Mount Vernon, Illinois climate: Normal weather by month, frost dates and records
Mount Vernon's normal year runs from 22°F January nights to 86°F July afternoons, with 45.0 inches of precipitation and 10 inches of snow a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 12.5°C, January lows of −6°C, July highs of 30°C, 1,142 mm of precipitation a year.
- NOAA stationMount Vernon (3 mi NE)
- Station IDUSC00115943
- Location38.35°N 88.85°W
- Elevation490 ft (149 m)
- From the center4 miles
- Population14,162
On October 14, the normal high in Mount Vernon is 69°F and the normal low 45°F, and the chance of measurable rain or snow is 28%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Mount Vernon.
- Jan 39° 22°
- Feb 44° 25°
- Mar 54° 34°
- Apr 65° 44°
- May 74° 55°
- Jun 82° 64°
- Jul 86° 67°
- Aug 85° 65°
- Sep 79° 57°
- Oct 68° 45°
- Nov 54° 34°
- Dec 43° 26°
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 Mount Vernon each month?
July is the warmest month, with normal highs of 86°F; January the coldest, with normal lows of 22°F. The most precipitation falls in May (5.06 in), the least in January (2.60 in).
| Month | High | Low | Mean | Precip. | Snow | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|---|
| January | 39°F | 22°F | 30.1°F | 2.60 | 3.2 | 9 | <1 | 26 | 9 h 50 min |
| February | 44°F | 25°F | 34.3°F | 2.62 | 3.1 | 8 | <1 | 22 | 10 h 50 min |
| March | 54°F | 34°F | 43.7°F | 4.00 | 1.0 | 11 | <1 | 15 | 11 h 50 min |
| April | 65°F | 44°F | 54.5°F | 4.96 | 0.0 | 11 | <1 | 4 | 13 h 10 min |
| May | 74°F | 55°F | 64.4°F | 5.06 | 0.0 | 13 | <1 | <1 | 14 h 10 min |
| June | 82°F | 64°F | 73.1°F | 4.84 | 0.0 | 10 | 4 | <1 | 14 h 50 min |
| July | 86°F | 67°F | 76.5°F | 3.78 | 0.0 | 9 | 8 | <1 | 14 h 40 min |
| August | 85°F | 65°F | 74.8°F | 3.33 | 0.0 | 8 | 7 | <1 | 13 h 40 min |
| September | 79°F | 57°F | 67.7°F | 3.37 | 0.0 | 8 | 2 | <1 | 12 h 30 min |
| October | 68°F | 45°F | 56.1°F | 3.53 | 0.2 | 9 | <1 | 4 | 11 h 20 min |
| November | 54°F | 34°F | 44.0°F | 3.99 | 0.4 | 9 | <1 | 14 | 10 h 10 min |
| December | 43°F | 26°F | 34.5°F | 2.89 | 2.5 | 10 | <1 | 24 | 9 h 30 min |
| Year (annual) | 64°F | 45°F | 54.5°F | 44.97 | 10.4 | 115 | 21 | 108 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. | Snow |
|---|---|---|---|---|---|
| January | 4°C | −6°C | −1.1°C | 66 mm | 8 cm |
| February | 6°C | −4°C | 1.3°C | 67 mm | 8 cm |
| March | 12°C | 1°C | 6.5°C | 102 mm | 3 cm |
| April | 18°C | 7°C | 12.5°C | 126 mm | 0 cm |
| May | 23°C | 13°C | 18.0°C | 129 mm | 0 cm |
| June | 28°C | 18°C | 22.8°C | 123 mm | 0 cm |
| July | 30°C | 20°C | 24.7°C | 96 mm | 0 cm |
| August | 29°C | 18°C | 23.8°C | 85 mm | 0 cm |
| September | 26°C | 14°C | 19.8°C | 86 mm | 0 cm |
| October | 20°C | 7°C | 13.4°C | 90 mm | 1 cm |
| November | 12°C | 1°C | 6.7°C | 101 mm | 1 cm |
| December | 6°C | −3°C | 1.4°C | 73 mm | 6 cm |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00115943; 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 Mount Vernon?
Normal highs sit between 65°F and 85°F in May, June, August, September and October. 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 USC00115943.
When is the last frost in Mount Vernon?
In Mount Vernon, the last spring frost (32°F) comes after April 11 in half of years and after April 26 in one year in ten; the first autumn frost comes before October 22 in half of years and before October 9 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 111 year in 10 after April 26; 9 in 10 after March 30
- First autumn frost, half of years before
- October 221 year in 10 before October 9; 9 in 10 before November 1
NOAA puts the median frost-free season at 193 days, and the season without a hard freeze (28°F) at 214 days.
A hard freeze (28°F) comes after April 1 in half of springs and before November 1 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Mount Vernon in zone 6b in ZIP code 62864. By the map's own method, the average of each year's coldest night over 1991-2020, Mount Vernon's NOAA station is in zone 6b: the coldest night of a typical year reaches −3°F (23 complete years).
Frost dates for every NOAA station in Illinois · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USC00115943; USDA 2023 Plant Hardiness Zone Map, ZIP listings: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed October 8, 2026; the station zone: ACIS daily lows, 1991-2020. A 10% date means one year in ten has a frost after it in spring or before it in autumn.
How hot and how cold does it get in Mount Vernon?
In a normal year in Mount Vernon, 21 days a year reach 90°F (1 of them 100°F or more), 108 nights fall to 32°F or colder and 115 days bring measurable precipitation.
- Days at 90°F or more
- 21a normal year
- Days at 100°F or more
- 1a normal year
- Nights at 32°F or colder
- 108a normal year
- Days that stay below freezing
- 23high of 32°F or less
- Days with 0.01 inch of precipitation
- 115a normal year
- Days with 1 inch of snow or more
- 4a normal year
The highest temperature in this station's record (since 1895) is 114°F, on July 14, 1936; the lowest is −22°F, on February 10, 1899.
The wettest calendar year on that record is 1945, with 63.07 in; the snowiest season is 1911–12, with 46.0 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USC00115943; records: ACIS (NOAA Regional Climate Centers), station USC00115943. Records use complete months only; a month missing more than three days is left out.
How sunny is Mount Vernon?
Over a year 75% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around Mount Vernon, 4.2 kWh per square metre a day. August is the sunniest month (83%) and December the cloudiest (63%).
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 65% | 2.0 |
| February | 66% | 2.8 |
| March | 67% | 3.7 |
| April | 73% | 5.0 |
| May | 73% | 5.6 |
| June | 82% | 6.5 |
| July | 83% | 6.3 |
| August | 83% | 5.7 |
| September | 81% | 4.7 |
| October | 76% | 3.4 |
| November | 71% | 2.4 |
| December | 63% | 1.7 |
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 Mount Vernon need?
A normal year in Mount Vernon brings 4,998 heating degree days, 7% fewer than the median U.S. place (5,373), and 1,191 cooling degree days, 31% more 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 3,832 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,082 | 0 |
| February | 860 | 0 |
| March | 663 | 2 |
| April | 331 | 16 |
| May | 111 | 92 |
| June | 10 | 251 |
| July | 1 | 357 |
| August | 3 | 306 |
| September | 60 | 139 |
| October | 301 | 25 |
| November | 633 | 2 |
| December | 945 | 0 |
| Year (annual) | 4,998 | 1,191 |
Source: NOAA NCEI 1991-2020 monthly normals, station USC00115943. 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.
Has Mount Vernon been warmer than normal lately?
2023 averaged 57.1°F, 2.6°F above the 1991-2020 normal of 54.5°F.
| Year | Mean | Against normal | Precip. | Snow |
|---|---|---|---|---|
| 2023 | 57.1°F | +2.6°F | – | – |
Over 88 complete years from 1899 to 2024, the station's annual mean temperature rose at a fitted -1.1°F per century (−0.06°C per decade). A fitted rate summarizes the whole record; single years swing well above and below it.
Source: observed years: ACIS, station USC00115943; trend: NOAA GHCN-Monthly v4. A year counts only with all twelve months complete.
How does Mount Vernon's climate compare?
Mount Vernon is warmer than 113 of the other 143 places with their own NOAA record in Illinois, and wetter than 117. Across the 7,247 U.S. stations with normals, its annual mean of 54.5°F is warmer than 59%.
In the Köppen classification computed from these normals, Mount Vernon 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 Mount Vernon share this climate record?
7 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.
- Wayne City, IL992 people · 14 mi E
- Woodlawn, IL607 people · 10 mi W
- Bluford, IL604 people · 7 mi E
- Bonnie, IL364 people · 10 mi S
- Belle Rive, IL300 people · 10 mi SE
- Opdyke, IL263 people · 7 mi SE
- Keenes, IL49 people · 11 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 Mount Vernon's climate
What is the coldest month in Mount Vernon?
January, with a normal high of 39°F and a normal low of 22°F. The warmest is July (86°F by day, 67°F at night).
Does it snow in Mount Vernon?
Yes: 10 inches in a normal year, falling on 5 days with 0.1 inch or more, the most in January (3.2 inches).
What is the rainiest month in Mount Vernon?
May, with 5.06 in of precipitation in a normal year; the driest is January with 2.60 in.
What plant hardiness zone is Mount Vernon in?
The USDA's 2023 map puts Mount Vernon in zone 6b in ZIP code 62864. By the same method at Mount Vernon's NOAA station, the coldest night of a typical year reaches −3°F (23 years, 1991-2020): zone 6b.
How late can frost come in Mount Vernon?
In half of years the last 32°F night comes after April 11; in one year in ten it comes after April 26. Waiting until April 26 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Illinois climateThe statewide normals and every place in the state
- Iuka (12 mi SW), IL12 miles from this station, 54.7°F a year
- Salem, IL21 miles from this station, 54.9°F a year
- Benton, IL22 miles from this station, 56.3°F a year
- Rend Lake Dam, IL22 miles from this station, 55.9°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made