527
FXUS63 KLSX 182311
AFDLSX
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE SAINT LOUIS MO
611 PM CDT MON AUG 18 2025
KEY MESSAGES
- PERIODS OF SCATTERED SHOWERS AND THUNDERSTORMS ARE FORECAST
THROUGH TUESDAY EVENING. THUNDERSTORMS THROUGH THIS EVENING AND
AGAIN TOMORROW AFTERNOON WILL BE CAPABLE OF ISOLATED DAMAGING
WIND GUSTS.
- OUR RECENT STRETCH OF HEAT BREAKS AFTER TOMORROW, WITH MORE
SEASONABLE WEATHER FORECAST THROUGH THE WEEKEND.
SHORT TERM
(THROUGH LATE TUESDAY NIGHT)
ISSUED AT 251 PM CDT MON AUG 18 2025
AIR MASS THUNDERSTORMS HAVE FORMED ACROSS PORTIONS OF CENTRAL AND
SOUTHEASTERN MISSOURI BENEATH THE CENTER OF THE UPPER-LEVEL RIDGE
RESPONSIBLE FOR OUR RECENT HEAT. TEMPERATURES HAVE WARMED INTO THE
90S FOR A VAST MAJORITY OF THE CWA, WITH MANY READINGS SHOWING MID
TO UPPER 90S. THESE TEMPERATURES PAIRED WITH DEW POINTS GENERALLY IN
THE MID 70S HAVE PUSHED HEAT INDEX VALUES ONCE AGAIN INTO THE 105-
110 RANGE AND SBCAPE TO VALUES OF AT LEAST 3,000 J/KG. WITH
TEMPERATURES HAVING RECENTLY REACHED CONVECTIVE VALUES AND A WEAK
DISTURBANCE MEANDERING THROUGH THE REGION, ISOLATED TO SCATTERED
CONVECTION HAS DEVELOPED AND IS EXPECTED TO CONTINUE THROUGH THE
EARLY EVENING. DEEP LAYER SHEAR IS NEARLY NON-EXISTENT, BUT DCAPE IS
IN THE 1,000-1,500 J/KG RANGE, WITH THE SPC MICROBURST COMPOSITE
CURRENTLY AT 9 OR GREATER (MICROBURSTS ARE "LIKELY"). THIS LEADS TO
A THREAT OF AT LEAST ISOLATED DAMAGING MICROBURSTS BENEATH STORMS
THAT CAN GROW TALL ENOUGH BEFORE THEY COLLAPSE.
AS INSTABILITY DECREASES THROUGH THE EVENING, SO WILL THE CHANCES
FOR THESE AIR MASS THUNDERSTORMS. HOWEVER, A COLD FRONT SINKING
SOUTHWARD INTO THE REGION IN RESPONSE TO A TROUGH DEEPENING OVER THE
EASTERN CONUS WILL SERVE AS THE FOCUS FOR ADDITIONAL SCATTERED
CONVECTION AS A WEAK LOW-LEVEL JET RAMPS UP OVER THE MIDWEST. A BULK
OF THIS CONVECTION IS EXPECTED TO STAY NORTH OF THE CWA TONIGHT,
THOUGH THERE IS A LOW CHANCE (30%) THAT SHOWERS AND THUNDERSTORMS
ALONG THE FRONT AND/OR OUTFLOW FROM EARLIER CONVECTION COULD IMPACT
AREAS ALONG AND NORTH OF I-70 LATE TONIGHT AND EARLY TUESDAY
MORNING.
THE FRONT AND MORESO POSSIBLE OUTFLOW COMPLICATE THE TEMPERATURE
FORECAST FOR TOMORROW. A SLOWER FRONT OR WEAK TO NO OUTFLOW WOULD
ALLOW FOR ANOTHER DAY OF DANGEROUS HEAT ON THE ORDER OF WHAT WE'VE
BEEN SEEING LATELY MAINLY FOR AREAS ALONG AND SOUTH OF I-70. A
QUICKER FRONT, STRONGER OUTFLOW, AND/OR CONVECTIVE DEBRIS WOULD
INHIBIT TEMPERATURES FROM WARMING ENOUGH TO POSE A THREAT, THOUGH
POOLING DEW POINTS MAY OFFSET THIS TO AN EXTENT. THE EXTENSION OF
THE HEAT ADVISORY FOR PORTIONS MAINLY ALONG AND SOUTH OF I-70
TOMORROW ERRS ON THE SIDE OF CAUTION AND LEANS MORE TOWARD THE FIRST
SCENARIO. ONCE TONIGHT'S CONVECTIVE ACTIVITY SHOWS ITS HAND,
ADDITIONAL ADJUSTMENTS CAN BE MADE TO THE HEAT ADVISORY.
ADDITIONAL CONVECTION IS FORECAST ALONG THE FRONT/OUTFLOW DURING
PEAK HEATING TOMORROW AFTERNOON. WITH THE PREVIOUSLY MENTIONED
POINTS OF UNCERTAINTY WITH THE LOCATION OF THE EFFECTIVE BOUNDARY,
THERE IS A SPREAD IN WHERE THE FOCUS FOR STORMS WILL BE. NORTHERN
SOLUTIONS FAVOR SOUTHEASTERN MISSOURI AND SOUTHWESTERN ILLINOIS,
WHILE SOUTHERN SOLUTIONS POINT TO CI SOUTH OF THE CWA. THE GOING
FORECAST IS A MIDDLE GROUND, WITH A 30-50% CHANCE FOR SHOWERS AND
THUNDERSTORMS ACROSS FAR SOUTHEASTERN MISSOURI AND SOUTHWESTERN
ILLINOIS. SHEAR WILL ONCE AGAIN BE MEAGER THANKS TO WEAK FLOW ALOFT,
LEADING TO SINGLE CELL STORM MODES. STEEP LAPSE RATES AND INVERTED
"V" SOUNDINGS WILL ONCE AGAIN LEAD TO A THREAT OF DAMAGING
MICROBURST WINDS, WITH THE THREAT FOR CONVECTION DIMINISHING DURING
THE EVENING.
ELMORE
LONG TERM
(WEDNESDAY THROUGH NEXT MONDAY)
ISSUED AT 251 PM CDT MON AUG 18 2025
THE UPPER-LEVEL TROUGH WILL ONLY BE DEEPENING ACROSS THE EASTERN
CONUS PER GUIDANCE CONSENSUS AT THE START OF THE EXTENDED FORECAST
RANGE ON WEDNESDAY. THIS WILL RESULT IN HIGH PRESSURE EDGING FURTHER
INTO THE REGION AT THE SURFACE, PUSHING TEMPERATURES DOWN TO AROUND
CLIMATOLOGICAL NORMALS (HIGHS IN MID 80S, LOWS IN LOW 60S) FOR
WEDNESDAY INTO THURSDAY.
BOTH ENSEMBLE CLUSTERS AND DETERMINISTIC GUIDANCE SHOW UPPER-LEVEL
RIDGING BUILDING BACK INTO THE MIDWEST FRIDAY AND SATURDAY. WHILE
THERE IS NOT A STRONG SIGNAL FOR SOUTHERLY LOW TO MID-LEVEL FLOW TO
ACCOMPANY THIS FEATURE, A MAJORITY OF GUIDANCE SHOWS THE NOSE OF A
MID-LEVEL THERMAL RIDGE EDGING INTO THE MIDDLE MISSISSIPPI VALLEY
FROM THE WEST. THIS WILL PRODUCE A SLIGHT BUMP IN TEMPERATURES AT
850 MB, CLIMATOLOGICALLY CORRELATING WITH WARMING AT THE SURFACE.
THIS IS SUPPORTED BY ENSEMBLE MEANS THAT SHOW A BRIEF, SUBTLE WARM-
UP FRIDAY AND SATURDAY. TEMPERATURES WILL GENERALLY STILL BE AROUND
CLIMATOLOGICAL NORMALS, WITH NBM-BASED PROBABILITIES MAXING OUT AT
45% FOR HIGHS ABOVE 90 FOR PORTIONS OF THE CWA SOUTH OF I-70 THROUGH
SATURDAY.
FROM LATE SATURDAY INTO EARLY NEXT WEEK, GUIDANCE CONSENSUS IS THAT
A RELATIVELY POTENT UPPER-LEVEL TROUGH WILL ONCE AGAIN DIG
EQUATORWARD OVER THE EASTERN CONUS. THIS WILL PLACE THE MIDDLE
MISSISSIPPI VALLEY BENEATH STRONG NORTHWESTERLY FLOW THAT WILL USHER
IN AN UNSEASONABLY COOL AIRMASS FOR SUNDAY INTO THE EARLY WORKWEEK.
SOME LOCATIONS MAY STRUGGLE TO GET OUT OF THE 70S FOR HIGHS, WITH
THE 75TH PERCENTILE OF ENSEMBLE GUIDANCE HOVERING IN THE UPPER 70S
TO AROUND 80 DEGREES FOR A MAJORITY OF THE AREA.
ELMORE
AVIATION
(FOR THE 00Z TAFS THROUGH 00Z TUESDAY EVENING)
ISSUED AT 603 PM CDT MON AUG 18 2025
SHOWERS AND THUNDERSTORMS ARE WEAKENING ACROSS THE REGION AND WILL
BE COMPLETELY GONE BY THE FIRST FEW HOURS OF THE TAF PERIOD,
THOUGH NONE ARE CURRENTLY IMPACTING THE TERMINALS. WINDS WILL BE
LARGELY LIGHT AND VARIABLE OVERNIGHT, THOUGH LESS SHELTERED SITES
MAY SEE A MORE SOUTHERLY WIND DOMINATE. OVERNIGHT A FRONT WILL
DROP SOUTH INTO THE AREA AND BY TOMORROW MORNING KUIN, KCOU, AND
KJEF ARE EXPECTED TO BE NORTH OF THE BOUNDARY WITH NORTHWESTERLY
WINDS. KSTL, KSUS, AND KCPS ARE EXPECTED TO BE SOUTH OF THE
BOUNDARY UNTIL THE AFTERNOON WHEN THE BOUNDARY WILL COME THROUGH
AND SOUTHWESTERLY WINDS WILL BECOME NORTHWESTERLY.
THERE IS A 20-30% CHANCE OF SHOWERS AND THUNDERSTORMS OVERNIGHT
AND THROUGH TOMORROW ALONG THE FRONT. CONFIDENCE IS HIGHEST IN
THIS HAPPENING OVERNIGHT AT KUIN, SO THE PROB30 GROUP CONTINUES AT
THIS SITE. ELSEWHERE, CONFIDENCE IS TOO LOW IN OCCURRENCE AND
LOCATION OF THUNDERSTORMS TO INCLUDE A MENTION IN THE TAFS FOR
NOW.
DELIA
LSX WATCHES/WARNINGS/ADVISORIES
MO...HEAT ADVISORY UNTIL 8 PM CDT THIS EVENING FOR AUDRAIN MO-BOONE
MO-CALLAWAY MO-KNOX MO-LEWIS MO-LINCOLN MO-MARION MO-MONROE
MO-MONTGOMERY MO-PIKE MO-RALLS MO-SHELBY MO.
HEAT ADVISORY UNTIL 8 PM CDT TUESDAY FOR COLE MO-CRAWFORD MO-
FRANKLIN MO-GASCONADE MO-IRON MO-JEFFERSON MO-MADISON MO-
MONITEAU MO-OSAGE MO-REYNOLDS MO-SAINT CHARLES MO-SAINT
FRANCOIS MO-SAINT LOUIS CITY MO-SAINT LOUIS MO-SAINTE
GENEVIEVE MO-WARREN MO-WASHINGTON MO.
IL...HEAT ADVISORY UNTIL 8 PM CDT THIS EVENING FOR ADAMS IL-BROWN IL-
CALHOUN IL-GREENE IL-JERSEY IL-MACOUPIN IL-MONTGOMERY IL-
PIKE IL.
HEAT ADVISORY UNTIL 8 PM CDT TUESDAY FOR BOND IL-CLINTON IL-
FAYETTE IL-MADISON IL-MARION IL-MONROE IL-RANDOLPH IL-SAINT
CLAIR IL-WASHINGTON IL.
WFO LSX
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