521
FXUS63 KLSX 261745
AFDLSX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
1245 PM CDT SAT SEP 26 2026
KEY MESSAGES
- THE CHANCE OF RAIN (30-60%) WILL CONTINUE THROUGH SUNDAY
MORNING FOR PORTIONS OF CENTRAL MISSOURI, NORTHEAST MISSOURI,
AND WEST- CENTRAL ILLINOIS.
- A GRADUAL WARM-UP IS EXPECTED THROUGH EARLY NEXT WEEK. HIGHS
NEAR 80 DEGREES ARE FORECAST FOR MOST LOCATIONS BY TUESDAY.
- A WIDESPREAD BENEFICIAL RAINFALL IS EXPECTED NEXT WEEK. THERE
IS HIGH CONFIDENCE (90-100%) THAT EVERYONE WILL SEE MEASURABLE
RAINFALL. MUCH OF THE AREA HAS MORE THAN A 50% CHANCE AT
SEEING 0.50"+ OF RAIN.
SHORT TERM /THROUGH SUNDAY/
ISSUED AT 130 AM CDT SAT SEP 26 2026
A MID-LEVEL HIGH PRESSURE CENTER CONTINUES TO SWIRL JUST OFF THE
TEXAS COAST, WITH ITS RIDGE AXIS EXTENDING INTO THE UPPER
MISSISSIPPI VALLEY. OUR CWA SITS JUST SOUTH OF ITS APEX AND, AS A
RESULT, JUST SOUTH OF A PARADE OF WEAK VORTICITY LOBES THAT KEEP
ROUNDING THE RIDGE'S CREST. SO DESPITE THE RIDGE HELPING TO ADVECT
ANOMALOUSLY RICH MID-LEVEL MOISTURE INTO THE REGION, WEAK LIFT
AND NON-EXISTENT FORCING HAVE PREVENTED ANYTHING MORE THAN LIGHT
RAIN IN PORTIONS OF MISSOURI NORTH OF I-70 THIS MORNING. LOW-
LEVEL DRY AIR ADVECTION FROM THE EAST ISN'T HELPING, EITHER.
SURFACE OBSERVATIONS SHOW THAT MUCH OF THE RAIN FALLING ISN'T
HITTING THE GROUND BECAUSE OF IT. AS THE RIDGE BREAKS DOWN THIS
MORNING, STRONGER MID-LEVEL PULSES WILL BE ALLOWED TO PASS
THROUGH THE REGION. THE INCREASE IN LIFT WILL BRING OUR HIGHEST
LIKELIHOOD FOR SHOWERS OF THE WEEKEND (40-60% CHANCE), THOUGH
ITS FOOTPRINT WILL BE MOSTLY RELEGATED TO NORTHEAST MISSOURI AND
WEST-CENTRAL ILLINOIS AND IT WILL MOSTLY FALL AS LIGHT RAIN DUE
TO THE UNDERCUTTING DRY AIR. THE PASSING OF A SHORTWAVE EARLY
SUNDAY MORNING WILL REINTRODUCE THE POTENTIAL FOR RAIN INTO
NORTHEAST AND CENTRAL MISSOURI BEFORE SUNRISE (30-50%). DESPITE
THE EARLY HOUR, MUCAPE IS EXPECTED TO BE MAXIMIZED DURING THIS
PERIOD (UP TO 250 J/KG) WITH THE RETURN OF LOW-LEVEL WARM AIR
ADVECTION AND A RUMBLE OR TWO OF THUNDER WILL BE POSSIBLE.
THE TEMPERATURE FORECAST WILL CONTINUE TO BE HEAVILY INFLUENCED BY
CLOUD COVER THIS WEEKEND. WHERE CLOUDS ARE MOST DENSE AND LINGER THE
LONGEST, HIGHS WILL BE COOLER AND LOWS WILL BE WARMER. THE OPPOSITE
IS TRUE FOR THOSE WHO SEE MORE SUN.
LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/
ISSUED AT 130 AM CDT SAT SEP 26 2026
FOCUS SHIFTS TO NEXT WEEK'S RAIN CHANCES. A DEEP LONGWAVE TROUGH IS
FORECAST TO BE PASSING THROUGH THE DESERT SOUTHWEST TUESDAY NIGHT.
DESPITE THE DISTANCE, MODEL GUIDANCE SHOWS THE SYSTEM EJECTING LOBES
OF VORTICITY INTO THE MID-MISSISSIPPI VALLEY DURING THE SAME
TIMEFRAME. CONCURRENTLY, HIGH PRESSURE WILL DOMINATE THE LOW-LEVEL
WIND PATTERN, RESULTING IN MOISTURE AND WARM AIR ADVECTION INTO THE
CENTER OF THE COUNTRY. IN THESE SOUTHEAST MISSOURI AND SOUTHWEST
ILLINOIS THE LOW-LEVELS MAY SATURATE IMMEDIATELY OR REMAIN DRY FOR
MUCH LONGER THAN TO THE NORTHWEST. THOUGH ENSEMBLES SHOW A 100%
CHANCE OF RAIN BETWEEN 06Z WEDNESDAY AND 06Z FRIDAY EVERYWHERE,
THESE AREAS HOLD THE MOST UNCERTAINTY REGARDING TIMING AND AMOUNTS.
ELSEWHERE, AND IN NORTHEAST MISSOURI ESPECIALLY, MOISTURE IS
EXPECTED TO POOL ALONG AN APPROACHING FRONT WITH RAIN ALL BUT
GUARANTEED (LREF 90-100% PROBABILITY OF 24 HOUR RAINFALL). THE LREF
PROBABILITY OF 24 HOUR RAINFALL >0.50" ENDING 06Z FRIDAY RANGES FROM
40%-80% FROM SOUTHEAST TO NORTHWEST. EVEN WITH THE UNCERTAINTY, THIS
SYSTEM STILL BRINGS OPTIMISM REGARDING THE ONGOING DROUGHT.
TEMPERATURES NEXT WEEK WILL BE ON THE UPSWING AS WARM AIR IS PULLED
INTO THE MID-MISSISSIPPI VALLEY AHEAD OF THE AFOREMENTIONED SYSTEM.
BY TUESDAY, MUCH OF THE AREA IS FORECAST TO REACH THE UPPER 70S TO
80 DEGREES. CONFIDENCE IN TEMPERATURES DROPS COME WEDNESDAY DUE TO
UNCERTAINTIES REGARDING THE TIMING OF THE RAIN'S ONSET AS SEEN IN
THE 13 DEGREES NBM IQR SPREAD AT KSTL THAT DAY. THE SPREAD TIGHTENS
SOME IN THE FOLLOWING DAYS, BUT THIS FALSE CONFIDENCE IS DISPELLED
WHEN CONSIDERING THE CONTINUED RAIN CHANCES AND POTENTIAL COLD
FRONTAL PASSAGE LATER IN THE WEEK.
AVIATION /18Z TAFS THROUGH 00Z MONDAY/
ISSUED AT 1232 PM CDT SAT SEP 26 2026
VFR CONDITIONS ARE FORECAST TO PREVAIL THROUGH THE TAF PERIOD,
WITH THE MAIN IMPACTS CONFINED TO THE NEXT FEW HOURS WITH LIGHT
RAIN IMPACTING KUIN, KCOU, AND KJEF. ANOTHER THREAT FOR RAIN,
AND POSSIBLY SOME WEAK THUNDERSTORMS, TOWARDS THE END OF THE TAF
PERIOD IN CENTRAL MISSOURI, BUT GIVEN THE LOW CONFIDENCE IN THAT
THREAT IT WAS EXCLUDED FROM THE TAF.
LSX WATCHES/WARNINGS/ADVISORIES
MO...NONE.
IL...NONE.
SHORT TERM...JAJA
LONG TERM...JAJA
AVIATION...MRB
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