569
FXUS62 KCAE 051758
AFDCAE
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE COLUMBIA SC
158 PM EDT TUE MAY 5 2026
WHAT HAS CHANGED
HIGHER CHANCE FOR THUNDERSTORMS OVERNIGHT WEDNESDAY INTO EARLY
THURSDAY MORNING. AVIATION DISCUSSION UPDATED FOR 18Z TAFS.
KEY MESSAGES
- 1. PERIODS OF MODERATE TO HEAVY RAIN ARE EXPECTED STARTING
OVERNIGHT WEDNESDAY, CONTINUING INTO THURSDAY WITH SEVERE
WEATHER POSSIBLE.
- 2. RAIN CHANCES PICK BACK UP LATE WEEK AND INTO THE WEEKEND.
DISCUSSION
KEY MESSAGE 1: PERIODS OF MODERATE TO HEAVY RAIN ARE EXPECTED
STARTING OVERNIGHT WEDNESDAY, CONTINUING INTO THURSDAY WITH
SEVERE WEATHER POSSIBLE.
OVERVIEW: A FRONT WILL BEGIN NEARING THE FA OVERNIGHT WEDNESDAY
INTO THURSDAY MORNING AS STRONG UPPER SUPPORT AND MOISTURE
ADVECTION OVERSPREADS THE REGION AS WELL. THIS IS EXPECTED TO
BRING MODERATE TO HEAVY RAINFALL ACROSS THE REGION STARTING AS
EARLY AS OVERNIGHT WEDNESDAY, CONTINUING INTO THE AFTERNOON
HOURS THURSDAY. AS HAS BEEN DISCUSSED PREVIOUSLY, A CONDITIONAL
THREAT FOR SEVERE WEATHER WILL EXIST WITH THIS SYSTEM. FAIRLY
BREEZY WINDS WILL BE POSSIBLE THROUGH THE DAY THURSDAY AS WELL
WHERE A LAKE WIND ADVISORY MAY BE NEEDED.
RAINFALL: ROBUST MOISTURE ADVECTION IS EXPECTED TO BEGIN
SHIFTING INTO THE AREA LATE WEDNESDAY INTO THURSDAY MORNING
AHEAD OF A FRONT AS A 35-45KT LLJ RAMPS UP AND PWAT'S REACH NEAR
1.75-1.90". ENHANCED CONVERGENCE AHEAD OF THE FRONT AND A
NEARING UPPER TROUGH SHOULD INCREASE RAIN CHANCES OVERNIGHT
WEDNESDAY INTO THURSDAY MORNING WHERE HEAVY RAINFALL WILL BE
POSSIBLE DUE TO THE AFOREMENTIONED FEATURES ALONG WITH DEEP WARM
CLOUD DEPTHS (OVER 11,000 FT) AND AT LEAST SOME WEAK
INSTABILITY. OVERALL, FORECAST RAIN AMOUNTS HAVE NOT SHIFTED TOO
MUCH WHERE A WIDESPREAD 0.50-1" SEEMS REASONABLE, BUT AS CAM
GUIDANCE REACHES FURTHER INTO THURSDAY, SPOTS OF HIGHER AMOUNTS
WILL BE POSSIBLE. THIS IS SEEN IN RECENT 12Z CAM'S WHERE SPOTS
OF 1-2.25" OF RAINFALL CAN BE SEEN, MAINLY WHERE ANY CONVECTION
TRACKS. THESE AMOUNTS ARE FURTHER SUPPORTED IN THE MOST RECENT
NBM 5.0 RUN WHERE 25TH PERCENTILE QPF AMOUNTS ARE AROUND
0.30-0.75", WITH THE 75TH PERCENTILE SHOWING AREAS OF 1-2.25".
PROBABILITIES FOR GREATER THAN 1" OF QPF THROUGH THURSDAY NIGHT
HAVE RISEN TOWARD 40-60%, MAINLY ALONG AND NORTH OF THE I-20
CORRIDOR. AS MENTIONED IN PREVIOUS DISCUSSIONS, THE OVERALL
FLASH FLOODING RISK IS LOW WITH ANTECEDENT DRY CONDITIONS, BUT
ISOLATED SPOTS OF FLASH FLOODING MAINLY IN URBAN OR FLOOD PRONE
AREAS WILL BE POSSIBLE WHERE CONVECTION MOVES OVER DUE TO HIGHER
RATES.
SEVERE THREAT: THE MAIN CHANGE IN SEVERE WEATHER CHANCES COMES
LATE WEDNESDAY INTO THURSDAY MORNING. AS THE UPPER TROUGH
PROGRESSES EASTWARD, ENHANCED MID LEVEL FLOW AROUND 50-65 KTS
SHOULD BEGIN OVERSPREADING THE FA WITH THE AFOREMENTIONED DEEP
MOISTURE MOVING INTO PLACE. THE MEAN 12Z HREF SOLUTION, ALONG
WITH MULTIPLE CAM'S (INCLUDING 12Z HRRR, NAM3KM, AND RRFS) SHOW
A BROKEN LINE OF CONVECTION SHIFTING INTO THE UPSTATE WEDNESDAY
EVENING BEFORE MOVING INTO THE FA LATE WEDNESDAY NIGHT,
CONTINUING SOUTHWARD INTO THE EARLY PARTS OF THURSDAY MORNING.
WITH ENHANCED MID LEVEL FLOW AND A STRENGTHENING LLJ MOVING IN,
STRONG DEEP LAYER SHEAR ON THE ORDER OF 50-65 KTS SHOULD SHIFT
IN PLACE OVERNIGHT. CONSIDERING THE TIME OF DAY, WEAK
INSTABILITY IS EXPECTED WITH MUCAPE GENERALLY UNDER 800 J/KG.
THEREFORE, A RATHER CONDITIONAL AND MARGINAL SEVERE THREAT IS
POSSIBLE LATE WEDNESDAY INTO THURSDAY MORNING, WHICH HAS BEEN
FURTHER SUPPORTED IN RECENT HRRR NEURAL NETWORK, CSU, AND NCAR
AI/ML GUIDANCE. OVERALL, THE MAIN RISK WILL BE HEAVY RAIN AS
DISCUSSED IN THE PREVIOUS SECTION, BUT IF A MORE ROBUST SEGMENT
OF CONVECTION CAN MAINTAIN ITSELF (MAINLY FROM THE STRONG
KINEMATICS), STRONG TO MARGINALLY SEVERE WIND GUSTS COULD BE
POSSIBLE MORE SO TOWARD THE NORTHERN FA. BEHIND THIS ACTIVITY
AND BEFORE THE FRONT MOVES THROUGH, REDEVELOPMENT OF CONVECTION
COULD BE POSSIBLE LATE THURSDAY MORNING INTO THE AFTERNOON AS
STRONG DEEP LAYER SHEAR REMAINS IN PLACE, BUT THIS THREAT IS
ALSO CONDITIONAL. A COUPLE OF FAILURE MODES EXIST IN THE
AFTERNOON HOWEVER WITH MODEL GUIDANCE FAVORING LINGERING CLOUD
COVER THROUGH THE DAY, DEEP MOISTURE GRADUALLY SHIFTING OUT OF
THE FA AND TOWARD THE COAST, AND THE BELT OF ENHANCED MID AND
UPPER FLOW SHIFTING NORTHWARD. IF INSTABILITY CAN BE REALIZED,
ANOTHER ROUND OF STRONG TO MARGINALLY SEVERE STORMS COULD BE
POSSIBLE, MAINLY TOWARD THE EASTERN MIDLANDS AND INTO THE PEE
DEE REGION.
KEY MESSAGE 2: RAIN CHANCES PICK BACK UP LATE WEEK AND INTO THE
WEEKEND
THERE CONTINUES TO BE A TREND TOWARD A MORE PROGRESSIVE PATTERN
THE REMAINDER OF THE FORECAST PERIOD ACROSS GLOBAL MODELS AND
ENSEMBLE GUIDANCE. THERE REMAINS UNCERTAINTY IN IF DRIER
CONDITIONS COULD WIN OUT IN THE FRIDAY AND SATURDAY TIME FRAME
WITH WEAK SHORTWAVES PASSING SO AT LEAST SLIGHT CHANCE POPS SEEM
REASONABLE DURING THIS PERIOD. THERE IS A BIT MORE CONSENSUS
THAT ANOTHER TROUGH WILL MOVE IN EARLY IN THE WEEK WITH DEEPER
MOISTURE RETURNING AND INCREASED RAIN CHANCES.
AVIATION /18Z TUESDAY THROUGH SUNDAY/
VFR CONDITIONS EXPECTED TO PREVAIL OVER THE NEXT 24 HOURS.
MOISTURE CONTINUE TO BE ON THE INCREASE ACROSS THE AREA,
ALLOWING FOR THE DEVELOPMENT OF SOME SCATTERED MID-LEVEL CUMULUS
THIS AFTERNOON. THIS SHOULD DISSIPATE TOWARDS SUNSET, LEAVING
MAINLY INCREASING CIRRUS CLOUDS MOVING IN FROM THE WEST
OVERNIGHT AND THROUGH MUCH OF WEDNESDAY. WINDS WILL BE OUT OF
THE SOUTH THROUGH THE PERIOD. DAYTIME WIND SPEEDS BOTH THIS
AFTERNOON AND AGAIN FOR WEDNESDAY WILL GENERALLY BE AROUND 10
KNOTS, WITH GUSTS BETWEEN 15-20 KNOTS. WINDS OVERNIGHT TONIGHT
SHOULD SEE THE GUSTS DIMINISH, BUT THE SUSTAINED WINDS WILL
STILL REMAIN UP BETWEEN 5-8 KNOTS, ALTHOUGH THERE COULD BE A
BRIEF PERIOD AROUND SUNRISE IN WHICH WINDS DROP BELOW 5 KNOTS.
EITHER WAY, THE COMBINATION OF INCREASING CIRRUS AND WIND
SPEEDS REMAINING STRONG ENOUGH OVERNIGHT SHOULD BE ENOUGH TO
TO HELP KEEP FOG FORMATION AT BAY. ANY RAINFALL POTENTIAL AHEAD
OF AN APPROACHING SYSTEM ON WEDNESDAY WILL HOLD OFF UNTIL AFTER
THE 18Z PERIOD.
EXTENDED AVIATION OUTLOOK...SYSTEM BRINGS A CHANCE FOR RESTRICTIONS
ONCE AGAIN WITH SHOWERS AND THUNDERSTORMS STARTING WEDNESDAY
EVENING INTO THURSDAY.
CAE WATCHES/WARNINGS/ADVISORIES
SC...NONE.
GA...NONE.
DISCUSSION...DH
AVIATION...CAL
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page