Average Weather in Denison Iowa, United States
In Denison, the summers are long, warm, humid, and wet; the winters are freezing, dry, and windy; and it is partly cloudy year round. Over the course of the year, the temperature typically varies from 14°F to 85°F and is rarely below -5°F or above 93°F.
Based on the tourism score, the best time of year to visit Denison for warm-weather activities is from mid June to early September.
The warm season lasts for 4.0 months, from May 22 to September 21, with an average daily high temperature above 74°F. The hottest day of the year is July 5, with an average high of 85°F and low of 65°F.
The cold season lasts for 3.2 months, from November 27 to March 1, with an average daily high temperature below 42°F. The coldest day of the year is January 20, with an average low of 14°F and high of 32°F.
Average High and Low Temperature
Average Hourly Temperature
In Denison, 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 Denison begins around June 8 and lasts for 4.5 months, ending around October 22. On July 16, the clearest day of the year, the sky is clear, mostly clear, or partly cloudy 73% of the time, and overcast or mostly cloudy 27% of the time.
The cloudier part of the year begins around October 22 and lasts for 7.5 months, ending around June 8. On December 29, the cloudiest day of the year, the sky is overcast or mostly cloudy 54% of the time, and clear, mostly clear, or partly cloudy 47% of the time.
Cloud Cover Categories
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. The chance of wet days in Denison varies significantly throughout the year.
The wetter season lasts 5.9 months, from April 7 to October 3, with a greater than 26% chance of a given day being a wet day. The chance of a wet day peaks at 44% on June 7.
The drier season lasts 6.1 months, from October 3 to April 7. The smallest chance of a wet day is 8% 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 in Denison changes throughout the year.
Rain alone is the most common for 9.6 months, from February 21 to December 9. The highest chance of a day with rain alone is 44% on June 7.
Snow alone is the most common for 2.4 months, from December 9 to February 21. The highest chance of a day with snow alone is 6% on December 29.
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. Denison experiences extreme seasonal variation in monthly rainfall.
The rainy period of the year lasts for 9.8 months, from February 22 to December 16, with a sliding 31-day rainfall of at least 0.5 inches. The most rain falls during the 31 days centered around June 15, with an average total accumulation of 4.4 inches.
The rainless period of the year lasts for 2.2 months, from December 16 to February 22. The least rain falls around January 23, with an average total accumulation of 0.2 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. Denison experiences some seasonal variation in monthly liquid-equivalent snowfall.
The snowy period of the year lasts for 5.2 months, from November 4 to April 10, with a sliding 31-day liquid-equivalent snowfall of at least 0.1 inches. The most snow falls during the 31 days centered around December 18, with an average total liquid-equivalent accumulation of 0.4 inches.
The snowless period of the year lasts for 6.8 months, from April 10 to November 4. The least snow falls around July 16, with an average total liquid-equivalent accumulation of 0.0 inches.
Average Liquid-Equivalent Monthly Snowfall
The length of the day in Denison varies significantly over the course of the year. In 2018, the shortest day is December 21, with 9 hours, 7 minutes of daylight; the longest day is June 21, with 15 hours, 15 minutes of daylight.
Hours of Daylight and Twilight
The earliest sunrise is at 5:45 AM on June 14, and the latest sunrise is 2 hours, 11 minutes later at 7:56 AM on November 3. The earliest sunset is at 4:49 PM on December 7, and the latest sunset is 4 hours, 11 minutes later at 9:01 PM on June 27.
Daylight saving time (DST) is observed in Denison 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
Denison experiences extreme seasonal variation in the perceived humidity.
The muggier period of the year lasts for 3.4 months, from June 3 to September 15, during which time the comfort level is muggy, oppressive, or miserable at least 14% of the time. The muggiest day of the year is July 21, with muggy conditions 54% of the time.
The least muggy day of the year is December 8, when muggy conditions are essentially unheard of.
Humidity Comfort Levels
The average hourly wind speed in Denison experiences significant seasonal variation over the course of the year.
The windier part of the year lasts for 8.1 months, from September 26 to May 29, with average wind speeds of more than 10.9 miles per hour. The windiest day of the year is April 11, with an average hourly wind speed of 13.3 miles per hour.
The calmer time of year lasts for 3.9 months, from May 29 to September 26. The calmest day of the year is August 3, with an average hourly wind speed of 8.5 miles per hour.
Average Wind Speed
The predominant average hourly wind direction in Denison varies throughout the year.
The wind is most often from the south for 7.5 months, from April 23 to December 6, with a peak percentage of 49% on September 5. The wind is most often from the north for 4.0 days, from December 6 to December 10 and for 4.4 months, from December 10 to April 23, with a peak percentage of 30% on December 9.
Best Time of Year to Visit
To characterize how pleasant the weather is in Denison 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 Denison for general outdoor tourist activities is from mid June to early September, with a peak score in the second 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 Denison for hot-weather activities is from late June to mid August, with a peak score in the third week of July.
The growing season in Denison typically lasts for 5.3 months (161 days), from around April 26 to around October 3, rarely starting before April 7 or after May 15, and rarely ending before September 15 or after October 23.
Time Spent in Various Temperature Bands and the Growing Season
Based on growing degree days alone, the first spring blooms in Denison should appear around April 9, only rarely appearing before March 28 or after April 27.
Growing Degree Days
The average daily incident shortwave solar energy experiences extreme seasonal variation over the course of the year.
The brighter period of the year lasts for 3.5 months, from May 3 to August 21, with an average daily incident shortwave energy per square meter above 6.0 kWh. The brightest day of the year is July 4, with an average of 7.1 kWh.
The darker period of the year lasts for 3.3 months, from November 1 to February 10, with an average daily incident shortwave energy per square meter below 2.9 kWh. The darkest day of the year is December 21, with an average of 1.8 kWh.
Average Daily Incident Shortwave Solar Energy
For the purposes of this report, the geographical coordinates of Denison are 42.018 deg latitude, -95.355 deg longitude, and 1,273 ft elevation.
The topography within 2 miles of Denison contains only modest variations in elevation, with a maximum elevation change of 256 feet and an average elevation above sea level of 1,241 feet. Within 10 miles also contains only modest variations in elevation (440 feet). Within 50 miles contains only modest variations in elevation (591 feet).
The area within 2 miles of Denison is covered by cropland (78%) and artificial surfaces (12%), within 10 miles by cropland (98%), and within 50 miles by cropland (97%).
This report illustrates the typical weather in Denison, 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 3 weather stations near enough to contribute to our estimation of the temperature and dew point in Denison.
For each station, the records are corrected for the elevation difference between that station and Denison 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 Denison is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Denison and a given station.
The stations contributing to this reconstruction are: Denison Municipal Airport (96%, 4.1 kilometers, southwest); Arthur N Neu Airport (2.5%, 47 kilometers, east); and Storm Lake Municipal Airport (1.5%, 65 kilometers, north).
Time zones for aiports and weather stations are provided by AskGeo.com .