Frost Dates for 61201 — Rock Island, Illinois

Half of springs at Rock Island L&D 15, IL see their last 32°F night by April 19; only one in ten is past it by April 6, and one in ten still has one after May 4. Planting tender crops after April 24 leaves a 30% risk of a frost on them, after April 29 20%, and after May 4 10%. The 15 days between the even-odds date and the one-in-ten date is narrower than at 54% of the 158 Illinois stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 22 in half of years, as early as October 7 one year in ten, and holds off past November 2 one year in ten. A hard freeze of 28°F follows 9 days later, around October 31; in spring the one-in-ten date for 28°F is April 23, 11 days before the 32°F one. The freeze-free season lasts 184 days in a typical year, shorter than at 51% of the 158 Illinois stations; it reaches 203 days one year in ten and falls short of 164 one year in ten. On average 118 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 April 30, and return around October 12. Severe cold of 16°F or below comes every winter, usually between November 27 and March 12.

July is the warmest month at Rock Island L&D 15, IL, averaging 84°F by day and 65°F at night; January is the coldest at 31°F and 13°F. A freezing night is all but certain in every month from November 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 16% of years.

Warmth for growing adds up to 3,293 growing degree days a year (base 50°F), fewer than at 65% of the 158 Illinois stations. 35% of them (1,150) have built up by the end of June, and July adds the most, 756. Precipitation totals 38.7 inches a year, most in June (5.2") and least in January (1.5"); May to September bring 56% of it.

The nearest other station, Moline Quad City International Airport, IL, 3 miles southeast of Rock Island, has a last frost 5 days later (April 24), a first frost 4 days earlier (October 18), a season 8 days shorter.

The first measurable snow (0.1 inch or more) in Rock Island usually arrives around November 24, and the last of the season around March 24. Those are the middle dates across the winters of 1991–2020 at Moline Quad City International Airport, IL, 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 26 days after the last snow.

ZIP 61201 is 2 miles from Rock Island L&D 15, IL, which stands at 568 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 6 other ZIP codes share the station; its figures are presented in full for 52722 (Bettendorf). The 2023 USDA Plant Hardiness Zone Map lists ZIP 61201 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.