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Average Weather in December in Sunnyside Washington, United States

In Sunnyside, the month of December is characterized by falling daily high temperatures, with daily highs decreasing by 5°F, from 42°F to 37°F over the course of the month, and rarely exceeding 54°F or dropping below 24°F. The lowest daily average high temperature is 37°F on December 29.

Daily low temperatures decrease by 4°F, from 29°F to 26°F, rarely falling below 14°F or exceeding 39°F. The lowest daily average low temperature is 26°F on December 23.

For reference, on July 30, the hottest day of the year, temperatures in Sunnyside typically range from 62°F to 94°F, while on December 23, the coldest day of the year, they range from 26°F to 37°F.

Average High and Low Temperature in December

The daily average high (red line) and low (blue line) temperature, with 25th to 75th and 10th to 90th percentile bands. The thin dotted lines are the corresponding average perceived temperatures.

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

Average Hourly Temperature in December in Sunnyside12 AM4 AM8 AM12 PM4 PM8 PM12 AM181522291122334455667788991010111112121313141415151616171718181919202021212222232324242525262627272828292930303131NovJanfreezingchillycoldcool
The average hourly temperature, color coded into bands: frigid < 15°F < freezing < 32°F < chilly < 45°F < cold < 55°F < cool < 65°F < comfortable < 75°F < warm < 85°F < hot < 95°F < sweltering. The shaded overlays indicate night and civil twilight.

Clouds

The month of December in Sunnyside 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 40% 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 in December

The percentage of time spent in each cloud cover band, categorized by the percentage of the sky covered by clouds: clear < 20% < mostly clear < 40% < partly cloudy < 60% < mostly cloudy < 80% < overcast.

Precipitation

A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In Sunnyside, the chance of a wet day over the course of December is gradually decreasing, starting the month at 23% and ending it at 19%.

For reference, the year's highest daily chance of a wet day is 23% on December 1, and its lowest chance is 2% on August 16.

Over the course of December in Sunnyside, the chance of a day with only rain decreases from 15% to 7%, the chance of a day with mixed snow and rain remains an essentially constant 4% throughout, and the chance of a day with only snow increases from 4% to 8%.

Probability of Precipitation in December

The percentage of days in which various types of precipitation are observed, excluding trace quantities: rain alone, snow alone, and mixed (both rain and snow fell in the same day).

Rainfall

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 Sunnyside is essentially constant, remaining about 0.7 inches throughout, and rarely exceeding 1.7 inches.

Average Monthly Rainfall in December

The average rainfall (solid line) accumulated over the course of a sliding 31-day period centered on the day in question, with 25th to 75th and 10th to 90th percentile bands. The thin dotted line is the corresponding average liquid-equivalent snowfall.

Snowfall

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 Sunnyside is essentially constant, remaining about 0.4 inches throughout, and rarely exceeding 1.1 inches or falling to 0.0 inches.

The highest average 31-day liquid-equivalent accumulation is 0.5 inches on December 30.

Average Monthly Liquid-Equivalent Snowfall in December

The average liquid-equivalent snowfall (solid line) accumulated over the course of a sliding 31-day period centered on the day in question, with 25th to 75th and 10th to 90th percentile bands. The thin dotted line is the corresponding average rainfall.

Sun

Over the course of December in Sunnyside, the length of the day is essentially constant. The shortest day of the month is December 21, with 8 hours, 36 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 number of hours during which the Sun is visible (black line). From bottom (most yellow) to top (most gray), the color bands indicate: full daylight, twilight (civil, nautical, and astronomical), and full night.

The earliest sunrise of the month in Sunnyside is 7:23 AM on December 1 and the latest sunrise is 20 minutes later at 7:43 AM on December 31.

The earliest sunset is 4:13 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 Sunnyside during 2017, 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 5:07 AM and sets 15 hours, 48 minutes later, at 8:55 PM, while on December 21, the shortest day of the year, it rises at 7:40 AM and sets 8 hours, 36 minutes later, at 4:16 PM.

Sunrise & Sunset with Twilight and Daylight Saving Time in December

The solar day over the course of December. From bottom to top, the black lines are the previous solar midnight, sunrise, solar noon, sunset, and the next solar midnight. The day, twilights (civil, nautical, and astronomical), and night are indicated by the color bands from yellow to gray.

Humidity

We 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 Sunnyside 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 percentage of time spent at various humidity comfort levels, categorized by dew point: dry < 55°F < comfortable < 60°F < humid < 65°F < muggy < 70°F < oppressive < 75°F < miserable.

Wind

This 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 Sunnyside is essentially constant during December, remaining within 0.2 miles per hour of 4.2 miles per hour throughout.

For reference, on March 31, the windiest day of the year, the daily average wind speed is 4.7 miles per hour, while on September 9, the calmest day of the year, the daily average wind speed is 3.9 miles per hour.

The lowest daily average wind speed during December is 4.0 miles per hour on December 20.

Average Wind Speed in December

The average of mean hourly wind speeds (dark gray line), with 25th to 75th and 10th to 90th percentile bands.
The hourly average wind direction in Sunnyside throughout December is predominantly from the north, with a peak proportion of 46% on December 31.

Wind Direction in December

The percentage of hours in which the mean wind direction is from each of the four cardinal wind directions (north, east, south, and west), excluding hours in which the mean wind speed is less than 1 mph. The lightly tinted areas at the boundaries are the percentage of hours spent in the implied intermediate directions (northeast, southeast, southwest, and northwest).

Solar Energy

This 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 Sunnyside 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

The average daily shortwave solar energy reaching the ground per square meter (orange line), with 25th to 75th and 10th to 90th percentile bands.

Topography

For the purposes of this report, the geographical coordinates of Sunnyside are 46.324 deg latitude, -120.009 deg longitude, and 778 ft elevation.

The topography within 2 miles of Sunnyside contains only modest variations in elevation, with a maximum elevation change of 308 feet and an average elevation above sea level of 768 feet. Within 10 miles contains only modest variations in elevation (2,116 feet). Within 50 miles contains large variations in elevation (5,597 feet).

The area within 2 miles of Sunnyside is covered by cropland (55%) and artificial surfaces (45%), within 10 miles by cropland (61%) and shrubs (25%), and within 50 miles by shrubs (60%) and cropland (27%).

Data Sources

This report illustrates the typical weather in Sunnyside 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 Sunnyside.

For each station, the records are corrected for the elevation difference between that station and Sunnyside 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 Sunnyside is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Sunnyside and a given station.

The stations contributing to this reconstruction are: Hanford (43%, 41 kilometers, northeast); Yakima Air Terminal Airport (32%, 49 kilometers, northwest); Hermiston Municipal Airport (16%, 80 kilometers, southeast); and The Dalles Municipal Airport (9%, 119 kilometers, southwest).

Other Data

All data relating to the Sun's position (e.g., sunrise and sunset) are computed using astronomical formulas from the book, Astronomical Tables of the Sun, Moon and Planets , 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 aiports and weather stations are provided by AskGeo.com .

Maps are © Esri, with data from National Geographic, Esri, DeLorme, NAVTEQ, UNEP-WCMC, USGS, NASA, ESA, METI, NRCAN, GEBCO, NOAA, and iPC.