September Weather in Twin Falls Idaho, United StatesDaily high temperatures decrease by 12°F, from 83°F to 71°F, rarely falling below 58°F or exceeding 91°F. Daily low temperatures decrease by 9°F, from 56°F to 46°F, rarely falling below 36°F or exceeding 64°F. For reference, on July 25, the hottest day of the year, temperatures in Twin Falls typically range from 62°F to 90°F, while on December 29, the coldest day of the year, they range from 23°F to 36°F. 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. Ivankovci, Macedonia (6,008 miles away) and Ankara, Turkey (6,389 miles) are the far-away foreign places with temperatures most similar to Twin Falls (view comparison). CloudsThe month of September in Twin Falls experiences gradually increasing cloud cover, with the percentage of time that the sky is overcast or mostly cloudy increasing from 22% to 30%. The clearest day of the month is September 3, with clear, mostly clear, or partly cloudy conditions 78% of the time. For reference, on March 1, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 54%, while on July 28, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 83%. PrecipitationA wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In Twin Falls, the chance of a wet day over the course of September is gradually increasing, starting the month at 8% and ending it at 10%. For reference, the year's highest daily chance of a wet day is 19% on May 2, and its lowest chance is 5% on July 4. RainfallTo 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 Twin Falls is essentially constant, remaining about 0.5 inches throughout, and rarely exceeding 1.3 inches. SunOver the course of September in Twin 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, 22 minutes, implying an average daily decrease of 2 minutes, 50 seconds, and weekly decrease of 19 minutes, 51 seconds. The shortest day of the month is September 30, with 11 hours, 45 minutes of daylight and the longest day is September 1, with 13 hours, 7 minutes of daylight. The earliest sunrise of the month in Twin Falls is 7:03 AM on September 1 and the latest sunrise is 31 minutes later at 7:34 AM on September 30. The latest sunset is 8:10 PM on September 1 and the earliest sunset is 51 minutes earlier at 7:19 PM on September 30. Daylight saving time is observed in Twin Falls during 2024, but it neither starts nor ends during September, so the entire month is in daylight saving time. For reference, on June 20, the longest day of the year, the Sun rises at 6:00 AM and sets 15 hours, 19 minutes later, at 9:18 PM, while on December 21, the shortest day of the year, it rises at 8:04 AM and sets 9 hours, 3 minutes later, at 5:07 PM. The figure below presents a compact representation of the sun's elevation (the angle of the sun above the horizon) and azimuth (its compass bearing) for every hour of every day in the reporting period. The horizontal axis is the day of the year and the vertical axis is the hour of the day. For a given day and hour of that day, the background color indicates the azimuth of the sun at that moment. The black isolines are contours of constant solar elevation. MoonThe figure below presents a compact representation of key lunar data for September 2024. The horizontal axis is the day, the vertical axis is the hour of the day, and the colored areas indicate when the moon is above the horizon. The vertical gray bars (new Moons) and blue bars (full Moons) indicate key Moon phases. The label associated with each bar indicates the date and time that the phase is obtained, and the companion time labels indicate the rise and set times of the Moon for the nearest time interval in which the moon is above the horizon.
HumidityWe 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 Twin Falls is essentially constant during September, remaining around 0% throughout. For reference, on July 25, 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. WindThis 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 Twin Falls is essentially constant during September, remaining within 0.2 miles per hour of 8.0 miles per hour throughout. For reference, on March 27, the windiest day of the year, the daily average wind speed is 9.9 miles per hour, while on August 10, the calmest day of the year, the daily average wind speed is 7.5 miles per hour. The hourly average wind direction in Twin Falls throughout September is predominantly from the west, with a peak proportion of 56% on September 30. Growing SeasonDefinitions 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 Twin Falls typically lasts for 5.6 months (171 days), from around April 27 to around October 15, rarely starting before April 5 or after May 22, and rarely ending before September 25 or after November 5. The month of September in Twin Falls is more likely than not fully within the growing season, with the chance that a given day is in the growing season decreasing from 100% to 82% over the course of the month. 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 Twin Falls are increasing during September, increasing by 389°F, from 2,333°F to 2,722°F, over the course of the month. Solar EnergyThis 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 Twin Falls is rapidly decreasing during September, falling by 1.6 kWh, from 6.3 kWh to 4.8 kWh, over the course of the month. TopographyFor the purposes of this report, the geographical coordinates of Twin Falls are 42.563 deg latitude, -114.461 deg longitude, and 3,730 ft elevation. The topography within 2 miles of Twin Falls contains only modest variations in elevation, with a maximum elevation change of 207 feet and an average elevation above sea level of 3,726 feet. Within 10 miles contains only modest variations in elevation (1,621 feet). Within 50 miles contains very significant variations in elevation (7,848 feet). The area within 2 miles of Twin Falls is covered by artificial surfaces (80%) and cropland (13%), within 10 miles by cropland (77%), and within 50 miles by shrubs (57%) and cropland (26%). Data SourcesThis report illustrates the typical weather in Twin Falls, based on a statistical analysis of historical hourly weather reports and model reconstructions from January 1, 1980 to December 31, 2016. Temperature and Dew PointThere are 3 weather stations near enough to contribute to our estimation of the temperature and dew point in Twin Falls. For each station, the records are corrected for the elevation difference between that station and Twin 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 Twin Falls is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Twin Falls and a given station. The stations contributing to this reconstruction are:
To get a sense of how much these sources agree with each other, you can view a comparison of Twin Falls and the stations that contribute to our estimates of its temperature history and climate. Please note that each source's contribution is adjusted for elevation and the relative change present in the MERRA-2 data. Other DataAll data relating to the Sun's position (e.g., sunrise and sunset) are computed using astronomical formulas from the book, Astronomical Algorithms 2nd Edition , 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 airports and weather stations are provided by AskGeo.com . Maps are © OpenStreetMap contributors. DisclaimerThe 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. Please review our full terms contained on our Terms of Service page. |