The first half of October historically is quiet for the most part but there have been years with plenty of excitement.  We have seen damaging tornadoes and winds and of course significant snowstorms.

From the National Weather Service:

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In 1875…very dense haze hid the mountains from view as observed from the city.
 
In 1933…rainfall of just 0.01 inch was the only precipitation of the month.  This was the second driest October on record.
 
In 1954…the low temperature cooled to only 60 degrees…the all-time record high minimum for the month October.

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In 1969…the first snowfall of the season totaled 16.0 inches at Stapleton International Airport.  There was a thunder snow shower on the evening of the 3rd…but otherwise little wind with the storm.  The greatest snow depth on the ground was 8 inches due to melting.  Heavy wet snow accumulated on trees…which were still in full leaf…and caused widespread damage from broken limbs and downed utility lines.

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In 1984…the remnants of Pacific Hurricane Polo produced heavy rain over northeastern Colorado.  Most locations received between 1.00 to 2.50 inches of rain…but 3.45 inches fell in Littleton.  Rainfall totaled 1.73 inches at Stapleton International Airport…where north winds gusted to 24 mph.

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In 1912…sustained south winds to 55 mph with gusts to 60 mph raised the temperature to a high of 83 degrees… The warmest temperature of the month that year.
 
In 1924…west winds were sustained to 46 mph with gusts to 50 mph in the city.  The apparent Bora winds cooled the temperature to a high of 57 degrees from a high of 70 degrees on the 3rd.
 
In 2004…several small tornadoes touched down near Brighton… Barr Lake…and Hudson in Adams and southern Weld counties. Most of these caused no damage.  However…a small tornado 5 miles southeast of Brighton caused extensive damage to a recreational vehicle and severely damaged a barn.  The barn was torn from its foundation…and the roof was thrown 100 feet.  Four llamas in the barn were injured when it collapsed.

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In 1997…unusually warm weather resulted in two temperature records.  High temperature of 87 degrees on the 4th exceeded the old record set in 1922 by one degree.  High temperature of 86 degrees on the 5th equaled the record set in 1990 and previous years.

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In 1962…unusually severe thunderstorms for this late in the season affected areas from Boulder northward.  Hail up to golf ball size and strong gusty winds did much damage to roofs…windows…and signs in Boulder.  Heavy rainfall caused local flooding.
 
In 1994…lightning caused a power outage to over 2400 homes for a few hours in and around Nederland in the foothills southwest of Boulder.  Very strong winds accompanied the thunderstorm.  Thunderstorm winds gusted to 60 mph and hail to 1/2 inch diameter fell in Lafayette.  Strong microburst winds gusting to 69 mph near Strasburg caused an oil rig to topple onto two vehicles…injuring one person.  The strong winds in the area also downed a few power poles… But caused power outages to only a few homes.
 
In 1995…strong winds spread from the foothills onto the plains.  Wind gusts to 77 mph were reported atop Squaw Mountain west of Denver.  On the plains…winds gusted to 60 mph at Kennesburg and to 62 mph near Strasburg. North winds gusted to 41 mph at Denver International Airport.

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In 1900…northwest winds were sustained to 40 mph with gusts as high as 50 mph in downtown Denver.
 
In 1903…northwest winds were sustained to 40 mph with gusts to 50 mph.  The strong winds warmed the temperature to a high of 71 degrees in the city.  The low reading was only 46 degrees.
 
In 1910…light smoke from forest fires drifted over the city.
 
In 1976…an arctic cold front brought light snow over the foothills above 6 thousand feet.  Traffic was snarled at many locations.  Only a trace of snow fell at Stapleton International Airport where rainfall totaled 0.20 inch and northeast winds gusted to 41 mph.
 
In 1991…the brilliant orange sunset was apparently the result of an extensive volcanic smoke layer in the upper atmosphere.
 
In 1994…strong west to northwest winds developed in the foothills above 9500 feet.  A wind gust to 78 mph was recorded atop Squaw Mountain west of Denver and to 72 mph at Ward northwest of Boulder.  Northwest winds gusted to 35 mph at Stapleton International Airport.

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In 1903…north winds were sustained to 40 mph with gusts to 48 mph.
 
In 1917…post-frontal northwest winds were sustained to 45 mph with gusts to 52 mph.  Rain was mixed with a trace of snow…the first of the season.  Precipitation totaled 0.22 inch and included the occurrence of hail… Even though no thunder was heard.
 
In 1950…strong winds caused a power outage in Boulder. This was the heaviest windstorm since January.  Damage was minor.  Northwest winds gusted to only 35 mph at Stapleton Airport.
 
In 1985…strong Chinook winds buffeted the Front Range foothills.  Wind gusts between 60 and 70 mph were reported in Boulder and atop Squaw Mountain west of Denver.  Southwest winds gusted to 41 mph at Stapleton International Airport.

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In 1990…the season’s first snow occurred.  Snowfall amounts varied from 3 to 7 inches across metro Denver. Snowfall totaled 4.0 inches at Stapleton International Airport where north winds gusted to 29 mph.

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In 1923…southeast winds were sustained to 44 mph with gusts to 47 mph.  The strong winds persisted through the afternoon.  The high temperature of 77 degrees was the warmest of the month that year.
 
In 1975…a wind gust to near 100 mph was recorded in Boulder. Frequent wind gusts to 60 mph were reported along the foothills causing only minor damage.  West winds gusted to 45 mph at Stapleton International Airport.

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In 1910…light smoke from forest fires in the mountains was sighted over the city.
 
In 1982…northwest winds gusted to 49 mph at Stapleton International Airport.

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In 2005…a major winter storm brought heavy…wet snowfall to the Front Range mountains…eastern foothills…portions of metro Denver…and the Palmer Divide.  Snow accumulations ranged from 8 to 26 inches with drifts from 3 to 4 feet in places.  The heaviest snow occurred to the east and southeast of the city…closing most major highways in that area…including I-70 from Denver to Limon.  The Red Cross opened four shelters for people who were stranded along I-70 in eastern Colorado.  Since many trees had not yet shed their leaves…the storm caused significant tree damage.  One woman in Denver was killed when a tree branch… 8 to 10 inches in diameter…snapped under the weight of the heavy…wet snow and struck her as she was shoveling her driveway.  Xcel Energy reported power outages to about 35 thousand customers.  Several incoming flights were delayed at Denver International Airport.  Snow totals included:  16 inches in the foothills near Boulder…12 inches at Genesee and near Golden…22 inches near Watkins…19 inches near Bennett…17 inches southeast of Aurora…14 inches near Parker…13 inches near Castle Rock…12 inches in Centennial… 11 inches in Parker…and 10 inches at Denver International Airport and in Littleton.  While many areas of metro Denver received heavy snow…others experienced almost entirely rain. This included west and northwest metro Denver…Boulder…and Longmont.  Rainfall amounts were significant as storm totals ranged between 1.50 and 2.50 inches.  The steady rainfall triggered 3 rockslides in foothills canyons.  Two of the slides occurred on State Highway 119 in Boulder Canyon and the longest slide…7 feet in length…on State Highway 74 in Bear Creek Canyon at Idledale.  North winds were sustained to around 23 mph with gusts to 31 mph at Denver International Airport on the 9th.  The high temperature of only 34 degrees on the 10th was a record low maximum for the date.  The low temperature on both days was 32 degrees.