Crystal Lake, Illinois climate: Normal weather by month, frost dates and records
Crystal Lake's normal year runs from 14°F January nights to 84°F July afternoons, with 39.4 inches of precipitation and 35 inches of snow a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 9.5°C, January lows of −10°C, July highs of 29°C, 999 mm of precipitation a year.
- NOAA stationCrystal Lake (4 mi NW)
- Station IDUSC00112048
- Location42.26°N 88.40°W
- Elevation940 ft (287 m)
- From the center4 miles
- Population41,513
On October 23, the normal high in Crystal Lake is 58°F and the normal low 40°F, and the chance of measurable rain or snow is 30%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Crystal Lake.
- Jan 32° 14°
- Feb 35° 16°
- Mar 47° 26°
- Apr 59° 37°
- May 71° 48°
- Jun 80° 58°
- Jul 84° 63°
- Aug 82° 61°
- Sep 74° 52°
- Oct 62° 42°
- Nov 48° 31°
- Dec 36° 20°
Each month: normal high (large) and low, °F. Fill: the month's normal mean, colder blue to hotter red.
What is the weather like in Crystal Lake each month?
July is the warmest month, with normal highs of 84°F; January the coldest, with normal lows of 14°F. The most precipitation falls in June (5.26 in), the least in February (1.84 in).
| Month | High | Low | Mean | Precip. | Snow | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|---|
| January | 32°F | 14°F | 22.9°F | 1.97 | 10.0 | 9 | <1 | 29 | 9 h 20 min |
| February | 35°F | 16°F | 25.8°F | 1.84 | 9.0 | 8 | <1 | 27 | 10 h 30 min |
| March | 47°F | 26°F | 36.6°F | 2.51 | 4.4 | 8 | <1 | 22 | 11 h 50 min |
| April | 59°F | 37°F | 48.0°F | 3.76 | 1.2 | 11 | <1 | 9 | 13 h 20 min |
| May | 71°F | 48°F | 59.6°F | 4.98 | 0.0 | 12 | 2 | <1 | 14 h 30 min |
| June | 80°F | 58°F | 69.4°F | 5.26 | 0.0 | 10 | 6 | <1 | 15 h 10 min |
| July | 84°F | 63°F | 73.3°F | 3.90 | 0.0 | 9 | 8 | <1 | 15 h |
| August | 82°F | 61°F | 71.6°F | 3.81 | 0.0 | 9 | 4 | <1 | 14 h |
| September | 74°F | 52°F | 63.4°F | 3.54 | 0.0 | 8 | 3 | <1 | 12 h 30 min |
| October | 62°F | 42°F | 52.2°F | 3.20 | 0.2 | 9 | <1 | 3 | 11 h 10 min |
| November | 48°F | 31°F | 39.0°F | 2.48 | 1.6 | 9 | <1 | 18 | 9 h 50 min |
| December | 36°F | 20°F | 28.0°F | 2.10 | 8.7 | 9 | <1 | 27 | 9 h 10 min |
| Year (annual) | 59°F | 39°F | 49.1°F | 39.35 | 35.1 | 110 | 22 | 136 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. | Snow |
|---|---|---|---|---|---|
| January | 0°C | −10°C | −5.1°C | 50 mm | 25 cm |
| February | 2°C | −9°C | −3.4°C | 47 mm | 23 cm |
| March | 8°C | −3°C | 2.6°C | 64 mm | 11 cm |
| April | 15°C | 3°C | 8.9°C | 96 mm | 3 cm |
| May | 22°C | 9°C | 15.3°C | 126 mm | 0 cm |
| June | 27°C | 15°C | 20.8°C | 134 mm | 0 cm |
| July | 29°C | 17°C | 22.9°C | 99 mm | 0 cm |
| August | 28°C | 16°C | 22.0°C | 97 mm | 0 cm |
| September | 24°C | 11°C | 17.4°C | 90 mm | 0 cm |
| October | 17°C | 6°C | 11.2°C | 81 mm | 1 cm |
| November | 9°C | −1°C | 3.9°C | 63 mm | 4 cm |
| December | 2°C | −6°C | −2.2°C | 53 mm | 22 cm |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00112048; annual normals. Wet days: 0.01 inch or more; 90°F days and freezing nights: NOAA's day counts. Daylight: sunrise to sunset on the 15th, computed from the latitude.
When is the best weather to visit Crystal Lake?
Normal highs sit between 65°F and 85°F in May, June, July, August and September. Of those, September has the fewest days with rain (8).
That is a measurement, not a recommendation: it counts the months whose normal afternoon high sits between 65°F and 85°F, where a light layer is enough by day.
Source: NOAA NCEI 1991-2020 monthly normals, station USC00112048.
When is the last frost in Crystal Lake?
In Crystal Lake, the last spring frost (32°F) comes after April 25 in half of years and after May 9 in one year in ten; the first autumn frost comes before October 22 in half of years and before October 7 in one year in ten.
Frost-free in half of yearsFrost in 1 to 9 years out of 10Frost most years
- Last spring frost, half of years after
- April 251 year in 10 after May 9; 9 in 10 after April 11
- First autumn frost, half of years before
- October 221 year in 10 before October 7; 9 in 10 before November 4
NOAA puts the median frost-free season at 179 days, and the season without a hard freeze (28°F) at 202 days.
A hard freeze (28°F) comes after April 12 in half of springs and before November 1 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Crystal Lake in zone 5b across its 2 ZIP code areas (5b in 60014, the largest).
Frost dates for every NOAA station in Illinois · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USC00112048; USDA 2023 Plant Hardiness Zone Map, ZIP listings: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed October 8, 2026. A 10% date means one year in ten has a frost after it in spring or before it in autumn.
What hardiness zone is each Crystal Lake ZIP code in?
The USDA's 2023 map gives each ZIP code area one zone. Crystal Lake's 2 ZIP code areas are all in zone 5b. Each ZIP's frost dates are in the frost tool.
Source: USDA 2023 Plant Hardiness Zone Map, ZIP listings: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed October 8, 2026; ZIP areas in the place: Census Bureau 2020 ZCTA-to-place relationship file. A ZIP area counts when at least a tenth of its land (and 0.5 km²) lies in the place.
How hot and how cold does it get in Crystal Lake?
In a normal year in Crystal Lake, 22 days a year reach 90°F (1 of them 100°F or more), 136 nights fall to 32°F or colder and 110 days bring measurable precipitation.
- Days at 90°F or more
- 22a normal year
- Days at 100°F or more
- 1a normal year
- Nights at 32°F or colder
- 136a normal year
- Days that stay below freezing
- 41high of 32°F or less
- Days with 0.01 inch of precipitation
- 110a normal year
- Days with 1 inch of snow or more
- 12a normal year
Source: NOAA NCEI 1991-2020 annual normals, station USC00112048.
How sunny is Crystal Lake?
Over a year 72% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around Crystal Lake, 3.9 kWh per square metre a day. July is the sunniest month (80%) and December the cloudiest (61%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 63% | 1.7 |
| February | 67% | 2.6 |
| March | 67% | 3.6 |
| April | 69% | 4.7 |
| May | 70% | 5.5 |
| June | 76% | 6.1 |
| July | 80% | 6.3 |
| August | 79% | 5.4 |
| September | 78% | 4.3 |
| October | 69% | 2.8 |
| November | 66% | 1.9 |
| December | 61% | 1.4 |
Source: NASA POWER solar climatology, 2001-2020 (CERES SYN1deg). Satellite-based, for the 1-degree cell (about 100 km across) around the station, so it describes the area rather than the airport.
How much heating and cooling does Crystal Lake need?
A normal year in Crystal Lake brings 6,520 heating degree days, 21% more than the median U.S. place (5,373), and 771 cooling degree days, 15% fewer than the median (908). Seven months need 300 or more heating degree days, a monthly mean of about 55°F or colder. For gardens and crops, NOAA counts 2,948 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,306 | 0 |
| February | 1,099 | 0 |
| March | 883 | 2 |
| April | 513 | 2 |
| May | 219 | 51 |
| June | 31 | 162 |
| July | 5 | 261 |
| August | 11 | 215 |
| September | 121 | 73 |
| October | 404 | 5 |
| November | 780 | 0 |
| December | 1,148 | 0 |
| Year (annual) | 6,520 | 771 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00112048. A degree day is one degree of a day's mean temperature below 65°F (heating) or above it (cooling); utilities use them to estimate energy use.
How does Crystal Lake's climate compare?
Crystal Lake is warmer than 19 of the other 143 places with their own NOAA record in Illinois, and wetter than 58. Across the 7,247 U.S. stations with normals, its annual mean of 49.1°F is warmer than 36%.
In the Köppen classification computed from these normals, Crystal Lake is Dfa: continental, no dry season, hot summer. What the classes mean.
Places with the most similar year elsewhere
Measured month by month on the normal high, low and precipitation, among places of 20,000 or more people in other states:
Source: NOAA NCEI 1991-2020 normals for every station PlainClimate covers. Similarity: the root-mean-square difference of the 36 monthly figures, precipitation weighted so an inch counts like 6°F.
Which places near Crystal Lake share this climate record?
6 places have no NOAA station with 1991-2020 normals of their own, and this station is the nearest full record. A place's own climate can differ from these figures, by several degrees where it sits much higher or lower than the station, nearer the coast, or inside a large city's heat; for the larger places the next nearest records are named with their yearly mean, so the spread around them is visible, and places of 50,000 or more have their own page with NOAA's gridded normals.
- Lake in the Hills, IL28,706 people · 7 mi SE
- Huntley, IL28,495 people · 7 mi S
- Woodstock, IL25,892 people · 4 mi NW
- Lakewood, IL4,287 people · 3 mi S
- Bull Valley, IL1,136 people · 5 mi N
- Ridgefield, IL218 people · 2 mi E
Source: Census Bureau 2024 Gazetteer (place centers) and Vintage 2024 population estimates. Distance and direction from the station to each place's center.
Questions about Crystal Lake's climate
What is the coldest month in Crystal Lake?
January, with a normal high of 32°F and a normal low of 14°F. The warmest is July (84°F by day, 63°F at night).
Does it snow in Crystal Lake?
Yes: 35 inches in a normal year, falling on 22 days with 0.1 inch or more, the most in January (10.0 inches).
What is the rainiest month in Crystal Lake?
June, with 5.26 in of precipitation in a normal year; the driest is February with 1.84 in.
What plant hardiness zone is Crystal Lake in?
The USDA's 2023 map puts Crystal Lake in zone 5b across its 2 ZIP code areas (5b in 60014, the largest).
How late can frost come in Crystal Lake?
In half of years the last 32°F night comes after April 25; in one year in ten it comes after May 9. Waiting until May 9 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Illinois climateThe statewide normals and every place in the state
- McHenry W.G. Stratton Lock and Dam, IL8 miles from this station, 48.6°F a year
- Marengo, IL11 miles from this station, 48.2°F a year
- Elgin, IL15 miles from this station, 49.0°F a year
- Barrington, IL16 miles from this station, 48.0°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made