Average Weather in Grass Valley California, United States
In Grass Valley, the summers are hot, arid, and mostly clear and the winters are long, cold, wet, and partly cloudy. Over the course of the year, the temperature typically varies from 39°F to 88°F and is rarely below 32°F or above 95°F.
Based on the tourism score, the best time of year to visit Grass Valley for warm-weather activities is from late June to mid September.
The hot season lasts for 3.1 months, from June 16 to September 19, with an average daily high temperature above 81°F. The hottest day of the year is July 29, with an average high of 88°F and low of 68°F.
The cool season lasts for 4.2 months, from November 15 to March 20, with an average daily high temperature below 59°F. The coldest day of the year is December 27, with an average low of 39°F and high of 52°F.
Average High and Low Temperature
The figure below shows you a compact characterization of the entire year of hourly average temperatures. The horizontal axis is the day of the year, 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 Grass Valley, the average percentage of the sky covered by clouds experiences extreme seasonal variation over the course of the year.
The clearer part of the year in Grass Valley begins around May 24 and lasts for 5.0 months, ending around October 22. On July 29, the clearest day of the year, the sky is clear, mostly clear, or partly cloudy 90% of the time, and overcast or mostly cloudy 10% of the time.
The cloudier part of the year begins around October 22 and lasts for 7.0 months, ending around May 24. On February 26, the cloudiest day of the year, the sky is overcast or mostly cloudy 60% of the time, and clear, mostly clear, or partly cloudy 40% 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 Grass Valley varies significantly throughout the year.
The wetter season lasts 5.9 months, from October 27 to April 24, with a greater than 18% chance of a given day being a wet day. The chance of a wet day peaks at 35% on February 27.
The drier season lasts 6.1 months, from April 24 to October 27. The smallest chance of a wet day is 0% on July 19.
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 throughout the year is rain alone, with a peak probability of 34% on February 28.
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. Grass Valley experiences extreme seasonal variation in monthly rainfall.
The rainy period of the year lasts for 8.8 months, from September 18 to June 10, with a sliding 31-day rainfall of at least 0.5 inches. The most rain falls during the 31 days centered around February 17, with an average total accumulation of 5.9 inches.
The rainless period of the year lasts for 3.2 months, from June 10 to September 18. The least rain falls around July 30, with an average total accumulation of 0.0 inches.
Average Monthly Rainfall
The length of the day in Grass Valley varies significantly over the course of the year. In 2017, the shortest day is December 21, with 9 hours, 24 minutes of daylight; the longest day is June 20, with 14 hours, 56 minutes of daylight.
Hours of Daylight and Twilight
The earliest sunrise is at 5:37 AM on June 13, and the latest sunrise is 1 hour, 58 minutes later at 7:35 AM on November 4. The earliest sunset is at 4:41 PM on December 7, and the latest sunset is 3 hours, 54 minutes later at 8:34 PM on June 27.
Daylight saving time (DST) is observed in Grass Valley during 2017, starting in the spring on March 12, lasting 7.8 months, and ending in the fall on November 5.
Sunrise & Sunset with Twilight and Daylight Saving Time
The perceived humidity level in Grass Valley, as measured by the percentage of time in which the humidity comfort level is muggy, oppressive, or miserable, does not vary significantly over the course of the year, remaining a virtually constant 0% throughout.
Humidity Comfort Levels
Average Wind Speed
The predominant average hourly wind direction in Grass Valley varies throughout the year.
The wind is most often from the south for 7.4 months, from February 10 to September 22, with a peak percentage of 55% on August 12. The wind is most often from the east for 4.6 months, from September 22 to February 10, with a peak percentage of 49% on January 1.
Best Time of Year to Visit
To characterize how pleasant the weather is in Grass Valley 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 Grass Valley for general outdoor tourist activities is from late June to mid 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 Grass Valley for hot-weather activities is from early July to late August, with a peak score in the last week of July.
For each hour between 8:00 AM and 9:00 PM of each day in the analysis period (1980 to 2016), independent scores are computed for perceived temperature, cloud cover, and total precipitation. Those scores are combined into a single hourly composite score, which is then aggregated into days, averaged over all the years in the analysis period, and smoothed.
Our cloud cover score is 10 for fully clear skies, falling linearly to 9 for mostly clear skies, and to 1 for fully overcast skies.
Our precipitation score, which is based on the three-hour precipitation centered on the hour in question, is 10 for no precipitation, falling linearly to 9 for trace precipitation, and to 0 for 0.04 inches of precipitation or more.
Our tourism temperature score is 0 for perceived temperatures below 50°F, rising linearly to 9 for 65°F, to 10 for 75°F, falling linearly to 9 for 80°F, and to 1 for 90°F or hotter.
Our beach/pool temperature score is 0 for perceived temperatures below 65°F, rising linearly to 9 for 75°F, to 10 for 82°F, falling linearly to 9 for 90°F, and to 1 for 100°F or hotter.
The growing season in Grass Valley typically lasts for 9.2 months (281 days), from around March 8 to around December 14, rarely starting after April 10, or ending before November 17.
Time Spent in Various Temperature Bands and the Growing Season
Based on growing degree days alone, the first spring blooms in Grass Valley should appear around February 25, only rarely appearing before February 4 or after March 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 3.4 months, from May 12 to August 24, with an average daily incident shortwave energy per square meter above 7.2 kWh. The brightest day of the year is June 29, with an average of 8.5 kWh.
The darker period of the year lasts for 3.6 months, from November 2 to February 20, with an average daily incident shortwave energy per square meter below 3.3 kWh. The darkest day of the year is December 20, with an average of 2.0 kWh.
Average Daily Incident Shortwave Solar Energy
For the purposes of this report, the geographical coordinates of Grass Valley are 39.219 deg latitude, -121.061 deg longitude, and 2,477 ft elevation.
The topography within 2 miles of Grass Valley contains significant variations in elevation, with a maximum elevation change of 764 feet and an average elevation above sea level of 2,545 feet. Within 10 miles contains significant variations in elevation (3,412 feet). Within 50 miles also contains extreme variations in elevation (9,298 feet).
The area within 2 miles of Grass Valley is covered by shrubs (61%), artificial surfaces (19%), and trees (13%), within 10 miles by shrubs (52%) and trees (35%), and within 50 miles by trees (45%) and cropland (19%).
This report illustrates the typical weather in Grass Valley, 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 Grass Valley.
For each station, the records are corrected for the elevation difference between that station and Grass Valley 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 Grass Valley is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Grass Valley and a given station.
The stations contributing to this reconstruction are: Nevada County Air Park (67%, 5.0 kilometers, east); Auburn Municipal Airport (24%, 29 kilometers, south); and Beale Air Force Base (9%, 33 kilometers, west).
Time zones for aiports and weather stations are provided by AskGeo.com .