USDA Hardiness Zone 7a
Frost Dates for 62946 — Harrisburg, Illinois
NOAA 1991–2020 normals from Harrisburg, IL (365 ft), 1 miles northeast.
Updated
In Harrisburg, the last spring frost (32°F) is around April 7 in half of years and has passed by April 25 in nine years out of ten. The first fall frost comes around October 26, as early as October 10 one year in ten, leaving a typical freeze-free season of 202 days (NOAA, Harrisburg, IL).
- Last spring frost
- April 7
- First fall frost
- October 26
- Growing season
- 202 days
- Hardiness zone
- 7a
50% probability
50% probability
freeze-free, 50%
0 to 5°F (-17.8 to -15.0°C) coldest night
- First snow
- January 21
- Last snow
- January 30
- Winters with snow
- 63%
- Snow per year
- —
median, 1991–2020
median, 1991–2020
12 of 19 observed
NOAA normal
Frost risk by date in Harrisburg
Half of springs at Harrisburg, IL see their last 32°F night by April 7; only one in ten is past it by March 21, and one in ten still has one after April 25. Planting tender crops after April 14 leaves a 30% risk of a frost on them, after April 18 20%, and after April 25 10%. The 18 days between the even-odds date and the one-in-ten date is wider than at 92% of the 158 Illinois stations behind this site's ZIP pages.
In fall the first 32°F night comes by October 26 in half of years, as early as October 10 one year in ten, and holds off past November 8 one year in ten. A hard freeze of 28°F follows 11 days later, around November 6; in spring the one-in-ten date for 28°F is April 12, 13 days before the 32°F one. The freeze-free season lasts 202 days in a typical year, longer than at 90% of the 158 Illinois stations; it reaches 224 days one year in ten and falls short of 180 one year in ten. On average 95 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 12 days longer, to about April 19, and return around October 16. Severe cold of 16°F or below comes every winter, usually between December 16 and February 19.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Apr 3 | Apr 9 | Apr 13 | Apr 16 | Apr 19 | Apr 23 | Apr 26 | Apr 30 | May 5 |
| 32°F | Mar 21 | Mar 28 | Mar 31 | Apr 3 | Apr 7 | Apr 10 | Apr 14 | Apr 18 | Apr 25 |
| 28°F | Mar 7 | Mar 14 | Mar 18 | Mar 22 | Mar 26 | Mar 29 | Apr 1 | Apr 5 | Apr 12 |
| 24°F | Feb 21 | Mar 1 | Mar 5 | Mar 8 | Mar 12 | Mar 16 | Mar 19 | Mar 23 | Mar 30 |
| 20°F | Feb 8 | Feb 15 | Feb 22 | Feb 28 | Mar 2 | Mar 5 | Mar 8 | Mar 12 | Mar 17 |
| 16°F | Jan 27 | Feb 3 | Feb 8 | Feb 13 | Feb 19 | Feb 25 | Mar 1 | Mar 4 | Mar 11 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Oct 1 | Oct 7 | Oct 11 | Oct 13 | Oct 16 | Oct 18 | Oct 21 | Oct 24 | Oct 28 |
| 32°F | Oct 10 | Oct 16 | Oct 21 | Oct 23 | Oct 26 | Oct 28 | Oct 31 | Nov 3 | Nov 8 |
| 28°F | Oct 23 | Oct 28 | Nov 1 | Nov 3 | Nov 6 | Nov 10 | Nov 13 | Nov 18 | Nov 25 |
| 24°F | Nov 3 | Nov 8 | Nov 12 | Nov 15 | Nov 19 | Nov 23 | Nov 28 | Dec 2 | Dec 9 |
| 20°F | Nov 13 | Nov 19 | Nov 23 | Nov 28 | Dec 2 | Dec 6 | Dec 11 | Dec 16 | Dec 23 |
| 16°F | Nov 23 | Dec 1 | Dec 5 | Dec 11 | Dec 16 | Dec 21 | Dec 25 | Dec 30 | Jan 6 |
Freeze probabilities 1991–2020 at Harrisburg, 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 62946 →Compare Harrisburg with another place →
Weather by month in Harrisburg
July is the warmest month at Harrisburg, IL, averaging 89°F by day and 68°F at night; January is the coldest at 43°F and 24°F. A freezing night is all but certain in every month from November to March (a 90% chance or more). From May to September the chance of a 32°F night stays under 10% each month. In spring, April still brings one in 67% of years.
Warmth for growing adds up to 4,395 growing degree days a year (base 50°F), more than at 97% of the 158 Illinois stations. 38% of them (1,692) have built up by the end of June, and July adds the most, 891. Precipitation totals 47.7 inches a year, most in April (5.3") and least in February (3.1"); May to September bring 41% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 43 | 24 | 3.8 | 100% | 25 | 11 |
| Feb | 48 | 28 | 3.1 | 100% | 20 | 17 |
| Mar | 58 | 36 | 4.9 | 99% | 13 | 94 |
| Apr | 69 | 46 | 5.3 | 67% | 3 | 266 |
| May | 78 | 57 | 4.3 | 4% | 0 | 538 |
| Jun | 86 | 65 | 4.9 | 0% | 0 | 766 |
| Jul | 89 | 68 | 3.5 | 0% | 0 | 891 |
| Aug | 88 | 66 | 3.6 | 0% | 0 | 834 |
| Sep | 82 | 57 | 3.1 | 3% | <1 | 596 |
| Oct | 71 | 45 | 3.8 | 69% | 3 | 285 |
| Nov | 57 | 36 | 4.0 | 99% | 12 | 82 |
| Dec | 47 | 29 | 3.4 | 100% | 21 | 16 |
Monthly normals 1991–2020 at Harrisburg, IL (365 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, Dixon Springs Agric Ctr, IL, 21 miles south of Harrisburg and 162 feet higher, has a last frost 7 days later (April 14), a first frost 5 days earlier (October 21), a season 13 days shorter.
When it snows in Harrisburg, Illinois
The first measurable snow (0.1 inch or more) in Harrisburg usually arrives around January 21, and the last of the season around January 30. Those are the middle dates across the winters of 1991–2020 at Harrisburg, IL, 1.4 miles away: half of years saw snow earlier, half later. Snow fell in 63% of those winters. The last 32°F night of spring typically comes 67 days after the last snow.
Planting calendar for 62946
| When | What to do |
|---|---|
| January 27 – February 10 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| February 10 – February 24 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| March 10 – March 24 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| April 7 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by August 3 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by October 12 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| October 26 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 62946 is 1 mile from Harrisburg, IL, which stands at 365 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 3 other ZIP codes share the station. The 2023 USDA Plant Hardiness Zone Map lists ZIP 62946 in zone 7a, the band where the coldest night of the year averaged 0 to 5°F (-17.8 to -15.0°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.