Climate and monthly weather forecast
Janesville, WI

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The climate of Janesville

Janesville, Wisconsin fits squarely within the Humid Continental zone of climate classification, adhering to the Dfb code within the Köppen system. This designation points to the overall climate being categorized as humid continental, having no dry season with warm summers.

The annual cycle in Janesville demonstrates significant temperature swings, with monthly average highs tallying around 25°F (-3.9°C) in January and peaking at approximately 79.7°F (26.5°C) in July. Moreover, monthly lows also make a tremendous leap from 12.9°F (-10.6°C) in the deep winter to 62.4°F (16.9°C) at the height of the summer season. The city reflects a clear humidity trend, with the driest point in April when the relative humidity drops to 76%, compared to the rest of the year when figures hover above 80%.

Rainfall appears throughout the year ranging from 0.75" (19mm) in February to 2.76" (70mm) in June. Furthermore, snowfall starts to accumulate from November onwards, reaching a climax in January with an average of 2.83" (72mm).

A singular aspect can be seen in daylight hours fluctuating from a maximum of 15.3 hours in June to a minimum of 9.1 hours in December. Such variations also correlate with the amount of sunshine, peaking in July with 9.7 hours a day. The UV index reflects a predictable pattern, curving upwards to a high of 6 around June and sinking to a low of 1 during the dark winter months.

The best time to visit Janesville

Factoring in temperatures, humidity, daylight hours, and the UV index, the peak summer months of June and July can be gauged as an optimum period to visit Janesville. These months offer ample daylight and abundant sunshine, making conditions perfect for outdoor activities. The average high temperatures revolve around 76.1°F (24.5°C) to 79.7°F (26.5°C), pairing with relative humidity levels of 82% to 84%.

The worst time to visit Janesville

January and February stand out as the least favorable times to be in Janesville due to the chilly conditions. These winter months present the coldest temperature range, with average highs merely managing to rise to 25°F (-3.9°C) to 28.9°F (-1.7°C) and lows sinking to a frigid 12.9°F (-10.6°C) to 16°F (-8.9°C). These stark conditions are further amplified by high relative humidity levels, reaching up to 86% to 87%.

Spring weather in Janesville

The spring months witness a noticeable thaw in temperatures, averaging between 43.2°F (6.2°C) to 67.1°F (19.5°C) from March to May. Nighttime lows, concurrently, rise from a chilly 28°F (-2.2°C) in March to a more comfortable 49.5°F (9.7°C) in May. Rainfall, however, increases significantly during this period, escalating from an initial 0.98" (25mm) in March to a considerable 2.32" (59mm) by the end of May.

Summer weather in Janesville

Janesville experiences warm summers with July clocking the highest average temperature of 79.7°F (26.5°C) and the lowest nightly temperatures around 62.4°F (16.9°C). Humidity reaches its zenith around this time with an average of 84%. Amid this heat, rainfall also sees an upsurge, surmounting to 2.76" (70mm) in June. However, these figures start to recede as the summer months progress.

Autumn weather in Janesville

Autumn merits a distinct transition from summer's warmth to the emerging chill of winter. Average temperatures make a steady descent from 72.1°F (22.3°C) in September to 43.9°F (6.6°C) in November, while nighttime lows accompany this downward trend, dropping from 53.1°F (11.7°C) to 31.1°F (-0.5°C). The rainfall marginally lessens over this period from 1.22" (31mm) in September to 0.94" (24mm) by November.

Winter weather in Janesville

Winter months in Janesville are marked by frigid temperatures and snowfall. Average temperatures dip to 25°F (-3.9°C) in January, while the lows stoop to a chilling 12.9°F (-10.6°C). Snowfall adds to the wintry feel, aggregating around 2.83" (72mm) in January. Comparatively, the daylight hours shorten and the amount of sunshine decreases, falling to a meager 3.9 hours a day in December.

Weather in January

January in Janesville, Wisconsin marks the peak of winter, often showcasing brisk and frosty conditions. Overall, lower than average temperatures dominate this month, which can often lead to a high chance of substantial snowfall. Weather in January »

Weather in February

With spring yet to set sight, February weather in Janesville, Wisconsin carries on the winter tradition of January. Cold temperatures remain, however, there is a gradual and slight easing as the month progresses. February records a reduced level of snowfall down to 2.36" (60mm) over about 10.3 days. Weather in February »

Weather in March

March in Janesville, Wisconsin ushers in signs of spring, with warming temperatures and a reducing snow canvas. The melting snow and increased hours of sunshine serve as suitable soil moisturizer for the sprouting flora. Nevertheless, it remains the month with the most rain, clocking at 0.98" (25mm) over a remarkably high 10.2 days, indicating a shift from snow to rain-dominated precipitation. Weather in March »

Weather in April

April in Janesville, Wisconsin blooms with the full onset of spring, and temperatures begin to climb and reflect this change. Flowers emerge vibrantly, marking the landscape with color, while trees regain their leafy garb. The April weather showcases a staggering increase in rainfall to 1.89" (48mm) but over a lengthy span of 13.7 days, signifying the spring showers. Weather in April »

Weather in May

May in Janesville, Wisconsin sees the consolidation of spring and teases the impending arrival of summer. Nature is in full blossom, with greenery spanning the panoramic view and people venturing outdoors to enjoy the balmy weather. Weather in May »

Weather in June

June in Janesville, Wisconsin celebrates the arrival of summer accompanied by sun-drenched days and warmer temperatures. It's a joyous time for concerts in the park, outdoor dining, and a wealth of activities on the Rock River. This month lays claim to the highest amount of daylight, basking in around 15.3 hours, ensuring ample time for fun under the sun. Weather in June »

Weather in July

July in Janesville, Wisconsin, is the pinnacle of the midwest summer, dominated by long, sun-filled days and high temperatures. This peak summer month allows residents to take full advantage of the wide array of outdoor delights Janesville offers. Weather in July »

Weather in August

August in Janesville, Wisconsin, carries on the torch of summer, ensuring warm temperatures, clear skies, and longer daylight hours. However, it also marks a transition period as temperatures gradually taper off hinting at the forthcoming autumn. Weather in August »

Weather in September

September ushers in the subtly changing season from summer to autumn in Janesville, Wisconsin. Temperatures begin to cool, adding a fresh crispness to the city’s weather. The transition is marked by the leaves changing colors from green to vibrant hues of yellow, orange, and red. Weather in September »

Weather in October

October in Janesville, Wisconsin, greets cooler temperatures and transforms the city into a colorful canvas of fall foliage. Residents thrill to the crunch of leaves underfoot, the smell of autumn rain, and the taste of seasonal harvest fruits. Weather in October »

Weather in November

November in Janesville, Wisconsin marks the onset of winter season and the advent of colder temperatures. As the last leaves fall, the landscape prepares for the winter blanket. Total snowfall almost triples to 1.81" (46mm) across four days when compared to October. Weather in November »

Weather in December

December in Janesville, Wisconsin signals the full arrival of winter, resplendent with cold temperatures, snowfall, and the joyous holiday season. Snowfall increases to 1.61" (41mm) over a significantly higher 9.1 days. Winter sports enthusiasts can enjoy the snow-covered landscape, and families can engage in delightful Christmas festivities. Weather in December »
Updated: Feb 14, 2024
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate

Frequently asked questions

What part of the year is the coldest in Janesville?

In Janesville, January is known for its average lowest temperatures, reaching a high of 25°F (-3.9°C) and a low of 12.9°F (-10.6°C).

What is the most humid month in Janesville?

The most humid month in Janesville, Wisconsin, is January, with an average relative humidity of 87%.

What is the driest month in Janesville?

The months with the least rainfall in Janesville, Wisconsin, are January and February Rain falls for 3.5 days and accumulates 0.75" (19mm) of rain.

How much does it rain in Janesville?

In Janesville, Wisconsin, during the entire year, the rain falls for 127.7 days and collects up to 17.87" (454mm) of precipitation.

When does it snow in Janesville?

Months with snowfall in Janesville, Wisconsin, are January through April, October through December.

What is the snowiest month in Janesville?

January is the month with the most snowfall in Janesville, Wisconsin. Snow falls for 12.5 days and accumulates 2.83" (72mm) of snow.

How many days does it snow in Janesville?

Throughout the year, in Janesville, there are 44.5 snowfall days, and 11.34" (288mm) of snow is accumulated.

What is the month with the least sunshine in Janesville?

The month with the least sunshine in Janesville is January, with an average of 3.5h of sunshine.

What is the month with the lowest UV index in Janesville?

The months with the lowest UV index in Janesville are January and December, with an average maximum UV index of 1.

When is Daylight Saving Time (DST) in Janesville?

On Sunday, March 10. 2024, at 2:00 am, Daylight Saving Time starts in Janesville, Wisconsin, and the time zone changes from CST to CDT. Daylight Saving Time ends Sunday, November 3. 2024, at 2:00 am, and the time zone reverts from CDT to CST.

What is the least humid month in Janesville?

The months with the lowest humidity are April and October, with an average relative humidity of 76%.

When it does not snow in Janesville?

In Janesville, Wisconsin, snow does not fall in May through September.

What is the rainiest month in Janesville?

June is the month with the most rainfall in Janesville. Rain falls for 16.3 days and accumulates 2.76" (70mm) of precipitation.

When are the longest days in Janesville?

With an average of 15h and 18min of daylight, June has the longest days of the year.

When is the highest UV index in Janesville?

With an average maximum UV index of 6, June is the month with the highest UV index.

What time of the year is the hottest in Janesville?

Janesville reaches its average highest temperatures in July, measuring 79.7°F (26.5°C) at the peak and 62.4°F (16.9°C) at the lowest.

What is the month with the most sunshine in Janesville?

The months with the most sunshine in Janesville are July and August, with an average of 9.7h of sunshine.

What is the month with the shortest days in Janesville?

December has the shortest days of the year in Janesville, Wisconsin, with an average of 9h and 6min of daylight.

Average temperature
Janesville, WI

Average temperature - Janesville, WI

The warmest month (with the highest average high temperature) is July (79.7°F).
The month with the lowest average high temperature is January (25°F).

The month with the highest average low temperature is July (62.4°F).
The coldest month (with the lowest average low temperature) is January (12.9°F).

Average pressure
Janesville, WI

Average pressure - Janesville, WI

The month with the highest atmospheric pressure is January (30.11"Hg).
The month with the lowest atmospheric pressure is June (29.91"Hg).

Average wind speed
Janesville, WI

Average wind speed - Janesville, WI

The windiest month (with the highest average wind speed) is April (10.1mph).
The calmest month (with the lowest average wind speed) is August (6.4mph).

Average humidity
Janesville, WI

Average humidity - Janesville, WI

The month with the highest relative humidity is January (87%).
The months with the lowest relative humidity are April and October (76%).

Average rainfall
Janesville, WI

Average rainfall - Janesville, WI

The wettest month (with the highest rainfall) is June (2.76").
The driest months (with the least rainfall) are January and February (0.75").

Average rainfall days
Janesville, WI

Average rainfall days - Janesville, WI

The month with the highest number of rainy days is June (16.3 days).
The month with the least rainy days is January (3.5 days).

Average snowfall
Janesville, WI

Average snowfall - Janesville, WI

The month with the highest snowfall is January (2.83").
The months with the least snowfall are May, June, July, August and September (0").

Average snowfall days
Janesville, WI

Average snowfall days - Janesville, WI

The month with the highest number of snowfall days is January (12.5 days).
The months with the least snowfall days are June, July, August and September (0 days).

Average daylight / Average sunshine
Janesville, WI

Average daylight / Average sunshine - Janesville, WI

The month with the longest days is June (Average daylight: 15h and 18min).
The month with the shortest days is December (Average daylight: 9h and 6min).

The months with the most sunshine are July and August (Average sunshine: 9h and 42min).
The month with the least sunshine is January (Average sunshine: 3h and 30min).

Average sunshine days
Janesville, WI

Average sunshine days - Janesville, WI

The month with the most sunshine days is November (19.1 days).
The month with the least sunshine days is June (10.9 days).

Average visibility
Janesville, WI

Average visibility - Janesville, WI

The months with the highest visibility are March, April, May, June, October, November and December (6mi).
The months with the lowest visibility are January, February, July, August and September (5mi).

Janesville, Wisconsin, USA

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