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Denver Climatological Preview - September 2009 |
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Preview of Thornton's September Weather - Summer Ends and Fall Arrives
Normal highs on the first of the month are 82 degrees with a low of 53. By the end of the month we see those high temperatures drop to an average of 73 and the lows get to a chilly 42. Overall the month averages 62.4 degrees. In some years summer hangs on as late as the end of September - right to the last day of the month. September 30, 1980 saw a record high temperature of 90 degrees. 97 degrees is the hottest temperature ever recorded for the month - that happening on four occasions, the most recently on September 1st and 5th in 1995. Interestingly enough, all but four days of the month have recorded record highs in the 90s! The ones that haven't - the 21st, 22nd, 24th and 28th - have record temperatures pretty close of either 88 or 89 degrees. The chance for thunderstorms still exists in September but they are infrequent and severe ones are pretty rare. All that sounds great for lovers of warm weather but winter too can make appearances in September - in fact, it can appear early on. The earliest measurable snow happened on September 3, 1961 when 4 inches of the white stuff fell at the old Stapleton International Airport and the mercury dropped to 33 degrees. The snowiest September on record occurred in 1971 which 17.2 inches of snow was recorded. Freezing has occurred in Denver as early as September 8, 1962 with a low of 31 degrees. Winter really hit home in 1985 when on September 29th, 9 inches of snow fell and Denver had a low of 17 degrees and a high of 29. Having said that though, in the 126 years since 1882, 81 Septembers have passed without a trace of snow. In conclusion, September can bring just about anything but the odds do favor a beautiful month. Looking back at September 2008 – Overall an average September Last September, Denver’s weather was pretty much on par with what is normally expected for the month by most measures. In terms of temperature, the average temperature for the month was 61.8 degrees which was 0.6 degrees below normal. Temperatures ranged from a high of 87 degrees down to the low mark of 40 degrees. Here in Thornton we were right on par with those numbers as we averaged 59.8 degrees with a high of 86 and a low of 40.5 degrees, There were no 90 plus degree temperatures and no freezing temperatures which helped to make for a pleasant month. Moisture too was near normal as September 2008 recorded 1.04 inches – 0.10 inch below the normal for the month. What precipitation did fall was recorded early on with the entire monthly accumulation being recorded by the 13th. From the 14th on there was only one day of precipitation recorded and that was merely a trace. The maximum daily precipitation was recorded on between the 11th and 12th with a total of 0.79 inch. In all, five days during the month had rainfall. Three days had thunderstorms, one of which brought rain. Thornton was able to top the official Denver numbers as we recorded 1.58 inches of precipitation for the month. Most of that fell between the 11th and 12th just like Denver but we recorded 1.41 inches during that period. The National Weather Service noted that September 2008 was the 8th year in a row in which September recorded no snow. The average snowfall for Denver in September 2.1 inches. Outlook for September 2009 Long range climate outlooks from the National Weather Service do not favor any particular pattern for temperature or precipitation. Climatological normals should be used for guidance (below). For More Information Temperature Normals and Extremes for September Monthly Temperature, Rainfall and Snowfall Extremes for September
* Historical weather statistics gathered from the National Weather Service's Denver / Boulder forecast office data archives. |
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As temperatures start to drop, September reminds us that summer is at an end and fall is now here. Sunshine is predominant though as the month actually has the highest percentage of sun out of any month. Sunny days and clear, cool nights are the standard weather pattern for the month. 
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