Following on three straight months of record-setting heat, the Mile High City is hoping September brings some relief. The month is typically when we start to see the transition from summer to fall-like temperatures and has been known to even bring the season’s first snowfall.
As temperatures start to drop, September usually 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.
Normal highs on the first of the month are 84 degrees with a low of 54. By the end of the month we see those high temperatures drop to an average of 72 and the lows get to a chilly 42. Overall the month averages 63.4 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 4th 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.
All that sounds great for lovers of warm weather but winter too can make appearances in September. The coldest temperature ever recorded in September was a winter-like 17 degrees on September 29, 1985. Temperatures below freezing have been recorded as early as September 8th and in fact the record low temperature for 21 of September’s 30 days is at or below freezing.
Snow is not unheard of in September and it can appear early on in the month. 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 over the entire month. 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.
In the 140 years since 1872, 45 Septembers have recorded snow. Of those, 28 had measureable snowfall at or above 0.1″ while the rest had a trace. have passed without a trace of snow. At the current time, Denver has gone 11 Septembers in a row without snow being recorded with the last being in September 2000 when 0.2 inch was recorded.
September usually brings an end to the monsoon flow from the southwest and instead moisture will oftentimes move in from the Pacific. The chance for thunderstorms still exists in September but they are infrequent, particularly in the latter half of the month, and severe ones are pretty rare.
In conclusion, September can bring just about anything but the odds do favor a beautiful month.
Denver’s September Extremes
September: Denver’s Top 5 Warmest (mean temperatures):
68.3 Degrees 1948
68.2 Degrees 1931, 1981
68.0 Degrees 1998
67.7 Degrees 1933
67.6 Degrees 1947
September: Denver’s Top 5 Coldest ((mean temperatures):
54.8 Degrees 1912
55.7 Degrees 1965
56.3 Degrees 1961
57.5 Degrees 1971
58.1 Degrees 1918
September: Denver’s Wettest
4.67 Inches 1961
3.78 Inches 1909
3.70 Inches 1902
3.42 Inches 1938
2.89 Inches 1875, 1918, 1936
September: Denver’s Driest
T Inches 1892, 1944
0.01 Inches 1956, 1992
0.02 Inches 1879, 1921
0.05 Inches 1893
0.06 Inches 1882, 1920, 2010
September: Denver’s Snowiest
17.2 Inches 1971
16.5 Inches 1936
12.9 Inches 1959
11.4 Inches 1895
8.7 Inches 1985
September: Denver’s Least Snowiest
Numerous years with 0.0″ snowfall (85)
Outlook for September 2012
From the National Weather Service: “After record breaking heat in June, July and August along with the 6th consecutive month of below normal precipitation in Denver, the mid to long range forecast models continue to indicate a bias toward the stable ridge of high pressure to continuing to dominate the central United States from the 10th through the end of September, 2012. The Climate Prediction Center’s long range outlooks for temperature and precipitation indicate a bias toward above normal temperatures with precipitation probabilities holding near to below seasonal normals.”
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