647
FXUS63 KLSX 211126
AFDLSX
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE SAINT LOUIS MO
626 AM CDT MON JUL 21 2025
KEY MESSAGES
-HEAVY RAINFALL AND FLASH FLOODING WILL DIMINISH THIS MORNING,
LEAVING A LARGELY DRY REMAINDER OF THE DAY.
-AFTER A RELATIVELY COOLER DAY TODAY, DANGEROUS HEAT RETURNS
TUESDAY AND LASTS THROUGH AT LEAST THURSDAY.
SHORT TERM
(THROUGH LATE TUESDAY AFTERNOON)
ISSUED AT 305 AM CDT MON JUL 21 2025
CONVECTION CONTINUES ACROSS MUCH OF THE FORECAST AREA WITH ANOTHER
ROUND OF TRAINING THUNDERSTORMS LINING UP FROM CHILLICOTHE, MO
SOUTHEAST INTO MONTGOMERY AND WARREN COUNTIES. ADDITIONAL RAINFALL
AMOUNTS UP TO 3-5 INCHES IS EXPECTED WITH THIS MASS OF
THUNDERSTORMS, WITH RAINFALL RATES UP TO 2-3"/HR. THUNDERSTORMS WILL
CONTINUE TO PUSH SOUTHEAST, EVENTUALLY MOVING INTO FRANKLIN, ST.
CHARLES, ST. LOUIS, AND JEFFERSON COUNTIES BUT ARE EXPECTED TO WEAK
AS THEY ARE SEPARATED FROM THE 925-850MB FRONTOGENESIS AND
SOUTHWESTERLY LOW-LEVEL JET SUPPORTING THEM. ADDITIONAL SHOWERS AND
THUNDERSTORMS PERSIST TO THE EAST, AND WHILE THEY MAY SLOW RECOVERY
IN AREAS THAT SAW SIGNIFICANT RAINFALL AND FLASH FLOODING OVERNIGHT,
THE LACK OF TRAINING WILL REDUCE THE RISK FOR NEW FLASH FLOOD
IMPACTS.
THE LOW-LEVEL JET WILL WEAKEN THROUGH THE MORNING HOURS AND COMBINED
WITH RISING 500 MB HEIGHTS THROUGH THE DAY WILL WEAKEN SHOWERS
THUNDERSTORMS EVEN FURTHER AND BEGIN THEM TO AN END BY LATE MORNING.
CLOUD COVER ASSOCIATED WITH THE CONVECTION WILL LINGER THROUGH THE
MORNING, FINALLY SCATTERING DURING THE AFTERNOON. DECREASED SOLAR
INSOLATION FROM THE MORNING CLOUD COVER WILL TAMP DOWN OUR HEAT
POTENTIAL TODAY, KNOCKING A FEW DEGREES OFF OUR HIGHS AND MAXIMUM
HEAT INDEX VALUES COMPARED TO YESTERDAY. MOST LOCATIONS WITHIN
THE EXTREME HEAT WARNING WILL STILL REACH 105F MAXIMUM HEAT INDEX
VALUES, THROUGH AREAS NORTH OF I-70 IN MISSOURI AND I-64 IN
ILLINOIS ARE UNLIKELY TO MEET EXTREME HEAT WARNING VALUES. DESPITE
THE BRIEF AND RELATIVE COOL OFF FOR SOME, WE ARE CONTINUING
WITHOUT ANY MODIFICATIONS TO THE EXTREME HEAT WARNING AS WE EXPECT
TUESDAY- THURSDAY TO REACH 105F HEAT INDEX VALUES ACROSS THE
WARNING AREA.
SOME SYNOPTIC AND ONE OR TWO HI-RES CAMS HAVE BEEN HINTING AT
ISOLATED CONVECTION FORMING ACROSS ILLINOIS TONIGHT, LIKELY A SMALL
MID-LEVEL DISTURBANCE FIRING OFF A REMNANT OUTFLOW BOUNDARY. IF
IT FORMS, CONVECTION WOULD BE LIGHT AND ISOLATED GIVEN THE
WIDESPREAD SUBSIDENCE.
BY TUESDAY, THE MID-LEVEL RIDGE WILL BE STRENGTHENING WITH ITS
CENTER ACROSS THE OHIO RIVER VALLEY. THIS WILL PUSH THE EDGE OF THE
RIDGE NORTHWARD, REMOVING THE FORECAST AREA FROM THE INFLUENCE OF
THE WESTERLIES (DECREASING OUR RAIN CHANCES) AND PUTTING US UNDER
MORE AGGRESSIVE SYNOPTIC FORCING FOR HEAT. THIS, COMBINED WITH
INCREASED SUNSHINE AND CONTINUED WARM AIR ADVECTION IN THE LOW-
LEVELS WILL FINALLY KICK OFF THE DANGEROUS HEAT NORTH OF I-70 (MO)
AND I-64 (IL). DANGEROUS HEAT WILL CONTINUE ACROSS OUR SOUTHERN CWA,
AND MAXIMUM HEAT INDEX VALUES ARE EXPECTED TO PEAK BETWEEN
105-110F.
DELIA
LONG TERM
(TUESDAY NIGHT THROUGH SUNDAY)
ISSUED AT 305 AM CDT MON JUL 21 2025
PRECIPITATION CHANCES WILL BE AT A MINIMUM WEDNESDAY AND INTO
THURSDAY UNDER THE INFLUENCE OF THE MID-LEVEL RIDGE AND WIDESPREAD
SUBSIDENCE, EVEN AS THE MID-LEVEL RIDGE CENTER SHIFTS EASTWARD.
TUESDAY'S HEAT INDEX VALUES WILL BE REPEATED WEDNESDAY AND THURSDAY
AS HOT, HUMID, AND PRECIPITATION-FREE CONDITIONS REMAIN LARGELY THE
SAME, AND OUR EXTREME HEAT WARNING AND WATCH CONTINUE THROUGH
THURSDAY.
THE PATTERN BEGINS TO SHIFT THURSDAY DURING THE DAY AS THE MID-
LEVEL WESTERLIES PUSH CLOSER TO THE FORECAST AREA AND THE REGION
OPENS BACK UP TO MID-LEVEL DISTURBANCES PASSING INTO THE AREA FROM
THE SOUTHWEST. BY FRIDAY MID-LEVEL FLOW BECOMES QUASI-ZONAL AS THE
MID-LEVEL RIDGE WEAKENS AND STRETCHES ACROSS THE SOUTHERN HALF OF
THE US. THESE DISTURBANCES WILL INCREASE PRECIPITATION CHANCES
FRIDAY TO 20-40%, THOUGH WITHOUT A SIGNIFICANT FOCUS FOR
PRECIPITATION AT THE SURFACE, CONFIDENCE IN WHERE AND WHEN SHOWERS
AND THUNDERSTORMS OCCUR REMAINS LOW AT THIS POINT. SATURDAY THROUGH
SUNDAY ANOTHER MID-LEVEL RIDGE DEVELOPS ACROSS THE ROCKIES, KEEPING
THE FORECAST AREA ON THE EASTERN EDGE AND OPEN TO RIDGE RUNNERS. AS
A RESULT, A 20-40% CHANCE FOR SHOWERS AND THUNDERSTORMS PERSISTS
THROUGH THE END OF THE FORECAST PERIOD.
THROUGHOUT THE LONG TERM PERIOD LOW-LEVEL AND SURFACE FLOW REMAINS
SOUTHWESTERLY, KEEPING WARM, HUMID AIR PUMPING INTO THE MID-
MISSISSIPPI VALLEY. THIS WILL KEEP THE CEILING FOR WEEKEND HIGH
TEMPERATURES SIMILAR TO OUR MID WEEK PERIOD, IN THE MID TO UPPER
90S. HOWEVER THE INTERQUARTILE SPREAD FOR HIGH TEMPERATURES
INCREASES FRIDAY AND BEYOND AS DUE TO THE INCREASING POTENTIAL FOR
PRECIPITATION AND CLOUD COVER. ADDITIONAL HEAT HEADLINES MAY BE
NEEDED BEYOND THURSDAY, BUT A GREATER UNDERSTANDING OF THE LOCATION
AND TIMING OF SPECIFIC MID-LEVEL IMPULSES IS NEEDED BEFORE WE CROSS
THAT BRIDGE.
DELIA
AVIATION
(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)
ISSUED AT 616 AM CDT MON JUL 21 2025
SHOWERS AND THUNDERSTORMS ARE ONGOING ACROSS THE REGION, WITH THE
HEAVIEST THUNDERSTORMS ACROSS CENTRAL MISSOURI. THESE WILL
CONTINUE TO IMPACT THE CENTRAL MISSOURI TERMINALS (KCOU AND KJEF)
FOR THE NEXT FEW HOURS OF THE TAF PERIOD, GRADUALLY WEAKENING AND
ENDING LATE MORNING. MVFR VISIBILITIES ARE EXPECTED UNDER THE
STRONGEST THUNDERSTORMS, THOUGH VISIBILITIES MAY BOUNCE ACROSS
CATEGORIES AS VARIOUS CELLS PASS OVER THE TERMINALS. WINDS WILL BE
VARIABLE WHILE THUNDERSTORMS ARE ONGOING BUT WILL BECOME SOUTHERLY
ONCE AGAIN AFTER THUNDERSTORMS HAVE ENDED.
SHOWERS AND THUNDERSTORMS ACROSS THE ST. LOUIS METRO TERMINALS
(KSTL, KSUS, KCPS) WILL CONTINUE TO WEAKEN OVER THE NEXT FEW
HOURS, AND IMPACTS TO THE TERMINALS ARE EXPECTED TO BE MINOR. WINDS WILL BE
VARIABLE WHILE THUNDERSTORMS ARE ONGOING BUT WILL BECOME SOUTHERLY
ONCE AGAIN AFTER THUNDERSTORMS HAVE ENDED.
IFR CEILINGS WILL CONTINUE AT KUIN FOR A FEW HOURS BEFORE LIFTING
WITH THE ONSET OF DAYTIME HEATING. VFR CONDITIONS ARE EXPECTED
BY EARLY AFTERNOON. WINDS WILL BE EASTERLY THROUGH THE DAY.
DELIA
LSX WATCHES/WARNINGS/ADVISORIES
MO...EXTREME HEAT WATCH FROM TUESDAY AFTERNOON THROUGH THURSDAY
EVENING FOR KNOX MO-LEWIS MO-MARION MO-MONROE MO-PIKE MO-
RALLS MO-SHELBY MO.
FLOOD WATCH UNTIL 1 PM CDT THIS AFTERNOON FOR AUDRAIN MO-BOONE
MO-CALLAWAY MO-COLE MO-LINCOLN MO-MONITEAU MO-MONROE MO-
MONTGOMERY MO-OSAGE MO-RALLS MO-SAINT CHARLES MO-SAINT
LOUIS CITY MO-SAINT LOUIS MO-WARREN MO.
EXTREME HEAT WARNING UNTIL 7 PM CDT THURSDAY FOR AUDRAIN MO-
BOONE MO-CALLAWAY MO-COLE MO-CRAWFORD MO-FRANKLIN MO-
GASCONADE MO-IRON MO-JEFFERSON MO-LINCOLN MO-MADISON MO-
MONITEAU MO-MONTGOMERY 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...EXTREME HEAT WATCH FROM TUESDAY AFTERNOON THROUGH THURSDAY
EVENING FOR ADAMS IL-BOND IL-BROWN IL-CALHOUN IL-CLINTON IL-
FAYETTE IL-GREENE IL-JERSEY IL-MACOUPIN IL-MARION IL-
MONTGOMERY IL-PIKE IL-WASHINGTON IL.
FLOOD WATCH UNTIL 1 PM CDT THIS AFTERNOON FOR BOND IL-CLINTON IL-
FAYETTE IL-MADISON IL-MARION IL-SAINT CLAIR IL-WASHINGTON
IL.
EXTREME HEAT WARNING UNTIL 7 PM CDT THURSDAY FOR MADISON IL-
MONROE IL-RANDOLPH IL-SAINT CLAIR IL.
WFO LSX
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