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Average Weather in September in American Falls Idaho, United States

Daily high temperatures decrease by 12°F, from 83°F to 70°F, rarely falling below 57°F or exceeding 91°F.

Daily low temperatures decrease by 9°F, from 50°F to 41°F, rarely falling below 32°F or exceeding 59°F.

For reference, on July 31, the hottest day of the year, temperatures in American Falls typically range from 56°F to 89°F, while on December 30, the coldest day of the year, they range from 18°F to 32°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 American Falls1815222911223344556677889910101111121213131414151516161717181819192020212122222323242425252626272728282929303012 AM4 AM8 AM12 PM4 PM8 PM12 AMAugOctvery coldcoldcoolcomfortablewarmhotvery coldcomfortable
The average hourly temperature, color coded into bands: frigid < 15°F < freezing < 32°F < very cold < 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.

Felahiye, Turkey (6,451 miles away) and Bījār, Iran (6,872 miles) are the far-away foreign places with temperatures most similar to American Falls (view comparison).

Clouds

The month of September in American Falls experiences gradually increasing cloud cover, with the percentage of time that the sky is overcast or mostly cloudy increasing from 24% to 30%.

The clearest day of the month is September 1, with clear, mostly clear, or partly cloudy conditions 76% of the time.

For reference, on January 17, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 57%, while on July 26, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 82%.

Cloud Cover Categories in September

Cloud Cover Categories in September in American Falls181522291122334455667788991010111112121313141415151616171718181919202021212222232324242525262627272828292930300%100%10%90%20%80%30%70%40%60%50%50%60%40%70%30%80%20%90%10%100%0%AugOctSep 176%Sep 176%Sep 3070%Sep 3070%Sep 1175%Sep 1175%Sep 2172%Sep 2172%clearmostly clearpartly cloudyovercastmostly cloudy
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 American Falls, the chance of a wet day over the course of September is essentially constant, remaining around 11% throughout.

For reference, the year's highest daily chance of a wet day is 20% on May 23, and its lowest chance is 5% on July 5.

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).

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 September in American Falls is essentially constant, remaining about 0.6 inches throughout, and rarely exceeding 1.6 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.

Sun

Over the course of September in American Falls, 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, 23 minutes, implying an average daily decrease of 2 minutes, 51 seconds, and weekly decrease of 19 minutes, 60 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, 9 minutes of daylight.

Hours of Daylight and Twilight in September

Hours of Daylight and Twilight in September in American Falls181522291122334455667788991010111112121313141415151616171718181919202021212222232324242525262627272828292930300 hr24 hr4 hr20 hr8 hr16 hr12 hr12 hr16 hr8 hr20 hr4 hr24 hr0 hrAugOctSep 2212 hr, 10 minSep 2212 hr, 10 minnightnightdaydaySep 113 hr, 9 minSep 113 hr, 9 min
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 American Falls is 6:56 AM on September 1 and the latest sunrise is 31 minutes later at 7:27 AM on September 30.

The latest sunset is 8:05 PM on September 1 and the earliest sunset is 51 minutes earlier at 7:14 PM on September 30.

Daylight saving time is observed in American Falls during 2018, 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 5:53 AM and sets 15 hours, 20 minutes later, at 9:13 PM, while on December 21, the shortest day of the year, it rises at 7:58 AM and sets 9 hours, 2 minutes later, at 5:00 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.

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

For reference, on July 4, 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

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 American Falls is essentially constant during September, remaining within 0.1 miles per hour of 7.4 miles per hour throughout.

For reference, on March 29, the windiest day of the year, the daily average wind speed is 9.4 miles per hour, while on August 4, the calmest day of the year, the daily average wind speed is 7.0 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 American Falls throughout September is predominantly from the west, with a peak proportion of 43% on September 5.

Wind Direction in September

Wind Direction in September in American Falls181522291122334455667788991010111112121313141415151616171718181919202021212222232324242525262627272828292930300%100%10%90%20%80%30%70%40%60%50%50%60%40%70%30%80%20%90%10%100%0%AugOctwestsoutheastnorth
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).

Growing Season

Definitions of the growing season vary throughout the world, but for the purposes of this report, we define it as the longest continuous period of non-freezing temperatures (≥ 32°F) in the year (the calendar year in the Northern Hemisphere, or from July 1 until June 30 in the Southern Hemisphere).

The growing season in American Falls typically lasts for 4.6 months (142 days), from around May 9 to around September 28, rarely starting before April 21 or after May 28, and rarely ending before September 9 or after October 20.

During September in American Falls, the chance that a given day is within the growing season is very rapidly decreasing falling from 97% to 46% over the course of the month.

Time Spent in Various Temperature Bands and the Growing Season in September

Time Spent in Various Temperature Bands and the Growing Season in September in American Fallsgrowing season181522291122334455667788991010111112121313141415151616171718181919202021212222232324242525262627272828292930300%100%10%90%20%80%30%70%40%60%50%50%60%40%70%30%80%20%90%10%100%0%AugOct97%Sep 197%Sep 1Sep 3046%Sep 3046%87%Sep 1187%Sep 1168%Sep 2168%Sep 21Oct 2010%Oct 2010%freezingvery coldcoldcoolcomfortablewarmhot
The percentage of time spent in various temperature bands: frigid < 15°F < freezing < 32°F < very cold < 45°F < cold < 55°F < cool < 65°F < comfortable < 75°F < warm < 85°F < hot < 95°F < sweltering. The black line is the percentage chance that a given day is within the growing season.

Growing degree days are a measure of yearly heat accumulation used to predict plant and animal development, and defined as the integral of warmth above a base temperature, discarding any excess above a maximum temperature. In this report, we use a base of 50°F and a cap of 86°F.

The average accumulated growing degree days in American Falls are increasing during September, increasing by 340°F, from 2,018°F to 2,358°F, over the course of the month.

Growing Degree Days in September

The average growing degree days accumulated over the course of September, with 25th to 75th and 10th to 90th percentile bands.

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 American Falls is rapidly decreasing during September, falling by 1.5 kWh, from 6.3 kWh to 4.8 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.

Topography

For the purposes of this report, the geographical coordinates of American Falls are 42.786 deg latitude, -112.854 deg longitude, and 4,400 ft elevation.

The topography within 2 miles of American Falls contains only modest variations in elevation, with a maximum elevation change of 466 feet and an average elevation above sea level of 4,427 feet. Within 10 miles contains only modest variations in elevation (2,644 feet). Within 50 miles contains large variations in elevation (5,207 feet).

The area within 2 miles of American Falls is covered by water (37%), cropland (29%), shrubs (15%), and artificial surfaces (11%), within 10 miles by cropland (54%) and shrubs (28%), and within 50 miles by shrubs (56%) and cropland (23%).

Data Sources

This report illustrates the typical weather in American Falls 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 American Falls.

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

The stations contributing to this reconstruction are: Pocatello Regional Airport (72%, 28 kilometers, northeast); Burley Municipal Airport (15%, 79 kilometers, west); and Malad City Airport (14%, 83 kilometers, southeast).

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.

Disclaimer

The information on this site is provided as is, without any assurances as to its accuracy or suitability for any purpose. Weather data is prone to errors, outages, and other defects. We assume no responsibility for any decisions made on the basis of the content presented on this site.

We draw particular cautious attention to our reliance on the MERRA-2 model-based reconstructions for a number of important data series. While having the tremendous advantages of temporal and spatial completeness, these reconstructions: (1) are based on computer models that may have model-based errors, (2) are coarsely sampled on a 50 km grid and are therefore unable to reconstruct the local variations of many microclimates, and (3) have particular difficulty with the weather in some coastal areas, especially small islands.

We further caution that our travel scores are only as good as the data that underpin them, that weather conditions at any given location and time are unpredictable and variable, and that the definition of the scores reflects a particular set of preferences that may not agree with those of any particular reader.