510
FXUS63 KLSX 231735
AFDLSX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
ISSUED BY NATIONAL WEATHER SERVICE KANSAS CITY/PLEASANT HILL MO
1235 PM CDT TUE JUN 23 2026
KEY MESSAGES
- SEASONABLY COOL CONDITIONS WILL CONTINUE THROUGH THE WORK WEEK.
- SHOWERS AND THUNDERSTORMS ARE FORECAST (70-80%) THURSDAY INTO
FRIDAY WITH THE MAIN CONCERN BEING HEAVY RAINFALL POTENTIALLY
LEADING TO FLASH FLOODING.
- A RETURN TO WARM AND HUMID SUMMERLIKE CONDITIONS IS ANTICIPATED
LATE THIS WEEKEND INTO THE START OF NEXT WEEK.
SHORT TERM /THROUGH WEDNESDAY NIGHT/
ISSUED AT 1233 PM CDT TUE JUN 23 2026
(THROUGH LATE WEDNESDAY AFTERNOON)
ISSUED AT 214 AM CDT TUE JUN 23 2026
RECENT SURFACE ANALYSIS SHOWS AN ELONGATED SURFACE HIGH WORKING ITS
WAY INTO THE REGION FROM THE UPPER MIDWEST. BOTH A CLEAR SKY AND
VERY CALM WINDS HAVE SETTLED INTO THE AREA, PROMOTING EFFICIENT
RADIATIONAL COOLING EARLY THIS MORNING. THESE CONDITIONS OVERLAID
WITH A SATURATED NEAR SURFACE-LAYER IS FAVORING THE FORMATION OF
FOG, WHICH IS BECOMING MORE NOTICEABLE ON NIGHTTIME MICROPHYSICS IN
RIVER VALLEYS ACROSS THE OZARKS AS OF 1AM. EXPANSION OF THIS PATCHY
FOG IS EXPECTED, WITH THE BETTER CHANCES IN RIVER VALLEYS/LOW-LYING
AREAS, WHERE POOLING OF COOLER AIR AND MORE CONSISTENT CALM WINDS
WILL FAVOR THE CONDITIONS FOR FOG. ANY PATCHY FOG WILL ERODE AFTER
SUNRISE THIS MORNING. NORTHWESTERLY FLOW ALOFT MAINTAINS HOLD ON THE
AREA TODAY, KEEPING TEMPERATURES SEASONABLY COOL, ALTHOUGH, SLIGHTLY
WARMER THAN YESTERDAY WITH HIGHS IN THE UPPER 70S/LOWER 80S THANKS
TO MORE ABUNDANT SUNSHINE TODAY. THE AREA IS EXPECTED TO REMAIN
PRECIPITATION FREE THROUGH TUESDAY NIGHT AS A MORE ACTIVE PATTERN
REMAINS OFF TO THE SOUTHWEST. LOW CHANCES (20-30%) FOR SHOWERS AND
(WEAK) THUNDERSTORMS CREEP INTO THE AREA ON WEDNESDAY, AS SOME HIGH-
RESOLUTION GUIDANCE PROGS THE REMNANTS FROM AN MCS FURTHER
WEST/SOUTHWEST FALLING APART AS THEY MOVE INTO THE AREA. IT IS
POSSIBLE THAT SOME OF THIS ACTIVITY BECOMES REINVIGORATED AS IT
MOVES INTO THE AREA ON WEDNESDAY, ESPECIALLY IF IT IS A TIME WHEN
INSTABILITY IS MAXIMIZED, DURING THE AFTERNOON/EVENING.
PEINE
LONG TERM /THURSDAY THROUGH MONDAY/
ISSUED AT 1233 PM CDT TUE JUN 23 2026
(WEDNESDAY NIGHT THROUGH MONDAY)
ISSUED AT 214 AM CDT TUE JUN 23 2026
BY THURSDAY, REGIONAL MID-LEVEL QUASI-ZONAL FLOW ENSUES, WITH LONG-
RANGE DETERMINISTIC GUIDANCE REVEALING A SHORTWAVE TRAVERSING INTO
THE GREAT PLAINS TOWARDS THE AREA. THIS FEATURE IS EXPECTED TO
INITIATE AN MCS/SERIES OF MCS'S OUT WEST, WITH CONFIDENCE INCREASING
THAT THESE MAY IMPACT THE REGION THURSDAY INTO FRIDAY. AS OF NOW,
THE MAIN CONCERN WITH THESE SYSTEMS FOR OUR AREA IS THE THREAT FOR
HEAVY RAINFALL LEADING TO FLASH FLOODING. NORMALLY, THESE SYSTEMS
ARE FAIRLY PROGRESSIVE WHICH LOWERS THE DURATION OF RAINFALL, ASIDE
FROM THE POLEWARD/EQUATORWARD ENDS WHERE BACK-BUILDING AND/OR
TRAINING MAY BE FAVORED. HOWEVER, WITH THE POTENTIAL FOR MORE THAN
ONE MCS OR ROUNDS OF THUNDERSTORMS TO IMPACT SIMILAR LOCATIONS, AND
WITH PWATS PROGGED TO BE NEAR 2", THE THREAT OF LOCALLY HEAVY
RAINFALL IS INCREASING FOR THURSDAY INTO FRIDAY.
INTO THIS WEEKEND, A PATTERN FLIP IS BEING REVEALED BY LONG-RANGE
GUIDANCE WITH LONGWAVE TROUGHING OUT WEST AND A RIDGE BUILDING
ACROSS THE SOUTHEAST. FOR THE AREA, THE MOST NOTICEABLE CHANGE IS
EXPECTED TO BE A RETURN OF MUCH WARMER TEMPERATURES. THIS IS
INDICATED WELL BY LREF TEMPERATURE IQRS THAT SHOW A CONSISTENT
SPREAD OF ONLY 3-5 DEGREES (HIGH CONFIDENCE) WITH MEANS JUMPING FROM
THE MID/UPPER 80S (LATE WEEK) TO THE LOW/MID 90S (END OF THE
WEEKEND/EARLY NEXT WEEK). ANALYSIS OF THE LREF MEAN 850MB
TEMPERATURES SHOWS VALUES NEAR 23C ACROSS THE AREA BY LATE THIS
WEEKEND, WHICH IS AN AIRMASS THAT WOULD SUPPORT HIGHS IN THE MID 90S
GIVEN FULL MIXING. OUR CHANCES FOR SHOWERS AND THUNDERSTORMS, ALONG
WITH HOW WARM IT GETS, WILL RELY UPON THE STRENGTH OF THE SOUTHERN
RIDGE. A STRONGER RIDGE MAY WORK TO PUSH MCS TRACKS/MORE ACTIVE
WEATHER NORTH OF THE AREA ALLOWING FOR WARMER TEMPERATURES, WHILE A
WEAKER RIDGE MAY FAVOR MORE PRECIPITATION CHANCES AND COOLER
TEMPERATURES. EITHER WAY, WITH INCREASING SURFACE MOISTURE AND TEMPS
ALOFT, SUMMERLIKE CONDITIONS ARE FORECAST TO RETURN INCLUDING THE
POTENTIAL FOR HEAT INDICES >100F ACROSS THE AREA.
PEINE
AVIATION /18Z TAFS THROUGH 00Z THURSDAY/
ISSUED AT 1233 PM CDT TUE JUN 23 2026
SURFACE HIGH PRESSURE REMAINS CENTERED ACROSS THE GREAT LAKES
REGION SOUTH TOWARDS KSTL. THE RIDGE WILL CONTINUE TO SLOWLY
MOVE EAST THIS AFTERNOON WITH WINDS VEERING FROM THE EAST AND
THEN SOUTHEAST. ONLY SOME CUMULUS ARE EXPECTED AT KCOU AND KJEF.
TONIGHT, SURFACE HIGH PRESSURE WILL BE EAST OF THE TERMINALS
WITH LIGHT SOUTHERLY WINDS. A MID LEVEL CLOUD DECK WILL START TO
SPREAD IN FROM THE WEST, BUT VFR CONDITIONS ARE EXPECTED TO
CONTINUE. DURING THE DAY WEDNESDAY, MOISTURE WILL RETURN WITH A
WIDESPREAD CU DECK FORECAST WITH WINDS OUT OF THE SOUTHWEST. A
WEAK COLD FRONT WILL THEN APPROACH THE TERMINALS FROM THE WEST.
FOR NOW, WE HAVE LEFT THE MENTION OF PRECIPITATION OUT OF THE
TAFS GIVEN THE UNCERTAINTY OF WHEN SHOWERS AND THUNDERSTORMS
WILL INITIATE. THIS WILL LIKELY NEED TO BE ADDED IN FUTURE TAF
ISSUANCES THOUGH.
LSX WATCHES/WARNINGS/ADVISORIES
MO...NONE.
IL...NONE.
AVIATION...WFO EAX
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