Thornton weather in December

In December, Thornton sees average daytime highs of 42°F and overnight lows near 18°F, with 0.8 in of precipitation across 4.8 wet days and about 9.2 hours of daylight. It is the 12th-warmest and 12th-wettest month of the year here.

Highs ease over the month, from about 44°F in the first days to 40°F by the end. The sky is clear or mostly clear about 53% 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 Thornton's 3rd-clearest and 4th-windiest month. For the whole year in context, see Thornton's year-round climate.

Daytime high: 42°; 12th warmest
Overnight low: 18°; 2nd coldest
Precipitation: 0.8 in; 4.8 wet days
Daylight: 9 h 12 min; 7:20 AM – 4:32 PM
Cloud cover: 40%; 3rd clearest
Wind: 5 mph; 4th windiest
Solar energy: 2.55 kWh/m²
Travel score: 0.3; out of 10

Thornton is city in Adams and Weld counties in Colorado, United States.

Density: 1,433/km²; people per km²
Founded: 1956

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

← November Thornton year-round climate January →Best places to visit in December

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

Temperature in December

Average highAverage lowShaded bands: 10–90% of days

Highs ease over the month, from about 44°F in the first days to 40°F by the end.

A typical December day in Thornton reaches about 42°F in the afternoon and slips back to 18°F overnight — a 23°F spread between the day's warmth and the night's chill. On most days the high lands between 27°F and 56°F. Set against its neighbours, December runs about 9°F cooler than November and on par with January.

	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)	45	44	44	44	44	43	43	43	42	42	42	42	42	42	41	41	41	41	41	40	40	40	40	40	40	40	40	40	40	40	40
Avg low (°F)	21	21	20	20	20	20	20	19	19	19	19	19	19	19	18	18	18	18	18	18	17	17	17	17	17	17	17	17	17	17	17

	Avg high (°F)	Avg low (°F)
1	45	21
2	44	21
3	44	20
4	44	20
5	44	20
6	43	20
7	43	20
8	43	19
9	42	19
10	42	19
11	42	19
12	42	19
13	42	19
14	42	19
15	41	18
16	41	18
17	41	18
18	41	18
19	41	18
20	40	18
21	40	17
22	40	17
23	40	17
24	40	17
25	40	17
26	40	17
27	40	17
28	40	17
29	40	17
30	40	17
31	40	17

How December really feels in Thornton

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

heat index over the day's high

Days feeling ≤ 32°F

31 feel bitter (≤ 14°F)

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

Thornton weather by month

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

Month	High / Low (°F)	Rainfall (inches)	Wet days	Snow days	Daylight (hours)	Travel score
Jan	42° / 18°	0.9	5.2	5	9.5	0.3
Feb	44° / 20°	0.9	5.8	5.5	10.4	1.0
Mar	53° / 27°	1.9	7.6	5.7	11.7	3.3
Apr	59° / 33°	2.7	9.9	4.7	13	4.7
May	69° / 43°	3.2	11	1	14.2	6.2
Jun	80° / 52°	2.1	8.3	0	14.8	6.8
Jul	85° / 58°	1.6	7.2	0	14.5	5.5
Aug	83° / 57°	1.5	6.4	0	13.6	6.3
Sep	76° / 49°	1.4	5.8	0.5	12.3	7.7
Oct	64° / 37°	1.6	6.1	2.2	10.9	6.4
Nov	51° / 26°	1.2	6	5.1	9.8	2.9
Dec	42° / 18°	0.8	4.8	4.9	9.2	0.3

Cloud cover in December

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 53% of the time in December.

Beyond those clear spells, partly cloudy skies cover about 16% of December, with mostly cloudy or overcast conditions the remaining 30%.

	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 (%)	69	69	69	70	70	70	70	70	70	70	70	70	70	70	70	70	70	70	71	71	71	71	70	70	70	70	70	70	69	69	69
Cloudier (%)	31	31	31	30	30	30	30	30	30	30	30	30	30	30	30	30	30	30	29	29	29	29	30	30	30	30	30	30	31	31	31

	Clearer (%)	Cloudier (%)
1	69	31
2	69	31
3	69	31
4	70	30
5	70	30
6	70	30
7	70	30
8	70	30
9	70	30
10	70	30
11	70	30
12	70	30
13	70	30
14	70	30
15	70	30
16	70	30
17	70	30
18	70	30
19	71	29
20	71	29
21	71	29
22	71	29
23	70	30
24	70	30
25	70	30
26	70	30
27	70	30
28	70	30
29	69	31
30	69	31
31	69	31

Chance of precipitation in December

Any precipitationSnow

Thornton gets around 0.8 in of rain and snow over 4.8 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 16% and peaks near 18% on the wettest days, and about 5 days bring snow.

	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 (%)	18	17	17	17	16	16	16	16	16	16	16	16	17	17	17	17	17	17	17	17	17	17	17	16	16	16	16	16	16	15	15
Snow chance (%)	18	17	17	17	16	16	16	16	16	16	16	16	16	17	17	17	17	17	17	17	17	17	17	17	17	17	16	16	16	15	15

	Rain chance (%)	Snow chance (%)
1	18	18
2	17	17
3	17	17
4	17	17
5	16	16
6	16	16
7	16	16
8	16	16
9	16	16
10	16	16
11	16	16
12	16	16
13	17	16
14	17	17
15	17	17
16	17	17
17	17	17
18	17	17
19	17	17
20	17	17
21	17	17
22	17	17
23	17	17
24	16	17
25	16	17
26	16	17
27	16	16
28	16	16
29	16	16
30	15	15
31	15	15

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.

	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 (%)	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100	100

	Dry (%)
1	100
2	100
3	100
4	100
5	100
6	100
7	100
8	100
9	100
10	100
11	100
12	100
13	100
14	100
15	100
16	100
17	100
18	100
19	100
20	100
21	100
22	100
23	100
24	100
25	100
26	100
27	100
28	100
29	100
30	100
31	100

Wind in December

Winds average 5 mph in December.

Across December, daily wind ranges from about 5 mph on the calmest days to 5 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)	5	5	5	5	5	5	5	5	5	5	5	5	5	5	5	5	5	5	5	5	5	5	5	5	5	5	5	5	5	5	5
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	5	calm
2	5	calm
3	5	calm
4	5	calm
5	5	calm
6	5	calm
7	5	calm
8	5	calm
9	5	calm
10	5	calm
11	5	calm
12	5	calm
13	5	calm
14	5	calm
15	5	calm
16	5	calm
17	5	calm
18	5	calm
19	5	calm
20	5	calm
21	5	calm
22	5	calm
23	5	calm
24	5	calm
25	5	calm
26	5	calm
27	5	calm
28	5	calm
29	5	calm
30	5	calm
31	5	calm

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 7:08 AM to 7:27 AM, and sunset from 4:31 PM to 4:39 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)	9.4	9.4	9.3	9.3	9.3	9.3	9.3	9.3	9.3	9.2	9.2	9.2	9.2	9.2	9.2	9.2	9.2	9.2	9.2	9.2	9.2	9.2	9.2	9.2	9.2	9.2	9.2	9.2	9.2	9.2	9.2
Sunrise (AM)	7:08	7:09	7:10	7:11	7:12	7:13	7:14	7:15	7:15	7:16	7:17	7:18	7:18	7:19	7:20	7:20	7:21	7:22	7:22	7:23	7:23	7:24	7:24	7:25	7:25	7:25	7:26	7:26	7:26	7:27	7:27
Sunset (PM)	4:31	4:31	4:31	4:31	4:30	4:30	4:30	4:30	4:30	4:31	4:31	4:31	4:31	4:31	4:31	4:32	4:32	4:32	4:33	4:33	4:33	4:34	4:34	4:35	4:35	4:36	4:37	4:37	4:38	4:39	4:39

	Daylight (h)	Sunrise (AM)	Sunset (PM)
1	9.4	7:08	4:31
2	9.4	7:09	4:31
3	9.3	7:10	4:31
4	9.3	7:11	4:31
5	9.3	7:12	4:30
6	9.3	7:13	4:30
7	9.3	7:14	4:30
8	9.3	7:15	4:30
9	9.3	7:15	4:30
10	9.2	7:16	4:31
11	9.2	7:17	4:31
12	9.2	7:18	4:31
13	9.2	7:18	4:31
14	9.2	7:19	4:31
15	9.2	7:20	4:31
16	9.2	7:20	4:32
17	9.2	7:21	4:32
18	9.2	7:22	4:32
19	9.2	7:22	4:33
20	9.2	7:23	4:33
21	9.2	7:23	4:33
22	9.2	7:24	4:34
23	9.2	7:24	4:34
24	9.2	7:25	4:35
25	9.2	7:25	4:35
26	9.2	7:25	4:36
27	9.2	7:26	4:37
28	9.2	7:26	4:37
29	9.2	7:26	4:38
30	9.2	7:27	4:39
31	9.2	7:27	4:39

Solar energy in December

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in December, about 2.55 kWh/m² — the year's lowest.

For context, solar energy here swings from a low near 2.55 kWh/m² to a high of 7.45 kWh/m² in June across the year — December's 2.55 kWh/m² sits near the bottom.

	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)	2.6	2.6	2.6	2.6	2.6	2.6	2.6	2.5	2.5	2.5	2.5	2.5	2.5	2.5	2.5	2.5	2.5	2.5	2.5	2.5	2.5	2.5	2.5	2.5	2.6	2.6	2.6	2.6	2.6	2.6	2.6
Level	Moderate	Moderate	Moderate	Moderate	Moderate	Moderate	Moderate	Moderate	Moderate	Moderate	Moderate	Moderate	Moderate	Moderate	Moderate	Moderate	Moderate	Moderate	Moderate	Moderate	Moderate	Moderate	Moderate	Moderate	Moderate	Moderate	Moderate	Moderate	Moderate	Moderate	Moderate

	Solar energy (kWh/m²)	Level
1	2.6	Moderate
2	2.6	Moderate
3	2.6	Moderate
4	2.6	Moderate
5	2.6	Moderate
6	2.6	Moderate
7	2.6	Moderate
8	2.5	Moderate
9	2.5	Moderate
10	2.5	Moderate
11	2.5	Moderate
12	2.5	Moderate
13	2.5	Moderate
14	2.5	Moderate
15	2.5	Moderate
16	2.5	Moderate
17	2.5	Moderate
18	2.5	Moderate
19	2.5	Moderate
20	2.5	Moderate
21	2.5	Moderate
22	2.5	Moderate
23	2.5	Moderate
24	2.5	Moderate
25	2.6	Moderate
26	2.6	Moderate
27	2.6	Moderate
28	2.6	Moderate
29	2.6	Moderate
30	2.6	Moderate
31	2.6	Moderate

Planning a trip in December

Is December a good time to visit Thornton?

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

0.3

Sightseeing

11th-best month of the year

0.0

Beach & pool

10th-best month of the year

December is a weaker month for outdoor sightseeing in Thornton.

What to pack for Thornton in December

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

In December, Thornton sees daytime highs around 42°F and nights near 18°F. Pack a warm layer and a heavy coat. About 5 days see rain.

a warm layera heavy coat

UV index in Thornton 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 Thornton peaks around July 12 at about 11 (extreme) — 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.

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

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

Air quality in Thornton 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 Thornton 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 Thornton?

Thornton sits at 39.9°N, 105.0°W, 5,351 ft above sea level, in United States. The nearest listed city is Northglenn, 1.2 mi away.

Topography around Thornton

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

Within 2 miles, the terrain around Thornton has only modest variations in elevation — a maximum elevation change of 472 ft around an average of 5,276 ft above sea level; within 10 miles, significant variations in elevation — a maximum elevation change of 856 ft; within 50 miles, extreme variations in elevation — a maximum elevation change of 9,708 ft.

The land around Thornton is covered by artificial surfaces (68%) within 2 miles, artificial surfaces (45%) and grassland (34%) within 10 miles, and grassland (43%) and trees (30%) within 50 miles.

2 miles

472 ft

artificial surfaces 68%

10 miles

856 ft

artificial surfaces 45%

50 miles

9,708 ft

grassland 43%

treesgrasslandcroplandartificial surfacesbare terrainwatermoss and lichen

← November Thornton year-round climate January →Best places to visit in December

December weather nearby: Northglenn 1.2 mi · Sherrelwood 2.5 mi · Westminster 4.3 mi · Commerce City 4.3 mi · Broomfield 6.8 mi · Arvada 7.5 mi · Denver 8.7 mi · Wheat Ridge 8.7 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 Thornton (39.868°, -104.9719°, elevation 5,351 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	45	21
2	44	21
3	44	20
4	44	20
5	44	20
6	43	20
7	43	20
8	43	19
9	42	19
10	42	19
11	42	19
12	42	19
13	42	19
14	42	19
15	41	18
16	41	18
17	41	18
18	41	18
19	41	18
20	40	18
21	40	17
22	40	17
23	40	17
24	40	17
25	40	17
26	40	17
27	40	17
28	40	17
29	40	17
30	40	17
31	40	17

	Clearer (%)	Cloudier (%)
1	69	31
2	69	31
3	69	31
4	70	30
5	70	30
6	70	30
7	70	30
8	70	30
9	70	30
10	70	30
11	70	30
12	70	30
13	70	30
14	70	30
15	70	30
16	70	30
17	70	30
18	70	30
19	71	29
20	71	29
21	71	29
22	71	29
23	70	30
24	70	30
25	70	30
26	70	30
27	70	30
28	70	30
29	69	31
30	69	31
31	69	31

	Rain chance (%)	Snow chance (%)
1	18	18
2	17	17
3	17	17
4	17	17
5	16	16
6	16	16
7	16	16
8	16	16
9	16	16
10	16	16
11	16	16
12	16	16
13	17	16
14	17	17
15	17	17
16	17	17
17	17	17
18	17	17
19	17	17
20	17	17
21	17	17
22	17	17
23	17	17
24	16	17
25	16	17
26	16	17
27	16	16
28	16	16
29	16	16
30	15	15
31	15	15

	Dry (%)
1	100
2	100
3	100
4	100
5	100
6	100
7	100
8	100
9	100
10	100
11	100
12	100
13	100
14	100
15	100
16	100
17	100
18	100
19	100
20	100
21	100
22	100
23	100
24	100
25	100
26	100
27	100
28	100
29	100
30	100
31	100

	Avg high (°F)	Avg low (°F)
1	45	21
2	44	21
3	44	20
4	44	20
5	44	20
6	43	20
7	43	20
8	43	19
9	42	19
10	42	19
11	42	19
12	42	19
13	42	19
14	42	19
15	41	18
16	41	18
17	41	18
18	41	18
19	41	18
20	40	18
21	40	17
22	40	17
23	40	17
24	40	17
25	40	17
26	40	17
27	40	17
28	40	17
29	40	17
30	40	17
31	40	17

	Clearer (%)	Cloudier (%)
1	69	31
2	69	31
3	69	31
4	70	30
5	70	30
6	70	30
7	70	30
8	70	30
9	70	30
10	70	30
11	70	30
12	70	30
13	70	30
14	70	30
15	70	30
16	70	30
17	70	30
18	70	30
19	71	29
20	71	29
21	71	29
22	71	29
23	70	30
24	70	30
25	70	30
26	70	30
27	70	30
28	70	30
29	69	31
30	69	31
31	69	31

	Rain chance (%)	Snow chance (%)
1	18	18
2	17	17
3	17	17
4	17	17
5	16	16
6	16	16
7	16	16
8	16	16
9	16	16
10	16	16
11	16	16
12	16	16
13	17	16
14	17	17
15	17	17
16	17	17
17	17	17
18	17	17
19	17	17
20	17	17
21	17	17
22	17	17
23	17	17
24	16	17
25	16	17
26	16	17
27	16	16
28	16	16
29	16	16
30	15	15
31	15	15

	Dry (%)
1	100
2	100
3	100
4	100
5	100
6	100
7	100
8	100
9	100
10	100
11	100
12	100
13	100
14	100
15	100
16	100
17	100
18	100
19	100
20	100
21	100
22	100
23	100
24	100
25	100
26	100
27	100
28	100
29	100
30	100
31	100

	Avg high (°F)	Avg low (°F)
1	45	21
2	44	21
3	44	20
4	44	20
5	44	20
6	43	20
7	43	20
8	43	19
9	42	19
10	42	19
11	42	19
12	42	19
13	42	19
14	42	19
15	41	18
16	41	18
17	41	18
18	41	18
19	41	18
20	40	18
21	40	17
22	40	17
23	40	17
24	40	17
25	40	17
26	40	17
27	40	17
28	40	17
29	40	17
30	40	17
31	40	17

	Clearer (%)	Cloudier (%)
1	69	31
2	69	31
3	69	31
4	70	30
5	70	30
6	70	30
7	70	30
8	70	30
9	70	30
10	70	30
11	70	30
12	70	30
13	70	30
14	70	30
15	70	30
16	70	30
17	70	30
18	70	30
19	71	29
20	71	29
21	71	29
22	71	29
23	70	30
24	70	30
25	70	30
26	70	30
27	70	30
28	70	30
29	69	31
30	69	31
31	69	31

	Rain chance (%)	Snow chance (%)
1	18	18
2	17	17
3	17	17
4	17	17
5	16	16
6	16	16
7	16	16
8	16	16
9	16	16
10	16	16
11	16	16
12	16	16
13	17	16
14	17	17
15	17	17
16	17	17
17	17	17
18	17	17
19	17	17
20	17	17
21	17	17
22	17	17
23	17	17
24	16	17
25	16	17
26	16	17
27	16	16
28	16	16
29	16	16
30	15	15
31	15	15

	Dry (%)
1	100
2	100
3	100
4	100
5	100
6	100
7	100
8	100
9	100
10	100
11	100
12	100
13	100
14	100
15	100
16	100
17	100
18	100
19	100
20	100
21	100
22	100
23	100
24	100
25	100
26	100
27	100
28	100
29	100
30	100
31	100