Frost Dates for 61068 — Rochelle, Illinois

Half of springs at Rochelle, IL see their last 32°F night by April 26; only one in ten is past it by April 11, and one in ten still has one after May 12. Planting tender crops after May 2 leaves a 30% risk of a frost on them, after May 6 20%, and after May 12 10%. The 16 days between the even-odds date and the one-in-ten date is narrower than at 22% of the 158 Illinois stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 13 in half of years, as early as September 29 one year in ten, and holds off past October 25 one year in ten. A hard freeze of 28°F follows 11 days later, around October 24; in spring the one-in-ten date for 28°F is April 30, 12 days before the 32°F one. The freeze-free season lasts 168 days in a typical year, shorter than at 91% of the 158 Illinois stations; it reaches 188 days one year in ten and falls short of 147 one year in ten. On average 145 nights a year drop to 32°F or below. Nights of 36°F, when frost can still settle on leaves in low, open spots, continue 9 days longer, to about May 5, and return around October 3. Severe cold of 16°F or below comes every winter, usually between November 22 and March 14.

July is the warmest month at Rochelle, IL, averaging 82°F by day and 61°F at night; January is the coldest at 28°F and 12°F. A freezing night is all but certain in every month from October to April (a 90% chance or more). From June to August the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 35% of years.

Warmth for growing adds up to 2,833 growing degree days a year (base 50°F), fewer than at 92% of the 158 Illinois stations. 34% of them (967) have built up by the end of June, and July adds the most, 676. Precipitation totals 36.7 inches a year, most in June (4.9") and least in February (1.7"); May to September bring 56% of it.

The nearest other station, Shabbona 5 NNE, IL, 13 miles southeast of Rochelle, has a last frost 2 days later (April 28), a first frost 3 days earlier (October 10), a season 5 days shorter.

The first measurable snow (0.1 inch or more) in Rochelle usually arrives around December 3, and the last of the season around March 24. Those are the middle dates across the winters of 1991–2020 at Rochelle, IL, 1.6 miles away: half of years saw snow earlier, half later. Snow fell in 97% of those winters. The last 32°F night of spring typically comes 33 days after the last snow.

ZIP 61068 is 2 miles from Rochelle, IL, which stands at 775 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 61068 in zone 5b, the band where the coldest night of the year averaged -15 to -10°F (-26.1 to -23.3°C) over 1991–2020; a zone describes winter lows, not frost dates.