302
FXUS63 KLSX 230515
AFDLSX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
1215 AM CDT WED SEP 23 2026
KEY MESSAGES
- HAZARDOUS WEATHER IS NOT ANTICIPATED THROUGH THE FORECAST
PERIOD AS TEMPERATURES SLOWLY WARM.
SHORT TERM /THROUGH THURSDAY/
ISSUED AT 150 PM CDT TUE SEP 22 2026
CURRENT WATER VAPOR IMAGERY SHOWS A MESSY UPPER-LEVEL PATTERN OVER
THE CONUS, WITH SPLIT FLOW ACROSS THE US-CANADIAN BORDER. THIS HAS
LOW-AMPLITUDE TROUGHING STRETCHING FROM THE NORTHERN PLAINS EASTWARD
INTO THE NORTHEAST. A SHORTWAVE ROUNDING THE BASE OF THE TROUGH IS
MOVING THROUGH THE MIDWEST CURRENTLY, AND IS RESPONSIBLE FOR OUR
CURRENT CLOUD COVER. THANKS TO THIS CLOUD COVER AND THE DECREASING
SUN ANGLE, OUR DIURNAL TEMPERATURE CURVE HAS BEEN MUTED, WITH
TEMPERATURES THIS AFTERNOON ONLY EXPECTING TO TOP OUT AROUND 70
DEGREES. THIS EFFECT WILL CARRY INTO TONIGHT, THOUGH A SURFACE HIGH
DIGGING FURTHER INTO THE MIDDLE MISSISSIPPI VALLEY WILL HELP PUSH
TEMPERATURES LOWER TONIGHT THAN LAST NIGHT - LOW TO MID 50S FOR MOST
LOCATIONS.
TOMORROW, THE SHORTWAVE WILL DIG SOUTHEASTWARD INTO THE SOUTHEAST AS
UPPER-LEVEL RIDGING BUILDS INTO THE PLAINS. AS A RESULT, WE'LL SEE
SOME THINNING OF THE CLOUD COVER THAT WILL ALLOW FOR A LITTLE MORE
SURFACE HEATING. HOWEVER, LOW-LEVEL FLOW WILL REMAIN NORTHEASTERLY,
HELPING KEEP TEMPERATURES SIMILAR TO TODAY'S FOR MUCH OF THE
AREA.
LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/
ISSUED AT 150 PM CDT TUE SEP 22 2026
BOTH ENSEMBLE CLUSTERS AND DETERMINISTIC GUIDANCE SHOW THE AXIS OF
AN UPPER-LEVEL RIDGE CENTERED OVER THE GREAT PLAINS. THROUGH FRIDAY,
THIS RIDGE WILL GRADUALLY SHIFT EASTWARD, BUT HOW AMPLIFIED IT
REMAINS AS IT DOES SO IS UNCERTAIN AS A SHORTWAVE MOVES INTO THE
CENTRAL PLAINS AND UPPER MIDWEST. WHILE THE NBM SHOWS SURFACE
TEMPERATURES WARMING IN RESPONSE TO THE RIDGE, A MAJORITY OF
GUIDANCE HAS 850MB TEMPERATURES HOLDING STEADY COMPARED TO THURSDAY,
WITH SOUTHERLY FLOW EAST-NORTHEASTERLY. CLIMATOLOGICALLY, THIS
DOESN'T FAVOR WARMING TEMPERATURES, SO I WOULDN'T BE SURPRISED TO
SEE FUTURE NBM RUNS COME IN A LITTLE COOLER. AFTER THE EFFECTS OF
THE SHORTWAVE DEPART THE REGION ON SATURDAY, ENSEMBLE CONSENSUS
SHOWS 850 MB TEMPERATURES GRADUALLY CREEPING WARMER, FAVORING A
SIMILAR EFFECT AT THE SURFACE. HOW WARM REMAINS UNCERTAIN, AS THE
NBM IS BEING DRIVEN BY BIAS-CORRECTED GUIDANCE, WHICH IS SOME CASES
IS NEARLY 10 DEGREES WARMER THAN ITS UNBIASED COUNTERPARTS. THIS
BIAS-CORRECTED GUIDANCE IS TRAINING ON OUR RECENT WARMTH, SO I
SUSPECT THAT IT AND THE RESULTING NBM ARE BEING TOO AGGRESSIVE WITH
WARMING EARLY NEXT WEEK. GOING STRICTLY OFF THE 25TH AND 75TH
PERCENTILE OF ENSEMBLE GUIDANCE, THE WARMEST OF GUIDANCE WOULD GIVE
US TEMPERATURES AROUND 5 DEGREES ABOVE NORMAL, WHILE COOLER GUIDANCE
WOULD BE RIGHT AROUND CLIMATOLOGY.
AS FOR RAIN CHANCES, CONFIDENCE IS HIGH THAT A MAJORITY OF THE AREA
WILL NOT EXPERIENCE A SOAKING RAINFALL THROUGH THE WEEKEND. THE LATE-
WEEK SHORTWAVE WILL BE PIVOTING NORTHEASTWARD AND TAKING THE
GREATEST LIFT WITH IT. ITS TRAILING COLD FRONT WILL ALSO STRUGGLE TO
MAKE EASTWARD PROGRESSION INTO THE CWA, LIMITING RAIN CHANCES (UP TO
50%) TO PORTIONS OF CENTRAL AND NORTHEASTERN MISSOURI. THIS WILL
SERVE AS THE MAIN FOCUS FOR RAIN POTENTIAL THROUGH THE FORECAST
PERIOD.
AVIATION /06Z TAFS THROUGH 12Z THURSDAY/
ISSUED AT 1212 AM CDT WED SEP 23 2026
NORTHEAST FLOW CONTINUES ACROSS THE REGION. OUR INITIAL LAYER OF
CLOUDS HAS LIFTED AND IS BREAKING UP, HOWEVER, ANOTHER MVFR DECK
OF CLOUDS IS MOVING EAST TO WEST ACROSS ILLINOIS AS LOW LEVEL
MOISTURE WRAPS IN FROM THE EAST. THIS IS LIKELY TO BRING MVFR
CEILINGS TO THE ST LOUIS METRO AND PERHAPS QUINCY AT TIMES THIS
MORNING, THOUGH THERE'S UNCERTAINTY ON HOW LONG IT LASTS. THE MOST
LIKELY SCENARIO IS THAT THESE CEILINGS LIFT AND THE CLOUDS
BREAK UP DURING THE EARLY AFTERNOON, BUT THERE'S A LOWER CHANCE
THAT THEY MAY LINGER LATER INTO THE DAY.
LSX WATCHES/WARNINGS/ADVISORIES
MO...NONE.
IL...NONE.
SHORT TERM...ELMORE
LONG TERM...ELMORE
AVIATION...KIMBLE
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