December Weather in Casper Wyoming, United StatesDaily high temperatures decrease by 5°F, from 39°F to 34°F, rarely falling below 19°F or exceeding 54°F. The lowest daily average high temperature is 34°F on December 29. Daily low temperatures decrease by 5°F, from 22°F to 17°F, rarely falling below -2°F or exceeding 38°F. The lowest daily average low temperature is 17°F on December 29. For reference, on July 18, the hottest day of the year, temperatures in Casper typically range from 57°F to 88°F, while on December 29, the coldest day of the year, they range from 17°F to 34°F. The figure below shows you a compact characterization of the hourly average temperatures for the quarter of the year centered on December. The horizontal axis is the day, the vertical axis is the hour of the day, and the color is the average temperature for that hour and day. Elmadağ, Turkey (6,190 miles away); Hozat, Turkey (6,383 miles); and Bījār, Iran (6,761 miles) are the far-away foreign places with temperatures most similar to Casper (view comparison). CloudsThe month of December in Casper experiences essentially constant cloud cover, with the percentage of time that the sky is overcast or mostly cloudy remaining about 48% throughout the month. The clearest day of the month is December 18, with clear, mostly clear, or partly cloudy conditions 53% of the time. For reference, on March 20, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 53%, while on July 3, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 77%. PrecipitationA wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In Casper, the chance of a wet day over the course of December is essentially constant, remaining around 7% throughout. For reference, the year's highest daily chance of a wet day is 27% on May 22, and its lowest chance is 5% on January 10. Over the course of December in Casper, the chance of a day with only rain remains an essentially constant 1% throughout, the chance of a day with mixed snow and rain remains an essentially constant 1% throughout, and the chance of a day with only snow remains an essentially constant 5% throughout. RainfallTo show variation within the month and not just the monthly total, we show the rainfall accumulated over a sliding 31-day period centered around each day. The average sliding 31-day rainfall during December in Casper is essentially constant, remaining about 0.1 inches throughout, and rarely exceeding 0.3 inches or falling below -0.0 inches. The lowest average 31-day accumulation is 0.1 inches on December 31. SnowfallAs with rainfall, we consider the snowfall accumulated over a sliding 31-day period centered around each day. The average sliding 31-day snowfall during December in Casper is essentially constant, remaining about 2.2 inches throughout, and rarely exceeding 4.9 inches or falling below 0.1 inches. The highest average 31-day accumulation is 2.3 inches on December 15. SunOver the course of December in Casper, the length of the day is essentially constant. The shortest day of the month is December 20, with 9 hours, 1 minute of daylight and the longest day is December 1, with 9 hours, 15 minutes of daylight. The earliest sunrise of the month in Casper is 7:17 AM on December 1 and the latest sunrise is 19 minutes later at 7:36 AM on December 31. The earliest sunset is 4:30 PM on December 8 and the latest sunset is 10 minutes later at 4:41 PM on December 31. Daylight saving time is observed in Casper during 2024, but it neither starts nor ends during December, so the entire month is in standard time. For reference, on June 20, the longest day of the year, the Sun rises at 5:26 AM and sets 15 hours, 21 minutes later, at 8:47 PM, while on December 21, the shortest day of the year, it rises at 7:33 AM and sets 9 hours, 1 minute later, at 4:34 PM. The figure below presents a compact representation of the sun's elevation (the angle of the sun above the horizon) and azimuth (its compass bearing) for every hour of every day in the reporting period. The horizontal axis is the day of the year and the vertical axis is the hour of the day. For a given day and hour of that day, the background color indicates the azimuth of the sun at that moment. The black isolines are contours of constant solar elevation. MoonThe figure below presents a compact representation of key lunar data for December 2024. The horizontal axis is the day, the vertical axis is the hour of the day, and the colored areas indicate when the moon is above the horizon. The vertical gray bars (new Moons) and blue bars (full Moons) indicate key Moon phases. The label associated with each bar indicates the date and time that the phase is obtained, and the companion time labels indicate the rise and set times of the Moon for the nearest time interval in which the moon is above the horizon.
HumidityWe base the humidity comfort level on the dew point, as it determines whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid. Unlike temperature, which typically varies significantly between night and day, dew point tends to change more slowly, so while the temperature may drop at night, a muggy day is typically followed by a muggy night. The chance that a given day will be muggy in Casper is essentially constant during December, remaining around 0% throughout. WindThis section discusses the wide-area hourly average wind vector (speed and direction) at 10 meters above the ground. The wind experienced at any given location is highly dependent on local topography and other factors, and instantaneous wind speed and direction vary more widely than hourly averages. The average hourly wind speed in Casper is gradually increasing during December, increasing from 14.4 miles per hour to 15.1 miles per hour over the course of the month. For reference, on January 9, the windiest day of the year, the daily average wind speed is 15.4 miles per hour, while on August 2, the calmest day of the year, the daily average wind speed is 8.6 miles per hour. The hourly average wind direction in Casper throughout December is predominantly from the west, with a peak proportion of 66% on December 15. Growing SeasonDefinitions of the growing season vary throughout the world, but for the purposes of this report, we define it as the longest continuous period of non-freezing temperatures (≥ 32°F) in the year (the calendar year in the Northern Hemisphere, or from July 1 until June 30 in the Southern Hemisphere). The growing season in Casper typically lasts for 4.3 months (134 days), from around May 14 to around September 25, rarely starting before April 25 or after May 31, and rarely ending before September 7 or after October 13. The month of December in Casper is reliably fully outside of the growing season. Growing degree days are a measure of yearly heat accumulation used to predict plant and animal development, and defined as the integral of warmth above a base temperature, discarding any excess above a maximum temperature. In this report, we use a base of 50°F and a cap of 86°F. The average accumulated growing degree days in Casper are essentially constant during December, remaining within 1°F of 2,490°F throughout. Solar EnergyThis section discusses the total daily incident shortwave solar energy reaching the surface of the ground over a wide area, taking full account of seasonal variations in the length of the day, the elevation of the Sun above the horizon, and absorption by clouds and other atmospheric constituents. Shortwave radiation includes visible light and ultraviolet radiation. The average daily incident shortwave solar energy in Casper is essentially constant during December, remaining within 0.1 kWh of 2.1 kWh throughout. The lowest average daily incident shortwave solar energy during December is 2.0 kWh on December 15. TopographyFor the purposes of this report, the geographical coordinates of Casper are 42.867 deg latitude, -106.313 deg longitude, and 5,171 ft elevation. The topography within 2 miles of Casper contains only modest variations in elevation, with a maximum elevation change of 289 feet and an average elevation above sea level of 5,195 feet. Within 10 miles contains only modest variations in elevation (3,153 feet). Within 50 miles contains large variations in elevation (4,823 feet). The area within 2 miles of Casper is covered by shrubs (76%), artificial surfaces (12%), and grassland (12%), within 10 miles by grassland (48%) and shrubs (41%), and within 50 miles by shrubs (57%) and grassland (39%). Data SourcesThis report illustrates the typical weather in Casper, based on a statistical analysis of historical hourly weather reports and model reconstructions from January 1, 1980 to December 31, 2016. Temperature and Dew PointThere are 3 weather stations near enough to contribute to our estimation of the temperature and dew point in Casper. For each station, the records are corrected for the elevation difference between that station and Casper 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 Casper is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Casper and a given station. The stations contributing to this reconstruction are:
To get a sense of how much these sources agree with each other, you can view a comparison of Casper and the stations that contribute to our estimates of its temperature history and climate. Please note that each source's contribution is adjusted for elevation and the relative change present in the MERRA-2 data. Other DataAll data relating to the Sun's position (e.g., sunrise and sunset) are computed using astronomical formulas from the book, Astronomical Algorithms 2nd Edition , by Jean Meeus. All other weather data, including cloud cover, precipitation, wind speed and direction, and solar flux, come from NASA's MERRA-2 Modern-Era Retrospective Analysis . This reanalysis combines a variety of wide-area measurements in a state-of-the-art global meteorological model to reconstruct the hourly history of weather throughout the world on a 50-kilometer grid. Land Use data comes from the Global Land Cover SHARE database , published by the Food and Agriculture Organization of the United Nations. Elevation data comes from the Shuttle Radar Topography Mission (SRTM) , published by NASA's Jet Propulsion Laboratory. Names, locations, and time zones of places and some airports come from the GeoNames Geographical Database . Time zones for airports and weather stations are provided by AskGeo.com . Maps are © OpenStreetMap contributors. DisclaimerThe information on this site is provided as is, without any assurances as to its accuracy or suitability for any purpose. Weather data is prone to errors, outages, and other defects. We assume no responsibility for any decisions made on the basis of the content presented on this site. We draw particular cautious attention to our reliance on the MERRA-2 model-based reconstructions for a number of important data series. While having the tremendous advantages of temporal and spatial completeness, these reconstructions: (1) are based on computer models that may have model-based errors, (2) are coarsely sampled on a 50 km grid and are therefore unable to reconstruct the local variations of many microclimates, and (3) have particular difficulty with the weather in some coastal areas, especially small islands. We further caution that our travel scores are only as good as the data that underpin them, that weather conditions at any given location and time are unpredictable and variable, and that the definition of the scores reflects a particular set of preferences that may not agree with those of any particular reader. Please review our full terms contained on our Terms of Service page. |