Average Weather in September in Acalanes Ridge California, United States
Daily high temperatures decrease by 3°F, from 82°F to 79°F, rarely falling below 69°F or exceeding 92°F.
Daily low temperatures decrease by 2°F, from 57°F to 55°F, rarely falling below 50°F or exceeding 61°F.
For reference, on July 28, the hottest day of the year, temperatures in Acalanes Ridge typically range from 58°F to 83°F, while on December 31, the coldest day of the year, they range from 40°F to 54°F.
Average High and Low Temperature in September
The figure below shows you a compact characterization of the hourly average temperatures for the quarter of the year centered on September. 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 September
The month of September in Acalanes Ridge experiences gradually increasing cloud cover, with the percentage of time that the sky is overcast or mostly cloudy increasing from 11% to 18%.
The clearest day of the month is September 1, with clear, mostly clear, or partly cloudy conditions 89% of the time.
For reference, on January 11, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 57%, while on July 20, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 92%.
Cloud Cover Categories in September
0% clear 20% mostly clear 40% partly cloudy 60% mostly cloudy 80% overcast 100%
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In Acalanes Ridge, the chance of a wet day over the course of September is gradually increasing, starting the month at 1% and ending it at 5%.
For reference, the year's highest daily chance of a wet day is 30% on February 20, and its lowest chance is 0% on July 24.
Probability of Precipitation in September
The average sliding 31-day rainfall during September in Acalanes Ridge is gradually increasing, starting the month at 0.1 inches, when it rarely exceeds 0.2 inches, and ending the month at 0.4 inches, when it rarely exceeds 1.2 inches.
Average Monthly Rainfall in September
Over the course of September in Acalanes Ridge, the length of the day is rapidly decreasing. From the start to the end of the month, the length of the day decreases by 1 hour, 10 minutes, implying an average daily decrease of 2 minutes, 24 seconds, and weekly decrease of 16 minutes, 48 seconds.
The shortest day of the month is September 30, with 11 hours, 50 minutes of daylight and the longest day is September 1, with 13 hours, 0 minutes of daylight.
Hours of Daylight and Twilight in September
The earliest sunrise of the month in Acalanes Ridge is 6:38 AM on September 1 and the latest sunrise is 25 minutes later at 7:02 AM on September 30.
The latest sunset is 7:37 PM on September 1 and the earliest sunset is 45 minutes earlier at 6:53 PM on September 30.
Daylight saving time is observed in Acalanes Ridge during 2019, but it neither starts nor ends during September, so the entire month is in daylight saving time.
For reference, on June 21, the longest day of the year, the Sun rises at 5:46 AM and sets 14 hours, 48 minutes later, at 8:33 PM, while on December 22, the shortest day of the year, it rises at 7:20 AM and sets 9 hours, 32 minutes later, at 4:52 PM.
Sunrise & Sunset with Twilight in September
The chance that a given day will be muggy in Acalanes Ridge is essentially constant during September, remaining around 0% throughout.
For reference, on September 7, 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 September
dry 55°F comfortable 60°F humid 65°F muggy 70°F oppressive 75°F miserable
The average hourly wind speed in Acalanes Ridge is decreasing during September, decreasing from 8.7 miles per hour to 7.5 miles per hour over the course of the month.
For reference, on June 21, the windiest day of the year, the daily average wind speed is 9.8 miles per hour, while on November 1, the calmest day of the year, the daily average wind speed is 6.7 miles per hour.
Average Wind Speed in September
Wind Direction in September
Acalanes Ridge 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 surface water temperature in Acalanes Ridge is essentially constant during September, remaining around 58°F throughout.
The highest average surface water temperature during September is 58°F on September 18.
Average Water Temperature in September
While it does not do so every year, freezing temperatures are seen in Acalanes Ridge over some winters. The day least likely to be in the growing season is January 2, with a 55% chance.
Time Spent in Various Temperature Bands and the Growing Season in September
The average accumulated growing degree days in Acalanes Ridge are rapidly increasing during September, increasing by 473°F, from 2,455°F to 2,929°F, over the course of the month.
Growing Degree Days in September
The average daily incident shortwave solar energy in Acalanes Ridge is rapidly decreasing during September, falling by 1.5 kWh, from 6.9 kWh to 5.3 kWh, over the course of the month.
Average Daily Incident Shortwave Solar Energy in September
For the purposes of this report, the geographical coordinates of Acalanes Ridge are 37.905 deg latitude, -122.079 deg longitude, and 276 ft elevation.
The topography within 2 miles of Acalanes Ridge contains very significant variations in elevation, with a maximum elevation change of 948 feet and an average elevation above sea level of 275 feet. Within 10 miles contains very significant variations in elevation (3,802 feet). Within 50 miles also contains extreme variations in elevation (4,324 feet).
The area within 2 miles of Acalanes Ridge is covered by artificial surfaces (94%), within 10 miles by grassland (34%) and artificial surfaces (32%), and within 50 miles by grassland (22%) and cropland (21%).
This report illustrates the typical weather in Acalanes Ridge 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 3 weather stations near enough to contribute to our estimation of the temperature and dew point in Acalanes Ridge.
For each station, the records are corrected for the elevation difference between that station and Acalanes Ridge 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 Acalanes Ridge is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Acalanes Ridge and a given station.
The stations contributing to this reconstruction are: Buchanan Field Airport (65%, 10 kilometers, north); Oakland International Airport (21%, 24 kilometers, southwest); and Livermore Municipal Airport (14%, 33 kilometers, southeast).
Time zones for aiports and weather stations are provided by AskGeo.com .