810
FXUS62 KCAE 071827
AFDCAE
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE COLUMBIA SC
227 PM EDT WED OCT 7 2026
WHAT HAS CHANGED
UPDATES RELATED TO TS ISAIAS. AVIATION DISCUSSION UPDATED FOR
18Z TAFS.
KEY MESSAGES
- 1. AN ACTIVE WEEKEND AHEAD AS TROPICAL STORM ISAIAS MOVES
INLAND TO OUR WEST. CONFIDENCE IN THE EXTENT OF IMPACTS IS
LOW BUT PERIODS OF HEAVY RAIN EXPECTED.
DISCUSSION
KEY MESSAGE 1: AN ACTIVE WEEKEND AHEAD AS TROPICAL STORM ISAIAS
MOVES INLAND TO OUR WEST. CONFIDENCE IN THE EXTENT OF IMPACTS
IS LOW BUT PERIODS OF HEAVY RAIN EXPECTED.
OVERVIEW: PERIODS OF HEAVY RAIN WITH BREEZY CONDITIONS POSSIBLE
THROUGHOUT SATURDAY INTO SUNDAY WITH A RANGE OF POTENTIAL
IMPACTS STILL ON THE TABLE.
DISCUSSION: TROPICAL STORM ISAIAS CONTINUES TO STEADILY
STRENGTHEN ACROSS THE SOUTHERN GULF WEDNESDAY AFTERNOON. TRACK
GUIDANCE IS GENERALLY CONSISTENT BRINGING THE STORM NORTHEAST,
THEN DUE NORTH INTO THE GULF COAST LATE FRIDAY. EVENTUALLY
TURNING NORTHEAST INTO THE UPPER LEVEL TROUGH AND SOUTHWEST
FLOW. A STRONG SURFACE RIDGE AND ASSOCIATED STEERING FLOW WILL
FORCE ISAIAS WEST, WHILE ALSO STRENGTHENING THE PRESSURE
GRADIENT OVER OUR AREA AND RAPIDLY INCREASING THE MOISTURE
ADVECTION INTO THE AREA. A PLUME OF PWATS OVER 2.4" WILL SURGE
INTO THE REGION AS RESULT WITH NEARLY FULLY SATURATED PROFILES
THROUGH 200MB.
FOR THE CSRA AND MIDLANDS IN SC, THIS YIELDS AN INTERESTING AND
COMPLICATED FORECAST COMBINING BOTH A HIGHLY CONDUCIVE
THERMODYNAMIC ENVIRONMENT FOR HEAVY RAIN, WITH A MORE COMPLEX
SYNOPTIC-MESOSCALE DYNAMIC ENVIRONMENT. FROM A PATTERN
RECOGNITION AND CONCEPTUAL MODEL STANDPOINT, THE LIFTING
PSEUDO- WARM FRONT, ASSOCIATED LARGE SCALE ISENTROPIC LIFT,
PWATS OVER 2.4", AND BROAD DIFFLUENCE ALOFT SHOULD ALL YIELD
RELATIVELY WIDESPREAD HEAVY RAIN. HOWEVER, MUCH OF THE GUIDANCE
SUGGESTS THE STRONGEST 850-700MB WAA QUICKLY PULLS NORTH AND
WEST OF OUR AREA ALONG THE LEADING EDGE OF THE PWAT GRADIENT AND
MESOSCALE SUBSIDENCE AND DRY SLOTTING DEVELOPS AS TWO AREAS OF
DEEP CONVECTION FLANK OUR CWA DYNAMICALLY LIMIT RAINFALL
POTENTIAL. THIS PUTS MUCH OF THE MIDLANDS AND CSRA IN A LOOSELY
UNSTABLE, EXTREMELY MOIST, BUT WEAKLY FORCED ENVIRONMENT FOR
MUCH OF SATURDAY. THERE ARE STILL NOTABLE DIFFERENCES ACROSS
GUIDANCE IN THIS INTERACTION, ESPECIALLY BETWEEN THE AI AND
GLOBAL MODEL SUITES. SO CONFIDENCE REMAINS FAIRLY LOW IN
RAINFALL TOTALS, BUT A MODERATE-HIGH CEILING, LOW FLOOR EVENT
REMAINS ON THE TABLE.
THE SEVERE POTENTIAL IS ALSO WORTH NOTING, WHILE STILL
UNCERTAIN. IMPRESSIVE HODOGRAPHS SOUTH OF THE PSUEDO-WARM FRONT
WITH A 50 KNOT 850MB JET SURGE NORTH WITH THE BULK OF THE
DEEPEST PWATS. INSTABILITY WILL NOT BE IMPRESSIVE DESPITE LCLS
SCRAPPING THE GROUND HOWEVER, BUT IT WILL NOT TAKE MUCH FROM A
CONVECTIVE UPDRAFT AND STRETCHING POTENTIAL TO PRODUCE A FEW
TORNADOES WITHIN THIS ENVIRONMENT.
WE HAVE SEEN A FEW EVENTS THIS YEAR WITH SIMILAR FORECAST
SCENARIOS TO THIS ONE, WITH AN ODD CONFLICTION OF GUIDANCE (AI,
HI-RES, GLOBAL, ETC.) AND THE PHYSICAL-CLIMATOLOGICAL
EXPECTATION OF THE SETUP. EXPECTATIONS OF HEAVY RAIN POTENTIAL
FROM A METEOROLOGICAL STANDPOINT ARE QUITE HIGH, BUT THE
GUIDANCE ENVELOPE OF SOLUTIONS PROVIDES NUMEROUS FAILURE MODES.
AVIATION /18Z WEDNESDAY THROUGH MONDAY/
EXPECT PREDOMINANTLY VFR CONDITIONS BUT PATCHY FOG MAY DEVELOP
EARLY THURSDAY MORNING.
SURFACE HIGH PRESSURE OVER THE AREA WILL KEEP WINDS LIGHT AND
VARIABLE THROUGHOUT MUCH OF THE 24 TAF PERIOD WITH CALM WINDS
OVERNIGHT. EXPECT CLEAR SKIES THROUGH THE REMAINDER OF THE DAY
WITH HIGH CLOUDS CREEPING INTO THE AREA OVERNIGHT.
THE DRY AIR MASS AND THIN HIGH CLOUDS TONIGHT WILL INHIBIT THE
OVERALL THREAT OF DENSE FOG. HOWEVER, CALM LOW LEVEL WINDS AND
CROSSOVER TEMPERATURES IN THE MID 50S COULD SUPPORT A PATCHY,
DENSE FOG THREAT FOR PORTIONS OF THE SOUTHERN FA. AGS AND OGB
WOULD BE THE MOST LIKELY TO BE IMPACTED SO WE HAVE ADDED BRIEF
FOG RESTRICTIONS AROUND SUNRISE TO THE FORECAST. FOG MAY IMPACT
THE OTHER TAF SITES AS WELL BUT CONFIDENCE IS LOW AT THIS TIME.
EXTENDED AVIATION OUTLOOK...THE THREAT OF RESTRICTIONS AND
RAINFALL INCREASES LATE WEEK AND INTO THE WEEKEND AS TROPICAL
MOISTURE SURGES INTO THE SOUTHEAST.
CAE WATCHES/WARNINGS/ADVISORIES
SC...NONE.
GA...NONE.
DISCUSSION...42
AVIATION...CJR
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