Climate and monthly weather forecastSullivan, IL
Climate and monthly weather forecast
Weather in January
January, like December, in Sullivan, Illinois, is an icy winter month, with temperature in the range of an average low of 21.6°F (-5.8°C) and an average high of 33.6°F (0.9°C). Sullivan's January weather reaches an average high of 33.6°F (0.9°C) and an average low of 21.6°F (-5.8°C), making it the coldest month. Weather in January »Weather in February
The last month of the winter, February, is also a wintry month in Sullivan, Illinois, with an average temperature varying between 25.5°F (-3.6°C) and 38.7°F (3.7°C). With the arrival of February, Sullivan's average high-temperature registers at a still cold 38.7°F (3.7°C), indicating a subtle variation from the previous month. Weather in February »Weather in March
March, the first month of the spring in Sullivan, is a fresh month, with an average temperature fluctuating between 36.1°F (2.3°C) and 50.5°F (10.3°C). The start of March is characterized by an increase in the average high-temperature, transitioning from a cold 38.7°F (3.7°C) in February to a fresh 50.5°F (10.3°C). Weather in March »Weather in April
April in Sullivan, Illinois, is an enjoyable spring month, with temperature in the range of an average low of 46°F (7.8°C) and an average high of 62.2°F (16.8°C). With the onset of April, the average high-temperature slightly shifts from March's fresh 50.5°F (10.3°C) to a comfortable 62.2°F (16.8°C). Weather in April »Weather in May
The last month of the spring, May, is a pleasant month in Sullivan, Illinois, with temperature in the range of an average low of 56.7°F (13.7°C) and an average high of 72.9°F (22.7°C). With the onset of May, Sullivan's average high-temperature experiences a rise, moving from April's refreshing 62.2°F (16.8°C) to a pleasant 72.9°F (22.7°C). Weather in May »Weather in June
The first month of the summer, June, is a moderately hot month in Sullivan, Illinois, with an average temperature fluctuating between 81.1°F (27.3°C) and 64.2°F (17.9°C). In June, the meteorological conditions subtly change with the average high-temperature edging from a pleasant 72.9°F (22.7°C) in May to a warm 81.1°F (27.3°C). Weather in June »Weather in July
July, the same as June, is another warm summer month in Sullivan, Illinois, with an average temperature varying between 82.2°F (27.9°C) and 65.8°F (18.8°C). Sullivan's temperatures tend to reach their peak averages in July, with a high of 82.2°F (27.9°C) and a low of 65.8°F (18.8°C). In July, the average heat index is evaluated at a hot 89.6°F (32°C). Weather in July »Weather in August
The last month of the summer, August, is also a moderately hot month in Sullivan, Illinois, with an average temperature varying between 81.5°F (27.5°C) and 64°F (17.8°C). In August, the average high-temperature registers at a still moderately hot 81.5°F (27.5°C), nearly identical to July's 82.2°F (27.9°C). Weather in August »Weather in September
The first month of the autumn, September, is also a moderately hot month in Sullivan, Illinois, with temperature in the range of an average low of 58.5°F (14.7°C) and an average high of 77.2°F (25.1°C). The introduction of September notes a subtle temperature variation to a still warm 77.2°F (25.1°C) from August's 81.5°F (27.5°C). Weather in September »Weather in October
October, like September, in Sullivan, Illinois, is another refreshing autumn month, with an average temperature varying between 63.9°F (17.7°C) and 48.2°F (9°C). As September shifts into October, a slight alteration in temperatures is observed, with average highs reducing from a moderately hot 77.2°F (25.1°C) to an enjoyable 63.9°F (17.7°C). Weather in October »Weather in November
November, the last month of the autumn in Sullivan, is also a frosty month, with an average temperature ranging between max 49.8°F (9.9°C) and min 36.1°F (2.3°C). The shift from October to November involves a decrease in the average high-temperature, dropping from an enjoyable 63.9°F (17.7°C) to a frosty 49.8°F (9.9°C). Weather in November »Weather in December
The first month of the winter, December, is also a wintry month in Sullivan, Illinois, with temperature in the range of an average low of 28.4°F (-2°C) and an average high of 38.8°F (3.8°C). December's onset corresponds with a shift in the average high-temperature, moving from a chilly 49.8°F (9.9°C) in November to a wintry 38.8°F (3.8°C). Weather in December »Updated: Feb 12, 2024
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate
Frequently asked questions
January, known for its average high temperature of 33.6°F (0.9°C) and an average low temperature of 21.6°F (-5.8°C), is the coldest month in Sullivan.
In Sullivan, Illinois, during the entire year, the rain falls for 130.9 days and collects up to 15.43" (392mm) of precipitation.
January through April, November and December are months with snowfall in Sullivan.
The month with the most snowfall is January, when snow falls for 6.4 days and typically aggregates up to 1.54" (39mm) of snow.
In Sullivan, Illinois, during the entire year, snow falls for 21.5 days and aggregates up to 4.53" (115mm) of snow.
January has the least sunshine of the year, with an average of 4.1h of sunshine.
The months with the lowest UV index in Sullivan are January, February, November and December, with an average maximum UV index of 2.
February is the month with the least rainfall. Rain falls for 5.9 days and accumulates 0.71" (18mm) of precipitation.
On Sunday, March 10. 2024, at 2:00 am, Daylight Saving Time starts in Sullivan, Illinois, 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.
May through October are months without snowfall.
The month with the most rainfall in Sullivan, Illinois, is June, when the rain falls for 13.9 days and typically aggregates up to 1.85" (47mm) of precipitation.
June has the longest days of the year in Sullivan, with an average of 14h and 54min of daylight.
With an average of 10.4h of sunshine, June has the most sunshine of the year in Sullivan, Illinois.
June through August, with an average maximum UV index of 6, are months with the highest UV index in Sullivan, Illinois.
July stands out as Sullivan's warmest month, with an average high-temperature of 82.2°F (27.9°C) and a low-temperature of 65.8°F (18.8°C).
July is the most humid month, with an average relative humidity of 84%.
With an average relative humidity of 70%, October is the least humid month.
The month with the shortest days is December, with an average of 9h and 24min of daylight.
Average temperature
Sullivan, IL
The warmest month (with the highest average high temperature) is July (82.2°F).
The month with the lowest average high temperature is January (33.6°F).
The month with the highest average low temperature is July (65.8°F).
The coldest month (with the lowest average low temperature) is January (21.6°F).
Average pressure
Sullivan, IL
- Average pressure in January:
30.15"Hg - Average pressure in February:
30.11"Hg - Average pressure in March:
30.08"Hg - Average pressure in April:
29.94"Hg - Average pressure in May:
29.96"Hg - Average pressure in June:
29.93"Hg
- Average pressure in July:
29.97"Hg - Average pressure in August:
29.98"Hg - Average pressure in September:
30.03"Hg - Average pressure in October:
30.03"Hg - Average pressure in November:
30.12"Hg - Average pressure in December:
30.13"Hg
The month with the highest atmospheric pressure is January (30.15"Hg).
The month with the lowest atmospheric pressure is June (29.93"Hg).
Average wind speed
Sullivan, IL
- Average wind speed in January:
10.7mph - Average wind speed in February:
10.6mph - Average wind speed in March:
10.3mph - Average wind speed in April:
10.4mph - Average wind speed in May:
8.7mph - Average wind speed in June:
7.5mph
- Average wind speed in July:
6.3mph - Average wind speed in August:
6.3mph - Average wind speed in September:
7.1mph - Average wind speed in October:
9.3mph - Average wind speed in November:
10mph - Average wind speed in December:
9.9mph
The windiest month (with the highest average wind speed) is January (10.7mph).
The calmest months (with the lowest average wind speed) are July and August (6.3mph).
Average humidity
Sullivan, IL
The month with the highest relative humidity is July (84%).
The month with the lowest relative humidity is October (70%).
Average rainfall
Sullivan, IL
- Average rainfall in January:
0.94" - Average rainfall in February:
0.71" - Average rainfall in March:
1.22" - Average rainfall in April:
1.65" - Average rainfall in May:
1.77" - Average rainfall in June:
1.85"
- Average rainfall in July:
1.65" - Average rainfall in August:
1.54" - Average rainfall in September:
1.06" - Average rainfall in October:
1.3" - Average rainfall in November:
0.87" - Average rainfall in December:
0.87"
The wettest month (with the highest rainfall) is June (1.85").
The driest month (with the least rainfall) is February (0.71").
Average rainfall days
Sullivan, IL
- Average rainfall days in January:
6.4 days - Average rainfall days in February:
5.9 days - Average rainfall days in March:
11.5 days - Average rainfall days in April:
13.8 days - Average rainfall days in May:
16.3 days - Average rainfall days in June:
13.9 days
- Average rainfall days in July:
14.9 days - Average rainfall days in August:
13 days - Average rainfall days in September:
10.6 days - Average rainfall days in October:
9.2 days - Average rainfall days in November:
7.9 days - Average rainfall days in December:
7.5 days
The month with the highest number of rainy days is May (16.3 days).
The month with the least rainy days is February (5.9 days).
Average snowfall
Sullivan, IL
The month with the highest snowfall is January (1.54").
The months with the least snowfall are May, June, July, August, September and October (0").
Average snowfall days
Sullivan, IL
- Average snowfall days in January:
6.4 days - Average snowfall days in February:
6 days - Average snowfall days in March:
2.5 days - Average snowfall days in April:
0.5 days - Average snowfall days in May:
0 days - Average snowfall days in June:
0 days
- Average snowfall days in July:
0 days - Average snowfall days in August:
0 days - Average snowfall days in September:
0 days - Average snowfall days in October:
0 days - Average snowfall days in November:
1.6 days - Average snowfall days in December:
4.5 days
The month with the highest number of snowfall days is January (6.4 days).
The months with the least snowfall days are May, June, July, August, September and October (0 days).
Average daylight / Average sunshine
Sullivan, IL
- Average daylight in January:
9h and 48min - Average daylight in February:
10h and 42min - Average daylight in March:
12h and 0min - Average daylight in April:
13h and 18min - Average daylight in May:
14h and 24min - Average daylight in June:
14h and 54min
- Average daylight in July:
14h and 36min - Average daylight in August:
13h and 42min - Average daylight in September:
12h and 24min - Average daylight in October:
11h and 6min - Average daylight in November:
10h and 0min - Average daylight in December:
9h and 24min
The month with the longest days is June (Average daylight: 14h and 54min).
The month with the shortest days is December (Average daylight: 9h and 24min).
- Average sunshine in January:
4h and 6min - Average sunshine in February:
4h and 18min - Average sunshine in March:
6h and 18min - Average sunshine in April:
8h and 12min - Average sunshine in May:
9h and 6min - Average sunshine in June:
10h and 24min
- Average sunshine in July:
10h and 6min - Average sunshine in August:
9h and 48min - Average sunshine in September:
9h and 0min - Average sunshine in October:
6h and 18min - Average sunshine in November:
5h and 24min - Average sunshine in December:
4h and 36min
The month with the most sunshine is June (Average sunshine: 10h and 24min).
The month with the least sunshine is January (Average sunshine: 4h and 6min).
Average sunshine days
Sullivan, IL
- Average sunshine days in January:
19.8 days - Average sunshine days in February:
16.7 days - Average sunshine days in March:
16.3 days - Average sunshine days in April:
14.9 days - Average sunshine days in May:
12.3 days - Average sunshine days in June:
12.5 days
- Average sunshine days in July:
12.6 days - Average sunshine days in August:
15.6 days - Average sunshine days in September:
18.2 days - Average sunshine days in October:
20.5 days - Average sunshine days in November:
19.7 days - Average sunshine days in December:
19.8 days
The month with the most sunshine days is October (20.5 days).
The month with the least sunshine days is May (12.3 days).
Average UV index
Sullivan, IL
The months with the highest UV index are June, July and August (UV index 6).
The months with the lowest UV index are January, February, November and December (UV index 2).
Average cloud cover
Sullivan, IL
The month with the most cloud cover is January (Cloud cover 56).
The month with the least cloud cover is June (Cloud cover 30).
Average visibility
Sullivan, IL
The months with the highest visibility are January, February, March, April, May, June, September, October, November and December (6mi).
The months with the lowest visibility are July and August (5mi).
