Boulder weather in August

In August, Boulder sees average daytime highs of 78°F and overnight lows near 52°F, with 2.8 in of rain across 14.9 wet days and about 13.6 hours of daylight. It is the 2nd-warmest and 5th-wettest month of the year here.

Day-to-day highs hold fairly steady near 78°F through the month. The sky is clear or mostly clear about 36% of the time in August, and the air most often feels dry.

Daylight stretches from about 14 h 06 min at the start of August to 13 hours by month's end. Set against the rest of the year, August is Boulder's 7th-clearest and 11th-windiest month. For the whole year in context, see Boulder's year-round climate.

Daytime high: 78°; 2nd warmest
Overnight low: 52°; 11th coldest
Rainfall: 2.8 in; 14.9 wet days
Daylight: 13 h 36 min; 5:17 AM – 6:53 PM
Cloud cover: 52%; 7th clearest
Wind: 4 mph; 11th windiest
Solar energy: 6.45 kWh/m²
Travel score: 6.2; out of 10

Boulder is city in and county seat of Boulder County, Colorado, United States.

Density: 1,606/km²; people per km²
Founded: 1858

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

← July Boulder year-round climate September →Best places to visit in August

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

Temperature in August

Average highAverage lowShaded bands: 10–90% of days

Day-to-day highs hold fairly steady near 78°F through the month.

A typical August day in Boulder reaches about 78°F in the afternoon and slips back to 52°F overnight — a 26°F spread between the day's warmth and the night's chill. On most days the high lands between 69°F and 85°F. Set against its neighbours, August runs about 2°F cooler than July and about 7°F warmer than September.

	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31
Avg high (°F)	79	79	78	78	78	78	78	78	78	78	78	78	78	78	78	78	78	78	78	78	78	78	77	77	77	77	77	77	76	76	76
Avg low (°F)	53	53	53	53	53	53	53	53	53	53	52	52	52	52	52	52	52	52	52	51	51	51	51	51	51	51	51	50	50	50	50

	Avg high (°F)	Avg low (°F)
1	79	53
2	79	53
3	78	53
4	78	53
5	78	53
6	78	53
7	78	53
8	78	53
9	78	53
10	78	53
11	78	52
12	78	52
13	78	52
14	78	52
15	78	52
16	78	52
17	78	52
18	78	52
19	78	52
20	78	51
21	78	51
22	78	51
23	77	51
24	77	51
25	77	51
26	77	51
27	77	51
28	77	50
29	76	50
30	76	50
31	76	50

How August really feels in Boulder

Once humidity and wind are folded in, August 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

heat index over the day's high

Days feeling ≤ 32°F

wind chill below the day's low

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

Boulder weather by month

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

Month	High / Low (°F)	Rainfall (inches)	Wet days	Snow days	Daylight (hours)	Travel score
Jan	37° / 14°	0.9	5.7	5.5	9.5	0.0
Feb	39° / 16°	1.0	6.7	7	10.4	0.0
Mar	48° / 22°	2.0	8.8	7.2	11.7	1.7
Apr	54° / 29°	3.1	11.1	7.9	13	3.1
May	63° / 38°	4.0	14.9	3.5	14.2	4.8
Jun	74° / 47°	3.0	14.3	0.3	14.8	6.2
Jul	80° / 53°	3.0	14.8	0	14.5	6.0
Aug	78° / 52°	2.8	14.9	0	13.6	6.2
Sep	71° / 44°	2.1	9.7	0.9	12.3	6.8
Oct	58° / 33°	1.9	7.4	3.9	10.9	4.9
Nov	46° / 22°	1.3	6.4	5.7	9.8	1.4
Dec	37° / 15°	0.9	5.3	5.4	9.2	0.0

Cloud cover in August

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 36% of the time in August.

Beyond those clear spells, partly cloudy skies cover about 28% of August, with mostly cloudy or overcast conditions the remaining 36%. Skies tend to open up as the month goes on.

	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31
Clearer (%)	57	58	59	60	60	61	61	63	63	64	64	64	65	65	65	65	65	65	65	65	64	65	65	65	65	66	67	67	68	68	68
Cloudier (%)	43	42	41	40	40	39	39	37	37	36	36	36	35	35	35	35	35	35	35	35	36	35	35	35	35	34	33	33	32	32	32

	Clearer (%)	Cloudier (%)
1	57	43
2	58	42
3	59	41
4	60	40
5	60	40
6	61	39
7	61	39
8	63	37
9	63	37
10	64	36
11	64	36
12	64	36
13	65	35
14	65	35
15	65	35
16	65	35
17	65	35
18	65	35
19	65	35
20	65	35
21	64	36
22	65	35
23	65	35
24	65	35
25	65	35
26	66	34
27	67	33
28	67	33
29	68	32
30	68	32
31	68	32

Chance of precipitation in August

Any precipitation

Boulder gets around 2.8 in of rain over 14.9 wet days in August. The line is the day-by-day chance of measurable precipitation.

Day to day, the chance of measurable rain averages around 47% and peaks near 55% on the wettest days. The odds ease toward the end of the month.

	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31
Rain chance (%)	55	55	55	54	53	53	52	51	50	50	49	48	48	47	47	47	46	46	46	46	45	45	45	44	43	42	42	41	40	40	39

	Rain chance (%)
1	55
2	55
3	55
4	54
5	53
6	53
7	52
8	51
9	50
10	50
11	49
12	48
13	48
14	47
15	47
16	47
17	46
18	46
19	46
20	46
21	45
22	45
23	45
24	44
25	43
26	42
27	42
28	41
29	40
30	40
31	39

Humidity in August

DryComfortableHumidMuggyOppressiveMiserable

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

By dew point, August lands in the dry band about 97% of days. It rarely turns muggy — the humid and sticky bands barely register.

	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31
Dry (%)	90	91	91	92	92	93	94	94	95	96	96	97	97	98	98	99	99	99	99	99	99	100	100	100	99	99	99	99	99	99	99
Comfortable (%)	10	9	9	8	8	7	6	6	5	4	4	3	3	2	2	1	1	1	1	1	1	0	0	0	1	1	1	1	1	1	1

	Dry (%)	Comfortable (%)
1	90	10
2	91	9
3	91	9
4	92	8
5	92	8
6	93	7
7	94	6
8	94	6
9	95	5
10	96	4
11	96	4
12	97	3
13	97	3
14	98	2
15	98	2
16	99	1
17	99	1
18	99	1
19	99	1
20	99	1
21	99	1
22	100	0
23	100	0
24	100	0
25	99	1
26	99	1
27	99	1
28	99	1
29	99	1
30	99	1
31	99	1

Wind in August

Winds average 4 mph in August.

Across August, daily wind ranges from about 4 mph on the calmest days to 4 mph at its breeziest. It stays fairly steady from day to day.

	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31
Wind speed (mph)	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4
Feels	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm	calm

	Wind speed (mph)	Feels
1	4	calm
2	4	calm
3	4	calm
4	4	calm
5	4	calm
6	4	calm
7	4	calm
8	4	calm
9	4	calm
10	4	calm
11	4	calm
12	4	calm
13	4	calm
14	4	calm
15	4	calm
16	4	calm
17	4	calm
18	4	calm
19	4	calm
20	4	calm
21	4	calm
22	4	calm
23	4	calm
24	4	calm
25	4	calm
26	4	calm
27	4	calm
28	4	calm
29	4	calm
30	4	calm
31	4	calm

Sunrise & sunset in August

DaylightNight

Daylight runs from about 14 h 06 min at the start of August to 13 hours by month's end. The lit band spans sunrise to sunset each day.

Days shrink by about 66 minutes over August. Sunrise moves from 5:03 AM to 5:32 AM, and sunset from 7:11 PM to 6:30 PM.

	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31
Daylight (h)	14.1	14.1	14.1	14.0	14.0	14.0	13.9	13.9	13.9	13.8	13.8	13.7	13.7	13.7	13.6	13.6	13.6	13.5	13.5	13.4	13.4	13.4	13.3	13.3	13.2	13.2	13.1	13.1	13.1	13.0	13.0
Sunrise (AM)	5:03	5:04	5:05	5:06	5:07	5:08	5:09	5:10	5:11	5:12	5:12	5:13	5:14	5:15	5:16	5:17	5:18	5:19	5:20	5:21	5:22	5:23	5:24	5:25	5:26	5:27	5:28	5:29	5:30	5:31	5:32
Sunset (PM)	7:11	7:10	7:09	7:08	7:07	7:06	7:05	7:03	7:02	7:01	7:00	6:58	6:57	6:56	6:54	6:53	6:52	6:50	6:49	6:47	6:46	6:44	6:43	6:41	6:40	6:38	6:37	6:35	6:33	6:32	6:30

	Daylight (h)	Sunrise (AM)	Sunset (PM)
1	14.1	5:03	7:11
2	14.1	5:04	7:10
3	14.1	5:05	7:09
4	14.0	5:06	7:08
5	14.0	5:07	7:07
6	14.0	5:08	7:06
7	13.9	5:09	7:05
8	13.9	5:10	7:03
9	13.9	5:11	7:02
10	13.8	5:12	7:01
11	13.8	5:12	7:00
12	13.7	5:13	6:58
13	13.7	5:14	6:57
14	13.7	5:15	6:56
15	13.6	5:16	6:54
16	13.6	5:17	6:53
17	13.6	5:18	6:52
18	13.5	5:19	6:50
19	13.5	5:20	6:49
20	13.4	5:21	6:47
21	13.4	5:22	6:46
22	13.4	5:23	6:44
23	13.3	5:24	6:43
24	13.3	5:25	6:41
25	13.2	5:26	6:40
26	13.2	5:27	6:38
27	13.1	5:28	6:37
28	13.1	5:29	6:35
29	13.1	5:30	6:33
30	13.0	5:31	6:32
31	13.0	5:32	6:30

Solar energy in August

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in August, about 6.45 kWh/m².

For context, solar energy here swings from a low near 2.56 kWh/m² to a high of 7.49 kWh/m² in June across the year — August's 6.45 kWh/m² falls in the middle.

	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31
Solar energy (kWh/m²)	6.8	6.7	6.7	6.7	6.7	6.7	6.7	6.7	6.6	6.6	6.6	6.6	6.6	6.5	6.5	6.5	6.5	6.5	6.4	6.4	6.4	6.3	6.3	6.3	6.2	6.2	6.2	6.2	6.1	6.1	6.0
Level	Intense	Intense	Intense	Intense	Intense	Intense	Intense	Intense	Intense	Intense	Intense	Intense	Intense	Intense	Intense	Intense	Intense	Intense	Intense	Intense	Intense	Intense	Intense	Intense	Intense	Intense	Intense	Intense	Intense	Intense	Intense

	Solar energy (kWh/m²)	Level
1	6.8	Intense
2	6.7	Intense
3	6.7	Intense
4	6.7	Intense
5	6.7	Intense
6	6.7	Intense
7	6.7	Intense
8	6.7	Intense
9	6.6	Intense
10	6.6	Intense
11	6.6	Intense
12	6.6	Intense
13	6.6	Intense
14	6.5	Intense
15	6.5	Intense
16	6.5	Intense
17	6.5	Intense
18	6.5	Intense
19	6.4	Intense
20	6.4	Intense
21	6.4	Intense
22	6.3	Intense
23	6.3	Intense
24	6.3	Intense
25	6.2	Intense
26	6.2	Intense
27	6.2	Intense
28	6.2	Intense
29	6.1	Intense
30	6.1	Intense
31	6.0	Intense

Planning a trip in August

Hazard calendar for Boulder

In seasonPeak

In August, Boulder sits inside its rainy season season. The full year is below, with each hazard's peak months called out.

Boulder's rainy season runs March–October, when most of the year's rain falls.

Rainy season

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Is August a good time to visit Boulder?

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

6.2

Sightseeing

2nd-best month of the year

5.7

Beach & pool

2nd-best month of the year

August is a reasonable time to visit Boulder for sightseeing.

What to pack for Boulder in August

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

In August, Boulder sees daytime highs around 78°F and nights near 52°F. Pack rain gear and sun protection. Worth having: light clothes. About 15 days see rain.

rain gearsun protectionlight clothes

UV index in Boulder in August

LowModerateHighVery highExtreme

Clear-sky midday UV in August peaks around 10 (very high — sun protection essential). The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in Boulder peaks around July 13 at about 11 (extreme) — 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.

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
UV index (midday)	2	4	7	6	7	11	11	10	7	5	3	2
Level	Moderate	Moderate	High	High	Very high	Extreme	Extreme	Very high	Very high	High	Moderate	Low

	UV index (midday)	Level
Jan	2	Moderate
Feb	4	Moderate
Mar	7	High
Apr	6	High
May	7	Very high
Jun	11	Extreme
Jul	11	Extreme
Aug	10	Very high
Sep	7	Very high
Oct	5	High
Nov	3	Moderate
Dec	2	Low

Air quality in Boulder 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 Boulder is worst in August — around 21 µg/m³ PM2.5 (moderate), about 1.6× the cleanest month (May, 13 µg/m³).

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

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
PM2.5 (µg/m³)	17	15	16	13	13	14	14	21	13	15	15	16
Level	Moderate	Moderate	Moderate	Moderate	Moderate	Moderate	Moderate	Moderate	Moderate	Moderate	Moderate	Moderate

	PM2.5 (µg/m³)	Level
Jan	17	Moderate
Feb	15	Moderate
Mar	16	Moderate
Apr	13	Moderate
May	13	Moderate
Jun	14	Moderate
Jul	14	Moderate
Aug	21	Moderate
Sep	13	Moderate
Oct	15	Moderate
Nov	15	Moderate
Dec	16	Moderate

Location & terrain

Where is Boulder?

Boulder sits at 40.0°N, 105.3°W, 5,328 ft above sea level, in United States. The nearest listed city is Louisville, 8.1 mi away.

Topography around Boulder

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

Within 2 miles, the terrain around Boulder has significant variations in elevation — a maximum elevation change of 1,703 ft around an average of 5,495 ft above sea level; within 10 miles, very significant variations in elevation — a maximum elevation change of 4,147 ft; within 50 miles, extreme variations in elevation — a maximum elevation change of 9,623 ft.

The land around Boulder is covered by trees (45%) and artificial surfaces (39%) within 2 miles, grassland (44%) and trees (41%) within 10 miles, and trees (41%) and grassland (34%) within 50 miles.

2 miles

1,703 ft

trees 45%

10 miles

4,147 ft

grassland 44%

50 miles

9,623 ft

trees 41%

treesgrasslandcroplandartificial surfacesbare terrainwatermoss and lichen

← July Boulder year-round climate September →Best places to visit in August

August weather nearby: Louisville 8.1 mi · Lafayette 9.9 mi · Broomfield 12 mi · Erie 12 mi · Longmont 14 mi · Westminster 17 mi · Northglenn 17 mi · Arvada 17 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

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 Boulder (40.015°, -105.2706°, elevation 5,328 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).

	Avg high (°F)	Avg low (°F)
1	79	53
2	79	53
3	78	53
4	78	53
5	78	53
6	78	53
7	78	53
8	78	53
9	78	53
10	78	53
11	78	52
12	78	52
13	78	52
14	78	52
15	78	52
16	78	52
17	78	52
18	78	52
19	78	52
20	78	51
21	78	51
22	78	51
23	77	51
24	77	51
25	77	51
26	77	51
27	77	51
28	77	50
29	76	50
30	76	50
31	76	50

	Clearer (%)	Cloudier (%)
1	57	43
2	58	42
3	59	41
4	60	40
5	60	40
6	61	39
7	61	39
8	63	37
9	63	37
10	64	36
11	64	36
12	64	36
13	65	35
14	65	35
15	65	35
16	65	35
17	65	35
18	65	35
19	65	35
20	65	35
21	64	36
22	65	35
23	65	35
24	65	35
25	65	35
26	66	34
27	67	33
28	67	33
29	68	32
30	68	32
31	68	32

	Rain chance (%)
1	55
2	55
3	55
4	54
5	53
6	53
7	52
8	51
9	50
10	50
11	49
12	48
13	48
14	47
15	47
16	47
17	46
18	46
19	46
20	46
21	45
22	45
23	45
24	44
25	43
26	42
27	42
28	41
29	40
30	40
31	39

	Dry (%)	Comfortable (%)
1	90	10
2	91	9
3	91	9
4	92	8
5	92	8
6	93	7
7	94	6
8	94	6
9	95	5
10	96	4
11	96	4
12	97	3
13	97	3
14	98	2
15	98	2
16	99	1
17	99	1
18	99	1
19	99	1
20	99	1
21	99	1
22	100	0
23	100	0
24	100	0
25	99	1
26	99	1
27	99	1
28	99	1
29	99	1
30	99	1
31	99	1

	Avg high (°F)	Avg low (°F)
1	79	53
2	79	53
3	78	53
4	78	53
5	78	53
6	78	53
7	78	53
8	78	53
9	78	53
10	78	53
11	78	52
12	78	52
13	78	52
14	78	52
15	78	52
16	78	52
17	78	52
18	78	52
19	78	52
20	78	51
21	78	51
22	78	51
23	77	51
24	77	51
25	77	51
26	77	51
27	77	51
28	77	50
29	76	50
30	76	50
31	76	50

	Clearer (%)	Cloudier (%)
1	57	43
2	58	42
3	59	41
4	60	40
5	60	40
6	61	39
7	61	39
8	63	37
9	63	37
10	64	36
11	64	36
12	64	36
13	65	35
14	65	35
15	65	35
16	65	35
17	65	35
18	65	35
19	65	35
20	65	35
21	64	36
22	65	35
23	65	35
24	65	35
25	65	35
26	66	34
27	67	33
28	67	33
29	68	32
30	68	32
31	68	32

	Rain chance (%)
1	55
2	55
3	55
4	54
5	53
6	53
7	52
8	51
9	50
10	50
11	49
12	48
13	48
14	47
15	47
16	47
17	46
18	46
19	46
20	46
21	45
22	45
23	45
24	44
25	43
26	42
27	42
28	41
29	40
30	40
31	39

	Dry (%)	Comfortable (%)
1	90	10
2	91	9
3	91	9
4	92	8
5	92	8
6	93	7
7	94	6
8	94	6
9	95	5
10	96	4
11	96	4
12	97	3
13	97	3
14	98	2
15	98	2
16	99	1
17	99	1
18	99	1
19	99	1
20	99	1
21	99	1
22	100	0
23	100	0
24	100	0
25	99	1
26	99	1
27	99	1
28	99	1
29	99	1
30	99	1
31	99	1

	Avg high (°F)	Avg low (°F)
1	79	53
2	79	53
3	78	53
4	78	53
5	78	53
6	78	53
7	78	53
8	78	53
9	78	53
10	78	53
11	78	52
12	78	52
13	78	52
14	78	52
15	78	52
16	78	52
17	78	52
18	78	52
19	78	52
20	78	51
21	78	51
22	78	51
23	77	51
24	77	51
25	77	51
26	77	51
27	77	51
28	77	50
29	76	50
30	76	50
31	76	50

	Clearer (%)	Cloudier (%)
1	57	43
2	58	42
3	59	41
4	60	40
5	60	40
6	61	39
7	61	39
8	63	37
9	63	37
10	64	36
11	64	36
12	64	36
13	65	35
14	65	35
15	65	35
16	65	35
17	65	35
18	65	35
19	65	35
20	65	35
21	64	36
22	65	35
23	65	35
24	65	35
25	65	35
26	66	34
27	67	33
28	67	33
29	68	32
30	68	32
31	68	32

	Rain chance (%)
1	55
2	55
3	55
4	54
5	53
6	53
7	52
8	51
9	50
10	50
11	49
12	48
13	48
14	47
15	47
16	47
17	46
18	46
19	46
20	46
21	45
22	45
23	45
24	44
25	43
26	42
27	42
28	41
29	40
30	40
31	39

	Dry (%)	Comfortable (%)
1	90	10
2	91	9
3	91	9
4	92	8
5	92	8
6	93	7
7	94	6
8	94	6
9	95	5
10	96	4
11	96	4
12	97	3
13	97	3
14	98	2
15	98	2
16	99	1
17	99	1
18	99	1
19	99	1
20	99	1
21	99	1
22	100	0
23	100	0
24	100	0
25	99	1
26	99	1
27	99	1
28	99	1
29	99	1
30	99	1
31	99	1