Normally one doesn’t associate tornadoes with September weather in Denver but they can and do happen as we see in our look back in Denver weather history for the week.  We have a couple of occasions of twisters and of a funnel cloud.  Other severe weather like hail, damaging wind and flooding rains have also occurred.   Oh, and should we mention the dreaded “S” word – 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.

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.

13

In 1899…west winds were sustained to 43 mph with gusts to 46 mph.

In 1928…northwest winds were sustained to 41 mph with gusts to 45 mph.

In 1937…an apparent dry microburst produced brief north winds sustained to 31 mph with gusts to 41 mph.  There was a trace of rain.

In 1982…torrential rains drenched both the foothills and plains from Denver north.  While the heaviest rain occurred north of Denver…just east of Denver 2 1/3 inches of rain fell in 5 hours along with hail that caused minor damage to a few airplanes.  Thunderstorm rainfall totaled 0.83 inch at Stapleton International Airport.

In 1993…an upper level system combined with a cold and moist upslope flow to bring the heaviest snowfall to metro Denver for so early in the season.  Snowfall from the storm totaled 5.4 inches at Stapleton International Airport; however…most of the snow melted as it fell leaving a maximum of one inch on the ground at any one time.  North winds gusted to 21 mph at Stapleton International Airport where a record low temperature of 33 degrees for the date was observed.

In 2002…Friday the 13th proved to be bad luck for several motorists when heavy thunderstorm rainfall caused flooding on I-25 in central Denver.  Water rose several feet under the Logan Street overpass…inundating several vehicles. Some motorists were rescued…while others simply waited atop their cars for the flood water to recede.  The highway had to be closed in both directions for about 3 hours.  The flooding was exacerbated by poor drainage due to the construction along the highway.  A 12-foot drainage pipe had not yet been installed beneath the underpass.  The deluge also flooded several businesses along Broadway.

14

In 1912…snow fell for most of the day…but melted as it fell. Precipitation from melted snow was 0.46 inch.  Some sleet was also observed.  Total precipitation was 0.61 inch.  North winds were sustained to 15 mph with gusts to 17 mph.

In 1934…a moderate dust storm blew into the city at 4:15 pm. North winds were sustained to 35 mph with gusts to 44 mph. By 5:25 pm the winds had decreased and the storm had ended. A trace of rain fell during the evening.

In 1976…a tornado touched down just west of I-25 between Arapahoe road and Dry Creek Road…tearing the roof from a house.  Nearby…a high tension wire fell on a house causing damage…and lightning ripped a hole in the side of a house. Three tornadoes were observed just east of Stapleton International Airport and northeast of Buckley Field.  No damage was reported.  Dime to quarter size hail fell in northeast Denver with only 1/4 inch hail at Stapleton International Airport.  The Colorado state patrol reported golf ball size hail 4 miles west of Franktown.  A funnel cloud was sighted 4 miles north of Franktown.

In 1983…a thunderstorm produced winds gusts as high as 56 mph across metro Denver along with thick blowing dust. Power was knocked out in many locations.  Thunderstorm winds gusting to 49 mph briefly reduced the visibility to 2 miles in blowing dust at Stapleton International Airport.

In 1996…a 54-year-old woman was struck by lightning near Franktown…as she was preparing an outdoor barbeque.  The woman was knocked unconscious…but received only minor injuries.  Thunderstorms over southern Jefferson County dumped heavy rain in the Buffalo Creek area.  Some minor roads were washed out by flash flooding…but no other damage was reported.  Hail ranging in size from 1/2 to 3/4 inch in diameter fell at the site of the former Stapleton International Airport.

In 2006…a microburst from a thunderstorm produced sustained winds to 40 mph with gusts to 53 mph at Denver International Airport.

15

In 1921…rainfall of 0.02 inch was the only measurable precipitation of the month.

In 1976…the public reported a funnel cloud and golf ball size hail east of Parker.

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

In 1874…a blast of west winds caused minor injuries during working hours in Boulder.

In Denver…the winds veered suddenly from the southwest to the northwest around noon and increased to a maximum sustained speed of 49 mph behind an apparent cold front.  The winds remained strong and backed to the west for the remainder of the afternoon.

In 2000…the record high temperature of 95 degrees at Denver International Airport established or equaled 3 different record extremes:  the high temperature broke the previous record high for the day of 92 degrees set over a century ago in 1895; it marked the warmest that it has been so late in September; it also marked the 60th day during the warm season that the temperature had reached 90 degrees or more…equaling the record first set on September 29…1994.

In 2006…strong Bora winds behind a pacific cold front raked the eastern slopes of the mountains and metro Denver during the afternoon.  Northwest winds were sustained to 40 mph with gusts as high as 54 mph at Denver International Airport.

In 2007…a severe thunderstorm produced a peak wind gust of 67 mph…about one mile east of Bennett.  At Denver International Airport…a peak wind gust of 48 mph was observed.

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.