Osco, IL Weather

This Hazardous Weather Outlook is for portions of north central Illinois: northwest Illinois: west central Illinois: east central Iowa: northeast Iowa: southeast Iowa and northeast Missouri.

Day one: TODAY AND TONIGHT

No hazardous weather is expected at this time.

Days two through seven: FRIDAY THROUGH WEDNESDAY

Thunderstorms will be possible Friday afternoon and Friday night, with severe storms not expected.

Spotter information statement

Spotter activation will not be needed today or tonight.

Key messages

- A cold front brings slightly cooler, drier air to the area today before rain chances return Friday into Saturday.

- A more active weather pattern could develop early next week, bringing more rain and breezy conditions.

Short term

Issued at 1253 AM CDT Thu Oct 29 2026

A cold front moves through the area today with some lingering rain showers and isolated storms, mainly east of the Mississippi River. Northeasterly flow will advect in slightly cooler, drier air into the CWA with highs in the mid-60s to low 70s. By tonight, the mid- level remnants of Vance in the East Pacific lifts northeastward into the Southern Plains. While the surface response will be weak, pressure falls across the Central Plains on Friday and southwesterly flow aloft ahead of Vance's remnants could drag a warm front northward towards the Highway 34 corridor. Isentropic upgliding and WAA to the north of this boundary are likely to support widespread rain showers (70-90% coverage) with embedded thunderstorms across the CWA Friday afternoon into Friday night. Latest NBM guidance favors rainfall amounts between 0.25-0.75 inches (50-70% chance) with this round, but a swath of 1+ inches cannot be ruled out, especially north of Highway 34.

Long term

Issued at 1253 AM CDT Thu Oct 29 2026

Saturday-Sunday: The warm front near the Highway 34 corridor finally moves further north into the CWA, spawning a smaller round of isolated showers and storms (20-30% coverage) on Saturday. As the boundary becomes diffuse Saturday night, dry conditions return as southeasterly flow advects in more mild air for Sunday. Attention turns west though as a longwave trough propagates eastward into the Rockies, setting the stage for a potentially active start to the work week.

Monday-Wednesday: As the longwave trough shifts eastward into the Plains, there are two potential scenarios:

Scenario 1 (70% chance per LREF cluster analysis): The troughs in the polar jet and subtropical jet become out of phase, leading to a slower, closed-heights center over the south- central Plains and a fast northern trough. This would support two low pressure centers: one over the Great Lakes and east- central Canada and another across the Southern Plains and Lower Mississippi River Valley. With a split system, rainfall amounts are likely to be lower.

Scenario 2 (30% chance per LREF cluster analysis): The troughs stay in phase, deepening a singular mid-latitude cyclone over the Central Plains that would move into the Mid-Mississippi River Valley. This solution would favor more rainfall and windier conditions for our CWA.

Regardless of scenario though, precipitation chances and winds are forecasted to increase heading into Monday night and stick around into Wednesday. With the background cyclonic flow aloft, there could be multiple rounds of rainfall over this time period. Once the mid-latitude cyclone or an associated cold front moves through or east of the CWA, northerly flow should set in and advect in some cooler, more seasonable air by the middle to end of next week.

Aviation

Issued at 607 AM CDT Thu Oct 29 2026

A cold front is making progress south through eastern Iowa the start of the period. This has already moved into CID and DBQ prior to 12Z, and will arrive at MLI around 12-14Z, followed by BRL at 13-15Z. A period of 1-2 hours of MVFR stratus is found behind the front, before dry air erodes the cloud cover. Thus, by 15Z today, nearly all sites will be VFR through the remaining next 24 hours. North winds around 10 kts will be expected today into tonight, which may decrease late in the night or tend toward east. Rains are expected Friday, but this is beyond the end of this TAF period forecast at this time.

Watches, warnings and advisories

IA: None. IL: None. MO: None.