Thornton, Colorado, USA
UpdatedThu, 20-Jan-2022 7:50am MST 


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Tuesday temperatures cool to near normal, day will offer a chance for a thunderstorm

Tuesday, September 14th, 2021 4:55am MST

A little bit of a break from the heat today as we finally see temperatures close to average. The afternoon will also bring us a chance for a shower / thunderstorm.

Partly cloudy skies will be above throughout the day today. Some breezy winds will be seen this afternoon. The average high for today’s date is 79 degrees and we should top out right near that. After noon, we begin to see slight chances for a shower or thunderstorm with chances increasing from about 2:00pm to 5:00pm.

This evening, any storm activity should be done by 7:00pm. Skies will then begin to clear and overnight lows will dip to the low 50s.

Keep an eye out for thunderstorms with our interactive radar here.

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Cooler, unsettled weather conditions start Thornton’s workweek

Monday, September 13th, 2021 5:06am MST

Not a dramatic change in our recent weather but at least we mix things up for a couple of days. Cooler, potentially wetter weather will be with us before warming back up for the latter half of the week.

Today starts off with mostly sunny skies. A cold front will be pushing through this morning and that will lead to an increase in cloud cover and some breezy winds. A few, random sprinkles of rain may be possible in the late morning and early afternoon. Mid to late afternoon into the evening brings a bit better chance for some shower and thunderstorm activity. High temperatures today will top out in the mid-40s.

Tonight, there is potential for additional shower activity. Skies will be partly clear with overnight lows in the mid-50s.

Looking ahead, tomorrow offers cooler temps and a better chance for precipitation. After that, we will dry out and warm back up for the balance of the week. More in the extended forecast here.

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Denver crushes the record high temperature for September 10

Friday, September 10th, 2021 4:30pm MST

Record High Temperature

We knew the record would be broken, it was only a question of by how much and the results are in.

As measured at Denver International Airport, the high temperature in the Mile High City topped out at 99 degrees. These destroys the previous record high for September 10 of 93 degrees set in 2018.

Here in Thornton we were close to Denver’s mark but “only” hit 98 degrees.

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Thornton’s weekend starts off with record-setting heat, then cools a bit

Friday, September 10th, 2021 5:26am MST

What will likely be a record-breaking day of heat starts off the three-day period. There will, however, be at least a little bit of relief later in the weekend.

Friday looks to be a bit of a scorcher with highs reaching the upper 90s. Denver’s record high for the date is 93 degrees (2018) and will likely be broken. Beyond the heat, conditions will be calm but smoky. Tonight, partly cloudy skies will be above with lows around 60 degrees.

Saturday sees at least a bit cooler weather. Mostly sunny skies will be above with highs in the low to mid-90s. The afternoon and evening will offer up just a slight chance for a thunderstorm. Saturday night, storm activity will be ending and partly clear skies will be left behind. Overnight lows will be near the 60-degree mark.

Sunday will be the coolest day of the period although temps remain above normal. Look for highs in the mid to upper 80s. Skies will be sunny in the morning then some cloud cover arrives in the afternoon. There will, once again, be a slight chance for a PM thunderstorm.

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Denver sets record high temperature for September 9

Thursday, September 9th, 2021 4:29pm MST

Record High Temperature

Mother Nature just delivered another reminder that our long, hot summer isn’t over yet.

Denver, as measured at Denver International Airport, reached a high temperature of 96 degrees today. This tops the previous record high temperature for September 9 of 94 degrees set in 1994.

Here in Thornton, we were a bit “cooler” with a 95 degree reading at 1:49pm.

More heat is yet to come. Tomorrow may see highs a couple of degrees warmer than today. The record high for September 10 is 93 degrees set in 2018 and previous years so it is quite likely that record will fall as well.

More in the extended forecast here.

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Hot and smoky weather return for Thornton’s Thursday

Thursday, September 9th, 2021 4:59am MST

After cooling down slightly for a couple of days, the mercury climbs again toward record-setting territory. Along with the heat will be the seemingly ever-present wildfire smoke.

The day starts off sunny and then we will see the smoke arrive later this morning and linger overnight. Overall conditions will be calm and dry. High temperatures look to top out in the mid-90s, well above the average high for the date of 81 degrees. Denver’s record high for today’s date is 94 degrees (1994) and there is a decent chance that mark will be broken.

Tonight, skies will be clear to mostly clear with the smoke hanging around. Overnight lows will be around the 60 degree mark.

You can keep an eye on current temps with our live gauges here.

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Wednesday again brings warmer than normal temps, smoky skies

Wednesday, September 8th, 2021 4:48am MST

Today’s weather will pretty much be a carbon copy of what we experienced yesterday. Temperatures will be five degrees or so above normal and hazy, smoky skies above.

Sunny to mostly sunny skies will be above. Of course with the smoke, it probably wouldn’t be able to tell that. High temperatures will top out in the mid to upper 80s. Overall conditions will be calm and dry.

Tonight, smoke will remain above with mostly clear skies. Overnight lows will be in the mid-50s.

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Mild temperatures, areas of smoke start off Thornton’s workweek

Tuesday, September 7th, 2021 4:46am MST

With the passage of a weak cold front we will see temperatures cool down a bit today, although temps will remain above normal. Unfortunately smoke will return preventing us from fully enjoying the calm conditions.

Sunny skies will be with us throughout the day today. There will be haze from smoke for the bulk of the day. Temperatures will be climbing to a high in the mid-80s.

Tonight, skies remain mostly clear with lows in the mid-50s.

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September 5 to September 11: This week in Denver weather history

Monday, September 6th, 2021 5:30am MST

This Week in Denver Weather History

September is typically one of our quietest weather months and in fact it is our sunniest.  That doesn’t however mean we can’t experience weather extremes.  This week in Denver weather history we see everything from scorching heat and severe thunderstorms to snow and damaging wind.  For more about September’s weather, check out our September weather preview.


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 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.


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.


In 1988…layers of smoke aloft from large forest fires in Yellowstone National Park completely obliterated the sun at times.  At Stapleton International Airport…surface visibility was reduced at times to 5 and 6 miles in smoke.


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.


In 1940…a thunderstorm pelted the city with small hail. The storm produced some lightning damage.  One woman was stunned by a bolt which struck near her.  Heavy rain from the storm raised the level of Cherry Creek by more than 3 feet during the height of the storm.  Rainfall downtown was only 0.26 inch.

In 1988…strong winds blew down two houses that were under construction in Castle Rock.  Northwest winds gusted to 44 mph at Stapleton International Airport.

In 1993…a man was struck and killed by lightning while standing outside his home in unincorporated Arapahoe County 11 miles south of Denver.  Lightning also struck a cabin in Marshdale…20 miles southwest of Denver…which started a fire and damaged one room and a portion of the roof.

In 1995…hail as large as 3/4 inch in diameter fell in Coal Creek Canyon in northern Jefferson County.

In 2001…a thunderstorm dropped 3/4 inch diameter hail in Aurora near Cherry Creek.


In 1875…the creeks were running dangerously high during the night from heavy rains in the mountains.

In 1885…a thunderstorm produced very white hail of irregular shape and about the size of beans.  Precipitation was only 0.10 inch.

In 1971…a vigorous cold front accompanied by a thunderstorm produced wind gusts to 48 mph at Stapleton International Airport and much upslope cloudiness and light rain across metro Denver.

In 1989…widespread thunderstorms produced lightning strikes that knocked out power to about 13 thousand homes in Boulder County. In a rugged area stripped of vegetation by a forest fire earlier in July…heavy rain triggered mud slides that destroyed one home and severely damaged another in Boulder canyon 10 miles west of Boulder. In one home…the mud caved in an exterior wall and poured into the residence only seconds after 2 people had evacuated the premises. Rainfall totaled 1 to 3 inches.  Hail 1 3/4 inches in diameter fell in Nederland…Idaho Springs…and Golden Gate Canyon.  Hail 1 inch in diameter was measured 10 miles north of Golden.

In 1993…thunderstorm winds toppled an overhead sign onto the intersection of I-70 and I-25 in Denver…causing considerable damage to 4 vehicles.  The winds also caused a police car to be blown off the road northeast of Denver. Thunderstorm winds gusting to 66 mph damaged the siding of a residence southeast of Brighton.  A thunderstorm wind gust to 53 mph was recorded at Stapleton International Airport.  Hail to 7/8 inch in diameter fell at Kittredge in the foothills of Jefferson County.

In 1994…lightning severely damaged a public television transmitter atop Squaw Mountain west of Denver.


In 1884…a windstorm from mid-afternoon until the early morning hours of the 8th produced south winds sustained to 48 mph.  The strong winds toppled several trees in the city.

In 1892…there was a trace of rainfall each day.  This together with a trace of rain on both the 2nd and 3rd was the only rainfall of the month…making the month the driest on record.  The record was equaled in 1944.

» Click here to read the rest of September 5 to September 11: This week in Denver weather history

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Thornton’s Labor Day weekend starts comfortable, will end on the hot side

Friday, September 3rd, 2021 4:52am MST

A little bit of a mixed bag of weather for the long weekend in Thornton. We will enjoy two days with temps near normal but then see things heat up on the later half of the four-day period.

For Friday, partly sunny skies will be above with high temperatures in the low 80s. A few sprinkles of rain may be seen intermittently during the day. The afternoon and evening bring a better chance for thunderstorms. Friday night, any storms will end by midnight and leave partly clear skies. Lows will dip to the mid-50s.

Saturday should be a downright pleasant day. Mostly sunny skies will be above with highs in the low to mid-80s. Saturday night, lows will be in the mid-50s under mostly clear skies.

Sunday sees things start to heat up. Clear skies are expected with highs in the mid-80s. Sunday night into Monday morning, lows will be in the mid-50s under clear skies.

Labor Day will be the warmest day of the period. Look for highs in the low 90s under sunny skies.

Have a fantastic weekend!

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