Mount Vernon weather in May

In May, Mount Vernon sees average daytime highs of 76°F and overnight lows near 59°F, with 5.1 in of rain across 12.9 wet days and about 14 hours of daylight. It is the 5th-warmest and 2nd-wettest month of the year here.

Highs climb over the month, from about 72°F in the first days to 80°F by the end. The sky is clear or mostly clear about 26% of the time in May, and the air most often feels dry.

Daylight stretches from about 13 h 36 min at the start of May to 14 h 24 min by month's end. Set against the rest of the year, May is Mount Vernon's 8th-clearest and 8th-windiest month. For the whole year in context, see Mount Vernon's year-round climate.

Daytime high
76°
5th warmest
Overnight low
59°
8th coldest
Rainfall
5.1 in
12.9 wet days
Daylight
14 h 06 min
4:50 AM – 6:54 PM
Cloud cover
63%
8th clearest
Wind
7 mph
8th windiest
Solar energy
5.83 kWh/m²
Travel score
6.3
out of 10

Mount Vernon is city located near the center of Jefferson County, Illinois, United States.

Density
396/km²
people per km²
Founded
1817

Air quality: WHO Ambient Air Quality Database. Density & description: Wikidata (CC0), GeoNames.

Temperature in May

Average highAverage lowShaded bands: 10–90% of days

Highs climb over the month, from about 72°F in the first days to 80°F by the end.

A typical May day in Mount Vernon reaches about 76°F in the afternoon and slips back to 59°F overnight — a 17°F spread between the day's warmth and the night's chill. On most days the high lands between 65°F and 86°F. Set against its neighbours, May runs about 9°F warmer than April and about 9°F cooler than June.

40°60°80°151015202531
Avg high (°F)Avg low (°F)
17254
27254
37255
47355
57356
67356
77456
87457
97457
107557
117558
127558
137558
147658
157659
167659
177759
187760
197760
207860
217861
227861
237862
247962
257962
267963
278063
288063
298064
308164
318164

How May really feels in Mount Vernon

Once humidity and wind are folded in, May averages 0 days that feel above 90°F and 0 that feel at or below 32°F — the comfort signal a plain temperature reading hides.

Days feeling ≥ 90°F
0
heat index over the day's high
Days feeling ≤ 32°F
0
wind chill below the day's low

May sits comfortably in between — no days that feel dangerously hot or drop to a hard freeze once humidity and wind are folded in.

Mount Vernon weather by month

How May compares with the rest of the year at a glance. May is the 5th-warmest and 2nd-wettest month here — the current month is highlighted below.

MonthHigh / Low (°F)Rainfall (inches)Wet daysSnow daysDaylight (hours)Travel score
Jan41° / 26°3.392.69.60.0
Feb45° / 30°2.98.42.710.51.1
Mar56° / 38°4.110.81.211.73.7
Apr67° / 49°5.211.30.1135.9
May76° / 59°5.112.90146.3
Jun85° / 68°3.910.4014.65.2
Jul88° / 71°3.410.3014.44.5
Aug86° / 69°2.88.4013.55.2
Sep80° / 61°3.07.3012.37.0
Oct68° / 49°3.67.90116.8
Nov55° / 39°3.88.80.69.93.6
Dec44° / 31°3.28.629.40.9

Cloud cover in May

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 26% of the time in May.

Beyond those clear spells, partly cloudy skies cover about 16% of May, with mostly cloudy or overcast conditions the remaining 58%.

0%25%50%75%100%151015202531
Clearer (%)Cloudier (%)
14159
24159
34159
44159
54159
64159
74159
84159
94258
104258
114357
124357
134357
144357
154357
164357
174159
184159
194258
204258
214159
224258
234159
244258
254258
264357
274357
284357
294456
304456
314456

Chance of precipitation in May

Any precipitation

Mount Vernon gets around 5.1 in of rain over 12.9 wet days in May. The line is the day-by-day chance of measurable precipitation.

Day to day, the chance of measurable rain averages around 42% and peaks near 45% on the wettest days. The odds ease toward the end of the month.

0%20%40%60%151015202531
Rain chance (%)
145
245
345
445
544
644
744
844
944
1043
1143
1243
1343
1443
1542
1642
1742
1842
1942
2041
2141
2241
2340
2439
2539
2639
2738
2838
2937
3037
3137

Humidity in May

DryComfortableHumidMuggyOppressiveMiserable

Most of May feels dry — the stacked bands show each day's mix of comfort levels, read off the dew point.

By dew point, May lands in the dry band about 48% of days. Sticky, muggy-or-worse air turns up on roughly 16% of them.

0%25%50%75%100%151015202531
Dry (%)Comfortable (%)Humid (%)Muggy (%)Oppressive (%)
167181320
265181430
363181540
462181640
561181650
659181760
758171870
857171880
955171990
10541719100
11541619110
12521620120
13511620130
14511520140
15501520150
16491520160
17481421170
18471421180
19461321191
20441322201
21431322211
22411322221
23401323231
24381323241
25371423252
26351423252
27341523262
28331523272
29321524272
30301624283
31291624283

Wind in May

Winds average 7 mph in May.

Across May, daily wind ranges from about 7 mph on the calmest days to 8 mph at its breeziest. It stays fairly steady from day to day.

0246810151015202531
Wind speed (mph)Feels
18light breeze
28light breeze
38light breeze
48light breeze
58light breeze
68light breeze
78light breeze
88light breeze
98light breeze
108light breeze
118light breeze
128light breeze
137light breeze
147calm
157calm
167calm
177calm
187calm
197calm
207calm
217calm
227calm
237calm
247calm
257calm
267calm
277calm
287calm
297calm
307calm
317calm

Sunrise & sunset in May

DaylightNight

Daylight runs from about 13 h 36 min at the start of May to 14 h 24 min by month's end. The lit band spans sunrise to sunset each day.

Days grow by about 48 minutes over May. Sunrise moves from 5:06 AM to 4:40 AM, and sunset from 6:40 PM to 7:06 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202531
Daylight (h)Sunrise (AM)Sunset (PM)
113.65:066:40
213.65:046:41
313.65:036:42
413.75:026:43
513.75:016:44
613.75:006:45
713.84:596:46
813.84:586:47
913.94:566:48
1013.94:556:49
1113.94:546:49
1213.94:536:50
1314.04:526:51
1414.04:526:52
1514.04:516:53
1614.14:506:54
1714.14:496:55
1814.14:486:56
1914.24:476:57
2014.24:466:58
2114.24:466:58
2214.24:456:59
2314.34:447:00
2414.34:447:01
2514.34:437:02
2614.34:427:03
2714.44:427:03
2814.44:417:04
2914.44:417:05
3014.44:407:06
3114.44:407:06

Solar energy in May

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in May, about 5.83 kWh/m².

For context, solar energy here swings from a low near 1.9 kWh/m² to a high of 6.46 kWh/m² in June across the year — May's 5.83 kWh/m² sits near the top of that range.

0246151015202531
Solar energy (kWh/m²)Level
15.4Bright
25.5Bright
35.5Bright
45.5Bright
55.6Bright
65.6Bright
75.6Bright
85.7Bright
95.7Bright
105.7Bright
115.8Bright
125.8Bright
135.8Bright
145.8Bright
155.9Bright
165.9Bright
175.9Bright
185.9Bright
196.0Bright
206.0Bright
216.0Bright
226.0Intense
236.0Intense
246.0Intense
256.0Intense
266.0Intense
276.1Intense
286.1Intense
296.1Intense
306.1Intense
316.1Intense
Planning a trip in May

Is May a good time to visit Mount Vernon?

Our two travel scores rate May for general sightseeing and for beach or pool weather — 0 (poor) to 10 (ideal).

6.3
Sightseeing
3rd-best month of the year
5.5
Beach & pool
5th-best month of the year

May is a reasonable time to visit Mount Vernon for sightseeing.

What to pack for Mount Vernon in May

From May's temperature range, rain chance, sun and wind — what's worth putting in the bag.

In May, Mount Vernon sees daytime highs around 76°F and nights near 59°F. Worth packing: light clothes, rain gear and sun protection. About 13 days see rain.

light clothesrain gearsun protection

UV index in Mount Vernon in May

LowModerateHighVery highExtreme

Clear-sky midday UV in May peaks around 8 — enough to warrant sun protection. The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in Mount Vernon peaks around July 10 at about 9 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near December 23 at about 2 (moderate).

The index reaches 3 or more — the level where the WHO recommends sun protection — in 10 months of the year.

025710JanFebMarAprMayJunJulAugSepOctNovDecModerateHighVery highHighModerateJul 10UV 9Dec 23UV 2
UV index (midday)Level
Jan2Moderate
Feb3Moderate
Mar5High
Apr7High
May8Very high
Jun9Very high
Jul9Very high
Aug8Very high
Sep7High
Oct4Moderate
Nov3Moderate
Dec2Low

Air quality in Mount Vernon in May

GoodModeratePoorUnhealthyVery unhealthy

Average fine-particle pollution (PM2.5) through the year — so you can see where May falls, not just the annual average.

Air quality in Mount Vernon is worst in July — around 18 µg/m³ PM2.5 (moderate), about 2.4× the cleanest month (October, 8 µg/m³).

Modeled monthly averages (CAMS reanalysis, 2015–2024).

01020JanFebMarAprMayJunJulAugSepOctNovDecGoodModerateGoodJul 1417 µg/m³Oct 238 µg/m³
PM2.5 (µg/m³)Level
Jan9Good
Feb11Good
Mar12Good
Apr11Good
May14Moderate
Jun16Moderate
Jul18Moderate
Aug14Moderate
Sep11Good
Oct8Good
Nov8Good
Dec9Good
Location & terrain

Where is Mount Vernon?

Mount Vernon sits at 38.3°N, 88.9°W, 512 ft above sea level, in United States. The nearest listed city is Marion, 40 mi away.

Topography around Mount Vernon

How much the land rises and falls, and what covers it, within 2, 10 and 50 miles of Mount Vernon.

Within 2 miles, the terrain around Mount Vernon has only modest variations in elevation — a maximum elevation change of 174 ft around an average of 489 ft above sea level; within 10 miles, only modest variations in elevation — a maximum elevation change of 279 ft; within 50 miles, only modest variations in elevation — a maximum elevation change of 499 ft.

The land around Mount Vernon is covered by trees (49%) within 2 miles, trees (42%) and cropland (37%) within 10 miles, and cropland (59%) and trees (31%) within 50 miles.

2 miles
174 ft
10 miles
279 ft
50 miles
499 ft
treesgrasslandcroplandartificial surfaceswater
May weather nearby: Marion 40 mi · Carbondale 44 mi · O'Fallon 58 mi · Belleville 60 mi · Fairview Heights 62 mi · Collinsville 63 mi · Edwardsville 66 mi · East Saint Louis 71 mi

United States travel facts

Power plugs
Type A / B
120 V · 60 Hz
Prices
≈ 100% of US
price level, 2025
GDP per capita
$90,027
2025
Happiness
6.8 / 10
World Happiness, 2025
Safe drinking water
98%
of population, 2024
Homicide rate
5.8
per 100k, 2023
Road deaths
12.7
per 100k/yr, 2019
Income group
High
World Bank
Religion
Protestant 47%unaffiliated 23%Roman Catholic 21%Jewish 2%

Sources: World Bank, US State Department, World Happiness Report, WHO/UNICEF, EF EPI, CIA World Factbook.

Data sources

Temperature, precipitation, cloud, humidity, wind and solar figures are a 1991–2020 climatology for Mount Vernon (38.3173°, -88.9031°, elevation 512 ft), computed from hourly ERA5 reanalysis — contains modified Copernicus Climate Change Service information. Sun figures are astronomical calculations, not observations. City data © GeoNames, CC BY 4.0. Map outlines from Natural Earth (public domain); interactive map © Google. UV index is derived from CAMS (Copernicus Atmosphere Monitoring Service) clear-sky UV data — contains modified Copernicus Atmosphere Monitoring Service information. Monthly air-quality (PM2.5) seasonality is from the CAMS EAC4 reanalysis (Copernicus Atmosphere Monitoring Service), scaled to the WHO annual mean where available. Topography is sampled from the Copernicus DEM GLO-90 elevation model (© ESA/Airbus) and ESA WorldCover 2021 land cover (CC BY 4.0).