Temperatures are dropping to 35°F across interior northern Illinois before sunrise Monday. Patchy frost is coming — and most residents don’t know it yet.
Frost Advisory — Act Before Bedtime
The National Weather Service in Chicago warns lows will fall to 35°F in interior suburbs west of I-39. Frost will develop in sheltered inland areas before sunrise Monday.
It’s May — and frost is still on the table. A surge of cold air is settling across northern Illinois overnight, and anyone who planted flowers, vegetables, or herbs this spring is at risk of waking up to damage on Monday morning.
Clear skies and light winds overnight will allow temperatures to fall steadily after midnight. That’s the dangerous combination: no cloud cover means no insulation, and no wind means cold air pools right at ground level — exactly where your plants are.
Who’s Most at Risk?
The coldest readings — as low as 35°F — will occur well west of Chicago’s lakeshore, which stays naturally milder. Communities along and west of Interstate 39 are most vulnerable. If you’re in any of these counties, act now:
DeKalbLaSalleKane
Chicago’s lakeside neighborhoods and communities near Lake Michigan will stay in the low-to-mid 40s — cold, but above the frost threshold.
Do this before you go to sleep tonight
Cover tender plants with fabric, old bedsheets, or frost cloth. Move potted plants and container gardens indoors or into a garage. Don’t wait until morning — frost can form in less than an hour once temps drop past 36°F.
No Commute Disruptions — Just Garden Damage
The good news: this frost event will not affect Monday morning travel. Roads will remain clear and dry, and temperatures will rebound into the mid-to-upper 50s by afternoon. The cold snap is brief, not dangerous — unless you’re a tomato seedling.
5-Day Forecast — Northern Illinois
| Monday 57–67° Low 38–44° Partly cloudy. Frost early morning. | Tuesday 72–78° Low 47–53° Windy. 30–60% chance of storms. | Wednesday 59–67° Low 40–46° Breezy, cooler near the lake. | Thursday 60–72° Low 48–52° Partly cloudy. Pleasant. | Friday 72–82° Low 50–60° Increasing clouds. Warm. |
Warmer Week Ahead After Monday’s Chill
Once Monday’s frost risk passes, the week turns noticeably warmer. Tuesday surges into the mid-to-upper 70s, though gusty winds and a chance of thunderstorms will accompany the warmup. Wednesday cools off again, especially near the lakefront. By Friday, highs could reach the low 80s — a proper spring warmup finally arriving.
The week’s biggest weather event after frost? Tuesday’s storm window. With a 30–60% chance of showers and thunderstorms and southerly winds, stay tuned for updates if you have outdoor plans.
