Janesville weather in December

In December, Janesville sees average daytime highs of 33°F and overnight lows near 20°F, with 2.0 in of precipitation across 7.8 wet days and about 8.9 hours of daylight. It is the 10th-warmest and 10th-wettest month of the year here.

Highs ease over the month, from about 37°F in the first days to 30°F by the end. The sky is clear or mostly clear about 23% of the time in December, and the air most often feels dry.

Daylight stretches from about 9 h 06 min at the start of December to 8 h 54 min by month's end. Set against the rest of the year, December is Janesville's 11th-clearest and 7th-windiest month. For the whole year in context, see Janesville's year-round climate.

Daytime high
33°
10th warmest
Overnight low
20°
3rd coldest
Precipitation
2.0 in
7.8 wet days
Daylight
8 h 54 min
7:26 AM – 4:19 PM
Cloud cover
69%
11th clearest
Wind
8 mph
7th windiest
Solar energy
1.59 kWh/m²
Travel score
0.0
out of 10

Janesville is city in and county seat of Rock County, Wisconsin, United States.

Density
720/km²
people per km²
Founded
1853

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 37°F in the first days to 30°F by the end.

A typical December day in Janesville reaches about 33°F in the afternoon and slips back to 20°F overnight — a 13°F spread between the day's warmth and the night's chill. On most days the high lands between 19°F and 46°F. Set against its neighbours, December runs about 12°F cooler than November and about 5°F warmer than January.

20°40°60°151015202531
Avg high (°F)Avg low (°F)
13825
23724
33724
43624
53623
63523
73522
83522
93422
103421
113421
123321
133320
143320
153320
163320
173220
183220
193219
203219
213219
223119
233119
243119
253118
263118
273118
283118
293017
303017
313017

How December really feels in Janesville

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
27 feel bitter (≤ 14°F)

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

Janesville weather by month

How December compares with the rest of the year at a glance. December is the 10th-warmest and 10th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°F)Rainfall (inches)Wet daysSnow daysDaylight (hours)Travel score
Jan28° / 14°1.87.76.49.20.0
Feb32° / 17°1.76.95.510.30.0
Mar44° / 28°2.49.43.511.61.0
Apr57° / 39°4.0121.613.13.7
May68° / 50°3.912.20.114.45.9
Jun78° / 60°4.111.6015.16.4
Jul81° / 64°3.310.1014.86.5
Aug79° / 62°3.610.3013.76.7
Sep72° / 54°3.38.8012.36.9
Oct59° / 42°2.88.90.310.84.8
Nov45° / 31°2.2829.61.1
Dec33° / 20°2.07.858.90.0

Cloud cover in December

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 23% of the time in December.

Beyond those clear spells, partly cloudy skies cover about 10% of December, with mostly cloudy or overcast conditions the remaining 67%.

0%25%50%75%100%151015202531
Clearer (%)Cloudier (%)
13664
23565
33565
43565
53565
63565
73565
83664
93664
103664
113664
123565
133565
143367
153367
163367
173367
183367
193268
203268
213268
223268
233169
243169
253268
263169
273169
283169
293268
303268
313268

Chance of precipitation in December

Any precipitationSnow

Janesville gets around 2.0 in of rain and snow over 7.8 wet days in December. The line is the day-by-day chance of measurable precipitation.

Day to day, the chance of measurable precipitation averages around 25% and peaks near 30% on the wettest days, and about 5 days bring snow.

0%10%20%30%40%151015202531
Rain chance (%)Snow chance (%)
13015
22915
32916
42916
52916
62816
72816
82716
92716
102616
112616
122515
132515
142415
152415
162314
172314
182314
192214
202214
212214
222214
232215
242315
252315
262316
272316
282416
292416
302417
312417

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 8 mph in December.

Across December, daily wind ranges from about 8 mph on the calmest days to 8 mph at its breeziest. It stays fairly steady from day to day.

051015151015202531
Wind speed (mph)Feels
18light breeze
28light breeze
38light breeze
48light breeze
58light breeze
68light breeze
78light breeze
88light breeze
98light breeze
108light breeze
118light breeze
128light breeze
138light breeze
148light breeze
158light breeze
168light breeze
178light breeze
188light breeze
198light breeze
208light breeze
218light breeze
228light breeze
238light breeze
248light breeze
258light breeze
268light breeze
278light breeze
288light breeze
298light breeze
308light breeze
318light breeze

Sunrise & sunset in December

DaylightNight

Daylight runs from about 9 h 06 min at the start of December to 8 h 54 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 7:13 AM to 7:32 AM, and sunset from 4:19 PM to 4:26 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202531
Daylight (h)Sunrise (AM)Sunset (PM)
19.17:134:19
29.17:144:18
39.17:154:18
49.07:164:18
59.07:174:18
69.07:184:18
79.07:194:18
89.07:204:18
99.07:214:18
108.97:214:18
118.97:224:18
128.97:234:18
138.97:244:18
148.97:254:18
158.97:254:18
168.97:264:19
178.97:274:19
188.97:274:19
198.97:284:20
208.97:284:20
218.97:294:20
228.97:294:21
238.97:304:21
248.97:304:22
258.97:314:22
268.97:314:23
278.97:314:24
288.97:324:24
298.97:324:25
308.97:324:26
318.97:324:26

Solar energy in December

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in December, about 1.59 kWh/m² — the year's lowest.

For context, solar energy here swings from a low near 1.59 kWh/m² to a high of 6.29 kWh/m² in June across the year — December's 1.59 kWh/m² sits near the bottom.

00.511.522.5151015202531
Solar energy (kWh/m²)Level
11.7Dim
21.7Dim
31.6Dim
41.6Dim
51.6Dim
61.6Dim
71.6Dim
81.6Dim
91.6Dim
101.6Dim
111.6Dim
121.6Dim
131.6Dim
141.6Dim
151.6Dim
161.6Dim
171.6Dim
181.6Dim
191.6Dim
201.6Dim
211.6Dim
221.6Dim
231.6Dim
241.6Dim
251.6Dim
261.6Dim
271.6Dim
281.6Dim
291.6Dim
301.6Dim
311.6Dim
Planning a trip in December

Is December a good time to visit Janesville?

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 Janesville.

What to pack for Janesville in December

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

In December, Janesville sees daytime highs around 33°F and nights near 20°F. Pack a warm layer and a heavy coat. About 8 days see rain.

a warm layera heavy coat

UV index in Janesville in December

LowModerateHighVery highExtreme

Clear-sky midday UV in December peaks around 1. The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in Janesville peaks around June 19 at about 9 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near December 22 at about 1 (low).

The index reaches 3 or more — the level where the WHO recommends sun protection — in 8 months of the year.

025710JanFebMarAprMayJunJulAugSepOctNovDecLowModerateHighVery highHighModerateLowJun 19UV 9Dec 22UV 1
UV index (midday)Level
Jan2Low
Feb3Moderate
Mar4Moderate
Apr6High
May8Very high
Jun9Very high
Jul8Very high
Aug8Very high
Sep6High
Oct3Moderate
Nov2Moderate
Dec1Low

Air quality in Janesville 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 Janesville is worst in July — around 15 µg/m³ PM2.5 (moderate), about 2.0× the cleanest month (October, 8 µg/m³).

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

01020JanFebMarAprMayJunJulAugSepOctNovDecGoodModerateModerateGoodJul 1715 µg/m³Oct 238 µg/m³
PM2.5 (µg/m³)Level
Jan11Good
Feb13Moderate
Mar13Moderate
Apr12Good
May13Moderate
Jun14Moderate
Jul15Moderate
Aug14Moderate
Sep11Good
Oct8Good
Nov8Good
Dec9Good
Location & terrain

Where is Janesville?

Janesville sits at 42.7°N, 89.0°W, 837 ft above sea level, in United States. The nearest listed city is Beloit, 12 mi away.

Topography around Janesville

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

Within 2 miles, the terrain around Janesville has only modest variations in elevation — a maximum elevation change of 200 ft around an average of 833 ft above sea level; within 10 miles, only modest variations in elevation — a maximum elevation change of 348 ft; within 50 miles, significant variations in elevation — a maximum elevation change of 1,063 ft.

The land around Janesville is covered by artificial surfaces (37%), trees (34%) and grassland (22%) within 2 miles, cropland (58%) within 10 miles, and cropland (56%) and trees (22%) within 50 miles.

2 miles
200 ft
10 miles
348 ft
50 miles
1,063 ft
treesgrasslandcroplandartificial surfacesbare terrainwater
December weather nearby: Beloit 12 mi · Machesney Park 23 mi · Loves Park 25 mi · Rockford 29 mi · Fitchburg 30 mi · Belvidere 30 mi · Madison 33 mi · Sun Prairie 36 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 Janesville (42.6828°, -89.0187°, elevation 837 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).