Weather Lookup

Key Messages

- a heat advisory has been issued for areas south of i-70 through thursday, with afternoon heat index values near 105 degrees. While humidity levels drop off a bit late in the week, highs in the 90S are likely to prevail in this area through the weekend.

- after heavy rain occurred last night over the northern parts of the forecast area, potential exists for additional heavy rain tonight. While the greatest threat is closer to i-80, a flood watch has been issued for knox, stark and marshall counties.

Discussion

Issued at 205 PM CDT wed sep 16 2026

Latest surface map shows the front draped just north of i-70. A large temperature range is in place over the forecast area early this afternoon, ranging from the lower 70S near galesburg, to the mid 90S south of i-70. Convection has recently been firing south of i-70, along an axis of sbcape over 3000 j/kg, while scattered showers persist over the northern third of the forecast area.

Not a lot of movement is expected with the front the next few days, remaining draped over central illinois courtesy of a large upper high over the southeast u.S. Gulf moisture has been feeding into the mid mississippi valley due to the high's circulation, and unseasonably high precipitable water values over 2 inches will remain pooled just north of the boundary. Two consequences of this pattern: 1) unseasonably hot weather with highs in the 90S (mainly south of i-70) continuing into the weekend, and 2) potential for additional heavy rain across northern illinois tonight.

- heat concerns: a heat advisory has been issued for areas south of i-70 through thursday. Dew points in the lower 70S will result in heat indices approaching 105 degrees both this afternoon and thursday afternoon. As the boundary slips a little further south thursday night, slightly lower temperatures and dew points should keep the heat index just under 100 degrees on friday.

- rain concerns: morning model suite has been advertising development of an mcs across southeast iowa later this evening, tracking eastward across northern illinois overnight into early thursday. With the excessive precipitable water values and training storms, potential for areas of flash flooding is high. Heavy rain last night of 2-4 inches fell from the southeast tip of iowa to north of peoria. While the core of the heaviest rain tonight is expected closer to i-80, a number of cam's do show storms potentially tracking as far south as i-74. Href and refs lpmm both suggest amounts around 2 inches from galesburg to lacon are not out of the question. Thus, a flood watch has been issued for knox, stark and marshall counties until 10 AM thursday.

Going further out in time, while the front begins lifting back north as a warm front friday night, the boundary never fully exits the region until early next week. At that point, a strong shortwave over the northern plains and upper mississippi valley should finally kick the front eastward. Until then, rain chances will persist, with the highest chances from saturday night into sunday night.

Aviation — 18Z Tafs Through 18Z Thursday

Issued at 1201 PM CDT wed sep 16 2026

IFR ceilings continue to lift north, with low MVFR expected at kpia/kbmi for another hour or two. While VFR conditions prevail into the evening, some visibility restrictions may become an issue at these sites, depending on how much clearing takes place. Toward daybreak, clusters of showers and thunderstorms may graze these sites as well, though most will be further north.

South of there, ceilings have lifted to around 7000 feet or higher, and VFR conditions will prevail through thursday morning.