671
FXUS63 KLSX 311954
AFDLSX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAINT LOUIS MO
254 PM CDT FRI OCT 31 2025
KEY MESSAGES
- A COLD FRONT WILL BRING A COOLER THAN NORMAL AIRMASS TO THE
REGION THIS WEEKEND WITH HIGH TEMPERATURES (40S/50S) 5-8
DEGREES BELOW NORMAL. TEMPERATURES GRADUALLY WARM NEAR TO ABOVE
NORMAL NEXT WEEK.
- THERE IS A SLIGHT CHANCE (15-30%) OF SHOWERS OVER MOST OF THE
AREA SATURDAY. CHANCES INCREASE TO NEAR 60% OVER FAR SOUTHEAST
MISSOURI. RAINFALL AMOUNTS WILL BE LIGHT (TRACE TO 0.10").
SHORT TERM
(THROUGH LATE SATURDAY NIGHT)
ISSUED AT 245 PM CDT FRI OCT 31 2025
(ANALYSIS/OVERVIEW)
A LONGWAVE UPPER TROUGH HAS CONSUMED MUCH OF THE CONUS WITH MID-
LEVEL RIDGING OVER THE WESTERN U.S. THE TROUGH INDUCES MULTIPLE
DISTURBANCES THAT ROTATE THROUGH THE BROADER CYCLONIC FLOW, KEEPING
AN ACTIVE UPPER LEVEL PATTERN OVER THE UPPER MIDWEST. SURFACE HIGH
PRESSURE OVER THE EASTERN PLAINS HAS EXHIBITED ENOUGH INFLUENCE OVER
THE MID-MISSISSIPPI VALLEY TO MAINTAIN MOSTLY CLEAR SKIES AHEAD OF A
COLD FRONT. CLOUDS INCREASE NEAR THE FRONT, WHICH EXTENDS EAST TO
WEST FROM NORTHERN ILLINOIS INTO IOWA. THE FRONT IS JUST BEGINNING
TO ENCROACH ON THE NORTHERN SECTIONS OF MISSOURI AND WEST-CENTRAL
ILLINOIS AS OF 19Z THIS AFTERNOON. SURFACE OBSERVATION SHOW NEAR
NORMAL TEMPERATURES (60S) SOUTH OF THE FRONT AND MUCH COOLER
(40S/50S), BELOW NORMAL TEMPERATURES NORTH OF THE BOUNDARY. COOLER
TEMPERATURES ARE ACCOMPANIED BY DRIER AIR WITH DEWPOINTS IN THE .
(THIS EVENING THROUGH 15Z SATURDAY)
THE COLD FRONT OVER IOWA WILL MOVE SOUTHWARD THROUGH THE CWA
OVERNIGHT AND INTO SOUTHERN SECTIONS OF MISSOURI AND ILLINOIS BY
SATURDAY MORNING. RELATIVELY HIGHER MOISTURE ASSOCIATED WITH
ANOTHER, WEAKER SHORTWAVE OVER COLORADO, WILL BE PULLED EASTWARD
WITHIN UPPER LEVEL WESTERLIES SOUTH OF THE UPPER LOW. CLOUDS WILL
CONTINUE TO INCREASE FROM WEST TO EAST AHEAD OF THE FRONT BEFORE
BEING SHUNTED INTO THE SOUTHERN SECTIONS OF THE CWA SATURDAY
MORNING. THE FRONT IS MOVING THROUGH DURING DIURNAL MINS IN ADDITION
TO HIGH-BASED (ALOFT OF 600MB) SATURATION OVER DRY AIR BELOW 850MB.
A STRAY SHOWER CANNOT BE ENTIRELY RULED OUT, BUT DRY CONDITIONS ARE
HEAVILY FAVORED WITH HREF PROBABILITIES SHOWING 10% OF THE MEMBERS
DOTTING THE FRONT RAINFALL POTENTIAL. GUSTY WINDS RUN ALONG AND JUST
BEHIND THE FRONT, BUT THIS LOOKS BRIEF (1-2 HOURS) CONSIDERING THE
COMPACT NATURE OF THE LLJ SPEED MAX FOLLOWING THE FRONT.
ANOTHER ITEMS NOTE WITH THE FRONT TONIGHT IS THE POTENTIAL FOR LOW
TEMPERATURES NEAR OR SLIGHTLY BELOW FREEZING SATURDAY MORNING. THIS
COMES IN A NARROW CORRIDOR OF DRY AIR THAT SEPARATES THE MOISTURE
POOL OVER THE PLAIN/MID-MISSISSIPPI VALLEY FROM THE POOL OF MOISTURE
ASSOCIATED WITH THE UPPER LOW TO THE NORTH. GUIDANCE HAS COME INTO
MUCH BETTER AGREEMENT IN THE TIMING AND PLACEMENT OF THE DRY AIR,
WHICH EXTEND OVER NORTHERN MO INTO WEST-CENTRAL IL. WIDESPREAD 30S
ARE EXPECTED SATURDAY MORNING WITH THE COLDEST TEMPERATURES LINING
UP WEST TO EAST ALONG AND NORTH OF HWY 36 IN MO AND I-72 IN IL. 50-
70% OF THE HREF MEMBERS SHOW LOWS AT OR BELOW 32 DEGREES IN THIS
REGION OF CLEARING AND LIGHT WINDS. SUFFICE TO SAY, TEMPERATURES ARE
LIKELY TO BRING AN OFFICIAL END TO THE GROWING SEASON. HOWEVER, IF
KUIN DROPS TO 32 OR COLDER, PERIOD-OF-RECORD DATA SHOWS THIS TO BE
THE 14TH LATEST FREEZE ON RECORD DATING BACK TO 1901, ALONG WITH THE
FACT THE AREA HAS DROPPED INTO THE LOW TO MID-30S MULTIPLE TIMES
ALREADY. MOST GROWING HAS CEASED, FREEZING TEMPERATURES BECOME MORE
WIDESPREAD SUNDAY MORNING AND TONIGHT'S WINDS STAY ELEVATED ENOUGH
TO MITIGATE FROST POTENTIAL. THEREFORE, HEADLINE DECISIONS WILL
FOCUS ON SUNDAY MORNING (SEE NEXT PARAGRAPH) TO SIMPLIFY MESSAGING
AND PREVENT CONFUSION.
(15Z SATURDAY THROUGH 12Z SUNDAY)
NOVEMBER ARRIVES WITH A WELCOME PACKAGE - COLD AIR ADVECTION WILL BE
IN FULL SWING UNDER SCATTERED TO BROKEN CLOUDS AND NORTHWEST WINDS.
AS THE UPPER LOW CONTINUES ON ITS SOUTHEAST PATH, THE 0C 850MB
ISOTHERM IS PULLED WELL INTO AR/TN AND NORTHERN MS. MID-LEVEL
TEMPERATURES OF -3 TO -5C ARE BROADLY DISPERSED OVER MO/IL SATURDAY
THROUGH LATE MORNING SUNDAY. THE COMBINATION WILL MAKE FOR A CHILLY
DAY WITH A NOTABLY COOLER TREND IN TEMPERATURES. HI-RES (HRRR/RAP)
AND MEDIUM RANGE (NAM) GUIDANCE HAS COME IN 2-4 DEGREES COLDER,
INCLUDING A LIMITED SPREAD IN THE NBM IQR DATA. MUCH OF THE ARE
STRUGGLES TO GET OUT OF THE 40S WITH THE WARMEST LOCATIONS OVER
SOUTHEAST MO/SOUTHWEST IL AND EVEN THERE THE NUMBER OF HREF MEMBERS
DROP DRAMATICALLY FOR EVERY DEGREE ABOVE 50, ULTIMATELY REVEALING
LESS THAN 20% OF THE MEMBERS ARE AT OR ABOVE 55 DEGREES ALONG AND
SOUTH OF I-44 (MO) AND I-70 (IL). SHOWERS WILL LARGELY BE CONFINED
TO AND AHEAD OF THE FRONT OVER SOUTHEAST MO AND SOUTHWEST IL,
WHERE AS MUCH AS 0.10" COULD FALL. FURTHER NORTH OF THE FRONT, THE
COLD UPPER AIRMASS (-30C AT 500MB) COULD SUPPORT A FEW ISOLATED TO
PERHAPS SCATTERED SHOWERS BETWEEN 18Z-00Z (DIURNAL PEAK).
CLOUDS BEGIN TO EVACUATE SATURDAY NIGHT AS DRIER AIR MOVES IN BEHIND
THE EXITING UPPER WAVE. WINDS LIGHTEN AND SURFACE HIGH PRESSURE
BUILDS FROM THE EASTERN PLAINS INTO CENTRAL MO. COOLING WILL BE MORE
EFFICIENT UNDER THE SURFACE HIGH, GENERALLY FROM QUINCY TO
COLUMBIA, WHERE LOWS FALL IN THE UPPER 20S TO LOW-30S. THE
NOTORIOUSLY COOLER MICROCLIMATES COULD YIELD LOW TO MID-20S WITH
WIDESPREAD LOW TO MID- 30S. NBM GUIDANCE HAS NUDGED TEMPERATURES
DOWN ELSEWHERE, TOO, WITH COOLER TRENDS SIGNALING LOW NEAR OR JUST
BELOW FREEZING THROUGH A LARGE MAJORITY OF THE CWA. COOLER
TRENDS, CLIMBING HREF PROBABILITIES FOR FREEZING TEMPERATURES, AND
THE SPREAD OF LOWS AROUND 30 DEGREES ARGUED FOR THE FREEZE WATCH
TO BE EXPANDED OVER THE ENTIRE CWA LATE SATURDAY NIGHT INTO SUNDAY
MORNING. THE LATE- SEASON TIMING SHOULD BE A GOOD POINT TO CALL
AN END TO THE GROWING SEASON, ESPECIALLY CONSIDERING THAT
TEMPERATURES HAVE BEEN IN THE 30S (WITH FROST) ON MULTIPLE
OCCASIONS ALREADY.
MAPLES
LONG TERM
(SUNDAY THROUGH NEXT FRIDAY)
ISSUED AT 245 PM CDT FRI OCT 31 2025
(12Z SUNDAY THROUGH 00Z MONDAY)
THE LONGWAVE TROUGH MOVES EAST THROUGH THE DAY SUNDAY WITH
NORTHWESTERLY FLOW ALOFT, WHILE AN UPPER RIDGE STAGES TO THE WEST.
WITH THE RIDGE TO THE WEST, WE WON'T SEE TOO MUCH OF A WARM-UP BUT
WILL TACK ON A FEW DEGREES OVER SATURDAY'S HIGH TEMPERATURES WITH
AMPLE SUNSHINE. HIGHS RETURN TO THE LOW TO MID-50S.
(00Z MONDAY THROUGH 12Z WEDNESDAY)
SURFACE HIGH PRESSURE SHIFTS FROM CENTRAL MO INTO WESTERN TN LATE
SUNDAY INTO MONDAY, TURNING WINDS OUT OF THE SOUTH AND SOUTHWEST.
MEANWHILE, THE UPPER LEVEL RIDGE BEGINS TO BUILD EASTWARD, AS WELL,
MARKING THE BEGINNING OF WAA AND A RETURN TO NEAR NORMAL
TEMPERATURES (LOW TO MID-60S). NBM'S IQR REMAINS TIGHTLY CLUSTERED
THROUGH MONDAY, BUT THEN BEGINS TO SPREAD TUESDAY. THOUGH GLOBAL
GUIDANCE HAS COME INTO BETTER AGREEMENT WITH THE SYNOPTIC PATTERN, A
COUPLE MINOR DISAGREEMENTS CONTINUE TO EXPAND THE SPREAD THROUGH
WEDNESDAY.
GLOBAL GUIDANCE SHOWS DE-AMPLIFICATION IN THE UPPER RIDGE AS IT
PROGRESSES EAST LATE MONDAY INTO TUESDAY. ANOTHER SURFACE RIDGE
QUICKLY BUILDS SOUTHEAST AND EVENTUALLY BECOMES CONJOINED WITH THE
SURFACE HIGH OVER TN. THE SURFACE HIGH BUILDING DOWN FROM THE
NORTHWEST FOLLOWS A COLD FRONT THAT ESSENTIALLY WASHES OUT AS THE
UPPER PATTERN BECOMES MORE ZONAL AND A WEAK SHORTWAVE ROCKETS OVER
THE REGION FROM WEST TO EAST WITHIN THE ZONAL UPPER LEVEL PATTERN.
THIS IS NOT AT ALL AN ORGANIZED, NOR STRONG SYSTEM, AND THE AMOUNT
OF DRY AIR AROUND THE SURFACE RIDGING IS EXPECTED TO KEEP THINGS DRY
AT THIS TIME. WHILE THERE IS SOME SPREAD IN THE DATA GOING INTO
MIDWEEK, THE GENERAL THEME SHOULD BE A MODEST STAIR STEP INTO MILDER
TEMPERATURES THROUGH WEDNESDAY.
(12Z WEDNESDAY THROUGH SATURDAY NIGHT)
WEDNESDAY IS FAVORED TO BE THE MILDEST DAY OF THE WEEK, BUT JUST HOW
WARM IS STILL IN QUESTION WITH SPREAD INCREASING TO AROUND 7-8
DEGREES WEDNESDAY AFTERNOON. GLOBAL GUIDANCE SHOWS A WEAK SURFACE
LOW QUICKLY EJECTING EASTWARD FROM THE NORTHERN ROCKIES, CROSSING
THE CENTRAL U.S., ALONG WITH A COLD FRONT THAT PRECEDES A SURFACE
HIGH. GUIDANCE DIVERGES ON BOTH THE SPEED AND PLACEMENT OF THESE
FEATURES, WHICH DOMINOES ON DOWN THE LINE FROM THERE. THE
BOUNDARY LINGERS SOMEWHERE IN THE REGION AS IT GETS HUNG UP ON THE
NORTHWEST SIDE OF RIDGING OVER THE SOUTHEASTERN U.S. EXACTLY HOW
THIS PLAYS OUT IS LESS CERTAIN AT THIS DISTANCE IN TIME, BUT THE
PLACEMENT COULD RESULT IN ANYTHING FROM SEASONABLY COOL
TEMPERATURES TO ABOVE NORMAL TEMPERATURES WITH 10-12 DEGREES
SEPARATING THE 25TH/75TH PERCENTILES IN THE NBM DATA. YET ANOTHER
SYSTEM APPROACHES LATE THURSDAY INTO FRIDAY, POTENTIALLY BRING A
ROUND OF SHOWERS ALONG ANOTHER COLD FRONT FRIDAY. GIVEN THE SPREAD
THAT DEVELOPS BY MIDWEEK, CONFIDENCE IN THE LATE WEEK ISN'T ANY
GREATER AT THIS TIME.
MAPLES
AVIATION
(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)
ISSUED AT 1234 PM CDT FRI OCT 31 2025
MOSTLY CLEAR SKIES AND LIGHT WINDS WILL GIVE WAY TO MID-LEVEL VFR
CLOUDS TONIGHT AS A COLD FRONT SINKS SOUTHWARD THROUGH THE REGION.
THE FRONT ARRIVES AT KUIN JUST AFTER 00Z THIS EVENING, MOVING
SOUTHWARD THROUGH CENTRAL MO AND METRO TERMINALS AROUND MIDNIGHT.
WINDS WILL REMAIN LIGHT IN MOST CASES WITH A BRIEF 1-2 HOUR
WINDOW FOR GUSTS NEAR 20KTS ALONG AND JUST BEHIND THE FRONT. THE
POTENTIAL IS GREATEST AROUND METRO TERMINALS WITH THE COMPACT
NATURE OF THE LOW LEVEL JET. NORTHWESTERLY SURFACE FLOW CONTINUE
THROUGH THE REMAINDER OF PERIOD WITH SCATTERED TO BROKEN VFR
CEILING FAVORED TO HOLD THROUGH SATURDAY AFTERNOON.
MAPLES
LSX WATCHES/WARNINGS/ADVISORIES
MO...FREEZE WATCH FROM LATE SATURDAY NIGHT THROUGH SUNDAY MORNING FOR
AUDRAIN MO-BOONE MO-CALLAWAY MO-COLE MO-CRAWFORD MO-
FRANKLIN MO-GASCONADE MO-IRON MO-JEFFERSON MO-KNOX MO-LEWIS
MO-LINCOLN MO-MADISON MO-MARION MO-MONITEAU MO-MONROE MO-
MONTGOMERY MO-OSAGE MO-PIKE MO-RALLS MO-REYNOLDS MO-SAINT
CHARLES MO-SAINT FRANCOIS MO-SAINT LOUIS CITY MO-SAINT
LOUIS MO-SAINTE GENEVIEVE MO-SHELBY MO-WARREN MO-WASHINGTON
MO.
IL...FREEZE WATCH FROM LATE SATURDAY NIGHT THROUGH SUNDAY MORNING FOR
ADAMS IL-BOND IL-BROWN IL-CALHOUN IL-CLINTON IL-FAYETTE IL-
GREENE IL-JERSEY IL-MACOUPIN IL-MADISON IL-MARION IL-MONROE
IL-MONTGOMERY IL-PIKE IL-RANDOLPH IL-SAINT CLAIR IL-
WASHINGTON IL.
WFO LSX
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