St. Louis, MO 63103 Weather

Key messages

- Unseasonably warm temperatures are expected to continue, but a change is coming this weekend.

- On and off rain chances begin Friday and last through next week. A more widespread, beneficial rainfall is likely early/mid next week.

Short term

Issued at 254 AM CDT Thu Oct 29 2026

A surface cold front currently extends from northeast Kansas into central Wisconsin. This boundary is forecast to continue to push southeast today, and should nearly bisect the CWA just after midday. Weak surface convergence and some building instability (SBCAPE >750 J/kg) could be just enough to produce some isolated showers, and possibly a rumble or two of thunder, along the boundary this afternoon. Given the expected location of the boundary nearing the I- 70 corridor mid-late afternoon, this is where the slight chance (~20%) PoPs are located later today. Higher coverage of rain showers are not expected due to rising mid/upper level heights (subsidence aloft). As the already limited instability wanes nocturnally, a period of dry weather areawide is forecast across the region as any lingering shower activity dissipates by early this evening.

After midnight, low-level moisture convergence strengthens north of the surface boundary, with a weak midlevel impulse also approaching from the west. Scattered showers and a few thunderstorms are expected across northeast Missouri and west-central Illinois into Friday morning. There may be a "lull" later on in the morning hours as the axis of low-level moisture convergence pushes off to the northeast. Additional development of scattered light rain showers are expected near the surface front as it retreats back northward as a warm front.

Temperature wise, look for a north to south gradient both this afternoon and on Friday due to the location of the frontal boundary. Most of the area today should top out in the upper 70s to low 80s, with exception of portions of northeast Missouri and west-central Illinois. There is more uncertainty on Friday as there is some spread (~50 miles) on how far north the boundary retreats during the day. The most likely location of the front Friday afternoon is somewhere near I-70, so the coolest (upper 60s) highs are expected to be across northeast Missouri and west-central Illinois, with upper 70s to near the 80 degree mark to the south in southeast Missouri and southwest Illinois.

Long term

Issued at 254 AM CDT Thu Oct 29 2026

(Friday Night - Saturday)

The vast majority of the region should stay dry Friday night through the day on Saturday, though a few spot showers are possible mainly across northeast Missouri and west-central Illinois. This is where the residual surface boundary may be located with a weak midlevel shortwave trough also moving across Missouri early Saturday morning. A mostly cloudy sky is favored otherwise, with very mild lows (mid 50s to near 60 degrees) and highs near 70 degrees.

(Saturday Night - Sunday)

Deterministic guidance shows better agreement with the timing/track of another midlevel shortwave trough moving out of the south-central Plains across southeast Missouri and southwest Illinois late Saturday night into Sunday morning. At least scattered light rain showers are expected ahead of this feature. The key word is "light" though. While LREF 24-hour probabilities for measurable rainfall are pretty high (60-75%) in southeast Missouri and southwest Illinois, chances for at least 0.25" drop to 25-35%.

(Sunday Night - Wednesday)

Ensemble guidance remains in good agreement that a deep mid/upper level trough will move out of the intermountain west Sunday night into Monday. Cluster analyses of the 500-hPa pattern generally show a closed, possibly cutoff, mid/upper level low across the central Plains on Tuesday, with deep south/southwest flow aloft across the mid-Mississippi Valley. Ahead of the closed mid/upper level low, a surface low is expected to slowly move into the Upper Midwest, with a cold front draped to its south. This boundary is expected to gradually move eastward in time, but exactly when is not certain. Regardless, the pattern still appears favorable for a long duration, significant (>1") rain event across the CWA through the middle of next week. LREF probabilities for at least 1" through Wednesday afternoon are 60-90% from southeast to northwest, and 20-50% for 2+". While this event is largely 4-6+ days out and things can certainly change, there does appear to be increasing potential for substantial drought improvements across the region.

Aviation

Issued at 522 AM CDT Thu Oct 29 2026

A weak cold front will move through KUIN later this morning before stalling out near or just south of the central Missouri and metro St. Louis terminals this afternoon. There may be a few spotty showers and even a rumble of thunder associated with the front later today, but the coverage looked too low to include anything in the TAFs. Light south/southwest winds are forecast ahead of the front, with the wind direction becoming variable in the vicinity of the front. For KUIN, winds are expected to veer behind the front to the northwest, and then eventually east/northeast overnight tonight.

Watches, warnings and advisories

MO: None. IL: None.