Vandalia, IL Weather

Key Messages

- High pressure remains in place allowing for our dry and warm weather continues well into next week.

Short Term

Issued at 347 AM CDT Fri Oct 23 2026

A slow moving upper-level ridge continues to dominate over the central CONUS bringing dry and seasonably warm conditions to the Mid- Mississippi Valley. Seasonably warm high temperatures are being primarily driven by the ridge continuing its residence over the region. High temperatures today and through the weekend will remain in the mid to upper 70s, possibly reaching 80s in some areas. The over night low temperatures on the other hand will remain more seasonal. The dry air mass that remains in the region associated with the surface high has allowed for efficient radiative cooling through the region creating low temperatures into the upper 40s and low 50s. Low temperatures overnight are expected to continue to be in the upper 40s to low 50s through the weekend. The 40s will primarily be located in the river valleys and in southeastern MO and southwestern IL, where fewer clouds will allow for more radiative cooling.

Long Term

Issued at 347 AM CDT Fri Oct 23 2026

Over the western CONUS, a deep upper-level trough propagates to the northeast toward the central CONUS early next week. Guidance indicates that as this trough slowly moves to the northeast, its amplitude will decrease enough to the point where the cold front associated with the trough will stay well to the north of our forecast region Tuesday into Wednesday, and allow for a ridge to remain over the region. This will allow for continued dry and seasonably warm conditions to continue through this forecast period with high temperatures remaining in the 70s each day. Another trough and associated cold front then begin to build over the western CONUS before moving to the east toward the end of the week. Guidance is uncertain on the exact timing and magnitude of this cold front in Missouri. NBM guidance from yesterday had IQRs of 15-20 degrees on Thursday and Friday with the 25th percentiles in the lower to mid- 60s and 75th percentiles near 80, but the most recent runs have brought the IQRs closer to 10-15 degrees with 25th percentiles brought up into the 70s on Thursday and mid to upper 60s on Friday while keeping the 75th percentiles near 80. This hints that model guidance is either pushing the cold front further into the future or decreasing the magnitude of the front. Latest ensemble guidance has increased the chances of rain associated with moisture ahead of the front with a 20-50 percent chance of measurable rain by Friday evening across the region.

Aviation

Issued at 625 AM CDT Fri Oct 23 2026

High pressure remains in place over the region allowing for light winds and continued VFR conditions. There is a chance of fog at SUS and CPS early this morning due to the light to calm winds, but will be very spotty. SUS has already experienced a few observations of IFR visibilities, but have been short lived.