Average Weather in Harristown Illinois, United States
In Harristown, the summers are long, warm, and humid; the winters are freezing and windy; and it is partly cloudy year round. Over the course of the year, the temperature typically varies from 21°F to 86°F and is rarely below 3°F or above 93°F.
Based on the tourism score, the best time of year to visit Harristown for warm-weather activities is from early June to mid September.
The hot season lasts for 4.1 months, from May 21 to September 23, with an average daily high temperature above 76°F. The hottest day of the year is July 19, with an average high of 86°F and low of 67°F.
The cold season lasts for 3.1 months, from November 30 to March 1, with an average daily high temperature below 45°F. The coldest day of the year is January 22, with an average low of 21°F and high of 35°F.
Average High and Low Temperature
The figure below shows you a compact characterization of the entire year of hourly average temperatures. The horizontal axis is the day of the year, the vertical axis is the hour of the day, and the color is the average temperature for that hour and day.
Average Hourly Temperature
In Harristown, the average percentage of the sky covered by clouds experiences significant seasonal variation over the course of the year.
The clearer part of the year in Harristown begins around June 14 and lasts for 4.4 months, ending around October 27. On August 27, the clearest day of the year, the sky is clear, mostly clear, or partly cloudy 70% of the time, and overcast or mostly cloudy 30% of the time.
The cloudier part of the year begins around October 27 and lasts for 7.6 months, ending around June 14. On December 28, the cloudiest day of the year, the sky is overcast or mostly cloudy 56% of the time, and clear, mostly clear, or partly cloudy 44% of the time.
Cloud Cover Categories
0% clear 20% mostly clear 40% partly cloudy 60% mostly cloudy 80% overcast 100%
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. The chance of wet days in Harristown varies throughout the year.
The wetter season lasts 5.6 months, from March 26 to September 13, with a greater than 27% chance of a given day being a wet day. The chance of a wet day peaks at 39% on June 8.
The drier season lasts 6.4 months, from September 13 to March 26. The smallest chance of a wet day is 15% on January 28.
Among wet days, we distinguish between those that experience rain alone, snow alone, or a mixture of the two. Based on this categorization, the most common form of precipitation throughout the year is rain alone, with a peak probability of 39% on June 8.
Daily Chance of Precipitation
To show variation within the months and not just the monthly totals, we show the rainfall accumulated over a sliding 31-day period centered around each day of the year. Harristown experiences significant seasonal variation in monthly rainfall.
Rain falls throughout the year in Harristown. The most rain falls during the 31 days centered around June 2, with an average total accumulation of 4.0 inches.
The least rain falls around January 26, with an average total accumulation of 1.1 inches.
Average Monthly Rainfall
We report snowfall in liquid-equivalent terms. The actual depth of new snowfall is typically between 5 and 10 times the liquid-equivalent amount, assuming the ground is frozen. Colder, drier snow tends to be on the higher end of that range and warmer, wetter snow on the lower end.
As with rainfall, we consider the snowfall accumulated over a sliding 31-day period centered around each day of the year. Harristown experiences some seasonal variation in monthly liquid-equivalent snowfall.
The snowy period of the year lasts for 4.2 months, from November 19 to March 27, with a sliding 31-day liquid-equivalent snowfall of at least 0.1 inches. The most snow falls during the 31 days centered around January 6, with an average total liquid-equivalent accumulation of 0.4 inches.
The snowless period of the year lasts for 7.8 months, from March 27 to November 19. The least snow falls around July 27, with an average total liquid-equivalent accumulation of 0.0 inches.
Average Liquid-Equivalent Monthly Snowfall
The length of the day in Harristown varies significantly over the course of the year. In 2018, the shortest day is December 21, with 9 hours, 21 minutes of daylight; the longest day is June 21, with 15 hours, 0 minutes of daylight.
Hours of Daylight and Twilight
The earliest sunrise is at 5:27 AM on June 14, and the latest sunrise is 2 hours, 0 minutes later at 7:27 AM on November 3. The earliest sunset is at 4:31 PM on December 7, and the latest sunset is 3 hours, 57 minutes later at 8:28 PM on June 27.
Daylight saving time (DST) is observed in Harristown during 2018, starting in the spring on March 11, lasting 7.8 months, and ending in the fall on November 4.
Sunrise & Sunset with Twilight and Daylight Saving Time
Harristown experiences extreme seasonal variation in the perceived humidity.
The muggier period of the year lasts for 3.9 months, from May 24 to September 21, during which time the comfort level is muggy, oppressive, or miserable at least 15% of the time. The muggiest day of the year is July 21, with muggy conditions 62% of the time.
The least muggy day of the year is December 25, when muggy conditions are essentially unheard of.
Humidity Comfort Levels
dry 55°F comfortable 60°F humid 65°F muggy 70°F oppressive 75°F miserable
The average hourly wind speed in Harristown experiences significant seasonal variation over the course of the year.
The windier part of the year lasts for 7.5 months, from October 9 to May 25, with average wind speeds of more than 9.9 miles per hour. The windiest day of the year is April 1, with an average hourly wind speed of 12.6 miles per hour.
The calmer time of year lasts for 4.5 months, from May 25 to October 9. The calmest day of the year is July 31, with an average hourly wind speed of 7.2 miles per hour.
Average Wind Speed
The predominant average hourly wind direction in Harristown varies throughout the year.
The wind is most often from the south for 5.0 days, from February 28 to March 5 and for 8.8 months, from March 12 to December 7, with a peak percentage of 39% on June 21. The wind is most often from the north for 1.0 weeks, from March 5 to March 12, with a peak percentage of 28% on March 8. The wind is most often from the west for 2.8 months, from December 7 to February 28, with a peak percentage of 37% on January 1.
Best Time of Year to Visit
To characterize how pleasant the weather is in Harristown throughout the year, we compute two travel scores.
The tourism score favors clear, rainless days with perceived temperatures between 65°F and 80°F. Based on this score, the best time of year to visit Harristown for general outdoor tourist activities is from early June to mid September, with a peak score in the last week of August.
The beach/pool score favors clear, rainless days with perceived temperatures between 75°F and 90°F. Based on this score, the best time of year to visit Harristown for hot-weather activities is from late June to late August, with a peak score in the third week of July.
For each hour between 8:00 AM and 9:00 PM of each day in the analysis period (1980 to 2016), independent scores are computed for perceived temperature, cloud cover, and total precipitation. Those scores are combined into a single hourly composite score, which is then aggregated into days, averaged over all the years in the analysis period, and smoothed.
Our cloud cover score is 10 for fully clear skies, falling linearly to 9 for mostly clear skies, and to 1 for fully overcast skies.
Our precipitation score, which is based on the three-hour precipitation centered on the hour in question, is 10 for no precipitation, falling linearly to 9 for trace precipitation, and to 0 for 0.04 inches of precipitation or more.
Our tourism temperature score is 0 for perceived temperatures below 50°F, rising linearly to 9 for 65°F, to 10 for 75°F, falling linearly to 9 for 80°F, and to 1 for 90°F or hotter.
Our beach/pool temperature score is 0 for perceived temperatures below 65°F, rising linearly to 9 for 75°F, to 10 for 82°F, falling linearly to 9 for 90°F, and to 1 for 100°F or hotter.
The growing season in Harristown typically lasts for 6.3 months (192 days), from around April 12 to around October 21, rarely starting before March 27 or after April 29, and rarely ending before October 1 or after November 12.
Time Spent in Various Temperature Bands and the Growing Season
Based on growing degree days alone, the first spring blooms in Harristown should appear around March 31, only rarely appearing before March 17 or after April 18.
Growing Degree Days
The average daily incident shortwave solar energy experiences significant seasonal variation over the course of the year.
The brighter period of the year lasts for 4.0 months, from April 28 to August 28, with an average daily incident shortwave energy per square meter above 5.9 kWh. The brightest day of the year is July 2, with an average of 6.9 kWh.
The darker period of the year lasts for 3.1 months, from November 5 to February 9, with an average daily incident shortwave energy per square meter below 2.9 kWh. The darkest day of the year is December 17, with an average of 1.9 kWh.
Average Daily Incident Shortwave Solar Energy
For the purposes of this report, the geographical coordinates of Harristown are 39.854 deg latitude, -89.084 deg longitude, and 659 ft elevation.
The topography within 2 miles of Harristown is essentially flat, with a maximum elevation change of 92 feet and an average elevation above sea level of 669 feet. Within 10 miles is essentially flat (190 feet). Within 50 miles also contains only modest variations in elevation (459 feet).
The area within 2 miles of Harristown is covered by cropland (100%), within 10 miles by cropland (85%), and within 50 miles by cropland (92%).
This report illustrates the typical weather in Harristown, based on a statistical analysis of historical hourly weather reports and model reconstructions from January 1, 1980 to December 31, 2016.
Temperature and Dew Point
There are 4 weather stations near enough to contribute to our estimation of the temperature and dew point in Harristown.
For each station, the records are corrected for the elevation difference between that station and Harristown according to the International Standard Atmosphere , and by the relative change present in the MERRA-2 satellite-era reanalysis between the two locations.
The estimated value at Harristown is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Harristown and a given station.
The stations contributing to this reconstruction are: Decatur Airport (54%, 19 kilometers, east); Logan County Airport (17%, 40 kilometers, northwest); Taylorville Municipal Airport (17%, 41 kilometers, southwest); and Abraham Lincoln Capital Airport (12%, 51 kilometers, west).
Time zones for aiports and weather stations are provided by AskGeo.com .