USDA Hardiness Zone 6a
Frost Dates for 60623 — Chicago, Illinois
NOAA 1991–2020 normals from Chicago Midway Airport, IL (612 ft), 5 miles south.
Updated
In Chicago, the last spring frost (32°F) is around April 11 in half of years and has passed by April 27 in nine years out of ten. The first fall frost comes around October 31, as early as October 20 one year in ten, leaving a typical freeze-free season of 201 days (NOAA, Chicago Midway Airport, IL).
- Last spring frost
- April 11
- First fall frost
- October 31
- Growing season
- 201 days
- Hardiness zone
- 6a
50% probability
50% probability
freeze-free, 50%
-10 to -5°F (-23.3 to -20.6°C) coldest night
- First snow
- November 21
- Last snow
- April 1
- Winters with snow
- 100%
- Snow per year
- 38.8"
median, 1991–2020
median, 1991–2020
30 of 30 observed
NOAA normal
Frost risk by date in Chicago
Half of springs at Chicago Midway Airport, IL see their last 32°F night by April 11; only one in ten is past it by March 30, and one in ten still has one after April 27. Planting tender crops after April 17 leaves a 30% risk of a frost on them, after April 21 20%, and after April 27 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 31 in half of years, as early as October 20 one year in ten, and holds off past November 14 one year in ten. A hard freeze of 28°F follows 11 days later, around November 11; in spring the one-in-ten date for 28°F is April 14, 13 days before the 32°F one. The freeze-free season lasts 201 days in a typical year, longer than at 88% of the 158 Illinois stations; it reaches 222 days one year in ten and falls short of 181 one year in ten. On average 106 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 23, and return around October 21. Severe cold of 16°F or below comes every winter, usually between December 7 and March 3.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Apr 9 | Apr 15 | Apr 17 | Apr 20 | Apr 23 | Apr 26 | Apr 30 | May 3 | May 8 |
| 32°F | Mar 30 | Apr 2 | Apr 5 | Apr 8 | Apr 11 | Apr 14 | Apr 17 | Apr 21 | Apr 27 |
| 28°F | Mar 15 | Mar 21 | Mar 26 | Mar 29 | Apr 1 | Apr 3 | Apr 6 | Apr 9 | Apr 14 |
| 24°F | Mar 5 | Mar 11 | Mar 14 | Mar 17 | Mar 20 | Mar 24 | Mar 27 | Mar 31 | Apr 3 |
| 20°F | Feb 24 | Mar 1 | Mar 5 | Mar 8 | Mar 11 | Mar 14 | Mar 17 | Mar 21 | Mar 26 |
| 16°F | Feb 13 | Feb 21 | Feb 26 | Mar 1 | Mar 3 | Mar 6 | Mar 10 | Mar 13 | Mar 17 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Oct 8 | Oct 13 | Oct 17 | Oct 19 | Oct 21 | Oct 24 | Oct 26 | Oct 28 | Nov 1 |
| 32°F | Oct 20 | Oct 23 | Oct 26 | Oct 29 | Oct 31 | Nov 2 | Nov 5 | Nov 9 | Nov 14 |
| 28°F | Oct 31 | Nov 2 | Nov 5 | Nov 8 | Nov 11 | Nov 14 | Nov 17 | Nov 21 | Nov 26 |
| 24°F | Nov 7 | Nov 11 | Nov 14 | Nov 17 | Nov 20 | Nov 24 | Nov 26 | Dec 1 | Dec 5 |
| 20°F | Nov 13 | Nov 18 | Nov 22 | Nov 26 | Nov 29 | Dec 1 | Dec 5 | Dec 10 | Dec 18 |
| 16°F | Nov 22 | Nov 27 | Dec 1 | Dec 3 | Dec 7 | Dec 11 | Dec 15 | Dec 21 | Dec 26 |
Freeze probabilities 1991–2020 at Chicago Midway Airport, 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 60623 →Compare Chicago with another place →
Weather by month in Chicago
July is the warmest month at Chicago Midway Airport, IL, averaging 85°F by day and 68°F at night; January is the coldest at 33°F and 19°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 84% of years.
Warmth for growing adds up to 3,526 growing degree days a year (base 50°F), more than at 53% of the 158 Illinois stations. 33% of them (1,177) have built up by the end of June, and July adds the most, 817. Precipitation totals 34.7 inches a year, most in May (4.1") and least in January (1.5"); May to September bring 53% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 33 | 19 | 1.5 | 100% | 27 | 1 |
| Feb | 37 | 23 | 1.5 | 100% | 23 | 4 |
| Mar | 48 | 32 | 1.9 | 100% | 18 | 34 |
| Apr | 60 | 41 | 3.6 | 84% | 3 | 123 |
| May | 71 | 52 | 4.1 | 5% | 0 | 367 |
| Jun | 81 | 62 | 4.0 | 0% | 0 | 648 |
| Jul | 85 | 68 | 3.6 | 0% | 0 | 817 |
| Aug | 83 | 66 | 4.0 | 0% | 0 | 761 |
| Sep | 76 | 59 | 2.8 | 0% | 0 | 527 |
| Oct | 63 | 47 | 3.5 | 52% | 1 | 205 |
| Nov | 49 | 35 | 2.4 | 100% | 11 | 35 |
| Dec | 38 | 25 | 1.8 | 100% | 24 | 4 |
Monthly normals 1991–2020 at Chicago Midway Airport, IL (612 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, Chicago Northerly Is, IL, 6 miles east of Chicago, has a last frost 1 day earlier (April 10), a first frost 5 days later (November 5), a season 7 days longer.
When it snows in Chicago, Illinois
The first measurable snow (0.1 inch or more) in Chicago usually arrives around November 21, and the last of the season around April 1. Those are the middle dates across the winters of 1991–2020 at Chicago Midway Airport 3SW, IL, 8.4 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 10 days after the last snow.
Planting calendar for 60623
| When | What to do |
|---|---|
| January 31 – February 14 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| February 14 – February 28 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| March 14 – March 28 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| April 11 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by August 8 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by October 17 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| October 31 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 60623 is 5 miles from Chicago Midway Airport, IL, which stands at 612 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 22 other ZIP codes share the station; its figures are presented in full for 60629 (Chicago). The 2023 USDA Plant Hardiness Zone Map lists ZIP 60623 in zone 6a, the band where the coldest night of the year averaged -10 to -5°F (-23.3 to -20.6°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.