Thornton, Colorado, USA
UpdatedThu, 20-Jan-2022 7:40am MST 


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Thornton’s September 2021 weather preview

Thursday, September 2nd, 2021 6:03am MST

Following an August that was unseasonably warm and dry, we find ourselves heading into September hoping for relief.  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.

Get a complete look at September’s weather and more details as to what we can expect this year here.

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Cooler temperatures, slight chance for a thunderstorm for Thornton’s Thursday

Thursday, September 2nd, 2021 4:49am MST

Finally, a bit of a break from the heat. Today we begin a period of a few days with mercury readings close to normal and with some chances for storms.

Partly sunny skies will be above throughout the day today as moisture aloft increases. High temperatures will be in the low 80s. The afternoon and evening offer just a slight chance for some thunderstorms. Unfortunately, the best chances for activity will be to our south.

Tonight, any storms will end by midnight and skies will be partly clear. Overnight lows will drop to around 60 degrees.

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August 29 to September 4: This week in Denver weather history

Wednesday, September 1st, 2021 3:18pm MST

This Week in Denver Weather History

Certainly this time of year we start to see temperatures drop and the conditions moderate.  This is usually one of Denver’s most pleasant times of years when the heat of summer fades and the snow and cold of winter is still far away.  That however wasn’t the case when the most notable event in Denver weather history this week occurred.  It was in 1961 on the 3rd of September that Denver received its earliest measurable snowfall – 4.2 inches!


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.


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.


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.


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.


In 1951…large hail pounded Boulder…causing thousands of dollars in damage to roofs and automobiles.  Heavy thunderstorm rainfall flooded basements and produced widespread street flooding.

In 1966…severe thunderstorms caused local flooding in areas from Denver to the north and east.  There was scattered damage from hail and lightning.  Streets were flooded in Boulder…and streets and basements were flooded in several areas of metro Denver.  The public reported 1 inch diameter hail in Aurora and near Cheery Creek Reservoir. Thunderstorm rainfall totaled only 0.39 inch at Stapleton International Airport.

In 1985…severe thunderstorms dumped heavy rain and hail at many locations along the Front Range from Denver south. The southern and eastern suburbs of metro Denver were especially hard hit.  Rainfall from 1 1/2 to 3 inches caused extensive street flooding in Aurora where two creeks rose out of their banks.  Two homes in the city suffered minor lightning damage.  Almost 4 inches of rain fell in the Parker area.  Hail up to ping-pong ball size piled up to a foot deep and closed a road in Evergreen. Hail as large as 1 3/4 inches in diameter was reported 8 miles northeast of Deckers.  Wind gusts to 65 mph were estimated in southeast Aurora.

In 1990…marble size hail piled up to 2 inches deep in the foothills community of Kittredge…18 miles southwest of Denver.  As much as half an inch of rain fell in just 15 minutes and caused minor road and small stream flooding. A thunderstorm dropped pea to marble size hail and brief heavy rain near Ward road and 64th avenue in Arvada. Minor street and small stream flooding was reported in the area.

In 1995…a strong thunderstorm microburst with only a few drops of rain produced a recorded wind gust to 85 mph at the site of the former Stapleton International Airport. The wind gust occurred at 8:30 pm MDT.  The all-time highest recorded temperature in September…97 degrees…occurred.  The same temperature also occurred on September 5…1899…September 4…1960…and September 4… 1995.

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.


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.


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.


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.


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.


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.

» Click here to read the rest of August 29 to September 4: This week in Denver weather history

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Wednesday to see temperatures cool a bit, offer a chance for thunderstorms

Wednesday, September 1st, 2021 4:58am MST

As the ridge that has dominated us shifts east, it will allow increased moisture from the southwest. This will mix things up for us cooling things down and perhaps offering some precipitation.

The day starts off with mostly sunny skies then cloud cover will slowly increase leading to partly clear conditions this afternoon. Smoke will still be around for the daytime hours. High temperatures today will top out in in the upper 80s. Scattered thunderstorms will develop this afternoon, largely offering gusty winds initially.

This evening brings a better chance for storms. Tonight, skies will be mostly cloudy with most thunderstorm activity ending by midnight. A few showers may linger overnight. Overnight lows will be around the 60 degree mark.

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August 2021 top shots: Monthly photo slideshow

Tuesday, August 31st, 2021 7:13pm MST
An eerie sunset in Adams County as smoke obscures the setting sun. (Bill Hutchinson)

An eerie sunset in Adams County as smoke obscures the setting sun. (Bill Hutchinson)

As the calendar turns to August, the summertime heat begins to fade and that makes it easier to get out and enjoy all of the outdoor activities Colorado has to offer.  From a walk in a park to afternoon thunderstorms to an abundance of wildlife, photo opportunities abound as is seen in our slideshow.

Our monsoon season typically arrives about now and that means better chances for moisture.  However with limited instability, the intensity of storms are more sedate.  That doesn’t mean however that the weather is any less photographic.

  • Slideshow updated August 26, 2021

By the end of the month some of our seasonal feathered friends will be looking to leave the state giving our last chance to see them till spring.  Larger mammals are gearing up for the rut (mating season) and that can make for some intense scenes.

Showcasing images captured by ThorntonWeather.com readers as well as some of our own, our monthly slideshow covers the entire gamut of weather and nature related imagery. Sunsets, sunrises, wildlife and of course every type of weather condition are vividly depicted.

To learn more about how to send your photo to us for inclusion in the slideshow, see below the slideshow.

What is missing in the slideshow above?  Your photo!

Our monthly photo slideshow is going to feature images that we have taken but more importantly images that you have captured.  The photos can be of anything even remotely weather-related.

Landscapes, current conditions, wildlife, pets, kids.  Whimsical, newsy, artsy.  Taken at the zoo, some other area attraction, a local park, a national park or your backyard.  You name it, we want to see and share it!

Images can be taken in Thornton, Denver or anywhere across the extraordinary Centennial State.  We’ll even take some from out of state if we can tie it to Colorado somehow.

We’ll keep the criteria very open to interpretation with just about any image eligible to be shown in our slideshows.

What do you win for having your image in our slideshow?  We are just a ‘mom and pop’ outfit and make no money from our site so we really don’t have the means to provide prizes.  However you will have our undying gratitude and the satisfaction that your images are shared on the most popular website in Thornton.

To share you images with us and get them included in the slideshow just email them to us or share them with ThorntonWeather.com on any of the various social media outlets.  Links are provided below.

So come on, get those camera’s rolling!

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Toasty temps Tuesday for Thornton along with a dose of smoke

Tuesday, August 31st, 2021 4:56am MST

Rinse and repeat. Well, no rinsing in this forecast really as there won’t be any precipitation – again. There is, however, another repeat of a forecast calling for above normal temps and smoky conditions.

The day starts off with sunny skies and those will stick around until the afternoon when, like yesterday, a few clouds will arrive. Smoke will be visible throughout the day. High temperatures will once again climb to the mid-90s, perhaps into the upper 90s depending on cloud cover.

Tonight, lows will be in the low 60s under partly cloudy skies. Smoke will be lingering throughout the night and through tomorrow.

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Heat and smoke return for Thornton’s Monday

Monday, August 30th, 2021 4:47am MST

After a little bit of a break, temperatures will climb to well-above normal levels today. Along for the ride will be smoke in the afternoon.

Sunny skies start us off and will be around through the morning. The afternoon will see just a few clouds and the arrival of the smoke. High temperatures will be topping out about 10 degrees above average in the mid-90s.

Tonight, lows will be around 60 degrees under partly cloudy skies.

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Thornton to enjoy a mild, pleasant weekend

Friday, August 27th, 2021 5:06am MST

A pretty nice looking weather forecast for the three day period. Temps will be very mild with only a couple, minor chances for thunderstorms.

For Friday, sunny skies start us off and will be with us till the afternoon when a few clouds will build. High temperatures will top out around the 90 degree mark. The late afternoon and evening bright just a slight chance for a thunderstorm. Light rain and gusty winds should be about the only outcome if a storm develops. Tonight, any thunderstorms will be done by 9:00pm and then skies will clear. Lows will dip to around 60 degrees.

Saturday will be a calm, pleasant day. Sunny to mostly sunny skies will be above as highs head toward 90 degrees again. No thunderstorms are expected. Saturday night, there will be a few clouds above. Overnight lows will dip to around 60 degrees.

Sunday sees a bit of a cool down as cooler air moves in from the north. Temperatures will be in the mid-80s with mostly sunny skies above. The afternoon and evening offer us just a slight chance for a thunderstorm.

Have a fantastic weekend!

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Temps a bit above normal for Thornton’s Thursday, some scattered thunderstorms possible

Thursday, August 26th, 2021 5:04am MST

A pretty good looking day in store for us. Mercury readings will be a few degrees above normal and we may see some PM thunderstorms.

Mostly sunny skies start us off and will be with us through the morning. After noon, cloud cover will increase. Highs will top out in the upper 80s. Scattered showers and thunderstorms will be possible after noon with the best chances coming between 3:00pm and 9:00pm. At this time, gusty winds look to be the most notable feature from these storms but it would be wise to keep an eye on them.

Tonight, any storm activity will end by midnight after which skies will begin to clear. Overnight lows will be around 60 degrees.

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Cold front brings a little bit of relief from the heat Wednesday, slight chance for an evening storm

Wednesday, August 25th, 2021 4:55am MST

It won’t be a huge cool down but we do get a bit of a break from the 90+ degree heat today. Temps will cool and there may be some isolated storms in the evening.

The day starts off with sunny skies and those will be with us through most of the day. The mid to late afternoon will bring a few clouds. Overall daytime conditions will be calm. Breezy winds look to arrive by late afternoon. High temperatures today will top out around 89 degrees, perhaps just barely avoiding giving us another 90 degree day.

Some isolated thunderstorm activity will be possible after 5:00pm until midnight. Once any storms are done, skies will be mostly clear overnight with lows around 60 degrees.

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