Mount Vernon weather in August

In August, Mount Vernon sees average daytime highs of 86°F and overnight lows near 69°F, with 2.8 in of rain across 8.4 wet days and about 13.5 hours of daylight. It is the 2nd-warmest and 12th-wettest month of the year here.

Day-to-day highs hold fairly steady near 86°F through the month. The sky is clear or mostly clear about 44% of the time in August, and the air most often feels muggy.

Daylight stretches from about 14 hours at the start of August to 12 h 54 min by month's end. Set against the rest of the year, August is Mount Vernon's 3rd-clearest and 12th-windiest month. For the whole year in context, see Mount Vernon's year-round climate.

Daytime high
86°
2nd warmest
Overnight low
69°
11th coldest
Rainfall
2.8 in
8.4 wet days
Daylight
13 h 30 min
5:15 AM – 6:45 PM
Cloud cover
50%
3rd clearest
Wind
5 mph
12th windiest
Solar energy
5.82 kWh/m²
Travel score
5.2
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 August

Average highAverage lowShaded bands: 10–90% of days

Day-to-day highs hold fairly steady near 86°F through the month.

A typical August day in Mount Vernon reaches about 86°F in the afternoon and slips back to 69°F overnight — a 17°F spread between the day's warmth and the night's chill. On most days the high lands between 79°F and 94°F. Set against its neighbours, August runs about 1°F cooler than July and about 6°F warmer than September.

60°70°80°90°151015202531
Avg high (°F)Avg low (°F)
18770
28770
38770
48770
58770
68770
78770
88770
98769
108769
118769
128769
138669
148669
158669
168669
178669
188669
198669
208669
218669
228669
238668
248668
258668
268668
278668
288668
298667
308567
318567

How August really feels in Mount Vernon

Once humidity and wind are folded in, August averages 1 day 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
1
heat index over the day's high
Days feeling ≤ 32°F
0
wind chill below the day's low

The story in August is heat — humidity pushes the afternoon "feels like" well above the raw temperature.

Mount Vernon weather by month

How August compares with the rest of the year at a glance. August is the 2nd-warmest and 12th-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 August

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 44% of the time in August.

Beyond those clear spells, partly cloudy skies cover about 17% of August, with mostly cloudy or overcast conditions the remaining 39%. Skies tend to open up as the month goes on.

0%25%50%75%100%151015202531
Clearer (%)Cloudier (%)
15941
25842
35941
45941
55941
66040
76040
86040
96040
106040
116040
126040
136040
146040
156139
166139
176139
186139
196139
206139
216139
226139
236139
246238
256238
266238
276238
286337
296337
306337
316337

Chance of precipitation in August

Any precipitation

Mount Vernon gets around 2.8 in of rain over 8.4 wet days in August, the driest month. The line is the day-by-day chance of measurable precipitation.

Day to day, the chance of measurable rain averages around 27% and peaks near 31% on the wettest days. The odds ease toward the end of the month.

0%10%20%30%40%151015202531
Rain chance (%)
131
231
331
430
530
629
729
829
929
1029
1129
1228
1328
1428
1527
1627
1726
1826
1926
2026
2126
2226
2325
2425
2525
2625
2724
2824
2924
3024
3124

Humidity in August

DryComfortableHumidMuggyOppressiveMiserable

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

By dew point, August lands in the muggy band about 32% of days. Sticky, muggy-or-worse air turns up on roughly 59% of them.

0%25%50%75%100%151015202531
Dry (%)Comfortable (%)Humid (%)Muggy (%)Oppressive (%)Miserable (%)
13132230321
23122230311
33122231311
44122231301
54122232291
64122232291
74122232291
85122232281
95122132281
105132132281
116132132271
126142032271
136142032271
146152032261
156152032261
166152132251
176162132251
186162132251
196162132251
206152132251
216152132251
226152132251
236152132251
246152132250
257152133250
267152133240
278152133230
288152133230
299152134220
3010152134210
3111162033200

Wind in August

Winds average 5 mph in August, the calmest month.

Across August, daily wind ranges from about 5 mph on the calmest days to 6 mph at its breeziest. It stays fairly steady from day to day.

0246810151015202531
Wind speed (mph)Feels
15calm
25calm
35calm
45calm
55calm
65calm
75calm
85calm
95calm
105calm
115calm
125calm
135calm
145calm
155calm
165calm
175calm
185calm
195calm
206calm
216calm
226calm
236calm
246calm
256calm
266calm
276calm
286calm
296calm
306calm
316calm

Sunrise & sunset in August

DaylightNight

Daylight runs from about 14 hours at the start of August to 12 h 54 min by month's end. The lit band spans sunrise to sunset each day.

Days shrink by about 66 minutes over August. Sunrise moves from 5:01 AM to 5:28 AM, and sunset from 7:02 PM to 6:23 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202531
Daylight (h)Sunrise (AM)Sunset (PM)
114.05:017:02
214.05:027:01
313.95:037:00
413.95:046:59
513.95:056:58
613.95:066:57
713.85:076:56
813.85:086:55
913.75:086:53
1013.75:096:52
1113.75:106:51
1213.65:116:50
1313.65:126:49
1413.65:136:47
1513.55:146:46
1613.55:156:45
1713.55:166:43
1813.45:176:42
1913.45:176:41
2013.35:186:39
2113.35:196:38
2213.35:206:36
2313.25:216:35
2413.25:226:34
2513.25:236:32
2613.15:246:31
2713.15:256:29
2813.05:266:28
2913.05:266:26
3013.05:276:25
3112.95:286:23

Solar energy in August

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in August, about 5.82 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 — August's 5.82 kWh/m² falls in the middle.

0246151015202531
Solar energy (kWh/m²)Level
16.2Intense
26.2Intense
36.1Intense
46.1Intense
56.1Intense
66.1Intense
76.0Intense
86.0Intense
96.0Bright
105.9Bright
115.9Bright
125.9Bright
135.9Bright
145.8Bright
155.8Bright
165.8Bright
175.8Bright
185.7Bright
195.7Bright
205.7Bright
215.7Bright
225.6Bright
235.6Bright
245.6Bright
255.5Bright
265.5Bright
275.5Bright
285.5Bright
295.4Bright
305.4Bright
315.3Bright
Planning a trip in August

Is August a good time to visit Mount Vernon?

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

5.2
Sightseeing
5th-best month of the year
7.2
Beach & pool
1st-best month of the year

August is a reasonable time to visit Mount Vernon for sightseeing. The water and warmth also suit a beach or pool day.

What to pack for Mount Vernon in August

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

In August, Mount Vernon sees daytime highs around 86°F and nights near 69°F. Pack light clothes. Worth having: rain gear and sun protection. About 8 days see rain.

light clothesrain gearsun protection

UV index in Mount Vernon in August

LowModerateHighVery highExtreme

Clear-sky midday UV in August peaks around 8 (very high — sun protection essential). 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 August

GoodModeratePoorUnhealthyVery unhealthy

Average fine-particle pollution (PM2.5) through the year — so you can see where August 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
August 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).