599
FXUS62 KCAE 210708
AFDCAE
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE COLUMBIA SC
308 AM EDT THU MAY 21 2026
WHAT HAS CHANGED
PAIRED BACK DOWN TO 2 KEY MESSAGES, FOCUSING ON TEMPERATURE
UNCERTAINTY AND THE BEST RAIN CHANCES FOR FRIDAY AND SATURDAY.
AVIATION DISCUSSION UPDATED FOR 06Z TAF ISSUANCE.
KEY MESSAGES
- 1. RAIN CHANCES INCREASE TODAY INTO EARLY NEXT WEEK.
- 2. UNCERTAINTY IN TEMPERATURES FRIDAY AND THIS WEEKEND.
DISCUSSION
KEY MESSAGE 1: RAIN CHANCES INCREASE TODAY INTO EARLY NEXT WEEK.
THE UPPER RIDGE WHICH HAS BEEN IN PLACE ALL WEEK WILL BEGIN TO SHIFT
SLIGHTLY EASTWARD ON FRIDAY, WHICH SHOULD WORK TO STRENGTHEN
SOUTHWEST FLOW ALOFT OVER THE AREA. AT THE SAME TIME, HIGH PRESSURE
OVER THE GREAT LAKES WILL SHIFT TOWARD NEW ENGLAND AND BEGIN TO
RIDGE DOWN THE EAST COAST. THE RESULT IS A COLD AIR DAMMING SCENARIO
OVER THE MID-ATLANTIC AS ATMOSPHERIC MOISTURE IS ON THE INCREASE.
THE WEDGE BOUNDARY WILL MOVE THROUGH THE CAROLINAS, THOUGH THERE
REMAINS SOME UNCERTAINTY IN HOW FAR SOUTH IT WILL GO, AS IS QUITE
COMMON IN THESE SETUPS. PW VALUES ARE PROGGED TO NEAR 2" INTO THE
WEEKEND, AND PERIODIC BURSTS OF SHORTWAVE ENERGY WILL ENHANCE SHOWER
AND THUNDERSTORM ACTIVITY OVER THE AREA. FRIDAY THROUGH SATURDAY MAY
BE PARTICULARLY ACTIVE, WITH THE POTENTIAL FOR CONVECTION TO
CONTINUE PAST THE DIURNALLY FAVORED TIMEFRAME AND INTO THE OVERNIGHT
PERIOD. WEAK INSTABILITY IN A WEAKLY SHEARED ENVIRONMENT SHOULD
LIMIT SEVERE POTENTIAL FRIDAY, BUT DYNAMICS BECOME A BIT MORE
FAVORABLE FOR STORM ORGANIZATION BY SATURDAY.
THE DEEPEST MOISTURE MOVES OUT OF THE REGION ON SUNDAY WITH UPPER
RIDGING BUILDING BACK IN OVER THE SOUTHEAST. HOWEVER, PWAT VALUES
REMAIN ABOVE NORMAL AND DIURNAL CONVECTION IS FAVORED, ALBEIT WITH
LESS UPPER SUPPORT AS THE AREA IS IN BETWEEN SHORTWAVES. THE RIDGE
AXIS MOVES NEARER TO THE FORECAST AREA FOR MEMORIAL DAY INTO TUESDAY
WHICH MAY FURTHER LIMIT COVERAGE, BUT THERE WILL STILL BE PLENTY OF
MOISTURE AND INSTABILITY TO SUPPORT ISOLATED TO SCATTERED
CONVECTION.
RAINFALL AMOUNTS WILL BE QUITE VARIED ACROSS THE REGION DEPENDING ON
THE WEDGE BOUNDARY AND ANY TRAINING THAT OCCURS. NBM QPF AMOUNTS
HAVE INCREASED SLIGHTLY, WITH ANYWHERE FROM 0.25" IN THE EASTERN
MIDLANDS TO OVER 1.5" POSSIBLE IN THE UPPER CSRA AND WESTERN
MIDLANDS. LOCALLY HIGHER AND LOWER AMOUNTS WILL OF COURSE BE
POSSIBLE BASED ON WHERE THE WEDGE BOUNDARY AND STATIONARY FRONT
SET UP.
KEY MESSAGE 2: UNCERTAINTY IN TEMPERATURES FRIDAY AND THIS
WEEKEND.
HIGHS TEMPERATURES TODAY WILL REMAIN ABOVE NORMAL IN THE LOW 90S,
BUT HEAT INDICES WILL FALL SHORT OF ANY HEAT HEADLINE THRESHOLDS.
GIVEN THE PREVIOUSLY DISCUSSED CAD SETUP, THERE SHOULD BE A LARGE
TEMPERATURE GRADIENT OVER THE FORECAST AREA FOR AT LEAST FRIDAY INTO
SATURDAY, WHICH IS NOT ALWAYS HANDLED WELL BY THE NBM. CONCEPTUALLY,
IT WOULDN'T BE OUT OF THE QUESTION TO SEE THE NORTHERN PORTION OF
THE FORECAST AREA STRUGGLE TO RISE OUT OF THE MID 70S FRIDAY AND
POSSIBLY SATURDAY, AND SLIGHT ADJUSTMENTS WERE MADE TO THE INHERITED
FORECAST HIGH TEMPS TO ACCOUNT FOR THESE BIASES. CONFIDENCE IN THE
WEDGE HOLDING LONGER THAN DEPICTED BY MODEL GUIDANCE IS INCREASED BY
THE EXPECTATION OF WIDESPREAD SHOWERS AND THUNDERSTORMS. AND WHILE
NBM TEMPERATURES WEREN'T ADJUSTED MUCH IF AT ALL FOR SUNDAY OR
MONDAY, WITH A FRONTAL BOUNDARY STALLED NEAR THE AREA AND THE
EXPECTED CONTINUATION OF WIDESPREAD CLOUD COVER AND PRECIPITATION,
WOULDN'T BE SURPRISED IF TEMPERATURES CONTINUED TO HOLD CLOSE TO
LATE MAY NORMALS INTO EARLY NEXT WEEK.
AVIATION /06Z THURSDAY THROUGH MONDAY/
VFR CONDITIONS CONTINUE WITH BRIEF RESTRICTIONS POSSIBLE AGAIN
EARLY THIS MORNING. ISOLATED SHOWERS AND THUNDERSTORMS POSSIBLE
LATER TODAY.
LIGHT AND VARIABLE WINDS WILL CONTINUE THROUGH THE NIGHT UNDER
PASSING HIGH CIRRUS CLOUDS. ABUNDANT LOW-LEVEL MOISTURE WILL
SUPPORT ANOTHER ROUND OF PATCHY FOG AND LOW STRATUS DEVELOPMENT
EARLY THIS MORNING, PRIMARILY AFTER 08-10Z. LATEST HREF AND SREF
GUIDANCE CONTINUES TO INDICATE A 40-60% PROBABILITY OF CIGS
BELOW 500 FT WITH THE HIGHEST RISK FOCUSED ACROSS THE
SOUTHEASTERN MIDLANDS AND SOUTHERN CSRA. THE TYPICAL FOG-PRONE
SITES OF AGS AND OGB REMAIN THE MOST LIKELY TERMINALS TO
EXPERIENCE IFR/LIFR RESTRICTIONS EARLY THIS MORNING. ANY
RESTRICTIONS SHOULD IMPROVE AFTER 12-14Z AS LIGHT SOUTHERLY TO
SOUTHWESTERLY WINDS AROUND 3-5 KTS DEVELOP.
SCT CUMULUS IS EXPECTED TO REDEVELOP THROUGH THE DAY AHEAD OF
AN APPROACHING FRONT, BRINGING GREATER COVERAGE OF
AFTERNOON/EVENING SHOWERS AND THUNDERSTORMS. WHILE THE PEAK
ACTIVITY IS EXPECTED TO REMAIN NORTH AND WEST OF OUR CWA,
ISOLATED COVERAGE CANNOT BE RULED OUT. BASED ON THE LATEST HREF
GUIDANCE, ISOLATED STORMS MAY DEVELOP NEAR ALL TERMINALS AFTER
20-22Z AND CONTINUE SPORADICALLY UNTIL THE END OF THE CURRENT
TAF UPDATE. THEREFORE, PROB30S HAVE BEEN ADDED IN ALL BUT THE
OGB SITES. THE FRONT IS EXPECTED TO LINGER AROUND, POSSIBLY
TRIGGERING CONTINUED SHOWERS AND PRODUCING MVFR TO IFR CIGS INTO
FRIDAY MORNING. WINDS WILL REMAIN LIGHT, MAINLY OUT OF THE SW,
BUT COULD BE VARIABLE IN AND AROUND CONVECTION.
EXTENDED AVIATION OUTLOOK...HIGH LOW LEVEL MOISTURE MAY BRING
MORE ROUNDS OF MORNING RESTRICTIONS FROM FOG/STRATUS INTO THE
WEEKEND. SCATTERED AFTERNOON SHOWERS AND STORMS BECOME POSSIBLE
TODAY WITH MORE CHANCES THIS WEEKEND.
CAE WATCHES/WARNINGS/ADVISORIES
SC...NONE.
GA...NONE.
DISCUSSION...EC
AVIATION...ND
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