Average Weather in Alum Rock California, United States
In Alum Rock, the summers are long, warm, arid, and mostly clear and the winters are short, cold, wet, and partly cloudy. Over the course of the year, the temperature typically varies from 42°F to 83°F and is rarely below 34°F or above 93°F.
The warm season lasts for 4.2 months, from June 6 to October 11, with an average daily high temperature above 78°F. The hottest day of the year is August 23, with an average high of 83°F and low of 59°F.
The cool season lasts for 2.7 months, from November 26 to February 18, with an average daily high temperature below 63°F. The coldest day of the year is December 31, with an average low of 42°F and high of 58°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 Alum Rock, the average percentage of the sky covered by clouds experiences significant seasonal variation over the course of the year.
The clearer part of the year in Alum Rock begins around May 22 and lasts for 5.2 months, ending around October 27. On July 29, the clearest day of the year, the sky is clear, mostly clear, or partly cloudy 92% of the time, and overcast or mostly cloudy 8% of the time.
The cloudier part of the year begins around October 27 and lasts for 6.8 months, ending around May 22. On January 11, the cloudiest day of the year, the sky is overcast or mostly cloudy 56% of the time, and clear, mostly clear, or partly cloudy 44% of the time.
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. The chance of wet days in Alum Rock varies throughout the year.
The wetter season lasts 5.2 months, from November 4 to April 10, with a greater than 15% chance of a given day being a wet day. The chance of a wet day peaks at 30% on February 20.
The drier season lasts 6.8 months, from April 10 to November 4. 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 30% on February 20.
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. Alum Rock experiences significant seasonal variation in monthly rainfall.
The rainy period of the year lasts for 7.4 months, from October 3 to May 14, with a sliding 31-day rainfall of at least 0.5 inches. The most rain falls during the 31 days centered around February 15, with an average total accumulation of 3.9 inches.
The rainless period of the year lasts for 4.6 months, from May 14 to October 3. 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 Alum Rock varies significantly over the course of the year. In 2017, the shortest day is December 21, with 9 hours, 35 minutes of daylight; the longest day is June 21, with 14 hours, 44 minutes of daylight.
Hours of Daylight and Twilight
The earliest sunrise is at 5:46 AM on June 13, and the latest sunrise is 1 hour, 49 minutes later at 7:35 AM on November 4. The earliest sunset is at 4:49 PM on December 6, and the latest sunset is 3 hours, 43 minutes later at 8:32 PM on June 27.
Daylight saving time (DST) is observed in Alum Rock 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 Alum Rock, 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
The average hourly wind speed in Alum Rock experiences mild seasonal variation over the course of the year.
The windier part of the year lasts for 4.8 months, from April 2 to August 26, with average wind speeds of more than 3.8 miles per hour. The windiest day of the year is June 8, with an average hourly wind speed of 4.5 miles per hour.
The calmer time of year lasts for 7.2 months, from August 26 to April 2. The calmest day of the year is October 21, with an average hourly wind speed of 3.2 miles per hour.
Average Wind Speed
The predominant average hourly wind direction in Alum Rock varies throughout the year.
The wind is most often from the west for 9.2 months, from February 8 to November 15, with a peak percentage of 92% on August 10. The wind is most often from the north for 2.8 months, from November 15 to February 8, with a peak percentage of 32% on January 1.
Alum Rock is located near a large body of water (e.g., ocean, sea, or large lake). This section reports on the wide-area average surface temperature of that water.
The average water temperature experiences some seasonal variation over the course of the year.
The time of year with warmer water lasts for 2.6 months, from July 31 to October 19, with an average temperature above 57°F. The day of the year with the warmest water is September 15, with an average temperature of 58°F.
The time of year with cooler water lasts for 5.7 months, from December 21 to June 12, with an average temperature below 54°F. The day of the year with the coolest water is May 3, with an average temperature of 53°F.
Average Water Temperature
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 3.6 months, from May 7 to August 26, with an average daily incident shortwave energy per square meter above 7.2 kWh. The brightest day of the year is June 27, with an average of 8.5 kWh.
The darker period of the year lasts for 3.5 months, from November 4 to February 19, with an average daily incident shortwave energy per square meter below 3.5 kWh. The darkest day of the year is December 26, with an average of 2.2 kWh.
Average Daily Incident Shortwave Solar Energy
For the purposes of this report, the geographical coordinates of Alum Rock are 37.366 deg latitude, -121.827 deg longitude, and 157 ft elevation.
The topography within 2 miles of Alum Rock contains very significant variations in elevation, with a maximum elevation change of 1,017 feet and an average elevation above sea level of 224 feet. Within 10 miles contains very significant variations in elevation (3,885 feet). Within 50 miles also contains extreme variations in elevation (4,285 feet).
The area within 2 miles of Alum Rock is covered by artificial surfaces (88%), within 10 miles by artificial surfaces (50%) and grassland (31%), and within 50 miles by water (24%) and grassland (23%).
This report illustrates the typical weather in Alum Rock, 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 Alum Rock.
For each station, the records are corrected for the elevation difference between that station and Alum Rock 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 Alum Rock is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Alum Rock and a given station.
The stations contributing to this reconstruction are: Norman Y. Mineta San José International Airport (80%, 9 kilometers, west); Livermore Municipal Airport (10%, 36 kilometers, north); Watsonville Municipal Airport (7%, 48 kilometers, south); and Modesto City-County Airport (3.0%, 83 kilometers, east).
Time zones for aiports and weather stations are provided by AskGeo.com .