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UpdatedWed, 25-Nov-2020 11:40am MST 
 

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Monday starts off the workweek with lots of sun, mild temperatures

Monday, September 14th, 2020 4:45am MST

After last week’s brief bout of unsettled weather, we are set to return to calm, dry and very warm conditions this week. Today starts things off with sunny skies and temps well above normal.

Sunny skies will be the rule throughout the day today. High temperatures will reach to the mid to upper 80s. Overall conditions will be calm and dry.

Tonight, skies remain clear and lows will dip to the mid-50s.

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September 13 to September 19: This week in Denver weather history

Sunday, September 13th, 2020 4:47am MST

This Week in Denver Weather History

Weather conditions in Colorado can of course vary greatly and we always see that in our weekly look back in the history books.  For this week, we see a dizzying array of weather events from record setting temperatures in the 90’s and summer-like thunderstorms with tornadoes to an early arrival of winter that brought a foot of snow!

From the National Weather Service:

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.

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.

In 2009…a severe thunderstorm produced large hail… Up to half dollar size in the foothills of Jefferson County…west of Denver.

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.

» Click here to read the rest of September 13 to September 19: This week in Denver weather history

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Thornton’s weekend to offer pleasant, seasonal weather conditions

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

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 MST

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 MST

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 MST

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 MST

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 MST

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.

1-7

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.

3-6

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.

5-9

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.

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.

6

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.

7

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.

7-8

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.

8

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.

9

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 MST

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 MST

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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