Average Weather in December in Walla Walla Washington, United States
Daily high temperatures decrease by 5°F, from 44°F to 40°F, rarely falling below 24°F or exceeding 57°F. The lowest daily average high temperature is 40°F on December 29.
Daily low temperatures decrease by 4°F, from 34°F to 30°F, rarely falling below 17°F or exceeding 45°F. The lowest daily average low temperature is 30°F on December 29.
For reference, on July 31, the hottest day of the year, temperatures in Walla Walla typically range from 65°F to 93°F, while on December 29, the coldest day of the year, they range from 30°F to 40°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 Walla Walla experiences essentially constant cloud cover, with the percentage of time that the sky is overcast or mostly cloudy remaining about 66% throughout the month.
The clearest day of the month is December 17, with clear, mostly clear, or partly cloudy conditions 35% of the time.
For reference, on January 16, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 68%, while on July 29, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 82%.
Cloud Cover Categories in December
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In Walla Walla, the chance of a wet day over the course of December is rapidly decreasing, starting the month at 37% and ending it at 30%.
For reference, the year's highest daily chance of a wet day is 37% on November 28, and its lowest chance is 7% on August 5.
Over the course of December in Walla Walla, the chance of a day with only rain decreases from 32% to 21%, the chance of a day with mixed snow and rain increases from 2% to 4%, and the chance of a day with only snow remains an essentially constant 4% throughout.
Probability of Precipitation in December
The average sliding 31-day rainfall during December in Walla Walla is gradually decreasing, starting the month at 2.0 inches, when it rarely exceeds 3.2 inches or falls below 0.8 inches, and ending the month at 1.7 inches, when it rarely exceeds 2.9 inches or falls below 0.5 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 Walla Walla is essentially constant, remaining about 0.2 inches throughout, and rarely exceeding 0.8 inches or falling to 0.0 inches.
The highest average 31-day liquid-equivalent accumulation is 0.3 inches on December 30.
Average Monthly Liquid-Equivalent Snowfall in December
Over the course of December in Walla Walla, the length of the day is essentially constant. The shortest day of the month is December 21, with 8 hours, 38 minutes of daylight and the longest day is December 1, with 8 hours, 54 minutes of daylight.
Hours of Daylight and Twilight in December
The earliest sunrise of the month in Walla Walla is 7:15 AM on December 1 and the latest sunrise is 20 minutes later at 7:35 AM on December 31.
The earliest sunset is 4:07 PM on December 10 and the latest sunset is 10 minutes later at 4:17 PM on December 31.
Daylight saving time is observed in Walla Walla 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 5:02 AM and sets 15 hours, 46 minutes later, at 8:48 PM, while on December 21, the shortest day of the year, it rises at 7:32 AM and sets 8 hours, 38 minutes later, at 4:10 PM.
Sunrise & Sunset with Twilight and Daylight Saving Time in December
The chance that a given day will be muggy in Walla Walla is essentially constant during December, remaining around 0% throughout.
For reference, on July 6, 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 Walla Walla is essentially constant during December, remaining within 0.3 miles per hour of 8.0 miles per hour throughout.
For reference, on November 19, the windiest day of the year, the daily average wind speed is 8.3 miles per hour, while on September 8, the calmest day of the year, the daily average wind speed is 6.6 miles per hour.
Average Wind Speed in December
Wind Direction in December
The growing season in Walla Walla typically lasts for 7.7 months (235 days), from around March 14 to around November 4, rarely starting before February 15 or after April 8, and rarely ending before October 13 or after November 26.
The month of December in Walla Walla is very likely fully outside of the growing season, with the chance that a given day is in the growing season gradually decreasing from 6% to 0% over the course of the month.
Time Spent in Various Temperature Bands and the Growing Season in December
The average accumulated growing degree days in Walla Walla are essentially constant during December, remaining within 6°F of 3,331°F throughout.
Growing Degree Days in December
The average daily incident shortwave solar energy in Walla Walla is essentially constant during December, remaining within 0.1 kWh of 1.2 kWh throughout.
The lowest average daily incident shortwave solar energy during December is 1.2 kWh on December 25.
Average Daily Incident Shortwave Solar Energy in December
For the purposes of this report, the geographical coordinates of Walla Walla are 46.065 deg latitude, -118.343 deg longitude, and 942 ft elevation.
The topography within 2 miles of Walla Walla contains only modest variations in elevation, with a maximum elevation change of 249 feet and an average elevation above sea level of 942 feet. Within 10 miles contains only modest variations in elevation (3,264 feet). Within 50 miles contains large variations in elevation (6,115 feet).
The area within 2 miles of Walla Walla is covered by artificial surfaces (69%) and cropland (25%), within 10 miles by cropland (78%) and grassland (10%), and within 50 miles by shrubs (39%) and cropland (30%).
This report illustrates the typical weather in Walla Walla 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 Walla Walla.
For each station, the records are corrected for the elevation difference between that station and Walla Walla 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 Walla Walla is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Walla Walla and a given station.
The stations contributing to this reconstruction are: Walla Walla Regional Airport (89%, 5.5 kilometers, northeast); Eastern Oregon Regional Airport (5%, 57 kilometers, southwest); Meacham, Meacham (2.1%, 62 kilometers, south); and Tri-Cities Airport (4.3%, 64 kilometers, west).
Time zones for aiports and weather stations are provided by AskGeo.com .