Following on an August that saw seasonal temperatures but little precipitation, some are certainly hoping for a bit of the wet stuff in September. The month can bring plenty of rain and even our first snow of the season but more often than not, it is one of the most pleasant along the Colorado Front Range.
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.
The month can bring extremes however. We will of course forever remember 2013’s devastating floods brought on by record-setting rain. Longtime residents might remember September 1971 which brought over 17 inches of snowfall.
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.
In 2014…two men in central Denver were struck by lightning as they sat under a tree to avoid a heavy downpour. One of the men was unconscious and had no pulse when emergency responders arrived. He was immediately taken to Denver Health was listed in critical condition. The other victim suffered less severe injuries. He was treated at the scene and hospitalized…then released a few hours later.
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.
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.
Thornton, Colorado’s September 2017 Temperature Summary. (ThorntonWeather.com)Thornton, Colorado’s September 2017 Precipitation Summary. (ThorntonWeather.com)
From the National Weather Service:
CLIMATE REPORT
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
244 AM MDT SUN OCT 1 2017
...................................
...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
...................................................
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.
September 24 to September 30: This week in Denver weather history
Colorado’s famously inconsistent weather can be seen in our look back at this week in Denver weather history. Not only do we see damaging thunderstorms and winds but even major snowstorms that deposited more than a foot of the white stuff on the city.
From the National Weather Service:
23-24
In 2000…the first snowstorm of the season brought heavy snow to areas in and near the foothills. While the heaviest snow fell north of metro Denver…6 inches were measured in Boulder…4 inches at both Castle Rock and Morrison…but only 0.2 inch at the site of the former Stapleton International Airport where most of the precipitation fell as rain. At Denver International Airport where drizzle and rain fell on the 23rd… Snowfall during the early morning of the 24th was estimated at 2.1 inches due to melting. The foothills west of Denver received more snow with 10 inches measured at conifer…9 inches 11 miles southwest of Morrison… 8 inches atop Crow Hill…7 inches at Chief Hosa…and 5 inches at Ralston Reservoir.
24
In 1901…northwest winds were sustained to 50 mph with gusts as high as 57 mph in the city.
In 1932…thunderstorm rainfall of only 0.11 inch was the only measurable precipitation for the month that year in the city.
In 1986…a very strong wind storm roared across metro Denver. Boulder was hit hardest. Winds peaked to 131 mph at the National Center for Atmospheric Research. This is thought to be the highest wind gust ever recorded in Boulder during September. A wind gust to 118 mph was clocked on Davidson Mesa and to 92 mph near Niwot. Gusts of 70 to 80 mph were common over all of Boulder where an estimated 70 to 90 large trees were uprooted. About a dozen of them hit cars. Two walls of a building under construction were toppled and solar panels were blown off a house. Traffic lights and power lines were downed. Damage to power equipment alone was estimated at 100 thousand dollars. Wind gusts to 87 mph at Jefferson County Airport damaged two planes. A woman was seriously injured in Boulder. She suffered a fractured skull when struck by a falling tree limb. Trees were also downed in Louisville and Lafayette. West wind gusts to 45 mph were recorded at Stapleton International Airport.
25
In 1873…a fire was sighted in the woods near Platte Canyon… Probably caused by high winds blowing sparks among the timber.
In 1896…an apparent cold front produced northeast sustained winds to 40 mph with gusts to 48 mph.
In 1910…a thunderstorm produced sustained north winds to 51 mph. This was the highest recorded wind speed in the city in September at the time.
In 1936…a vigorous cold front produced a deadly dust storm in the city. North winds sustained to 36 mph with gusts to 38 mph produced much blowing dense dust…greatly restricting the visibility. The temperature plunged from a high of 84 degrees to a low of 38 degrees by midnight. The weather observer described the event with the following. “at 6:00 pm the temperature was 82 degrees and the wind velocity was only 4 mph; but with the wind shifting to the north and the barometer rising quite rapidly…the temperature fell sharply. By 6:30 pm…the wind velocity increased rapidly and by 7:00 pm had reached a maximum sustained velocity of 36 mph…bringing with it clouds of dust which had been picked up by gale force winds in southern Wyoming and northern Colorado…covering the city. The visibility was generally reduced to about 1/4 mile; however…the whirling of the dust down the streets and alleys…the visibility was at times somewhat less. Airplanes were grounded…traffic was halted at times…and homes filled with dust. The strong winds damaged electric power and telephone lines…leaving homes in darkness for a few hours in the city and for 18 hours in suburban towns and putting 2500 telephones out of service because of broken lines. An electric lineman was killed while repairing damage by the high winds. The dust storm was followed by rain that began falling at 10:55 pm…which turned to snow during the early morning hours of the 26th. A major snow storm followed on the 27th through the 29th.”
In 1999…high winds developed in the foothills of Boulder County. Winds gusted to 90 mph at Wondervu.
25-26
In 1908…apparent post-frontal rain changed to snow overnight and totaled 6.5 inches in downtown Denver. This was the first snow of the season. Precipitation totaled 0.76 inch. North winds were sustained to 39 mph on the 25th.
25-27
In 1996…an early season snowstorm brought heavy snow to the Front Range eastern foothills. Snowfall totals included: 8 to 12 inches around conifer…7 inches on Floyd Hill…and 6 inches at both Bailey and Chief Hosa. Snowfall totaled only 4.7 inches at the site of the former Stapleton International Airport. This was the first measurable snow of the season. After the passage of a strong cold front…north winds gusted to 38 mph at Denver International Airport on the 25th.
September 17 to September 23: This week in Denver weather history
The calendar may still say it is summer for a few more days but our look back at this week in Denver weather history shows that Old Man Winter can still make an appearance.
From the National Weather Service:
15-17
In 2000…unusually hot weather for so late in the season occurred when temperatures climbed into the 90’s setting daily record maximum temperatures on each of the 3 days. The high temperature was 92 degrees on the 15th and 95 degrees on both the 16th and 17th.
15-19
In 1906…rain on 5 consecutive days totaled 1.61 inches. A thunderstorm occurred on the 17th. High temperatures ranged from 48 degrees on the 16th to 65 degrees on the 15th. Low temperatures were in the lower to mid 40’s.
16-19
In 1971…a record breaking early fall snow storm caused extensive damage to trees and utility lines. The heavy wet snow occurred with little wind…but caused record breaking cold temperatures for so early in the season. Snowfall totaled 15.6 inches at Stapleton International Airport with most of the snowfall…12.0 inches…occurring on the 17th. This was the heaviest first snow of the season. The maximum snow depth on the ground was 13 inches. Record low temperatures were set on three consecutive days: 31 degrees on the 17th…23 degrees on the 18th…and 20 degrees on the 19th…which was also a new all-time record minimum for the month at that time. Record low maximum temperatures were set on 4 consecutive days: 48 degrees on the 16th…35 degrees on the 17th…40 degrees on the 18th… And 42 degrees on the 19th.
17
In 1873…brisk west to northwest winds at different times during the day…generally in sudden gusts…spread a good deal of dust into the city.
In 1953…strong winds caused thousands of dollars in damage to Boulder. The winds blew for most of the day with great gustiness…and a freak twister was reported during the afternoon. Damage was minor. A thunderstorm wind gust to 40 mph caused some blowing dust at Stapleton Airport.
In 1992…a tornado touched down briefly near Bennett. No damage was reported.
In 1993…severe thunderstorms rumbled across northern portions of metro Denver. Hail as large as 1 3/4 inches in diameter fell in Brighton. Dime size hail damaged several roofs of residences in Lafayette.
In 2000…for the second day in a row…the high temperature of 95 degrees at Denver International Airport broke three record temperature extremes: the high temperature broke the previous record for the day of 94 degrees set in 1895; it marked the warmest it has been for so late in the season; it also marked the 61st day in the year that the temperature had equaled or exceeded 90 degrees…eclipsing the record equaled the previous day and first set on September 29… 1994.
18
In 1901…northeast winds were sustained to 42 mph with gusts to 50 mph behind an apparent cold front.
In 1948…the low temperature cooled to only 69 degrees…the all-time record high minimum for the month.
In 1988…a strong cold front blasted metro Denver with high winds. Gusts reached 82 mph in Longmont and 81 mph at Jefferson County Airport near Broomfield where the winds flipped over and destroyed a small airplane. Wind gusts to 60 mph were recorded in Boulder and Wheat Ridge. West wind gusts to 54 mph were clocked at Stapleton International Airport. The strong winds downed trees and power lines and damaged homes and cars. A Longmont man was slightly injured…when a tree fell on top of his car.
In 1990…a slow moving thunderstorm over southwest metro Denver spawned an ominous looking funnel cloud near the intersection of Sheridan Blvd. and U.S. Highway 285. The funnel cloud nearly touched down a few times before lifting back into the main cloud. No damage was reported. Pea to marble size hail and 3/4 inch of rain fell over central and northeast Denver. Numerous streets and underpasses became flooded on Denver’s south side when the heavy runoff backed up storm sewers. Thunderstorm rainfall totaled 1.02 inches at Stapleton International Airport.
In 1993…a severe thunderstorm rolled through southeast metro Denver. Dime size hail was reported in many areas. Straight-line winds from the thunderstorm…measured by a weather spotter at 70 mph…tore the roof off 6 apartments of an apartment complex in Aurora. Heavy rain which accompanied the winds caused major damage to the apartments as well as the contents. Many trees…fences… And power poles were knocked down by the strong winds. Heavy rain flooded roadways in Denver and Aurora. Thunderstorm rainfall totaled 1.08 inches and north winds gusted to 44 mph at Stapleton International Airport where the visibility was briefly reduced to as low as 1/4 mile in heavy rain.
In 1996…a late summer snowstorm struck the northern mountains and Front Range eastern foothills. Golden Gate Canyon received 6 inches of new snow with 5 inches reported at both Nederland and Blackhawk. Thunderstorms produced heavy rain across metro Denver…which was mixed with snow by late evening. Rainfall totaled 0.83 inch at the site of the former Stapleton International Airport and 1.22 inches at Denver International Airport where northwest winds gusted to 39 mph.
18-19
In 1955…heavy rains caused flash flooding across portions of metro Denver. Rainfall totaled 1.71 inches at Stapleton Airport.
19
In 1955…hail stones to 2 1/2 inches in diameter were reported north of Denver. The large stones broke many automobile windshields.
In 1963…hail to 3/4 inch in diameter fell in Westminster.
In 1983…an unusually strong cold front roared through metro Denver during the afternoon hours. At Stapleton International Airport…the temperature dropped 51 degrees… From a sunny 86 degrees to a snowy 35 degrees…in just 7 hours. Strong winds and a wall of blowing dust followed the front. Northeast winds gusting to 36 mph briefly reduced the surface visibility to 1 mile in blowing dust at Stapleton International Airport where only a trace of snow fell later.
In 1996…high winds gusting to 84 mph were measured at Golden Gate Canyon in the foothills west of Denver. West winds gusted to only 25 mph at Denver International Airport.
September 10 to September 16: This Week in Denver Weather History
Severe weather is less common as we enter the fall season but it is not entirely unheard of. As we see in our look back at this week in Denver weather history, we have seen everything ranging from torrential rains to tornadoes and even heavy snow.
5-13
In 2010…the Fourmile Canyon Wildfire…northwest of Boulder…broke out on the morning of the 5th. It originated from an unattended fire pit at a local residence. The wildfire quickly consumed 5 1/2 square miles or 3500 acres the first day…and forced the evacuation of over three thousand residents. Erratic 45-mph gusts sent the fire in two directions at times. Very dry weather conditions preceded the fire. The combination of strong winds…low relative humidities and dry fuels allowed the wildfire spread rapidly through the steep…heavily forested terrain. The flames were reportedly 20 to 50 feet in length. Towns within the burn area included Salina…Wallstreet and Gold Hill. The dry conditions coupled with gusty winds ranging from 45 to 64 mph persisted for several more days. Fire managers used as many as 700 firefighters and support personnel from 35 agencies and seven air tankers to battle the wildfire. A total of 6181 square acres or approximately 10 square miles were burned. The Fourmile Canyon Wildfire was the most destructive fire in Colorado history in terms of the damage to personal property. It destroyed 171 homes with an estimated cost of 217 million dollars.
9-10
In 1933…heavy rain over the Cherry Creek…Plum Creek…Big Dry Creek…and Little Dry Creek watersheds caused flooding on the South Platte River in Denver overnight. Nearly an inch of rain…0.98 inch…fell in the city.
In 1944…a trace of rain fell on each day. This together with a trace of rain on the 4th and 30th was the only precipitation for the month. The total of a trace of precipitation for the month equaled the driest September on record first set in 1892.
In 1994…unusually very warm weather resulted in three temperature records being equaled. High temperatures of 94 degrees on the 9th and 93 degrees on the 10th equaled record maximums for the dates. Low temperature of 63 degrees on the 9th equaled the record high minimum for the date.
10
In 1985…golf ball size hail was reported just east of Parker.
In 1989…3/4 inch diameter hail fell in Littleton. Heavy rain produced local flooding in Lakewood. The heavy rain caused the wall of a house to collapse.
In 1993…thunderstorm winds downed power lines…which caused a power outage in Castle Rock.
11
In 1910…west winds were sustained to 42 mph.
In 1951…a vigorous Canadian cold front produced a dust storm across metro Denver. Northeast wind gusts to 43 mph reduced the visibility at Stapleton Airport to as low as 1 1/2 miles for nearly 5 hours. The temperature dropped 47 degrees in 8 hours…from a high of 92 degrees to a low of 45 degrees.
In 1967…a microburst wind gust to 52 mph produced blowing dust and briefly reduced the visibility to 1/2 mile at Stapleton International Airport.
In 1974…a trace of snow…the first of the season…ended the shortest period without snow…94 days from June 9th through September 10th. A trace of snow also fell on June 8th.
In 1995…strong post-frontal winds associated with a fast moving pacific cold front knocked down power poles and trees as it moved through metro Denver. Numerous power outages affected nearly one thousand people in Denver and Jefferson counties. West winds gusted to 34 mph at Denver International Airport.
11-16
In 2013…a deep southerly flow over Colorado… Ahead of a nearly stationary low pressure system over the great basin… Pumped copious amounts of monsoonal moisture into the area. In addition…a weak stationary front stretched along the Front Range foothills and Palmer Divide. This resulted in a prolonged period of moderate to heavy rain across the Front Range foothills…Palmer Divide…urban corridor. By the 14th…storm totals ranged from 6 to 18 inches… Highest in the foothills of Boulder County. The headwaters then moved down the South Platte River and caused widespread flooding with record flood stages at several locations as it made its way downstream. The record high flood stages resulted in widespread flooding along the South Platte River basin. The flood damage encompassed 4500 square miles of the Front Range…left 7 dead… Forced thousands to evacuate…and destroyed thousands of homes and farms. Record amounts of rainfall generated flash floods that tore up roads and lines of communication… Leaving many stranded. Nearly 19000 homes were damaged… And over 1500 destroyed. Colorado department of transportation estimated at least 30 state highway bridges were destroyed and an additional 20 seriously damaged. Preliminary assessments of the state`s infrastructure showed damage of $40 million to roads and $112 million to bridges. Repair costs for state and county roads ran into the hundreds of millions of dollars. Miles of freight and passenger rail lines were washed out or submerged… Including a section servicing Amtrak`s iconic California Zephyr. The town of Lyons was isolated by the flooding of St. Vrain creek…and several earth dams along the Front Range burst or were over-topped. Floodwaters swept through Estes Park; damaged hundreds of buildings and destroyed large sections of U.S. 34 from Loveland and U.S. 36 from Lyons to Boulder. U.S. 34 suffered the most damage… With 85 percent of its roadway and bridges destroyed. In Weld County…about nearly two thousand gas wells were damaged and had to be closed off as the floodwaters inundated entire communities. Sewage treatment plants and other utilities were knocked out in a number of towns. Governor Hickenlooper declared a disaster emergency on September 13th…in 11 counties across northeast Colorado including: Adams…Arapahoe…Broomfield…Boulder…Denver… Jefferson…Larimer…Logan…Morgan… Washington and Weld. By the 15th…federal emergency declarations covered those counties as well as Clear Creek County. Projected losses from the flooding statewide was nearly two billion dollars in property damage…according to Eqecat… A catastrophe modeling firm. The damage was most severe in and around Lyons and Boulder. More than 11 thousand people were evacuated…reportedly the largest since Hurricane Katrina. President Obama declared a state of emergency for Boulder and Larimer counties. An additional 10 counties were added on the 16th and included: Adams… Arapahoe…Broomfield…Clear Creek…Denver…Jefferson… Morgan…Logan… Washington and Weld counties. The president also declared a major disaster specifically for Boulder County. There were six fatalities directly attributed to flash flooding. Two 19-yr old teenagers died on the 11th…after they were swept away by floodwaters after abandoning their car on Lindon Drive in Boulder. In Jamestown…a 72-yr old man was killed when the building he was in collapsed. An 80-yr old Lyons resident died in the early morning hours of the 12th…when his truck was swept into the St. Vrain River near his home. Later on the 12th…a 79-yr old Larimer County resident was killed when she was swept away while trying to climb to safety from her home in Cedar Point. A 61-yr old cedar point resident died when her home was swept down the Big Thompson River by the floodwaters. An 80-yr old Idaho Springs resident drowned in Clear Creek when the embankment he was standing on collapsed. In Boulder…some of the monthly records broken included: one-day all-time record: 9.08 inches which shattered the previous wettest day of 4.8 inches set on July 31… 1919; one-month record of 18.16 inches…which broke the previous all-time monthly record of 9.59 inches set in May of 1995; wettest September on record which broke the previous record of 5.5 inches set in September of 1940; one-year record of 34.15 inches broke the previous wettest year of 29.93 inches set in 1995. At Denver International Airport…the total precipitation for the month of September was 5.61 inches…which was 4.65 inches above the normal of 0.96 inches. This is the most precipitation ever recorded in Denver for the month of September. Daily precipitation records included 1.11 inches on the 12th and 2.01 inches on the 14th.
11-12
In 1974…post-frontal rain changed to snow overnight for the first snow of the season. Snowfall totaled only 1.8 inches at Stapleton International Airport where north winds gusted to 40 mph on the 11th. High temperature of only 46 degrees on the 12th set a new record low maximum for the date.
12
In 1887…west winds to 42 mph were recorded in the city.
In 1952…a thunderstorm outflow produced strong southeast winds gusting to 52 mph. Surface visibility at Stapleton Airport was briefly reduced to 2 miles in blowing dust.
In 1963…a nearly stationary…white tornado near Bennett was sighted from Denver. No damage was reported.
In 1989…an early snowfall and the first of the season brought 2 to 3 inches of slush to metro Denver. More snow whitened the foothills west of Denver where 6 inches were measured at Evergreen. The snow fell on leaf laden trees… And sagging branches onto power lines caused outages. Much of Denver’s snow fell during the evening rush hour…creating traffic chaos. Snowfall totaled 2.3 inches at Stapleton International Airport where the maximum snow depth on the ground was only 1 inch due to melting.
In 1994…thunderstorm microburst winds gusted to 67 mph in Boulder. No damage was reported.
In 2002…a severe thunderstorm produced hail as large as 1 inch in diameter near Castle Rock.
September 3 to September 9: This Week in Denver Weather History
The first full week of September sees us start one of the most pleasant times of year in Denver. While less common this time year, severe weather can and does occur. Our look back at this week in Denver weather history includes hail, damaging wind and even smoke from wildfires hundreds of miles away.
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.
2-3
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.
3-6
In 1909…rainfall for the 4 days accumulated to 3.97 inches in Boulder…while in Denver rainfall totaled 2.45 inches on the 4th…5th…and 6th.
4
In 1909…apparent post-frontal heavy rainfall totaled 1.94 inches in downtown Denver. North winds were sustained to 19 mph.
In 1944…a trace of rain fell. This together with a trace of rain on the 9th…10th…and 30th was the only precipitation for the month. The total of a trace of precipitation for the month equaled the driest September on record first set in 1892.
In 1960…the highest recorded temperature in September…97 degrees…occurred. The same temperature also occurred on September 5…1899…September 1…1995…and September 4… 1995.
In 1989…a strong thunderstorm wind gust flipped a plane taxiing on a private runway in Adams County east of Denver. Two people were slightly injured and the plane was heavily damaged.
In 1992…strong winds developed across metro Denver behind a pacific cold front. Sustained winds above 40 mph with gusts as high as 60 mph were recorded mainly in and near the foothills. Pre-frontal south winds gusted to 37 mph at Stapleton International Airport.
In 1995…two people were injured when lightning struck their home in Lakewood. The lightning entered the attic where it started a small fire. It then traveled through the walls… Exploding a mirror and spraying glass on the residents. Lightning also sparked small grass fires near Aurora…Denver International Airport…and Bennett. The highest recorded temperature in September…97 degrees…occurred. The same temperature also occurred on September 5…1899…September 4…1960…and September 1…1995.
In 2000…thunderstorm winds gusted to 64 mph in Castle Rock.
5
In 1899…the highest recorded temperature in September…97 degrees…occurred. The same temperature was also reached on September 4…1960…and September 1 and 4…1995.
In 1940…a severe wind and hail storm confined mostly to the west and north parts of the city occurred shortly after 4:30 pm. Hail stones ranged in size from 1/4 to 1/2 inch in diameter. In north Denver…hail piled to a depth of 4 inches. Flooding occurred in one underpass…which stalled 2 cars. One girl was injured when the weight of the hail flattened a porch on which she stood. Northeast winds were sustained to 29 mph with gusts to 32 mph in downtown Denver.
In 1987…a thunderstorm complex produced hail as large as 1 3/8 inches in diameter…2 miles east of Buckley Field in Aurora. No damage was reported.
Following on what was a cool but dry August, some are certainly hoping for a bit of precipitation. The month can bring plenty of rain and even our first snow of the season but more often than not, it is one of the most pleasant along the Colorado Front Range.
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.
The month can bring extremes however. We will of course forever remember 2013’s devastating floods brought on by record-setting rain. Longtime residents might remember September 1971 which brought over 17 inches of snowfall.
August 28 to September 2: This week in Denver weather history
This time of year we usually see calm conditions as we begin the transition to fall. However, that is not always the case as is seen in our look back at this week in history. Everything from thunderstorms with hail to tornadoes can and have been experienced.
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.
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.
27-28
In 2004…a brief chilly spell resulted in three temperature records. The high temperature of 55 degrees on the 27th was a record low maximum for the date. The low temperature of 48 degrees on the 27th equaled the record minimum for the date. The low temperature of 42 degrees on the 28th was a record minimum for the date.
28
In 1887…a dry thunderstorm produced north winds to 48 mph but only a trace of rainfall.
In 1968…one man was seriously injured by lightning while riding on a roller coaster at a Denver amusement park. An airline employee was injured when lightning struck a jetliner he was servicing at Stapleton International Airport. A lightning-caused fire did extensive damage to one house and minor damage to several others in the city of Denver.
In 1970…a microburst wind gust to 53 mph was recorded at Stapleton International Airport.
In 2002…a severe thunderstorm produced 3/4 inch diameter hail near Parker.
In 2005…lightning sparked a small fire near Jamestown. The blaze was quickly contained and consumed less than an acre.
29
In 1876…after the passage of a gentle rain shower to the east during the late evening hours…the moon shone brightly and a remarkably bright lunar rainbow appeared.
In 1910…an apparent cold front produced sustained northeast winds to 40 mph.
In 1946…the high temperature warmed to only 55 degrees…the record low maximum for the month.
In 1989…a spectacular lightning display knocked out power to 300 blocks in southeast Denver. One bolt started a fire in a lumber yard in the northeast part of the city…and the attic of a home in the same area was set ablaze by a lightning bolt.
In 1996…3/4 inch diameter hail was measured in Parker.
In 2000…lightning struck two homes in Thornton. The extent of damage was unknown.
In 2002…two small tornadoes caused damage in southeast metro Denver. The first tornado…associated with a multi-vortex storm…touched down briefly near E-470 and South Jordan Road. Some fences were damaged…and a few trees were blown down. A few of the homes also sustained minor roof damage. Damage from this storm totaled 100 thousand dollars. The second tornado associated with the storm touched down in a subdivision that was under construction at Gartrell and Arapahoe roads. Four large condominiums under construction were destroyed. The most heavily damaged portions of the structures were still in the framing stages. Adjacent sections where enclosed walls were in place were not destroyed. A man suffered 4 broken ribs and several cuts and bruises when the trailer he sought shelter in was flipped three times and torn apart by the twister. Damage from this storm totaled 6 million dollars. A severe thunderstorm produced 1 inch diameter hail near Evergreen.
In 2006…severe thunderstorms produced large hail in the foothills west of Denver. Hail to 1 inch in diameter fell near Blackhawk. Hail as large as 7/8 inch was measured near Idaho Springs…along with 3/4 inch hail near Nederland and conifer.
30
In 1981…60 mph winds were reported in Boulder.
In 2004…a severe thunderstorm produced hail as large as 1 inch in diameter in south Aurora near Cherry Creek.
31
In 1951…hail as large as 1 3/4 inches in diameter caused an estimated 300 thousand dollars damage in metro Denver. Hail as large as 1 1/2 inches in diameter was measured at Stapleton Airport.
In 1978…strong thunderstorm winds tore the roof off an apartment building in Aurora…downed trees…and damaged windows in Denver. A microburst wind gust to 58 mph was recorded at Stapleton International Airport.
In 1985…a thunderstorm wind gust to 60 mph was clocked at Buckley Field in Aurora.
In 1997…hail to 1 1/4 inches in diameter was measured in Aurora.
In 2006…a female postal worker was struck and injured by lightning while delivering mail in Westminster.
In 2008…lightning struck a home in Brighton…damaging the roof and a bedroom. The damaged totaled 20 thousand dollars.
The month of September was overall a pleasant one however that came at a price. A very distinct lack of precipitation led to dry conditions, a trend that had started earlier in the summer.
High pressure was the general rule for the month and that helped to ensure that any significant weather potential was steered away from the state. A few troughs and cold fronts mixed things up but in the end, we only saw precipitation on three days during the month and the amounts were negligible.
Thornton’s average temperature for the month came in at 63.7 degrees. This was just slightly above Denver’s long term average for September of 63.4 degrees. Out at the airport where Denver’s official measurements are taken, it was a good bit warmer with an average of 66.0 degrees.
Temperatures here ranged from a high of 91.6 degrees on the 5th of the month down to a low of 39.8 degrees on the 24th. DIA recorded a maximum of 93 degrees, also on the 5th, and a low of 37 degrees on the 10th.
In terms of precipitation, Thornton saw a measly 0.05 inches fall into our rain bucket. The airport fared far better with 0.28 inches. However, both measurements were well below the September average for Denver of 0.96 inches. The reading in Thornton would have been low enough to tie for the third driest reading in Mile High City history.
Thornton, Colorado’s September 2016 temperature summary. (ThorntonWeather.com)Thornton, Colorado’s September 2016 precipitation summary. (ThorntonWeather.com)
From the National Weather Service:
CLIMATE REPORT
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
933 AM MDT SAT OCT 1 2016
...................................
...THE DENVER CO CLIMATE SUMMARY FOR THE MONTH OF SEPTEMBER 2016...
CLIMATE NORMAL PERIOD 1981 TO 2010
CLIMATE RECORD PERIOD 1872 TO 2016
WEATHER OBSERVED NORMAL DEPART LAST YEAR`S
VALUE DATE(S) VALUE FROM VALUE DATE(S)
NORMAL
................................................................
TEMPERATURE (F)
RECORD
HIGH 97 09/06/2013
09/05/2013
09/04/1995
LOW 17 09/29/1985
HIGHEST 93 09/05 91 2 92 09/02
LOWEST 37 09/10 35 2 44 09/19
AVG. MAXIMUM 82.3 78.5 3.8 85.2
AVG. MINIMUM 49.7 48.3 1.4 53.5
MEAN 66.0 63.4 2.6 69.4
DAYS MAX >= 90 6 3.4 2.6 7
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 0.28 0.96 -0.68 0.11 DAILY AVG. 0.01 0.03 -0.02 0.00 DAYS >= .01 4 6.5 -2.5 3
DAYS >= .10 1 3.3 -2.3 0
DAYS >= .50 0 0.6 -0.6 0
DAYS >= 1.00 0 0.1 -0.1 0
GREATEST
24 HR. TOTAL 0.18 09/12 TO 09/12 08/31 TO 09/01
SNOWFALL (INCHES)
RECORDS
TOTAL 0.0 1.3
RECORD SEPTEMBER 17.2 1971
DEGREE_DAYS
HEATING TOTAL 64 125 -61 9
SINCE 7/1 79 141 -62 27
COOLING TOTAL 99 76 23 148
SINCE 1/1 861 764 97 861
FREEZE DATES
RECORD
EARLIEST 09/08/1962
LATEST 06/08/2007
EARLIEST 10/07
LATEST 05/05
.....................................................
WIND (MPH)
AVERAGE WIND SPEED 9.5
RESULTANT WIND SPEED/DIRECTION 2/171
HIGHEST WIND SPEED/DIRECTION 37/170 DATE 09/23
HIGHEST GUST SPEED/DIRECTION 51/200 DATE 09/04
SKY COVER
POSSIBLE SUNSHINE (PERCENT) MM
AVERAGE SKY COVER 0.40
NUMBER OF DAYS FAIR 13
NUMBER OF DAYS PC 13
NUMBER OF DAYS CLOUDY 4
AVERAGE RH (PERCENT) 45
WEATHER CONDITIONS. NUMBER OF DAYS WITH
THUNDERSTORM 6 MIXED PRECIP 0
HEAVY RAIN 0 RAIN 0
LIGHT RAIN 6 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 3
HAZE 4
- INDICATES NEGATIVE NUMBERS.
R INDICATES RECORD WAS SET OR TIED.
MM INDICATES DATA IS MISSING.
T INDICATES TRACE AMOUNT.
Weather, natural disasters & climate news and information.
Following on an August that saw seasonal temperatures but little precipitation, some are certainly hoping for a bit of the wet stuff in September. The month can bring plenty of rain and even our first snow of the season but more often than not, it is one of the most pleasant along the Colorado Front Range.
