East Saint Louis, IL Weather

Key Messages

- Seasonably warm and predominantly dry conditions will continue through the work week.

- There is a 60 to 80 percent chance of rain next (Halloween) weekend, although timing is not certain.

Short Term

Issued at 234 PM CDT Sun Oct 25 2026

An Omega Block spanning the CONUS will keep an upper-level ridge locked in place over the Mid-Mississippi River Valley through late Monday. As a result, there will be little/no change in airmass, but increasing/thickening upper-level clouds will result in slightly warmer low temperatures tonight and high temperatures a degree or two cooler on Monday, although still firmly in the 70s F.

Long Term

Issued at 234 PM CDT Sun Oct 25 2026

An upper-level trough ejecting northeastward across the Central Plains to Upper Midwest will result in a weakening of the Omega Block and a slight eastward displacement of the upper-level ridge around Tuesday into Wednesday. The glancing passage of the trough will at least provide increasing clouds, but it is unlikely to be sufficient for any precipitation with limited moisture return. However, the pattern will subsequently become more favorable for moisture return, which, when combined with a wavering front reaching as far southeastward as northern/northeastern MO during the second half of the week, leads to increasing ensemble membership with measurable rainfall in that portion of the CWA. This rainfall would be in the form of a few showers at times, with the vast majority of the period still expected to be dry while low-level southwesterly flow south of the front maintains seasonably warm conditions. Thursday is forecast to be the warmest day of the forecast period as the ridge briefly amplifies again, accompanied by high temperatures in the 80s F for parts of the CWA.

As the ridge weakens again next weekend with another upper-level trough passage and more time for moisture to increase, there is a stronger signal for rainfall across the CWA. Around 70 to 90 percent of global ensemble model membership has measurable rainfall at some point next weekend with 40 to 50 percent probabilities of greater than 0.25". However, PoPs in the current forecast are slightly lower due to them being 6 hourly with timing uncertainty. There is little support for this trough to have a front that provides much, if any, airmass change, but clouds and precipitation have the potential to temporarily cool temperatures. For context, although the NBM interquartile temperature range does increase to around 8 F next weekend, even the 25th percentile is still above average for the end of October/beginning of November.

Aviation

Issued at 1033 PM CDT Sun Oct 25 2026

Dry, VFR conditions will persist through the period. The potential for fog, primarily at KSUS, is a bit higher tonight than it appeared a few hours ago. That said, high clouds overhead are still working against radiative cooling and may keep conditions just warm enough to preclude much fog.