Frost Dates for 61326 — Granville, Illinois

Half of springs at Hennepin Wtr Trmt Plt, IL see their last 32°F night by April 24; only one in ten is past it by April 11, and one in ten still has one after May 10. Planting tender crops after May 1 leaves a 30% risk of a frost on them, after May 4 20%, and after May 10 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 17 in half of years, as early as October 1 one year in ten, and holds off past October 29 one year in ten. A hard freeze of 28°F follows 10 days later, around October 27; in spring the one-in-ten date for 28°F is April 29, 11 days before the 32°F one. The freeze-free season lasts 174 days in a typical year, shorter than at 76% of the 158 Illinois stations; it reaches 194 days one year in ten and falls short of 154 one year in ten. On average 140 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 11 days longer, to about May 5, and return around October 7. Severe cold of 16°F or below comes every winter, usually between November 27 and March 15.

July is the warmest month at Hennepin Wtr Trmt Plt, IL, averaging 86°F by day and 63°F at night; January is the coldest at 33°F and 15°F. A freezing night is all but certain in every month from October to April (a 90% chance or more). From June to September the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 32% of years.

Warmth for growing adds up to 3,355 growing degree days a year (base 50°F), fewer than at 59% of the 158 Illinois stations. 35% of them (1,181) have built up by the end of June, and July adds the most, 767.

The nearest other station, Peru, IL, 9 miles northeast of Granville and 160 feet higher, has the same 50% last-frost date, a first frost 1 day later (October 18), a season 2 days longer.

The first measurable snow (0.1 inch or more) in Granville usually arrives around December 1, and the last of the season around March 3. Those are the middle dates across the winters of 1991–2020 at Hennepin Wtr Trmt Plt, IL, 5.3 miles away: half of years saw snow earlier, half later. Every one of those winters saw snow. The last 32°F night of spring typically comes 52 days after the last snow.

ZIP 61326 is 5 miles from Hennepin Wtr Trmt Plt, IL, which stands at 460 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 61326 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.