Alton weather in May

In May, Alton sees average daytime highs of 75°F and overnight lows near 58°F, with 5.0 in of rain across 13.5 wet days and about 14.1 hours of daylight. It is the 5th-warmest and 1st-wettest month of the year here.

Highs climb over the month, from about 71°F in the first days to 79°F by the end. The sky is clear or mostly clear about 27% 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 30 min by month's end. Set against the rest of the year, May is Alton's 8th-clearest and 8th-windiest month. For the whole year in context, see Alton's year-round climate.

Daytime high
75°
5th warmest
Overnight low
58°
8th coldest
Rainfall
5.0 in
13.5 wet days
Daylight
14 h 06 min
4:54 AM – 7:00 PM
Cloud cover
62%
8th clearest
Wind
7 mph
8th windiest
Solar energy
5.8 kWh/m²
Travel score
6.2
out of 10

Alton is city in Madison County, Illinois, United States.

Density
623/km²
people per km²
Founded
1818

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 71°F in the first days to 79°F by the end.

A typical May day in Alton reaches about 75°F in the afternoon and slips back to 58°F overnight — a 17°F spread between the day's warmth and the night's chill. On most days the high lands between 63°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)
17052
27053
37153
47153
57254
67254
77255
87355
97355
107356
117456
127456
137456
147457
157557
167557
177558
187658
197658
207659
217659
227760
237760
247760
257861
267861
277861
287962
297962
307962
318063

How May really feels in Alton

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.

Alton weather by month

How May compares with the rest of the year at a glance. May is the 5th-warmest and 1st-wettest month here — the current month is highlighted below.

MonthHigh / Low (°F)Rainfall (inches)Wet daysSnow daysDaylight (hours)Travel score
Jan38° / 24°2.68.23.29.60.0
Feb43° / 27°2.47.6310.50.6
Mar54° / 36°3.610.41.511.73.3
Apr66° / 47°4.611.60.2135.7
May75° / 58°5.013.5014.16.2
Jun83° / 67°4.010.9014.75.6
Jul87° / 70°3.29.5014.45.0
Aug85° / 67°2.98.9013.55.5
Sep79° / 59°3.37.5012.37.2
Oct67° / 48°3.38.40.1116.5
Nov53° / 37°3.68.60.79.93.2
Dec42° / 28°2.48.12.39.30.4

Cloud cover in May

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 27% 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 57%.

0%25%50%75%100%151015202531
Clearer (%)Cloudier (%)
14159
24060
34159
44159
54159
64159
74159
84258
94258
104258
114357
124357
134456
144357
154357
164456
174456
184456
194357
204456
214456
224357
234357
244357
254357
264357
274456
284456
294456
304555
314555

Chance of precipitation in May

Any precipitation

Alton gets around 5.0 in of rain over 13.5 wet days in May, the wettest month. The line is the day-by-day chance of measurable precipitation.

Day to day, the chance of measurable rain averages around 43% and peaks near 46% on the wettest days.

0%20%40%60%151015202531
Rain chance (%)
146
246
346
445
545
645
744
844
944
1043
1143
1243
1343
1443
1543
1643
1743
1843
1943
2044
2144
2244
2344
2443
2543
2643
2743
2842
2942
3041
3140

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 51% of days. Sticky, muggy-or-worse air turns up on roughly 14% of them.

0%25%50%75%100%151015202531
Dry (%)Comfortable (%)Humid (%)Muggy (%)Oppressive (%)
17218820
27019920
367191130
466191230
563201340
662201440
760201550
860191560
959191660
1058181770
1156181880
1255171990
1355171990
14541620100
15531620110
16521521120
17511521130
18501421141
19481422161
20471422171
21451422181
22441422191
23421422201
24401422222
25391522232
26371522232
27361622242
28351622252
29331722262
30321722263
31301822273

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
107light breeze
117light breeze
127calm
137calm
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 30 min by month's end. The lit band spans sunrise to sunset each day.

Days grow by about 54 minutes over May. Sunrise moves from 5:10 AM to 4:43 AM, and sunset from 6:46 PM to 7:13 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202531
Daylight (h)Sunrise (AM)Sunset (PM)
113.65:106:46
213.65:096:47
313.75:076:48
413.75:066:49
513.85:056:50
613.85:046:51
713.85:036:52
813.95:026:53
913.95:006:54
1013.94:596:55
1114.04:586:56
1214.04:576:57
1314.04:566:58
1414.14:556:59
1514.14:547:00
1614.14:547:00
1714.14:537:01
1814.24:527:02
1914.24:517:03
2014.24:507:04
2114.34:497:05
2214.34:497:06
2314.34:487:07
2414.34:477:07
2514.44:477:08
2614.44:467:09
2714.44:457:10
2814.44:457:11
2914.54:447:12
3014.54:447:12
3114.54:437:13

Solar energy in May

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in May, about 5.8 kWh/m².

For context, solar energy here swings from a low near 1.88 kWh/m² to a high of 6.44 kWh/m² in June across the year — May's 5.8 kWh/m² sits near the top of that range.

0246151015202531
Solar energy (kWh/m²)Level
15.4Bright
25.4Bright
35.4Bright
45.5Bright
55.5Bright
65.5Bright
75.6Bright
85.6Bright
95.7Bright
105.7Bright
115.7Bright
125.8Bright
135.8Bright
145.8Bright
155.8Bright
165.9Bright
175.9Bright
185.9Bright
195.9Bright
205.9Bright
216.0Bright
226.0Bright
236.0Bright
246.0Bright
256.0Intense
266.0Intense
276.0Intense
286.0Intense
296.0Intense
306.1Intense
316.1Intense
Planning a trip in May

Hazard calendar for Alton

In seasonPeak

None of Alton's seasonal hazards are active in May. The full-year calendar below shows when the rainy season, cyclone risk and dust haze do peak.

Alton sits in the Atlantic hurricane belt; the season peaks August–October.

Atlantic hurricane
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec

Is May a good time to visit Alton?

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

6.2
Sightseeing
3rd-best month of the year
5.1
Beach & pool
5th-best month of the year

May is a reasonable time to visit Alton for sightseeing.

What to pack for Alton in May

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

In May, Alton sees daytime highs around 75°F and nights near 58°F. Worth packing: light clothes, rain gear and sun protection. About 14 days see rain.

light clothesrain gearsun protection

UV index in Alton 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 Alton peaks around June 21 at about 9 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near December 23 at about 2 (low).

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

025710JanFebMarAprMayJunJulAugSepOctNovDecModerateHighVery highModerateJun 21UV 9Dec 23UV 2
UV index (midday)Level
Jan2Low
Feb3Moderate
Mar5Moderate
Apr7High
May8Very high
Jun9Very high
Jul9Very high
Aug8Very high
Sep7High
Oct4Moderate
Nov3Moderate
Dec2Low

Air quality in Alton 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 Alton is worst in August — around 18 µg/m³ PM2.5 (moderate), about 2.2× the cleanest month (October, 8 µg/m³).

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

0102030JanFebMarAprMayJunJulAugSepOctNovDecGoodModerateGoodModerateGoodAug 1018 µg/m³Oct 228 µg/m³
PM2.5 (µg/m³)Level
Jan10Good
Feb13Moderate
Mar13Moderate
Apr11Good
May14Moderate
Jun16Moderate
Jul18Moderate
Aug18Moderate
Sep13Moderate
Oct8Good
Nov9Good
Dec10Good
Location & terrain

Where is Alton?

Alton sits at 38.9°N, 90.2°W, 492 ft above sea level, in United States. The nearest listed city is Upper Alton, 2.5 mi away.

Topography around Alton

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

Within 2 miles, the terrain around Alton has only modest variations in elevation — a maximum elevation change of 256 ft around an average of 476 ft above sea level; within 10 miles, only modest variations in elevation — a maximum elevation change of 636 ft; within 50 miles, only modest variations in elevation — a maximum elevation change of 801 ft.

The land around Alton is covered by trees (38%) and water (28%) within 2 miles, trees (41%) and cropland (28%) within 10 miles, and cropland (47%) and trees (39%) within 50 miles.

2 miles
256 ft
10 miles
636 ft
50 miles
801 ft
treesgrasslandcroplandartificial surfacesbare terrainwater
May weather nearby: Upper Alton 2.5 mi · Godfrey 4.3 mi · Old Jamestown 6.8 mi · Spanish Lake 7.5 mi · Florissant 9.9 mi · Ferguson 12 mi · Hazelwood 13 mi · Granite City 13 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 Alton (38.8906°, -90.1843°, elevation 492 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. Tropical-cyclone seasons are the published climatological basin seasons (NOAA National Hurricane Center / regional warning centres). 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).