The month of September 2017 saw significant differences between the start and the end. The first two-thirds of the month were extraordinarily dry with temperatures well above normal. The last 10 days brought a big change though with damp conditions and much cooler conditions.
High pressure dominated the region for the first few weeks of the month. During this period when we normally see cooler temperatures, we instead saw highs oftentimes at or above 90 degrees and a couple of record high readings. Additionally, it was exceedingly dry with Thornton only received 0.03 inches of precipitation through the first 22 days of the month.
Big changes arrived and the last nine days of the month stood it stark contrast to the rest of September. Low pressure and a series of disturbances brought much cooler temperatures and much-needed precipitation, including snowfall in the high country. Seven out of the last eight days saw below normal high temperature readings and enough precipitation fell to push us to just above normal.
Thornton’s overall average temperature for the month came in at 62.4 degrees. This was a full degree cooler than Denver’s long term September average of 63.4 degrees. Out at DIA where Denver’s official measurements are taken, it was a good bit warmer with an average temperature of 65.1 degrees.
Temperatures in Thornton ranged from a high of 98.5 degrees on the third and a low of 40.9 degrees on the morning of the 29th. Denver saw their high of 97 degrees on the third as well and their coldest reading of 40 degrees on the 20th.
Two record high temperatures were officially set or tied for the Mile High City. The high temperature of 97 degrees on the third tied the record high for the date. A reading of 92 degrees on the 21st set a new record high for that date.
In terms of precipitation, Denver averages 0.96 inches during September. Thornton tallied 1.05 inches in the rain bucket while Denver bested us with 1.26 inches.
Click here to view Thornton’s September 2017 climate report.
From the National Weather Service:
CLIMATE REPORT
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
244 AM MDT SUN OCT 1 2017
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...THE DENVER CO CLIMATE SUMMARY FOR THE MONTH OF SEPTEMBER 2017...
CLIMATE NORMAL PERIOD 1981 TO 2010
CLIMATE RECORD PERIOD 1872 TO 2017
WEATHER OBSERVED NORMAL DEPART LAST YEAR`S
VALUE DATE(S) VALUE FROM VALUE DATE(S)
NORMAL
................................................................
TEMPERATURE (F)
RECORD
HIGH 97 09/03/2017
09/06/2013
09/05/2013
LOW 17 09/29/1985
HIGHEST 97R 09/03 91 6 93 09/05
LOWEST 40 09/20 35 5 37 09/10
AVG. MAXIMUM 79.0 78.5 0.5 82.3
AVG. MINIMUM 51.3 48.3 3.0 49.7
MEAN 65.1 63.4 1.7 66.0
DAYS MAX >= 90 9 3.4 5.6 6
DAYS MAX <= 32 0 0.0 0.0 0
DAYS MIN <= 32 0 0.8 -0.8 0
DAYS MIN <= 0 0 0.0 0.0 0 PRECIPITATION (INCHES) RECORD MAXIMUM 5.61 2013 MINIMUM T 1892 1944 TOTALS 1.26 0.96 0.30 0.28 DAILY AVG. 0.04 0.03 0.01 0.01 DAYS >= .01 6 6.5 -0.5 4
DAYS >= .10 2 3.3 -1.3 1
DAYS >= .50 1 0.6 0.4 0
DAYS >= 1.00 0 0.1 -0.1 0
GREATEST
24 HR. TOTAL 0.83 09/23 TO 09/23 09/12 TO 09/12
SNOWFALL (INCHES)
RECORDS
TOTAL 0.0
TOTALS 0.0 1.3
DEGREE_DAYS
HEATING TOTAL 122 125 -3 64
SINCE 7/1 130 141 -11 79
COOLING TOTAL 131 76 55 99
SINCE 1/1 880 764 116 861
FREEZE DATES
RECORD
EARLIEST 09/08/1962
LATEST 06/08/2007
EARLIEST 10/07
LATEST 05/05
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WIND (MPH)
AVERAGE WIND SPEED 9.6
RESULTANT WIND SPEED/DIRECTION 2/165
HIGHEST WIND SPEED/DIRECTION 40/020 DATE 09/19
HIGHEST GUST SPEED/DIRECTION 48/030 DATE 09/19
SKY COVER
POSSIBLE SUNSHINE (PERCENT) MM
AVERAGE SKY COVER 0.50
NUMBER OF DAYS FAIR 9
NUMBER OF DAYS PC 15
NUMBER OF DAYS CLOUDY 6
AVERAGE RH (PERCENT) 48
WEATHER CONDITIONS. NUMBER OF DAYS WITH
THUNDERSTORM 0 MIXED PRECIP 0
HEAVY RAIN 1 RAIN 1
LIGHT RAIN 10 FREEZING RAIN 0
LT FREEZING RAIN 0 HAIL 0
HEAVY SNOW 0 SNOW 0
LIGHT SNOW 0 SLEET 0
FOG 8 FOG W/VIS <= 1/4 MILE 1
HAZE 10
- INDICATES NEGATIVE NUMBERS.
R INDICATES RECORD WAS SET OR TIED.
MM INDICATES DATA IS MISSING.
T INDICATES TRACE AMOUNT.