Boulder weather in December

In December, Boulder sees average daytime highs of 37°F and overnight lows near 15°F, with 0.9 in of precipitation across 5.3 wet days and about 9.2 hours of daylight. It is the 11th-warmest and 12th-wettest month of the year here.

Highs ease over the month, from about 39°F in the first days to 36°F by the end. The sky is clear or mostly clear about 51% of the time in December, and the air most often feels dry.

Daylight stretches from about 9 h 24 min at the start of December to 9 h 12 min by month's end. Set against the rest of the year, December is Boulder's 3rd-clearest and 2nd-windiest month. For the whole year in context, see Boulder's year-round climate.

Daytime high
37°
11th warmest
Overnight low
15°
2nd coldest
Precipitation
0.9 in
5.3 wet days
Daylight
9 h 12 min
7:22 AM – 4:32 PM
Cloud cover
42%
3rd clearest
Wind
6 mph
2nd windiest
Solar energy
2.56 kWh/m²
Travel score
0.0
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.

Temperature in December

Average highAverage lowShaded bands: 10–90% of days

Highs ease over the month, from about 39°F in the first days to 36°F by the end.

A typical December day in Boulder reaches about 37°F in the afternoon and slips back to 15°F overnight — a 23°F spread between the day's warmth and the night's chill. On most days the high lands between 23°F and 50°F. Set against its neighbours, December runs about 9°F cooler than November and on par with January.

20°40°60°151015202531
Avg high (°F)Avg low (°F)
14017
24017
33917
43917
53916
63916
73816
83816
93816
103815
113815
123715
133715
143715
153715
163714
173714
183614
193614
203614
213614
223613
233613
243613
253613
263613
273613
283613
293613
303613
313613

How December really feels in Boulder

Once humidity and wind are folded in, December averages 0 days that feel above 90°F and 31 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
31
31 feel bitter (≤ 14°F)

The story in December is cold — wind chill drags the overnight "feels like" below the raw low.

Boulder weather by month

How December compares with the rest of the year at a glance. December is the 11th-warmest and 12th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°F)Rainfall (inches)Wet daysSnow daysDaylight (hours)Travel score
Jan37° / 14°0.95.75.59.50.0
Feb39° / 16°1.06.7710.40.0
Mar48° / 22°2.08.87.211.71.7
Apr54° / 29°3.111.17.9133.1
May63° / 38°4.014.93.514.24.8
Jun74° / 47°3.014.30.314.86.2
Jul80° / 53°3.014.8014.56.0
Aug78° / 52°2.814.9013.66.2
Sep71° / 44°2.19.70.912.36.8
Oct58° / 33°1.97.43.910.94.9
Nov46° / 22°1.36.45.79.81.4
Dec37° / 15°0.95.35.49.20.0

Cloud cover in December

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 51% of the time in December.

Beyond those clear spells, partly cloudy skies cover about 18% of December, with mostly cloudy or overcast conditions the remaining 31%.

0%25%50%75%100%151015202531
Clearer (%)Cloudier (%)
16931
26931
36931
46931
56931
66931
76931
86931
96931
106931
116832
126832
136832
146832
156832
166931
176931
186931
196931
207030
217030
227030
237030
247030
257030
267030
277030
287030
297030
307030
316832

Chance of precipitation in December

Any precipitationSnow

Boulder gets around 0.9 in of rain and snow over 5.3 wet days in December, the driest month. The line is the day-by-day chance of measurable precipitation.

Day to day, the chance of measurable precipitation averages around 18% and peaks near 19% on the wettest days, and about 5 days bring snow.

0%10%20%30%151015202531
Rain chance (%)Snow chance (%)
11918
21818
31818
41818
51818
61818
71818
81818
91818
101818
111818
121818
131818
141819
151819
161919
171919
181819
191819
201819
211819
221718
231718
241718
251717
261717
271717
281716
291616
301616
311616

Humidity in December

DryComfortableHumidMuggyOppressiveMiserable

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

By dew point, December lands in the dry band about 100% of days. It rarely turns muggy — the humid and sticky bands barely register.

0%25%50%75%100%151015202531
Dry (%)
1100
2100
3100
4100
5100
6100
7100
8100
9100
10100
11100
12100
13100
14100
15100
16100
17100
18100
19100
20100
21100
22100
23100
24100
25100
26100
27100
28100
29100
30100
31100

Wind in December

Winds average 6 mph in December.

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

0246810151015202531
Wind speed (mph)Feels
16calm
26calm
36calm
46calm
56calm
66calm
76calm
86calm
96calm
106calm
116calm
126calm
136calm
146calm
156calm
166calm
176calm
186calm
196calm
206calm
216calm
226calm
236calm
246calm
256calm
266calm
276calm
286calm
296calm
306calm
316calm

Sunrise & sunset in December

DaylightNight

Daylight runs from about 9 h 24 min at the start of December to 9 h 12 min by month's end. The lit band spans sunrise to sunset each day.

Days shrink by about 12 minutes over December. Sunrise moves from 7:10 AM to 7:28 AM, and sunset from 4:32 PM to 4:40 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202531
Daylight (h)Sunrise (AM)Sunset (PM)
19.47:104:32
29.37:114:32
39.37:124:31
49.37:134:31
59.37:144:31
69.37:144:31
79.37:154:31
89.27:164:31
99.27:174:31
109.27:184:31
119.27:194:31
129.27:194:32
139.27:204:32
149.27:214:32
159.27:214:32
169.27:224:32
179.27:234:33
189.27:234:33
199.27:244:33
209.27:244:34
219.27:254:34
229.27:254:35
239.27:264:35
249.27:264:36
259.27:274:36
269.27:274:37
279.27:274:37
289.27:284:38
299.27:284:39
309.27:284:39
319.27:284:40

Solar energy in December

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in December, about 2.56 kWh/m² — the year's lowest.

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 — December's 2.56 kWh/m² sits near the bottom.

0123151015202531
Solar energy (kWh/m²)Level
12.6Moderate
22.6Moderate
32.6Moderate
42.6Moderate
52.6Moderate
62.6Moderate
72.6Moderate
82.5Moderate
92.5Moderate
102.5Moderate
112.5Moderate
122.5Moderate
132.5Moderate
142.5Moderate
152.5Moderate
162.5Moderate
172.5Moderate
182.5Moderate
192.5Moderate
202.5Moderate
212.5Moderate
222.5Moderate
232.5Moderate
242.6Moderate
252.6Moderate
262.6Moderate
272.6Moderate
282.6Moderate
292.6Moderate
302.6Moderate
312.6Moderate
Planning a trip in December

Hazard calendar for Boulder

In seasonPeak

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

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 December a good time to visit Boulder?

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

0.0
Sightseeing
10th-best month of the year
0.0
Beach & pool
8th-best month of the year

December is a weaker month for outdoor sightseeing in Boulder.

What to pack for Boulder in December

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

In December, Boulder sees daytime highs around 37°F and nights near 15°F. Pack a warm layer and a heavy coat. About 5 days see rain.

a warm layera heavy coat

UV index in Boulder in December

LowModerateHighVery highExtreme

Clear-sky midday UV in December peaks around 2. 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.

025710JanFebMarAprMayJunJulAugSepOctNovDecModerateHighVery highExtremeVery highHighModerateJul 13UV 11Dec 23UV 2
UV index (midday)Level
Jan2Moderate
Feb4Moderate
Mar7High
Apr6High
May7Very high
Jun11Extreme
Jul11Extreme
Aug10Very high
Sep7Very high
Oct5High
Nov3Moderate
Dec2Low

Air quality in Boulder in December

GoodModeratePoorUnhealthyVery unhealthy

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

0102030JanFebMarAprMayJunJulAugSepOctNovDecModerateAug 1620 µg/m³May 1113 µg/m³
PM2.5 (µg/m³)Level
Jan17Moderate
Feb15Moderate
Mar16Moderate
Apr13Moderate
May13Moderate
Jun14Moderate
Jul14Moderate
Aug21Moderate
Sep13Moderate
Oct15Moderate
Nov15Moderate
Dec16Moderate
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
10 miles
4,147 ft
50 miles
9,623 ft
treesgrasslandcroplandartificial surfacesbare terrainwatermoss and lichen
December 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
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 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).