558
FXUS63 KLSX 270301
AFDLSX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
1001 PM CDT SAT SEP 26 2026
KEY MESSAGES
- CONFIDENCE CONTINUES TO INCREASE IN WIDESPREAD RAINFALL
ARRIVING TUESDAY THROUGH MID-WEEK, WITH THE HIGHEST AMOUNTS
(AS HIGH AS 5.00 INCHES LOCALLY) CONFINED ACROSS NORTHERN AND
NORTH- CENTRAL MISSOURI.
- TEMPERATURES GRADUALLY WARM THROUGH THE NEXT SEVERAL DAYS
BEFORE COOLING AGAIN, ALL STAYING ROUGHLY AROUND LATE-
SEPTEMBER NORMALS.
SHORT TERM /THROUGH SUNDAY NIGHT/
ISSUED AT 231 PM CDT SAT SEP 26 2026
MID-LEVEL WATER VAPOR IMAGERY FROM GOES-EAST NICELY DEPICTS
DIFFLUENT 500MB FLOW ACROSS THE CENTRAL CONUS THAT IS PROVIDING
ENOUGH ASCENT COINCIDENT WITH AMPLE MOISTURE TO FORCE SHOWERS
AND MID-LEVEL STRATUS OVER THE REGION. NO INSTABILITY OF NOTE
EXISTS, PRECLUDING A THREAT FOR DEEP CONVECTION OR
THUNDERSTORMS. THE MAIN EFFECT OF THE RAIN AND CLOUDS IS TO
KEEP TEMPERATURES IN CHECK, WITH MOST LOCATIONS STRUGGLING TO
WARM PAST THE UPPER 60S/LOW 70S AGAIN TODAY. FORCING AND
MOISTURE AVAILABILITY BOTH BECOME FAR LESS IMPRESSIVE THIS
EVENING, WHICH WILL END THE LIGHT RAIN FROM WEST TO EAST.
WE REMAIN SEASONABLY-COOL AND LARGELY DRY UNDER THE INFLUENCE OF
EASTERLY LOW-LEVEL FLOW FROM THE RIDGE CENTERED ACROSS THE GREAT
LAKES. AS A MODEST LOW-LEVEL JET AMPLIFIES TONIGHT OVER EASTERN
KANSAS AND FAR WESTERN MISSOURI, ADDITIONAL SHOWERS AND WEAK
THUNDERSTORMS ARE EXPECTED TO REDEVELOP AND MEANDER ACROSS WESTERN
AND CENTRAL MISSOURI OVERNIGHT. WITH THE LLJ WANING AND CONVECTION
MOVING FURTHER FROM THE INITIATION SOURCE, ANY RAIN WILL STRUGGLE TO
MAINTAIN ITSELF EAST OF A LINE ROUGHLY FROM KNOX COUNTY THROUGH
OSAGE COUNTY. SUNDAY APPEARS LARGELY DRY AND TRANQUIL AFTER THE RAIN
DISSIPATES, WITH WINDS GRADUALLY TURNING MORE SOUTHEASTERLY
RESULTING A WARMUP OF A FEW DEGREES COMPARED TO 24 HOURS PRIOR. THE
ONLY POTENTIAL FOR SHOWERS EXISTS ACROSS THE NORTHERN OZARKS, WHERE
TOPOGRAPHY MAY AID IN SOME WEAK LIFT OF A HUMID AIRMASS. ANY THREAT
FOR RAIN ENDS WITH SUNSET, AT WHICH POINT YET ANOTHER SEASONABLY-
COOL NIGHT IS IN STORE.
LONG TERM /MONDAY THROUGH SATURDAY/
ISSUED AT 231 PM CDT SAT SEP 26 2026
WE BEGIN THE WORK WEEK MUCH LIKE WE ENDED IT: SEASONABLE (MID/UPPER
70S FOR HIGHS) AND LARGELY DRY. THE SURFACE RIDGE STALLED OVER THE
GREAT LAKES DROPS FURTHER SOUTH AND WEST BY THEN, SHUNTED IN THIS
DIRECTION BOTH BY IMPULSES IN THE LONGWAVE TROUGH ACROSS THE WESTERN
CONUS/SOUTHERN CANADA AND BY THE SLIGHT RETROGRADE OF THE NOR'EASTER
ONGOING OFF THE NORTHEAST U.S. COASTLINE. THE LONGWAVE TROUGH WILL
ALSO SERVE TO ASSIST IN THE TRANSPORT OF TROPICAL MOISTURE FROM WHAT
REMAINS OF T.C. ODALYS AND T.C. POLO IN THE EASTERN PACIFIC (SEE NHC
BULLETINS FOR MORE INFORMATION). PRECIPITABLE WATER VALUES ARE
CONSISTENTLY FORECAST TO APPROACH CLIMATOLOGICAL MAXIMA AND COUPLE
WITH DEEP SOUTHWEST DIFFLUENCE, TWO IMPORTANT LARGE-SCALE FACTORS
NEEDED FOR AN INCREASED HEAVY RAIN THREAT.
THE PATTERN CURRENTLY MODELED IN A PREPONDERANCE OF ENSEMBLE AND
DETERMINISTIC GUIDANCE CLOSELY RESEMBLES THOSE OF PREDECESSOR RAIN
EVENTS (PRES) THAT ALLOW FOR EXTREMELY EFFICIENT RAINFALL.
RESULTANTLY, RAIN CHANCES WILL BE ON THE RISE ACROSS NORTHERN
MISSOURI AND WEST-CENTRAL ILLINOIS BY LATE TUESDAY AND BECOME MORE
WIDESPREAD BY WEDNESDAY. THIS GENERAL AREA, PARTICULARLY NORTHERN
AND NORTH-CENTRAL MISSOURI, HAVE THE BEST CHANCES LOCALLY FOR HEAVY
RAIN AND FLOODING (BOTH FLASH FLOOD AND RIVER) DUE TO A COMBINATION
OF RELATIVELY MOIST SOIL (PER NASA SPORT ANALYSIS) AND QUALITY OF
ATMOSPHERIC MOISTURE. GLOBAL-SCALE GUIDANCE IS CURRENTLY BEARISH ON
THE PROBABILITIES OF HIGH RAINFALL TOTALS (FOR EXAMPLE, ONLY A 30-
40% CHANCE OF 2.00" OF RAIN AT MOST PER THE NBM), PARTIALLY DUE TO
ITS COARSE SPATIAL RESOLUTION AND PARTIALLY OWING TO UNCERTAINTY IN
WHERE THE HEAVIEST RAIN FALLS. THAT SAID, MODEL SOUNDINGS LEAVE
LITTLE DOUBT IN EFFICIENT WARM RAIN PROCESSES THAT COULD PUSH MULTI-
DAY LOCALIZED TOTALS AS HIGH AS 5.00 INCHES. CURRENTLY THE
EXPERIMENTAL WPC EXCESSIVE RAINFALL OUTLOOK HIGHLIGHTS NORTHERN
MISSOURI IN A 25-40% CHANCE AREA (TRANSLATING TO THE NEW "ENHANCED
RISK" IN THIS PRODUCT).
FURTHER INTO THE WEEK, RAIN BECOMES MORE WIDESPREAD (PARTICULARLY
LATE WEDNESDAY ONWARD) AS THAT REMNANT MOISTURE LINGERS OVER THE MID-
MISSISSIPPI VALLEY. BY THIS POINT, WHILE RAIN CHANCES ARE FAIRLY
HIGH (60-80%) AREAWIDE, RAINFALL TOTALS AND THE THREAT OF FLOODING
IMPACTS BECOMES MORE UNCERTAIN. SOME GUIDANCE BEGINS TO SUGGEST THE
QUALITY OF THIS MOISTURE BECOMES MORE MODIFIED NOW THAT IS SEVERAL
DAYS AND OVER 1000 MILES REMOVED FROM ITS SOURCE REGION. IF THIS
COMES TO FRUITION, WHILE STILL MORE THAN SUFFICIENT FOR RAIN TO
OCCUR, THE EFFICIENCY OF THAT RAIN WOULD LESSEN AND IMPACTS WOULD BE
MORE LIMITED. STILL, SOME DETERMINISTIC GUIDANCE AND ENSEMBLE
MEMBERS POINT TO THAT MOISTURE STAYING VERY MUCH IN PLACE WITH
LITTLE MODIFICATION. THAT SCENARIO CAN'T BE DISCOUNTED, AS PRES HAVE
A TENDENCY TO OVERPERFORM AND REMAIN PROLIFIC LONGER THAN MODELS
SUGGEST. THIS THREAT WILL NEED TO BE MONITORED, HOWEVER ONE FACTOR
DECIDEDLY IN OUR FAVOR IS THE FAR DRIER CONDITIONS ACROSS THE
SOUTHERN TWO-THIRDS OF MISSOURI AND SOUTHERN ILLINOIS. REGARDLESS OF
WHICH SCENARIO PREVAILS, EVEN THE MORE PARCHED PARTS OF THE REGION
SOUTH OF I-70 CAN EXPECT AT LEAS 0.50 INCHES OF RAIN (PER THE NBM).
A QUASI-ZONAL PATTERN LOOKS POISED TO SETTLE OVER THE CONUS, OPENING
OUR REGION TO RENEWED RAIN CHANCES THROUGH NEXT WEEKEND WHILE
KEEPING TEMPERATURES IN CHECK AS WE START OCTOBER.
AVIATION /00Z TAFS THROUGH 06Z MONDAY/
ISSUED AT 1000 PM CDT SAT SEP 26 2026
SHOWERS WILL INCREASE IN COVERAGE OVERNIGHT MAINLY ACROSS
CENTRAL/NORTHEASTERN MO INTO WEST-CENTRAL IL INCLUDING KCOU, KJEF,
AND KUIN WITH UNCERTAINTY IN HOW FAR EAST THEY WILL REACH BEFORE
WANING THROUGH MID-SUNDAY MORNING. MOST SHOWERS WILL BE LIGHT AND
UNIMPACTFUL, BUT A FEW BRIEF, HEAVIER SHOWERS COULD RESULT IN MVFR
FLIGHT CONDITIONS AT KCOU AND KJEF. OTHERWISE, VFR FLIGHT CONDITIONS
WILL PREVAIL WITH LIGHT WINDS.
LSX WATCHES/WARNINGS/ADVISORIES
MO...NONE.
IL...NONE.
SHORT TERM...MRB
LONG TERM...MRB
AVIATION...PFAHLER
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