USDA Hardiness Zone 5b
Frost Dates for 61071 — Rock Falls, Illinois
NOAA 1991–2020 normals from Dixon 1W, IL (660 ft), 11 miles northeast.
Updated
In Rock Falls, the last spring frost (32°F) is around April 21 in half of years and has passed by May 5 in nine years out of ten. The first fall frost comes around October 19, as early as October 4 one year in ten, leaving a typical freeze-free season of 180 days (NOAA, Dixon 1W, IL).
- Last spring frost
- April 21
- First fall frost
- October 19
- Growing season
- 180 days
- Hardiness zone
- 5b
50% probability
50% probability
freeze-free, 50%
-15 to -10°F (-26.1 to -23.3°C) coldest night
- First snow
- December 1
- Last snow
- March 16
- Winters with snow
- 96%
- Snow per year
- 28.8"
median, 1991–2020
median, 1991–2020
24 of 25 observed
NOAA normal
Frost risk by date in Rock Falls
Half of springs at Dixon 1W, IL see their last 32°F night by April 21; only one in ten is past it by April 7, and one in ten still has one after May 5. Planting tender crops after April 28 leaves a 30% risk of a frost on them, after May 1 20%, and after May 5 10%. The 14 days between the even-odds date and the one-in-ten date is narrower than at 82% of the 158 Illinois stations behind this site's ZIP pages.
In fall the first 32°F night comes by October 19 in half of years, as early as October 4 one year in ten, and holds off past October 30 one year in ten. A hard freeze of 28°F follows 11 days later, around October 30; in spring the one-in-ten date for 28°F is April 26, 9 days before the 32°F one. The freeze-free season lasts 180 days in a typical year, shorter than at 60% of the 158 Illinois stations; it reaches 200 days one year in ten and falls short of 158 one year in ten. On average 138 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 2, and return around October 9. Severe cold of 16°F or below comes every winter, usually between November 26 and March 11.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Apr 18 | Apr 22 | Apr 26 | Apr 29 | May 2 | May 4 | May 7 | May 11 | May 16 |
| 32°F | Apr 7 | Apr 11 | Apr 15 | Apr 18 | Apr 21 | Apr 24 | Apr 28 | May 1 | May 5 |
| 28°F | Mar 27 | Apr 2 | Apr 5 | Apr 8 | Apr 10 | Apr 13 | Apr 16 | Apr 21 | Apr 26 |
| 24°F | Mar 15 | Mar 20 | Mar 25 | Mar 29 | Apr 1 | Apr 3 | Apr 6 | Apr 9 | Apr 14 |
| 20°F | Mar 5 | Mar 10 | Mar 14 | Mar 17 | Mar 19 | Mar 22 | Mar 27 | Mar 31 | Apr 3 |
| 16°F | Feb 26 | Mar 2 | Mar 5 | Mar 8 | Mar 11 | Mar 14 | Mar 17 | Mar 20 | Mar 25 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 24 | Sep 29 | Oct 3 | Oct 5 | Oct 9 | Oct 12 | Oct 15 | Oct 18 | Oct 22 |
| 32°F | Oct 4 | Oct 10 | Oct 14 | Oct 16 | Oct 19 | Oct 21 | Oct 24 | Oct 26 | Oct 30 |
| 28°F | Oct 17 | Oct 22 | Oct 25 | Oct 27 | Oct 30 | Nov 1 | Nov 3 | Nov 7 | Nov 12 |
| 24°F | Oct 28 | Nov 1 | Nov 3 | Nov 6 | Nov 8 | Nov 11 | Nov 14 | Nov 18 | Nov 22 |
| 20°F | Nov 4 | Nov 8 | Nov 11 | Nov 15 | Nov 17 | Nov 20 | Nov 23 | Nov 27 | Dec 3 |
| 16°F | Nov 10 | Nov 15 | Nov 19 | Nov 23 | Nov 26 | Nov 29 | Dec 1 | Dec 6 | Dec 13 |
Freeze probabilities 1991–2020 at Dixon 1W, IL, from NOAA NCEI U.S. Climate Normals. Where a temperature is reached in fewer than 99.5% of years, the dates describe only the years that reach it. Not a forecast.
Frost risk on any date in 61071 →Compare Rock Falls with another place →
Weather by month in Rock Falls
July is the warmest month at Dixon 1W, IL, averaging 83°F by day and 64°F at night; January is the coldest at 29°F and 14°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 21% of years.
Warmth for growing adds up to 3,126 growing degree days a year (base 50°F), fewer than at 75% of the 158 Illinois stations. 35% of them (1,091) have built up by the end of June, and July adds the most, 728. Precipitation totals 40.6 inches a year, most in June (5.6") and least in February (1.8"); May to September bring 56% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 29 | 14 | 2.0 | 100% | 29 | 0 |
| Feb | 34 | 17 | 1.8 | 100% | 26 | 1 |
| Mar | 46 | 28 | 2.6 | 100% | 22 | 26 |
| Apr | 60 | 39 | 4.0 | 97% | 8 | 107 |
| May | 71 | 51 | 4.8 | 21% | 1 | 348 |
| Jun | 80 | 61 | 5.6 | 0% | 0 | 607 |
| Jul | 83 | 64 | 4.3 | 0% | 0 | 728 |
| Aug | 81 | 62 | 4.2 | 0% | 0 | 679 |
| Sep | 75 | 54 | 3.7 | 6% | <1 | 441 |
| Oct | 63 | 42 | 3.0 | 91% | 6 | 160 |
| Nov | 48 | 31 | 2.4 | 100% | 19 | 25 |
| Dec | 35 | 20 | 2.2 | 100% | 27 | 2 |
Monthly normals 1991–2020 at Dixon 1W, IL (660 ft), NOAA NCEI. "32°F night": chance of at least one in the month. GDD: growing degree days, base 50°F.
Compared with the next station
The nearest other station, Morrison, IL, 14 miles west of Rock Falls, has a last frost 5 days later (April 26), a first frost 6 days earlier (October 13), a season 13 days shorter.
When it snows in Rock Falls, Illinois
The first measurable snow (0.1 inch or more) in Rock Falls usually arrives around December 1, and the last of the season around March 16. Those are the middle dates across the winters of 1991–2020 at Rock Falls 3 NE, IL, 3.8 miles away: half of years saw snow earlier, half later. Snow fell in 96% of those winters. The last 32°F night of spring typically comes 36 days after the last snow.
Planting calendar for 61071
| When | What to do |
|---|---|
| February 10 – February 24 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| February 24 – March 10 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| March 24 – April 7 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| April 21 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by July 27 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by October 5 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| October 19 onward | Plant garlic, mulch beds, lift tender bulbsGarlic wants a cold spell; bare soil loses structure over winter. |
The weeks before and after the 50% dates are general rules of thumb, not NOAA figures; a seed packet gives the timing for each variety.
Where these figures come from
ZIP 61071 is 11 miles from Dixon 1W, IL, which stands at 660 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 3 other ZIP codes share the station; its figures are presented in full for 61021 (Dixon). The 2023 USDA Plant Hardiness Zone Map lists ZIP 61071 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.
Hardiness zone and temperature range: USDA Plant Hardiness Zone Map 2023 (USDA-ARS, Oregon State University), ZIP-code listing, unchanged. °C converted from °F by this site.
Thirty-year averages, not a forecast: check the forecast before planting out. How stations are matched and which pages are offered to search engines: methodology.