Janesville weather in September

In September, Janesville sees average daytime highs of 72°F and overnight lows near 54°F, with 3.3 in of rain across 8.8 wet days and about 12.3 hours of daylight. It is the 4th-warmest and 6th-wettest month of the year here.

Highs ease over the month, from about 77°F in the first days to 67°F by the end. The sky is clear or mostly clear about 41% of the time in September, and the air most often feels dry.

Daylight stretches from about 13 hours at the start of September to 11 h 36 min by month's end. Set against the rest of the year, September is Janesville's 1st-clearest and 9th-windiest month. For the whole year in context, see Janesville's year-round climate.

Daytime high
72°
4th warmest
Overnight low
54°
9th coldest
Rainfall
3.3 in
8.8 wet days
Daylight
12 h 18 min
5:42 AM – 5:59 PM
Cloud cover
51%
1st clearest
Wind
7 mph
9th windiest
Solar energy
4.34 kWh/m²
Travel score
6.9
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 September

Average highAverage lowShaded bands: 10–90% of days

Highs ease over the month, from about 77°F in the first days to 67°F by the end.

A typical September day in Janesville reaches about 72°F in the afternoon and slips back to 54°F overnight — a 19°F spread between the day's warmth and the night's chill. On most days the high lands between 62°F and 83°F. Set against its neighbours, September runs about 7°F cooler than August and about 13°F warmer than October.

40°60°80°151015202530
Avg high (°F)Avg low (°F)
17859
27759
37759
47758
57658
67658
77657
87557
97556
107556
117456
127455
137455
147354
157354
167254
177253
187253
197152
207152
217052
227051
236951
246950
256950
266849
276849
286749
296748
306748

How September really feels in Janesville

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

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

Janesville weather by month

How September compares with the rest of the year at a glance. September is the 4th-warmest and 6th-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 September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 41% of the time in September, the clearest month of the year.

Beyond those clear spells, partly cloudy skies cover about 14% of September, with mostly cloudy or overcast conditions the remaining 45%.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
15941
25941
35941
45941
55941
65941
75941
85941
95842
105743
115743
125644
135644
145644
155644
165446
175446
185446
195446
205347
215347
225347
235347
245248
255248
265149
275149
285149
295248
305248

Chance of precipitation in September

Any precipitation

Janesville gets around 3.3 in of rain over 8.8 wet days in September. The line is the day-by-day chance of measurable precipitation.

Day to day, the chance of measurable rain averages around 30% and peaks near 31% on the wettest days.

0%10%20%30%40%151015202530
Rain chance (%)
129
229
328
428
528
628
728
828
928
1029
1129
1230
1330
1431
1531
1631
1731
1831
1931
2031
2131
2231
2331
2431
2531
2630
2730
2830
2929
3029

Humidity in September

DryComfortableHumidMuggyOppressiveMiserable

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

By dew point, September lands in the dry band about 57% of days. Sticky, muggy-or-worse air turns up on roughly 10% of them.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)Muggy (%)Oppressive (%)
1312522184
2332521174
3352521164
4372421153
5392420143
6402420143
7422319132
8442319122
9462318122
10472218112
11492217111
12512116111
13522116101
14542015101
1555201591
1657191491
1759191381
1861181380
1963181270
2064171270
2167161160
2269151060
2371141050
247313950
257413940
267612840
277811830
287910830
298010730
30829720

Wind in September

Winds average 7 mph in September.

Across September, daily wind ranges from about 7 mph on the calmest days to 8 mph at its breeziest. It stays fairly steady from day to day.

0246810151015202530
Wind speed (mph)Feels
17calm
27calm
37calm
47calm
57calm
67calm
77calm
87calm
97calm
107calm
117calm
127calm
137calm
147calm
157calm
167calm
177calm
187calm
197calm
207light breeze
217light breeze
228light breeze
238light breeze
248light breeze
258light breeze
268light breeze
278light breeze
288light breeze
298light breeze
308light breeze

Sunrise & sunset in September

DaylightNight

Daylight runs from about 13 hours at the start of September to 11 h 36 min by month's end. The lit band spans sunrise to sunset each day.

Days shrink by about 84 minutes over September. Sunrise moves from 5:25 AM to 5:58 AM, and sunset from 6:26 PM to 5:33 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
113.05:256:26
213.05:266:25
312.95:276:23
412.95:296:21
512.85:306:19
612.85:316:17
712.75:326:16
812.75:336:14
912.65:346:12
1012.65:356:10
1112.55:366:08
1212.55:376:06
1312.45:396:05
1412.45:406:03
1512.35:416:01
1612.35:425:59
1712.25:435:57
1812.25:445:55
1912.15:455:53
2012.15:465:52
2112.05:475:50
2212.05:495:48
2311.95:505:46
2411.95:515:44
2511.85:525:42
2611.85:535:40
2711.75:545:39
2811.75:555:37
2911.65:565:35
3011.65:585:33

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 4.34 kWh/m².

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 — September's 4.34 kWh/m² falls in the middle.

024151015202530
Solar energy (kWh/m²)Level
14.9Bright
24.9Bright
34.8Bright
44.8Bright
54.8Bright
64.7Bright
74.7Bright
84.6Bright
94.6Bright
104.5Bright
114.5Bright
124.5Bright
134.4Bright
144.4Bright
154.3Bright
164.3Bright
174.2Bright
184.2Bright
194.2Bright
204.1Bright
214.1Bright
224.0Bright
234.0Bright
244.0Moderate
253.9Moderate
263.9Moderate
273.8Moderate
283.8Moderate
293.8Moderate
303.7Moderate
Planning a trip in September

Is September a good time to visit Janesville?

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

6.9
Sightseeing
1st-best month of the year
5.0
Beach & pool
4th-best month of the year

September is a reasonable time to visit Janesville for sightseeing.

What to pack for Janesville in September

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

In September, Janesville sees daytime highs around 72°F and nights near 54°F. Worth packing: light clothes and rain gear. About 9 days see rain.

light clothesrain gear

UV index in Janesville in September

LowModerateHighVery highExtreme

Clear-sky midday UV in September peaks around 6 — enough to warrant sun protection. 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 September

GoodModeratePoorUnhealthyVery unhealthy

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