Average Weather in September in La Roche-sur-Foron France
Daily high temperatures decrease by 9°F, from 73°F to 64°F, rarely falling below 55°F or exceeding 82°F.
Daily low temperatures decrease by 6°F, from 53°F to 47°F, rarely falling below 40°F or exceeding 60°F.
For reference, on August 4, the hottest day of the year, temperatures in La Roche-sur-Foron typically range from 57°F to 78°F, while on January 15, the coldest day of the year, they range from 27°F to 38°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 La Roche-sur-Foron experiences rapidly increasing cloud cover, with the percentage of time that the sky is overcast or mostly cloudy increasing from 39% to 51%.
The clearest day of the month is September 1, with clear, mostly clear, or partly cloudy conditions 61% of the time.
For reference, on December 31, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 58%, while on July 21, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 68%.
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 La Roche-sur-Foron, the chance of a wet day over the course of September is essentially constant, remaining around 30% throughout.
For reference, the year's highest daily chance of a wet day is 40% on May 26, and its lowest chance is 25% on March 3.
Probability of Precipitation in September
The average sliding 31-day rainfall during September in La Roche-sur-Foron is gradually increasing, starting the month at 3.0 inches, when it rarely exceeds 5.1 inches or falls below 1.0 inches, and ending the month at 3.3 inches, when it rarely exceeds 6.2 inches or falls below 1.1 inches.
Average Monthly Rainfall in September
Over the course of September in La Roche-sur-Foron, 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, 33 minutes, implying an average daily decrease of 3 minutes, 12 seconds, and weekly decrease of 22 minutes, 26 seconds.
The shortest day of the month is September 30, with 11 hours, 46 minutes of daylight and the longest day is September 1, with 13 hours, 18 minutes of daylight.
Hours of Daylight and Twilight in September
The earliest sunrise of the month in La Roche-sur-Foron is 6:55 AM on September 1 and the latest sunrise is 36 minutes later at 7:31 AM on September 30.
The latest sunset is 8:13 PM on September 1 and the earliest sunset is 56 minutes earlier at 7:17 PM on September 30.
Daylight saving time is observed in La Roche-sur-Foron 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 5:43 AM and sets 15 hours, 46 minutes later, at 9:29 PM, while on December 21, the shortest day of the year, it rises at 8:13 AM and sets 8 hours, 38 minutes later, at 4:51 PM.
Sunrise & Sunset with Twilight and Daylight Saving Time in September
The chance that a given day will be muggy in La Roche-sur-Foron is essentially constant during September, remaining around 0% throughout.
For reference, on July 23, 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 La Roche-sur-Foron is essentially constant during September, remaining within 0.1 miles per hour of 5.1 miles per hour throughout.
For reference, on April 2, the windiest day of the year, the daily average wind speed is 5.7 miles per hour, while on August 10, the calmest day of the year, the daily average wind speed is 4.9 miles per hour.
Average Wind Speed in September
Wind Direction in September
The growing season in La Roche-sur-Foron typically lasts for 6.6 months (201 days), from around April 12 to around October 31, rarely starting before March 22 or after May 2, and rarely ending before October 10 or after November 21.
The month of September in La Roche-sur-Foron is reliably fully within the growing season.
Time Spent in Various Temperature Bands and the Growing Season in September
The average accumulated growing degree days in La Roche-sur-Foron are increasing during September, increasing by 279°F, from 1,766°F to 2,045°F, over the course of the month.
Growing Degree Days in September
The average daily incident shortwave solar energy in La Roche-sur-Foron is rapidly decreasing during September, falling by 1.6 kWh, from 5.4 kWh to 3.8 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 La Roche-sur-Foron are 46.067 deg latitude, 6.312 deg longitude, and 1,991 ft elevation.
The topography within 2 miles of La Roche-sur-Foron contains very significant variations in elevation, with a maximum elevation change of 1,319 feet and an average elevation above sea level of 1,937 feet. Within 10 miles contains very significant variations in elevation (6,634 feet). Within 50 miles also contains extreme variations in elevation (15,079 feet).
The area within 2 miles of La Roche-sur-Foron is covered by grassland (43%), artificial surfaces (21%), cropland (20%), and trees (16%), within 10 miles by trees (39%) and grassland (24%), and within 50 miles by trees (43%) and grassland (20%).
This report illustrates the typical weather in La Roche-sur-Foron 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 4 weather stations near enough to contribute to our estimation of the temperature and dew point in La Roche-sur-Foron.
For each station, the records are corrected for the elevation difference between that station and La Roche-sur-Foron 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 La Roche-sur-Foron is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between La Roche-sur-Foron and a given station.
The stations contributing to this reconstruction are: Annecy-Meythet (46%, 23 kilometers, southwest); Aéroport Genève-Cointrin (38%, 25 kilometers, northwest); Sion (9%, 80 kilometers, east); and Aosta Airport (8%, 89 kilometers, southeast).
Time zones for aiports and weather stations are provided by AskGeo.com .