Denver has seen a record-setting summer with extraordinarily warm temperatures and dry conditions. The question on everyone’s mind now is whether or not September will bring some relief.
Current indications are that overall the month will remain unseasonably warm and dry. However, temperatures will cool as is normal for September.
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.
September 2 to September 8 - This Week in Denver Weather History
Normally September is a relatively quiet month however we do occasionally see some extraordinary conditions. Our look back at this week in Denver weather history shows the earliest seasonal snowfall in Denver history, damaging lightning and the destruction of the Fourmile Canyon wildfire.
From the National Weather Service:
1-5
In 1995…record breaking heat occurred on the first 5 days of the month when the temperature climbed into the 90’s on each day. Record high temperatures of 97 degrees on both the 1st and 4th equaled the all-time record maximum for the month. High temperature of 95 degrees on the 3rd was a record for the date. High temperatures of 94 degrees on both the 2nd and the 5th were not records. The low temperature of 64 degrees on the 4th equaled the record high minimum for the date.
1-7
In 1978…the temperature reached 90 degrees or more on seven consecutive days with the highest temperature…94 degrees… Recorded on both the 4th and 6th.
2
In 1938…heavy cloudbursts in the foothills near the top of Genesee Mountain caused flash flooding on Bear Creek at Morrison. Nearly 8 inches of rain fell just north of Morrison in 6 hours and drowned 6 people in a car between Morrison and Kittredge. Damage was estimated at nearly a half million dollars. Flash flooding also occurred on south Boulder Creek in Eldorado Springs. Rainfall totaled 4.42 inches in Eldorado Springs…and rainfall was estimated to more than 6 inches in the foothills west of the town. Many buildings and residences were damaged in Eldorado Springs…and bridges were swept away. The high waters forced residents from their homes as far downstream as Erie. This was the flood of record on South Boulder Creek.
In 1973…hail to 3/4 inch diameter was reported in Boulder.
In 1987…lightning struck two men who were standing under a tree in downtown Denver. Both were seriously injured and hospitalized.
In 1996…lightning sparked a brush fire in the south buffer zone of the Rocky Flats Environmental Test Facility. No structures were damaged…but the fire burned about 100 acres of grassland before being contained.
2-3
In 1892…there was a trace of rainfall each day. This… Together with a trace of rain on both the 7th and 8th…was the only rainfall of the month…making the month the driest on record. The monthly record was equaled in 1944.
3
In 1901…a thunderstorm produced rain…hail of unknown size… And south winds sustained to 40 mph with gusts to 43 mph.
In 1961…Labor Day snow storm is the earliest date of the first snow…trace and measurable…of the season. The heavy wet snow broke many limbs from trees that were still in full foliage. The storm produced 4.2 inches of snowfall at Stapleton Airport with nearly a foot of snow in western suburbs and in the foothills. Minimum temperature of 33 degrees was a record for the date and the coldest ever recorded so early in the season.
In 1999…severe thunderstorms dumped large hail across metro Denver. Hail as large as 1 inch in diameter was measured near Cherry Creek in Aurora and near Bennett. Hail to 3/4 inch in diameter fell in the city of Denver.
In 2002…a thunderstorm produced a wind gust to 51 mph at Denver International Airport.
In 2003…very heavy thunderstorm rain washed out parts of the Virginia Canyon Road above Idaho Springs. Up to 4 feet of mud reportedly washed down the road during the storm. Several vehicles were trapped on the road. In Idaho Springs…several streets…including the main street… Were also buried in mud and gravel. Some buildings in town experienced minor flooding…including the basement of the town library and the police station.
August 26 to September 1 - This Week in Denver Weather History
Significant events on Denver’s weather history calendar get a bit less numerous as we enter what is historically a relatively quiet period of the year. That isn’t to say however that major weather events can’t occur. Our look back at this week in Denver weather history includes a massive hail storm in 1944, many events in which lightning injured people and the warmest temperature ever recorded in September.
From the National Weather Service:
19-30
In 1875…grasshoppers appeared in great numbers at 10:00 am on the 19th. Thousands landed on the ground. The streets were literally covered with them. Swarms of grasshoppers were seen on each day. All gardens in the city were devastated…and in the countryside the grasshoppers were very destructive to ripened grain. On the 30th the grasshoppers were so numerous as to almost darken the sun.
24-26
In 1910…the lowest temperature ever recorded in August…40 degrees…occurred on each of these days and on August 22… 1904. The unusually cold weather for so early in the season brought sub-freezing minimum temperatures to much of the Colorado northeastern plains.
26
In 1944…one of the most destructive hailstorms in the city in a decade caused damage estimated at nearly one million dollars. The storm occurred within a period of 10 to 30 minutes…between 2:00 pm and 3:00 pm. The hail varied in size from very small to as large as 1 1/2 inches in diameter. Hail covered the ground to a depth of 5 to 6 inches in some sections of the city. Several people were cut by broken glass. The hail and heavy rain flooded underpasses to a depth of 6 feet…and the occupants of stalled autos had to be rescued. Sewers were unable to handle the sudden amount of water and water backed up and flooded a number of basements. A few first floors of buildings were flooded. The water department had a busy time replacing manhole covers that had been displaced by the water pressure. Trees were stripped…one was severely broken…and telephone lines were downed. Roofs…windows… automobiles…awnings…and gardens were severely damaged. Flowers and gardens in some sections of the city were a total loss. Greenhouses were extensively broken with an estimated 20 carloads of glass shattered. Vegetable and truck crops in and around the city were severely shredded. The next day the American Red Cross was designated by the war agency to grant any and all priorities needed to obtain materials and supplies to replace and repair the damage. In downtown Denver…the thunderstorm produced 0.95 inch of rain and heavy hail along with sustained northwest winds to 25 mph.
In 1961…strong winds blew in the walls of a warehouse under construction in Denver. Two workmen suffered a fractured foot and body bruises.
26-27
In 1980…two heavy thunderstorms hit Arvada and Westminster… Dumping up to 1.50 inches of rain in less than an hour. At least two streets were washed out and a number of homes and cars were damaged when a creek flooded. Three homes in Arvada sustained minor lightning damage.
27
In 1910…a thunderstorm produced south winds sustained to 40 mph.
In 1961…strong thunderstorm winds and heavy rain occurred at 79th and federal blvd. In Westminster. The strong winds blew the roofs off lumber sheds onto parked cars.
In 1967…a young woman was killed by lightning while horseback riding in the suburbs just west of Denver. Her horse died several hours after the incident. A young man and another young woman were also knocked from their horses by the impact of the lightning and required hospitalization.
In 1991…heavy thunderstorm rainfall totaled 0.91 inch at Stapleton International Airport…where 1/4 inch diameter hail was measured.
In 1996…localized street flooding occurred in the Fort Lupton area when 2 to 3 inches of rain fell in 45 minutes. The roof of a community college began leaking…which caused damage to ceiling tiles. The roof was under repair from hail damage which had occurred earlier in the summer. A weak tornado (f0) was sighted near Fort Lupton. No damage was reported.
In 1999…a slow moving thunderstorm dumped 5 inches of rain in 2 hours near Dacono. A severe thunderstorm produced 3/4 inch diameter hail in Castle Rock.
In 2002…severe thunderstorms spread large hail over metro Denver. Hail as large as 2 inches in diameter fell in Jefferson County 5 to 11 miles northwest of Golden. Other large hail reports included: 1 1/2 inches near Golden and in Lakewood; 1 1/4 inches in Nederland; 1 inch hail near Elizabeth…Louviers…Rollinsville…and Blackhawk; 7/8 inch hail near Acequia in Douglas County. A thunderstorm produced a trace of rain and a microburst wind gust to 52 mph at Denver International Airport.
In 2003…lightning struck a house and sparked a fire in Arvada. Damage to the roof and ceiling was extensive.
In 2005…lightning struck an unoccupied home in Parker. The resulting fire damaged the roof…attic…and second floor bedroom. Damage was estimated at 15 thousand dollars.
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.
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 63.4 degrees.
The Mile High City's September weather was unusually dry and warm. (iStockphoto / johnnyscriv)
Wildfires and record-setting temperatures provided a clue as to what the highlights of September’s weather would be and with the month over we now see it in the statistics. September 2010 will go down in the record books as not only one of the driest Septembers on record but also one of the warmest.
A mere 0.06 inch of precipitation was recorded at the official monitoring station at Denver International Airport over the month. Most of that fell during a four-day period from the 18th to the 22nd and in the end 25 days had no moisture at all. That scarcity of precipitation allowed the month to finish in a tie with 1882 and 1920 for the 5th driest September on record. Here in Thornton we fared a bit better having recorded 0.09 inch of precipitation but that paltry difference is not hardly worth noting.
Not only was precipitation in short supply, so too were even clouds. Zero days were reported as cloudy, 10 days as partly cloudy and 20 days were fair (sunny). Thornton recorded over 200 hours of sunshine for the month – more than any other month in 2010.
Temperatures were well above normal for the month and into top 10 status as well. The average temperature of 67.0 degrees was 4.6 degrees above normal. This puts September 2010 in a tie with 1939 as the seventh warmest September on record. Thornton was thankfully quite a bit cool as we recorded an average temperature of 64.7 degrees.
Four record high temperatures were tied or broken during the month. On the 19th a scorching 96 degrees was recorded easily besting the old record for the date of 93 degrees last set in 1980. That also was the hottest temperature ever recorded that late in the season. Other dates this past month setting records were: 94 on the 20th beating the old record of 92 last set in 1956; tied the record on the 26th with 1892; 92 on the 28th topping the old record of 89 last set in 1994.
In all the month recorded eight 90 degree days, well above the normal of 2 for September. An amazing 25 days had temperature at or above 80 degrees which is the highest number of 80 degree temperatures in September since 1872. Overall temperatures ranged from the high of 96 on the 19th down to a low of 40 on the 3rd. Thornton’s temperatures ranged from a high of 93.6 on the 19th to a low of 40.7 degrees on the 7th.
Looking beyond the statistics, the most noteworthy events of September 2010 were the wildfires in the foothills west of Denver. The Fourmile Canyon Fire northwest of Boulder became the most destructive in state history in terms of the number of homes destroyed. West of Loveland the Reservoir Road Fire claimed homes as well but was thankfully controlled relatively quickly due to the quick response of firefighters.
What does the October 2010 weather hold for Denver and the Colorado Front Range? Right now the dry and warm weather is expected to continue. Get all the details in our October 2010 preview.
From the National Weather Service:
...THE DENVER CO CLIMATE SUMMARY FOR THE MONTH OF SEPTEMBER 2010...
CLIMATE NORMAL PERIOD 1971 TO 2000
CLIMATE RECORD PERIOD 1872 TO 2010
WEATHER OBSERVED NORMAL DEPART LAST YEAR'S
VALUE DATE(S) VALUE FROM VALUE DATE(S)
NORMAL
................................................................
TEMPERATURE (F)
RECORD
HIGH 97 09/04/1995
09/01/1995
09/04/1960
09/05/1899
LOW 17 09/29/1985
HIGHEST 96 09/19 97 -1 91 09/01
LOWEST 40 09/03 17 23 36 09/28
AVG. MAXIMUM 84.8 77.4 7.4 78.0
AVG. MINIMUM 49.1 47.3 1.8 48.9
MEAN 67.0 62.4 4.6 63.5
DAYS MAX >= 90 8 2.2 5.8 1
DAYS MAX <= 32 0 0.2 -0.2 0
DAYS MIN <= 32 0 0.8 -0.8 0
DAYS MIN <= 0 0 0.0 0.0 0
PRECIPITATION (INCHES)
RECORD
MAXIMUM 4.67 1961
MINIMUM T 1892
1944
TOTALS 0.06 1.14 -1.08 0.74
DAILY AVG. T 0.04 -0.04 0.02
DAYS >= .01 3 6.3 -3.3 5
DAYS >= .10 0 MM MM 4
DAYS >= .50 0 MM MM 0
DAYS >= 1.00 0 MM MM 0
GREATEST
24 HR. TOTAL 0.03 09/22 TO 09/22 0.42 09/22 TO 09/23
SNOWFALL (INCHES)
RECORDS
TOTAL 17.2 1971
TOTALS 0.0 2.1 0.0
DEGREE_DAYS
HEATING TOTAL 32 136 -104 117
SINCE 7/1 35 146 -111 139
COOLING TOTAL 100 57 43 78
SINCE 1/1 862 696 166 533
FREEZE DATES
RECORD
EARLIEST 09/08/1962
LATEST 06/08/2007
EARLIEST 10/07
LATEST 05/05
.................................................................
WIND (MPH)
AVERAGE WIND SPEED 9.3 9.2
RESULTANT WIND SPEED/DIRECTION 2/190
HIGHEST WIND SPEED/DIRECTION 37/310 09/06 36/210 09/30
HIGHEST GUST SPEED/DIRECTION 44/320 09/06 45/280 09/30
SKY COVER
POSSIBLE SUNSHINE (PERCENT) MM
NUMBER OF DAYS FAIR 20
NUMBER OF DAYS PC 10
NUMBER OF DAYS CLOUDY 0
AVERAGE RH (PERCENT) 36
WEATHER CONDITIONS. NUMBER OF DAYS WITH
THUNDERSTORM 3 MIXED PRECIP 0
HEAVY RAIN 0 RAIN 0
LIGHT RAIN 4 FREEZING RAIN 0
LT FREEZING RAIN 0 HAIL 0
HEAVY SNOW 0 SNOW 0
LIGHT SNOW 0 SLEET 0
FOG 4 FOG W/VIS <= 1/4 MILE 2
HAZE 2
- INDICATES NEGATIVE NUMBERS.
R INDICATES RECORD WAS SET OR TIED.
MM INDICATES DATA IS MISSING.
T INDICATES TRACE AMOUNT.
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.
However that isn’t to say the weather can’t be a lot more “interesting.” Extremes can occur during September ranging from heat to cold to yes, even snow.
Denver has seen a record-setting summer with extraordinarily warm temperatures and dry conditions. The question on everyone’s mind now is whether or not September will bring some relief.
