1. WeatherSpark.com
  2. United States
  3. California
  4. Alturas
  5. September

Average Weather in September in Alturas California, United States

In Alturas, the month of September is characterized by rapidly falling daily high temperatures, with daily highs decreasing by 10°F, from 83°F to 73°F over the course of the month, and rarely exceeding 91°F or dropping below 59°F.

Daily low temperatures decrease by 7°F, from 42°F to 36°F, rarely falling below 28°F or exceeding 49°F.

For reference, on July 29, the hottest day of the year, temperatures in Alturas typically range from 48°F to 88°F, while on December 31, the coldest day of the year, they range from 21°F to 40°F.

Average High and Low Temperature in September

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 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

Average Hourly Temperature in September in Alturas12 AM4 AM8 AM12 PM4 PM8 PM12 AM18152229112233445566778899101011111212131314141515161617171818191920202121222223232424252526262727282829293030AugOctfreezingchillycoldcoolcomfortablewarmhot
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.


The month of September in Alturas experiences increasing cloud cover, with the percentage of time that the sky is overcast or mostly cloudy increasing from 18% to 28%.

The clearest day of the month is September 1, with clear, mostly clear, or partly cloudy conditions 82% of the time.

For reference, on January 10, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 61%, while on July 28, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 88%.

Cloud Cover in September

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.


A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In Alturas, the chance of a wet day over the course of September is increasing, starting the month at 4% and ending it at 9%.

For reference, the year's highest daily chance of a wet day is 25% on December 7, and its lowest chance is 3% on August 14.

Probability of Precipitation in September

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).


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 September in Alturas is essentially constant, remaining about 0.4 inches throughout, and rarely exceeding 1.2 inches or falling below -0.0 inches.

Average Monthly Rainfall in September

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.


Over the course of September in Alturas, 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, 19 minutes, implying an average daily decrease of 2 minutes, 44 seconds, and weekly decrease of 19 minutes, 6 seconds.

The shortest day of the month is September 30, with 11 hours, 47 minutes of daylight and the longest day is September 1, with 13 hours, 6 minutes of daylight.

Hours of Daylight and Twilight in September

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 Alturas is 6:28 AM on September 1 and the latest sunrise is 30 minutes later at 6:58 AM on September 30.

The latest sunset is 7:34 PM on September 1 and the earliest sunset is 50 minutes earlier at 6:44 PM on September 30.

Daylight saving time is observed in Alturas during 2017, 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 5:28 AM and sets 15 hours, 11 minutes later, at 8:39 PM, while on December 21, the shortest day of the year, it rises at 7:25 AM and sets 9 hours, 10 minutes later, at 4:35 PM.

Sunrise & Sunset with Twilight in September

The solar day over the course of September. 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.


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 Alturas is essentially constant during September, remaining around 0% throughout.

Humidity Comfort Levels in September

Humidity Comfort Levels in September in Alturas0%10%20%30%40%50%60%70%80%90%100%18152229112233445566778899101011111212131314141515161617171818191920202121222223232424252526262727282829293030AugOctSep 160%Sep 160%Sep 10%Sep 10%Sep 300%Sep 300%drydrycomfortablecomfortable
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.


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 Alturas is essentially constant during September, remaining within 0.1 miles per hour of 3.8 miles per hour throughout.

For reference, on March 16, the windiest day of the year, the daily average wind speed is 5.1 miles per hour, while on August 6, the calmest day of the year, the daily average wind speed is 3.5 miles per hour.

Average Wind Speed in September

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 Alturas throughout September is predominantly from the west, with a peak proportion of 44% on September 1.

Wind Direction in September

Wind Direction in September in AlturasWS0%20%40%60%80%100%18152229112233445566778899101011111212131314141515161617171818191920202121222223232424252526262727282829293030AugOctwestsoutheastnorth
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 Alturas is rapidly decreasing during September, falling by 1.6 kWh, from 6.7 kWh to 5.1 kWh, over the course of the month.

Average Daily Incident Shortwave Solar Energy in September

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


For the purposes of this report, the geographical coordinates of Alturas are 41.487 deg latitude, -120.543 deg longitude, and 4,383 ft elevation.

The topography within 2 miles of Alturas contains only modest variations in elevation, with a maximum elevation change of 187 feet and an average elevation above sea level of 4,382 feet. Within 10 miles contains only modest variations in elevation (2,031 feet). Within 50 miles contains large variations in elevation (6,535 feet).

The area within 2 miles of Alturas is covered by shrubs (45%) and cropland (41%), within 10 miles by shrubs (80%) and cropland (12%), and within 50 miles by shrubs (78%) and trees (11%).

Data Sources

This report illustrates the typical weather in Alturas 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 is only a single weather station, Alturas Municipal Airport, in our network suitable to be used as a proxy for the historical temperature and dew point records of Alturas.

At a distance of 2 kilometer from Alturas, closer than our threshold of 150 kilometers, this station is deemed sufficiently nearby to be relied upon as our primary source for temperature and dew point records.

The station records are corrected for the elevation difference between the station and Alturas according to the International Standard Atmosphere , and by the relative change present in the MERRA-2 satellite-era reanalysis between the two locations.

Please note that the station records themselves may additionally have been back-filled using other nearby stations or the MERRA-2 reanalysis.

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.