Lake St. Clair, MO Weather

Key messages

- Above average temperatures will continue into early next week.

- Showers and a few thunderstorms are expected at times Friday through the weekend, mainly Friday morning and Saturday night/Sunday morning with plenty of dry time otherwise.

- Confidence is high in widespread, beneficial rainfall early to mid-next week.

Short term

Issued at 232 PM CDT Thu Oct 29 2026

Early this afternoon, a cold front is slowly advancing southward into the I-70 corridor. Surface convergence, increasing instability, and a weak capping inversion may be sufficient to overcome weak mid- level height rises/subsidence and produce isolated showers, perhaps a thunderstorm, in the next couple of hours through sunset. CAMs disagree on whether or not development actually occurs, however, with HREF probabilities of measurable rainfall only around 10 to 20 percent.

As a modest (20 to 25-kt) southwesterly LLJ develops overnight, a more robust signal for showers and some thunderstorms exists late tonight through Friday morning across northern MO into IA, including portions of northeastern MO/west-central IL within low-level WAA extending to the north of the stalling front. These showers and thunderstorms may continue at times well into the day Friday as the LLJ is slow to weaken and some additional development could occur along the surface front as it lifts northward, but the strongest forcing and greatest coverage is anticipated to gradually shift northward through the day. There will be a spread in temperatures on Friday with highs ranging from near 80 F in southeastern MO to the 60s F across northeastern MO/west-central IL north of the front and within clouds and precipitation through the day. In between, exact temperatures are uncertain due to sensitivity on how quickly the front lifts northward.

Long term

Issued at 232 PM CDT Thu Oct 29 2026

Between Friday night and Sunday, a series of upper-level shortwave troughs are progged to track northeastward through the Mid- Mississippi River Valley. The first of which will pass Friday night into Saturday, but only widespread clouds with isolated light showers or sprinkles are anticipated, since forcing will be mainly confined to mid-levels and there will be a deep dry layer below. Therefore, conditions will be mainly dry on Saturday, through evening Halloween festivities. With the second shortwave trough, low- level forcing and moisture will be more favorable for showers late Saturday night into into Sunday morning, supported by 30 to 60 percent probabilities of measurable rainfall in global ensemble model guidance. These showers will be light, but probabilities of 0.25"+ are 30 to 40 percent across southeastern MO/southwestern IL, suggesting showers could be more persistent and relatively "heavier" in those areas. With considerable cloud cover both Saturday and Sunday, high temperatures will be limited to the upper 60 to low-70s F and with a small diurnal range including low temperatures in the 50s to around 60 F. These temperatures are still above average for the end of October/beginning of November.

Global model guidance continues to be in agreement that a more potent upper-level trough will slowly propagate across the central CONUS from Monday through mid to late next week. There is considerable variability across model guidance solutions on the structure and speed of the trough since it will likely be composed of multiple shorter wavelength troughs interacting and phasing (or not phasing) with one another. Although these details are uncertain, an anomalous (>90th climatological percentile), deep meridional component to the flow with anomalous PW around the 97.5 to 99th climatological percentile and slow system motion all provide strong support for a widespread rainfall event across the region. NBM probabilities of 1"+ in 48 hours are 40 to 70 percent across the CWA, highest in central and northeastern MO. However, there is spread on the timing and duration of this rainfall which will impact amounts. Temperatures are also uncertain with the NBM interquartile reaching around 10 F by late next week, but an underlying cooling trend increases confidence that clouds and precipitation, then eventual CAA with this system will inevitably cool temperatures closer to average.

Aviation

Issued at 607 PM CDT Thu Oct 29 2026

Mainly dry and VRY conditions are expected through the period. The only exceptions will be some light scattered showers early in the period near the St. Louis metro area, so have included some unrestricted -SHRA in a PROB30 group through 01Z at STl/SUS/CPS. There is also an increasing chance for showers and isolated thunderstorms across northeast Missouri and west central Illinois late tonight into Friday, so have included a PROB30 group between 13-17Z for MVFR conditions in showers. Otherwise mainly light winds tonight will turn out of the east late tonight into Friday morning at around 10 knots.

Watches, warnings and advisories

MO: None. IL: None.