778
FXUS62 KCAE 041804
AFDCAE
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE COLUMBIA SC
204 PM EDT MON MAY 4 2026
WHAT HAS CHANGED
MINIMAL CHANGE TO KEY MESSAGES, CONFIDENCE CONTINUES TO
INCREASE IN PERIODS OF HEAVY RAIN THURSDAY. AVIATION DISCUSSION
UPDATED FOR 18Z TAFS.
KEY MESSAGES
- 1. PERIODS OF MODERATE TO HEAVY RAINFALL ARE EXPECTED DURING
THE MID WEEK WITH THE POTENTIAL SEVERE WEATHER.
- 2. RAIN CHANCES PICK BACK UP LATE WEEK AND INTO THE WEEKEND.
DISCUSSION
KEY MESSAGE 1: PERIODS OF MODERATE TO HEAVY RAINFALL ARE
EXPECTED DURING THE MID WEEK WITH THE POTENTIAL SEVERE WEATHER.
THE FORECAST FOR THE MID WEEK SYSTEM GENERALLY REMAINS ON TRACK
AS DEEP MOISTURE WITH PWAT'S NEAR 1.75-1.90" OVERSPREAD THE
REGION BY THURSDAY MORNING AHEAD OF A COLD FRONT. A NORTHERN
STREAM TROUGH WILL START DIGGING SOUTHWARD THROUGH THE DAY
TUESDAY AND WEDNESDAY, INTERACTING WITH A CUT-OFF LOW CURRENTLY
NEARING THE CALIFORNIA COAST. AS MEDIUM RANGE MODELS REACH OUT
TOWARD WEDNESDAY AND THURSDAY, THERE REMAINS UNCERTAINTY IN
WHETHER THIS NORTHERN TROUGH WILL PHASE WITH SOME ENERGY FROM
THE CUT-OFF LOW OR IF THIS LOW WILL REMAIN INTACT. IN THE MOST
RECENT LREF CLUSTER ANALYSIS, 70% OF THE GRAND ENSEMBLE SOLUTION
FALLS WITHIN TWO CLUSTERS. EACH OF THESE FAVOR AT LEAST SOME
INTERACTION BETWEEN THE CUT-OFF LOW AND NORTHERN STREAM TROUGH,
LEADING TO A SLIGHTLY SLOWER PROGRESSING TROUGH. OVERALL, THIS
WOULD FAVOR A FRONTAL PASSAGE DURING THE LATE AFTERNOON TO
EVENING HOURS THURSDAY.
AHEAD OF THIS FRONT, ROBUST IVT, WARM CLOUD LAYER DEPTHS
BETWEEN 11,000-12,000 FT, ELEVATED INSTABILITY, GENEROUS UPPER
SUPPORT, AND A 35-45 KT LLJ WILL BRING THE POTENTIAL FOR PERIODS
OF HEAVY RAIN THURSDAY MORNING AND INTO THE AFTERNOON. RAIN
CHANCES COULD MOVE IN AS EARLY AS LATE WEDNESDAY, BUT THE
PRIMARY WINDOW COMES THURSDAY. THE LATEST RUN OF DETERMINISTIC
GUIDANCE IS GENERALLY SHOWING BETWEEN 0.50-1" OF QPF FROM THIS
SYSTEM WITH POCKETS OF HIGHER AMOUNTS. THESE AMOUNTS ARE FURTHER
SUPPORTED BY ENSEMBLE GUIDANCE WITH 13Z NBM PROBABILITIES FOR
GREATER THAN 0.50" OF QPF REACHING 50-70% ACROSS THE CWA. THE
FLASH FLOOD RISK REMAINS FAIRLY LOW AS 3-HR FFG IS AROUND
2.5-3.5" ACROSS THE FA AND 6-HR FFG IS OVER 3.5-4". SOME
NUISANCE FLOODING IN URBAN SPOTS CANNOT BE RULED OUT IN ANY
CONVECTION HOWEVER. A TIGHTENING SURFACE GRADIENT AND SOME
MIXING DOWN OF THE ROBUST LLJ, SHOULD BRING GUSTY CONDITIONS
WHERE A LAKE WIND ADVISORY COULD BE NEEDED.
FOR THE SEVERE THREAT, THE TIMING OF THE FRONT WILL GREATLY
MODULATE THIS RISK. THOUGH WITH LESS VARIABILITY ACROSS LREF
CLUSTER GUIDANCE, CONFIDENCE IS SLIGHTLY GREATER IN A FROPA
FAVORING LATER IN THE DAY AS MESSAGED ABOVE. STRONG UPPER
DYNAMICS SHOULD OVERSPREAD THE REGION THROUGH THE DAY WITH DEEP
LAYER SHEAR EXCEEDING 50-65 KTS. THE QUESTION WILL REMAIN
DESTABILIZATION AND THE OVERLAP WITH DEEP MOISTURE AS STRONG
KINEMATICS LOOK TO BE IN PLACE. WIDESPREAD CLOUD COVER AND
MORNING SHOWERS/WEAK STORMS THURSDAY COULD LIMIT DESTABILIZATION
AND THE GREATEST AXIS OF MOISTURE LOOKS TO BEGIN SHIFTING
TOWARD THE COAST THROUGH THE AFTERNOON. IF INSTABILITY CAN
BUILD, A COUPLE STRONG TO MARGINALLY SEVERE STORMS COULD FORM IN
THIS HIGHLY SHEAR ENVIRONMENT, MAINLY TOWARD THE EASTERN
MIDLANDS, EXTENDING INTO THE PEE DEE, BUT AT THIS TIME
CONFIDENCE IN THIS IS LOW.
KEY MESSAGE 2: RAIN CHANCES PICK BACK UP LATE WEEK AND INTO THE
WEEKEND
GLOBAL DETERMINISTIC GUIDANCE AND ENSEMBLES FAVOR A RATHER
ACTIVE SYNOPTIC PATTERN THROUGH THE END OF THE PERIOD, WHERE
ANOTHER TROUGH IS EXPECTED TO NEAR THE REGION BY THE WEEKEND AND
INTO EARLY NEXT WEEK. PWAT'S SHOULD GRADUALLY RAISE BACK ABOVE
1" BEHIND THURSDAY'S FRONT THIS WEEKEND, BUT THERE REMAINS LARGE
SPREAD IN THE TIMING OF THE NEXT TROUGH AND ANY WEAK SHORTWAVES
AHEAD OF IT. OVERALL, MORE RAIN CHANCES SEEM POSSIBLE IN THIS
PATTERN, ESPECIALLY TOWARD EARLY NEXT WEEK, BUT CONFIDENCE IN
COVERAGE OR TIMING IS LOW.
AVIATION /18Z MONDAY THROUGH SATURDAY/
VFR CONDITIONS EXPECTED TO PREVAIL THROUGH 18Z WEDNESDAY.
FAIR WEATHER ACROSS THE REGION WITH SATELLITE IMAGERY SHOWING
MAINLY CLEAR SKIES EXCEPT FOR SOME PASSING CIRRUS CLOUDS. A DRY
AIR MASS IN IS PLACE WITH DEWPOINTS IN THE 30S AND LOWER 40S.
HIGH PRESSURE AXIS HAS SHIFTED OFFSHORE AND A SOUTHERLY FLOW HAS
DEVELOPED WITH WINDS 5 TO 10 KNOTS EXPECTED WITH SOME POSSIBLE
INTERMITTENT GUSTS TO 15 KNOTS UNTIL SUNSET WHEN WINDS SHOULD
SUBSIDE.
WHILE BRIEF RIVER VALLEY FOG CANNOT BE TOTALLY RULED OUT,
WIDESPREAD FOG IS NOT EXPECTED GIVEN THE DRY AIR MASS AND A 25KT
LOW LEVEL JET FORECAST OVERNIGHT. WINDS SHOULD PICK BACK UP FROM
THE SOUTHWEST BY 14Z TO AROUND 7 TO 10 KTS.
EXTENDED AVIATION OUTLOOK...DRIER CONDITIONS ARE EXPECTED
THROUGH TUESDAY, THEN A MIDWEEK SYSTEM BRINGS A CHANCE FOR
RESTRICTIONS ONCE AGAIN WITH SHOWERS AND THUNDERSTORMS.
CAE WATCHES/WARNINGS/ADVISORIES
SC...NONE.
GA...NONE.
DISCUSSION...DH
AVIATION...23
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