTURE CONVERGENCE BUT ALSO A LACK OF SYNOPTIC SCALE
FORCING OVER OUR AREA. IN THE PREFRONTAL WAVE OF PRECIP, WE
COULD SEE AN ISOLATED THUNDERSTORM IN THE DEEPEST MOISTURE
ACROSS THE EASTERN MIDLANDS; GEFS AND EC DEVELOPS SOME LOW END
SURFACE BASED INSTABILITY BETWEEN 300-500 J/KG BUT MID-LEVEL
LAPSE RATES ARE VERY WEAK. THE FRONT SHOULD PUSH THROUGH THE
AREA LATE WEDNESDAY AND OVERNIGHT THURSDAY, SHIFTING WINDS OUT
OF THE NORTHWEST BY THURSDAY MORNING.
LONG TERM /THURSDAY THROUGH MONDAY/
KEY MESSAGE(S):
- A GENERAL COOL DOWN IS EXPECTED THROUGH THE WEEKEND. THE
COLDEST AIR OF THE SEASON WILL LIKELY PUSH IN FOR SUNDAY AND
INTO MONDAY.
BROAD TROUGHING ALOFT IS EXPECTED TO SETTLE IN ACROSS THE
EASTERN CONUS THROUGHOUT THE LONG TERM PERIOD WITH WELL BELOW
AVERAGE TEMPS EXPECTED BY LATE IN THE WEEKEND. A SERIES OF SHARP
SHORTWAVES WILL PUSH IN FROM THE NORTHWEST, DRIVING SOME
REINFORCING FRONTS INTO THE AREA AND DIGGING THE TROUGH FURTHER.
WELL BELOW AVERAGE TEMPS WILL THEN LIKELY DEVELOP FOR SATURDAY
ALONG WITH EXTREMELY DRY AIR AS PWAT'S FALL TO AROUND 0.25".
DETERMINISTIC AND ENSEMBLE GUIDANCE ARE ALL IN GOOD AGREEMENT
OVER THIS INITIAL SLUG OF COLD, DRY AIR WITH ONLY A 5 DEGREE
INTERQUARTILE RANGE IN THE NBM MEMBERS FOR HIGH TEMPS ON
SATURDAY (MEDIAN OF 49 F), DESPITE BEING DAY 5. ANOTHER
REINFORCING SHORTWAVE IS EXPECTED SUNDAY AND INTO MONDAY WHICH
MUCH OF THE GUIDANCE CONTINUES TO HIT AT. BASED ON THE GEFS AND
ECE, MEAN 850 MB ANOMALIES PUSH OVER -15 C BY SUNDAY MORNING AND
INTO MONDAY. EC AND GEFS ENSEMBLE PERCENTILES ARE HIGHLIGHTING
THIS TIME PERIOD WITH TEMPS AND HEIGHTS BELOW IN THE 1-10TH
PERCENTILE; MUCH THE SAME FOR THE EC EFI, WITH THE ENTIRE
HIGHLIGHTED, BUT NOT NOTABLE SOT AT THIS TIME. SO THE ENSEMBLE
SOLUTION WOULD SUGGEST A COLD, BUT NOT QUITE THREATENING
RECORDS, TYPE OF EVENT WITH DAYTIME HIGHS IN THE 40'S AND
OVERNIGHT LOWS IN THE 20'S, MAYBE INTO THE 10'S. AS AN FYI,
CURRENT FORECASTED WIND CHILLS ARE BELOW 20 F WHICH IS NEAR COLD
WEATHER ADVISORY CRITERIA (A NEW PRODUCT FOR 2024).
AVIATION /06Z TUESDAY THROUGH SATURDAY/
IFR TO LIFR RESTRICTIONS EXPECTED AFTER 06Z DUE TO DENSE FOG
DEVELOPMENT.
SATELLITE IMAGERY AND SURFACE OBS SHOW FOG CONTINUING TO EXPAND
AND THICKEN WEST AND EAST OF THE TAF SITES. THROUGH DAYBREAK
EXPECT FOG AND LOW CIGS AT ALL TERMINALS WITH LIFR RESTRICTIONS
FROM THE EARLY MORNING THROUGH SUNRISE. WITH MIXING THIS MORNING
CONDITIONS WILL IMPROVE WITH ALL SITES RETURNING TO VFR BY 15Z.
MOSTLY TO PARTLY SUNNY SKIES THIS AFTERNOON WILL GIVE WAY TO
INCREASING CLOUDS NEAR THE END OF THE PERIOD AS A FRONTAL
BOUNDARY NORTHWEST OF THE AREA. WINDS THROUGH THE PERIOD WILL BE
VARIABLE AT 5 KNOTS OR LESS.
EXTENDED AVIATION OUTLOOK...POTENTIAL FOR SHOWERS AND ASSOCIATED
RESTRICTIONS WEDNESDAY AND WEDNESDAY NIGHT.
CAE WATCHES/WARNINGS/ADVISORIES
SC...DENSE FOG ADVISORY UNTIL 8 AM EST THIS MORNING FOR SCZ018-020-
021-025-026.
GA...DENSE FOG ADVISORY UNTIL 8 AM EST THIS MORNING FOR GAZ040-063-
064.
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