Thornton, Colorado, USA
UpdatedTue, 22-Sep-2020 3:20pm MDT 


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Thornton’s weekend to offer pleasant, seasonal weather conditions

Friday, September 11th, 2020 4:54am MDT

A fine looking weekend ahead for us and one like we expect and hope for this time of year. It does start out on the cool side Friday but Saturday and Sunday will be warming up nicely and conditions will be dry and calm.

For today, there might be a few spots of fog early on then we will have mostly sunny skies for the rest of the day. High temperatures today will be a bit cool and top out in the mid to upper 60s. Tonight, skies will be clear with overnight lows in the mid-40s. Saturday sees a nice warm up with highs in the upper 70s.

We will have sunny skies, calm and dry conditions. Saturday night into Sunday morning, skies remain clear with overnight lows in the upper 40s.

The weekend closes out on Sunday with another calm, dry day. Sunny skies will be above with highs in the low to mid-80s. Have a great weekend and enjoy that weather!

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Thursday brings a slow warm up, drier conditions

Thursday, September 10th, 2020 5:00am MDT

As the low pressure system slowly wends its way away, weather conditions in Thornton will begin to show some slow improvement. A few sprinkles of rain will be possible and there will be a good bit of cloud cover but temperatures will be warming.

Mostly cloudy skies start us off and will be with us through mid-morning. After that, some of that Colorado blue should start to peek out for the afternoon. Scattered light rain / sprinkles will be seen first thing this morning then be coming to an end in the afternoon. High temperatures will reach to the low to mid-50s.

This evening, a few more scattered showers will be possible, ending by midnight. Then, overnight lows will drop to the mid-30s under mostly cloudy skies.

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Denver ties one cold weather temperature record for September 9, breaks another

Wednesday, September 9th, 2020 11:59pm MDT

As our first taste of wintry weather for the season comes to an end, we close it out with two more weather records in the books.

This morning, as measured at Denver International Airport, the temperature dropped to 31 degrees. This ties the Mile High City’s record low for September 9 set in 1962.

The daytime didn’t bring much relief as the high at the airport only reached 42 degrees. This shatters the old record low maximum for the date of 53 degrees set in 1989.

Here in Thornton, we matched both of those marks with a low of 31 degrees and a high of 42 degrees.

The past few days have seen an extraordinary bout of weather as we went from record heat to record cold. The graphic below shows just some of what has occurred.

Some of the weather records tied or broken in the first part of September 2020. Click for a larger view. (National Weather Service)

Some of the weather records tied or broken in the first part of September 2020. Click for a larger view. (National Weather Service)

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Early season snow comes to an end Wednesday, temperatures remain chilly

Wednesday, September 9th, 2020 5:01am MDT

While a few more flakes may fall this morning, the bulk of our early season snow is done. In its wake, Thornton will have a good bit of cloud cover and remain on the chilly side.

We received 2.2 inches of snow and while the white stuff itself may not have been welcome, the moisture definitely was. This was Denver’s first September snow in 20 years and brought about a 60 degree drop in temperatures over 24 hours.

Today, the low pressure system is a bit slow to move out and that may bring a few more flakes of snow this morning. However, no additional accumulation is expected at this time. Skies will be cloudy this morning then we may start to see a hint of blue peeking out in the afternoon. High temperatures today will only reach the low 40s.

Tonight, skies remain mostly cloudy with overnight lows dipping to around the freezing mark.

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Denver ties two cold weather records for September 8, sees second earliest snow on record

Tuesday, September 8th, 2020 11:59pm MDT

Record Cold Temperatures

From record heat to record cold. You must live in Colorado. 😉  Today, Denver tied two cold weather records and saw its second earliest snow on record.

As measured at Denver International Airport, the low temperature in the Mile High City dropped to 31 degrees at 7:33pm. This ties the record low temperature for September 8 last set in 1962. Going hand-in-hand with that record, it tied the record for the earliest freeze in Denver history last set on the same date.

Here in Thornton, we managed to stay just a hair warmer with a low of 32 degrees.

Notable as well is that the Mile High City’s official 1.0 inch of snow is the second earliest snowfall on record. The snow was also the first September snowfall seen in 20 years. The number one spot for earliest snow on record, September 3, 1962, remains secure.

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September 6 to September 12: This week in Denver weather history

Tuesday, September 8th, 2020 11:27am MDT

This Week in Denver Weather History

Colorado weather is certainly varied and this week’s look back at weather history proves that.  We have seen everything from deadly lightning, hail and severe winds to even snow during the second week of September.  Most notably however were the devastating – and deadly – floods of 2013.


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 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.


In 1886…the last thunderstorm of the season pelted the city with hail the size of beans and dropped 0.81 inch of precipitation.

In 1962…the earliest first freeze of the season occurred. The temperature dipped to a low of 31 degrees.

In 1973…hail up to 1 1/2 inches in diameter fell northeast of Boulder.  A tornado was reported by a pilot east of Parker.  No damage was reported.


In 1933…heavy rain in the foothills over the clear creek and Golden gate canyon watersheds caused flooding in Golden and damaged the roadway in Golden gate canyon… Which resulted in its closure.

In 1969…a funnel cloud was sighted in southeast Denver. There was also considerable thunderstorm activity and local heavy rain across metro Denver.  Rainfall totaled 1.30 inches at Stapleton International Airport where small hail also fell.

In 1973…hail from 3/4 inch to 1 3/4 inches in diameter fell in Westminster and south of Broomfield.

In 2009…a man was critically injured when he was struck by lightning while riding his bicycle.  He was nearing a paramedic van when he was hit.  His heart stopped but paramedics quickly responded and were able to resuscitate him.

In 2011…a man was struck by lightning at the Adams County Fairgrounds.  He was leaning against a tree while watching a cross country meet when the tree was hit.  The lightning traveled down the tree and up through the ground…using him as a conductor.  The victim received second and third degree burns.

» Click here to read the rest of September 6 to September 12: This week in Denver weather history

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Thornton’s first taste of wintry weather for the season arrives Tuesday

Tuesday, September 8th, 2020 5:08am MDT

From record heat to record cold, such is life in Colorado. The much-anticipated storm system has arrived with temperatures 50+ degrees colder than yesterday and snow soon to begin.

Early this morning precipitation is falling as rain but a transition to snow will occur later and by mid-afternoon and evening, it should be all snow. The National Weather Service is calling for 3 to 7 inches between now and tomorrow AM but we continue to believe 2 to 4 is possible here in Thornton with an outside chance for more.

Much is going to depend on the timing of the transition to snow. Any accumulations will mainly occur on vegetated areas but some slush could be seen on roadways at the height of activity this evening and overnight.

As for temperatures, we are waking up this morning to mercury readings in the mid-30s and those will actually be our warmest temperatures of the day. By this evening the temps will be near freezing and overnight they will drop below the mark.

A Winter Weather Advisory is in effect now until noon tomorrow and a Freeze Warning kicks in at 6:00pm and will run till noon Wednesday as well. Stay warm and stay aware! Our Winter Weather Briefing Page has the latest.

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Labor Day to offer up well above normal temperatures but major changes arrive tonight

Monday, September 7th, 2020 5:12am MDT

Labor Day to offer up well above normal temperatures but major changes arrive tonight. The proverbial warm before the storm as Thornton will see a very warm day today.

Tonight, a powerful cold front will be pushing through bringing a jarring change to wintry conditions. We start out the day with sunny skies and those will be with us much of the day. There will continue to be haze and smoke from the Cameron Peak Fire over the area. High temperatures today will be near the 90 degree mark.

Change arrives right around sunset, maybe a bit after as the cold front will push through around 8:00pm. As it does, winds will increase considerably and temperatures are going to plummet. Some light precipitation, initially rain, perhaps with some snow mixed in will be seen, mainly after midnight and in the pre-dawn hours tomorrow. Overnight lows will be dropping to near the freezing mark.

The bulk of the snow looks to fall during the daytime hours tomorrow and into tomorrow night. The National Weather Service has issued a Winter Weather Advisory calling for 3 to 7 inches for the entire event. We see Thornton toward the lower end of that, more on the order of 2 to 4 inches but with the potential for higher amounts.

Accumulating snow will be fighting the warm ground plus the warmer daytime temperatures tomorrow and that may limit things. The biggest concern will be possible damage to fully leafed out trees as the snow will be heavy and wet. Any sensitive vegetation that you want to save should be covered or brought inside.

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Denver sets record high minimum and ties record high for September 6

Sunday, September 6th, 2020 11:59pm MDT

Record High Temperature

Our recent warm weather not only impacts daily high temperatures, it also impacts overnight lows as seen by the record set tonight.

As measured at Denver International Airport, the Mile High City saw a low of 67 degrees. This set a record high minimum for the date, beating the old mark of 66 degrees set in 1933.

Here in Thornton, we were quite a bit cooler seeing a low of 56 degrees.

Additionally, Denver’s official high temperature came in at 97 degrees. This tied the record high for September 6, last set in 2013. Thornton was actually hotter with a high of 99 degrees.

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Multiple high temperature records broken on September 5

Saturday, September 5th, 2020 6:24pm MDT

Record High Temperature

While snow and cold are on the horizon, that will wait and until then, we continue to experience extraordinarily warm weather. Today, September 5, Denver actually broke three records.

As measured at Denver International Airport, the high temperature topped out at 101 degrees. This easily bested the record high temperature for the date of 98 degrees set just last year.

Additionally, the 101 degree reading is the warmest temperature ever recorded in Denver during the month of September. Only one other time has it been 100 degrees or warmer in the month, that coming on September 2, 2019 with a 100 degree reading.

Lastly, this is the latest in the year a 100 degree or higher reading has been recorded.

Here in Thornton, we managed to stay just a bit cooler with a high of 99 degrees.

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