Average Weather in December in Zillah Washington, United States
Daily high temperatures decrease by 5°F, from 42°F to 36°F, rarely falling below 24°F or exceeding 53°F. The lowest daily average high temperature is 36°F on December 23.
Daily low temperatures decrease by 3°F, from 29°F to 25°F, rarely falling below 13°F or exceeding 39°F. The lowest daily average low temperature is 25°F on December 23.
For reference, on July 30, the hottest day of the year, temperatures in Zillah typically range from 60°F to 92°F, while on December 23, the coldest day of the year, they range from 25°F to 36°F.
Average High and Low Temperature in December
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.
Average Hourly Temperature in December
The month of December in Zillah experiences essentially constant cloud cover, with the percentage of time that the sky is overcast or mostly cloudy remaining about 62% throughout the month.
The clearest day of the month is December 6, with clear, mostly clear, or partly cloudy conditions 39% of the time.
For reference, on January 16, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 65%, while on August 4, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 83%.
Cloud Cover Categories in December
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In Zillah, the chance of a wet day over the course of December is gradually decreasing, starting the month at 29% and ending it at 26%.
For reference, the year's highest daily chance of a wet day is 29% on November 28, and its lowest chance is 3% on August 16.
Over the course of December in Zillah, the chance of a day with only rain decreases from 20% to 11%, the chance of a day with mixed snow and rain remains an essentially constant 5% throughout, and the chance of a day with only snow increases from 5% to 10%.
Probability of Precipitation in December
To 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 Zillah is gradually decreasing, starting the month at 1.4 inches, when it rarely exceeds 2.9 inches or falls below 0.3 inches, and ending the month at 1.0 inches, when it rarely exceeds 2.2 inches or falls below 0.1 inches.
Average Monthly Rainfall in December
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. As with rainfall, we consider the liquid-equivalent snowfall accumulated over a sliding 31-day period centered around each day.
The average sliding 31-day liquid-equivalent snowfall during December in Zillah is gradually increasing, starting the month at 0.4 inches, when it rarely exceeds 0.8 inches, and ending the month at 0.6 inches, when it rarely exceeds 1.5 inches.
The highest average 31-day liquid-equivalent accumulation is 0.6 inches on December 30.
Average Monthly Liquid-Equivalent Snowfall in December
Over the course of December in Zillah, the length of the day is essentially constant. The shortest day of the month is December 21, with 8 hours, 35 minutes of daylight and the longest day is December 1, with 8 hours, 52 minutes of daylight.
Hours of Daylight and Twilight in December
The earliest sunrise of the month in Zillah is 7:24 AM on December 1 and the latest sunrise is 20 minutes later at 7:44 AM on December 31.
The earliest sunset is 4:14 PM on December 10 and the latest sunset is 10 minutes later at 4:23 PM on December 31.
Daylight saving time is observed in Zillah during 2018, but it neither starts nor ends during December, so the entire month is in standard time.
For reference, on June 21, the longest day of the year, the Sun rises at 5:08 AM and sets 15 hours, 49 minutes later, at 8:57 PM, while on December 21, the shortest day of the year, it rises at 7:41 AM and sets 8 hours, 35 minutes later, at 4:16 PM.
Sunrise & Sunset with Twilight and Daylight Saving Time in December
The chance that a given day will be muggy in Zillah is essentially constant during December, remaining around 0% throughout.
For reference, on July 15, the muggiest day of the year, there are muggy conditions 0% of the time, while on January 1, the least muggy day of the year, there are muggy conditions 0% of the time.
Humidity Comfort Levels in December
The average hourly wind speed in Zillah is essentially constant during December, remaining within 0.3 miles per hour of 7.0 miles per hour throughout.
For reference, on March 31, the windiest day of the year, the daily average wind speed is 8.0 miles per hour, while on December 20, the calmest day of the year, the daily average wind speed is 6.7 miles per hour.
The lowest daily average wind speed during December is 6.7 miles per hour on December 20.
Average Wind Speed in December
Wind Direction in December
The growing season in Zillah typically lasts for 5.9 months (180 days), from around April 18 to around October 16, rarely starting before March 31 or after May 7, and rarely ending before September 28 or after November 2.
The month of December in Zillah is reliably fully outside of the growing season.
Time Spent in Various Temperature Bands and the Growing Season in December
The average accumulated growing degree days in Zillah are essentially constant during December, remaining within 2°F of 3,202°F throughout.
Growing Degree Days in December
The average daily incident shortwave solar energy in Zillah is essentially constant during December, remaining within 0.1 kWh of 1.3 kWh throughout.
The lowest average daily incident shortwave solar energy during December is 1.2 kWh on December 26.
Average Daily Incident Shortwave Solar Energy in December
For the purposes of this report, the geographical coordinates of Zillah are 46.402 deg latitude, -120.262 deg longitude, and 801 ft elevation.
The topography within 2 miles of Zillah contains only modest variations in elevation, with a maximum elevation change of 318 feet and an average elevation above sea level of 813 feet. Within 10 miles contains only modest variations in elevation (2,405 feet). Within 50 miles contains large variations in elevation (6,709 feet).
The area within 2 miles of Zillah is covered by cropland (76%) and artificial surfaces (22%), within 10 miles by cropland (59%) and shrubs (28%), and within 50 miles by shrubs (63%) and cropland (20%).
This report illustrates the typical weather in Zillah year round, 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 Zillah.
For each station, the records are corrected for the elevation difference between that station and Zillah 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 Zillah is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Zillah and a given station.
The stations contributing to this reconstruction are: Yakima Air Terminal Airport (59%, 28 kilometers, northwest); Hanford (24%, 54 kilometers, east); Hermiston Municipal Airport (9%, 100 kilometers, southeast); and The Dalles Municipal Airport (8%, 112 kilometers, southwest).
Time zones for aiports and weather stations are provided by AskGeo.com .