026
FXUS63 KLSX 071057
AFDLSX
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE SAINT LOUIS MO
557 AM CDT THU AUG 7 2025
KEY MESSAGES
- TYPICAL SUMMER WARMTH AND HUMIDITY WILL PREVAIL INTO THE
WEEKEND WITH THE HIGHEST AFTERNOON HEAT INDEX VALUES FLIRTING
WITH 100 F.
- THERE IS A CONDITIONAL, 20 PERCENT CHANCE OF SHOWERS AND
THUNDERSTORMS TODAY INTO TONIGHT, BUT HIGHER CHANCES (20 TO 50
PERCENT) EXIST SATURDAY EVENING INTO NEXT WEEK.
SHORT TERM
(THROUGH LATE FRIDAY AFTERNOON)
ISSUED AT 325 AM CDT THU AUG 7 2025
UPPER/MID-LEVEL NORTHWESTERLY FLOW WILL PERSIST ACROSS THE MID-
MISSISSIPPI RIVER VALLEY THROUGH FRIDAY WITH A RIDGE POSITIONED JUST
UPSTREAM ACROSS THE SOUTHERN AND CENTRAL PLAINS. THIS PATTERN WILL
BE SUPPORTIVE OF SHOWERS AND THUNDERSTORMS AT TIMES ACROSS THE
BROADER REGION, INITIATING ON THE NOCTURNAL LLJ AND POTENTIALLY
LATER SUPPORTED BY EMANATING MCVS. THE LATEST HREF SUGGEST THE
GREATEST CHANCE OF SHOWERS AND THUNDERSTORMS WILL REMAIN ACROSS IA
INTO IL CLOSER TO THE LLJ'S NOSE, BUT THERE ARE A HANDFUL OF CAMS
THAT DEPICT SHOWERS AND THUNDERSTORMS REACHING THE CWA, EITHER AS AN
MCS AND/OR REDEVELOPMENT WITH A REMNANT MCV BETWEEN LATER THIS
MORNING AND FRIDAY MORNING. THIS UNCERTAINTY IS ADDRESSED BY BROAD-
BRUSHED (CONDITIONAL) 20 PERCENT POPS ACROSS MOST OF THE CWA, BUT
THESE POPS DECREASE OVERNIGHT TONIGHT/FRIDAY MORNING AS MID-LEVEL
TEMPERATURES WARM AND BECOME LESS FAVORABLE FOR CONVECTION. THERE
ARE STILL SOME INGREDIENTS THAT SUGGEST THERE IS A NON-ZERO CHANCE
OF A FEW SEVERE THUNDERSTORMS WITH DAMAGING WINDS AND HEAVY
RAINFALL, BUT CONFIDENCE IS FAR TOO LOW TO COMMUNICATE THESE THREAT
AT THIS POINT. ALL OF THESE BEING SAID, PREDOMINANTLY DRY CONDITIONS
ARE STILL THE MOST LIKELY SCENARIO FOR THE CWA.
OTHERWISE, THE GRADUAL WARMING TREND WILL CONTINUE TODAY AND FRIDAY
WITH WEAK, STEADY LOW-LEVEL WAA. HIGH TEMPERATURES TODAY ARE
EXPECTED TO REACH THE UPPER 80S TO MID-90S F, WITH CONVECTIVE DEBRIS
AND ANY PRECIPITATION LIKELY KEEPING TEMPERATURES TOWARD THE LOWER
END OF THIS RANGE. ON FRIDAY, 850-HPA TEMPERATURES WILL BEGIN TO
PEAK NEAR THE 90TH CLIMATOLOGICAL PERCENTILE TRANSLATING TO MORE
WIDESPREAD 90 TO MID-90 F HIGH TEMPERATURES. DEWPOINTS IN THE UPPER
60S TO MID-70S F WILL YIELD AFTERNOON HEAT INDEX VALUES IN THE UPPER
90S TO JUST ABOVE 100 F TODAY AND FRIDAY, JUST BELOW SINGLE-DAY
CRITERIA FOR A HEAT ADVISORY.
PFAHLER
LONG TERM
(FRIDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 325 AM CDT THU AUG 7 2025
LATE FRIDAY THROUGH THE WEEKEND, THE UPPER-LEVEL RIDGE IS EXPECTED
TO BECOME POSITIONED OVER THE MID-MISSISSIPPI RIVER VALLEY WHILE
BREAKING DOWN AS AN UPPER-LEVEL LONGWAVE TROUGH PROPAGATES ACROSS
THE NORTHERN-TIER OF THE CONUS. THE LAST RELATIVELY CONFIDENT DRY
DAY WILL BE SATURDAY BENEATH THE RIDGE AXIS WITH HIGH TEMPERATURES
AND HEAT INDEX VALUES ALSO SIMILAR TO FRIDAY. HOWEVER, UPPER/MID-
LEVEL QUASI-ZONAL AND/OR SOUTHWESTERLY FLOW WILL BECOME ESTABLISHED
LATE SATURDAY INTO SUNDAY, CONTINUING INTO NEXT WEEK, LEADING TO A
WETTER AND MORE ACTIVE PATTERN ACROSS THE MID-MISSISSIPPI RIVER
VALLEY. MODEL GUIDANCE HAVE STRUGGLED TO IDENTIFY THE ORIENTATION OF
THIS FLOW BUT IN EITHER CASE IT WILL BE FREQUENTED BY PASSING
SHORTWAVE TROUGHS OR MCVS. ADDITIONALLY, THERE HAS BEEN A TREND
TOWARD A COLD FRONT ONLY CLIPPING THE NORTHERN PORTION OF THE CWA AS
IT OSCILLATES INTO MID-NEXT WEEK. ENSEMBLE MODEL GUIDANCE HAVE
VARYING 20 TO 60 PERCENT 6-HOUR PROBABILITIES OF SHOWERS AND
THUNDERSTORMS SATURDAY EVENING INTO NEXT WEEK, MAINLY ACROSS
NORTHEASTERN MO AND WEST-CENTRAL IL THROUGH SUNDAY NIGHT, BEFORE
EXPANDING INTO MUCH OF THE REST OF THE CWA THEREAFTER. THESE SHOWERS
AND THUNDERSTORMS WOULD BE EPISODIC IN NATURE WITH PLENTY OF DRY
PERIODS IN BETWEEN, BUT THEIR EXACT PLACEMENT AND TIMING ARE QUITE
UNCERTAIN IN THIS PATTERN.
NBM TEMPERATURE DISTRIBUTIONS HAVE BEEN SLOWLY CLOSING ON HIGH
TEMPERATURES COOLING SLIGHTLY FROM SATURDAY, WITH COOLING MOST
PRONOUNCED NORTH OF I-70, CLOSER TO THE FRONT AND IN HIGHER
PROBABILITIES OF CLOUDS AND PRECIPITATION. MORE SPECIFICALLY, THE
INTERQUARTILE RANGE SPANS UPPER 80S TO MID-90S F ALONG/SOUTH OF I-70
AND MID-80S TO AROUND 90 F TO THE NORTH. ACCORDINGLY, CONFIDENCE IS
LOW THAT HEAT INDEX VALUES WILL REMAIN HIGH ENOUGH AFTER SATURDAY TO
SATISFY THE HEAT ADVISORY DURATION CRITERIA OF 4+ DAYS OF 100+ F.
PFAHLER
AVIATION
(FOR THE 12Z TAFS THROUGH 12Z FRIDAY MORNING)
ISSUED AT 557 AM CDT THU AUG 7 2025
THE MAIN CONCERN THIS TAF PERIOD WILL BE THE POTENTIAL FOR SHOWERS
AND THUNDERSTORMS ACROSS THE REGION. A THUNDERSTORM COMPLEX IS
CURRENTLY SLOWLY ADVANCING SOUTHEASTWARD OUT OF IA, BUT IT IS
UNCERTAIN HOW LONG-LIVED IT WILL BE AND IF IT REACHES KUIN,
JUSTIFYING THE INTRODUCTION OF A PROB30 GROUP. UNCERTAINTY ONLY
GROWS BEYOND THIS MORNING AND WHETHER OR NOT SHOWER AND THUNDERSTORM
REDEVELOP OCCURS THIS AFTERNOON AND EVENING WITH CONFIDENCE EVEN
LOWER AS TO IF THERE WILL BE ANY ADDITIONAL IMPACTS AT THE
TERMINALS.
PFAHLER
LSX WATCHES/WARNINGS/ADVISORIES
MO...NONE.
IL...NONE.
WFO LSX
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