Thornton Weather

Part 2: Data shows Denver weather records skewed by move to DIA

Two airports, two different climates. How Denver's weather and climate records are skewed by a 12 mile move. (ThorntonWeather.com)
Two airports, two different climates. How Denver’s weather and climate records are skewed by a 12 mile move. (ThorntonWeather.com)

ThorntonWeather.com’s owner and operator used to write for a now-defunct website called Examiner. This was a national site but with locally focused content. As the Denver Weather Examiner, Tony covered a number of topics related to Denver and Colorado weather.

Among them, he was always quick to point out how Denver’s weather records were being skewed by the move of Denver’s official weather station to Denver International Airport. In 2009, he wrote a three-part series explaining why this was an issue and why it mattered.

Fifteen years later, this continues to be a problem and thus we are re-publishing the series here. While the data is not current and some of the images were lost with time, readers can still understand and appreciate the problem.

Part 2: Data shows Denver weather records skewed by move to DIA
Originally published March 3, 2009, Examiner.

Did you hear February was Denver’s least snowiest month?  Or was it?  As we discussed yesterday, a growing chorus of voices are objecting to the National Weather Service’s use of measurements at Denver International Airport for official Denver weather record keeping.  They claim that comparing data from DIA to previous records compiled for more than 40 years at Stapleton and more than 75 years before that in downtown isn’t a fair analysis.

In this second of a three part series, we take a look at some of the data to see just how big of a difference the 12 mile move from Stapleton to DIA made.  We also investigate potential issues with accuracy at the automated monitoring station at DIA that could forever be altering our climate records.  Tomorrow we will take a look at why all of this matters and why you should care.

Temperatures

An analysis shows that in just the last eight years DIA registers warmer high temperatures and cooler low temperatures than stations closer to downtown and in areas where people actually live.  For our comparison, we compared the last eight years of data for Denver International Airport versus the measurements taken at Buckley Air Force Base.  We chose Buckley because that is the closest official measuring station to the location of the old Stapleton International Airport.

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As you can see, the differences between where measurements have been taken for the last 14 years at DIA and where they were taken previously is significant.  DIA’s highest recorded temperatures each year averages nearly 2 degrees more than those closer to Denver.  Similarly, the station’s low temperatures are more than 2 degrees cooler.  This essentially throws any record high or record low temperatures that were recorded in the last 14 years out the window.  Any comparison of today’s data with historical records taken at Stapleton are invalid because the location move to DIA has clearly impacted the measurements.

Precipitation

This is probably the single most astonishing statistic and helps to show just how much of a difference 12 miles can make.  The National Weather Service has been taking precipitation measurements at both DIA and at the former Stapleton site so we can do a direct comparison between the two sites.  The results are astonishing.

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The chart clearly shows that precipitation measurements at DIA consistently underperform as compared to those at Stapleton.  Over the 8 year period, DIA on average measures 13% less precipitation than Stapleton.

One year in particular stands out.  In 2002 Colorado was in a drought by any measurement.  At the end of the year the National Weather Service proclaimed it as Denver’s driest on record.  However, that claim was based on measurements at DIA.  If you use the measurements at Stapleton – where weather records were kept for more than 40 years – the claim doesn’t stand up to scrutiny.  Stapleton’s 8.49 inches of precipitation in 2002, while certainly a dry, below normal year, would actually make it only the 6th driest year.  It can easily be argued that the claim that 2002 was Denver’s driest year should be discarded.

As a more recent example, March 2008 was proclaimed the “third driest March on record” when a mere 0.17 inch of precipitation was recorded at DIA.  However, 0.55 inch was recorded at Stapleton, an amount which would not put the month anywhere near the top 10 driest.

Snowfall

Historical snowfall measurement comparisons between the two locations unfortunately cannot be directly performed as it was only this year that the National Weather Service began measuring snow at DIA.  However, we can infer from the precipitation measurements noted above that there will be a comparable discrepancy in snowfall measurements as well.  This stands to reason as the plains receive less snow than areas closer to the mountains and going 12 miles east can make a big difference.

Issues of accuracy?

The precipitation and snowfall issue gets even further convoluted this year with the move to measuring snowfall at DIA.  While this would seem to solve the problem of inconsistency between taking precipitation measurements at DIA but snowfall at Stapleton, it turns out things aren’t quite that easy.

Weather enthusiasts have noticed problems with recent snowfall and precipitation measurements.  Just recently on Monday, January 12th, when a small snow storm moved through the Front Range the National Weather Service recorded 3 inches of snowfall but only 0.03 inch precipitation.

On average snow has a 10:1 moisture content which means that 1 inch of snow equals 0.1 inch of moisture.  Using the standard, approximately 0.3 inch precipitation should have been recorded – 10 times what was actually reported.

Extending the observation period out to include the two month period from December 1, 2008 to January 31, 2009, similar problems have occurred.  At Stapleton, where measurements are taken manually, 12 inches of snowfall was recorded with a moisture content of 1.08 inches – approximately an 11:1 ratio and one that could be expected.  By contrast, DIA – using automated precipitation measurements – recorded 15 inches of snow but a meager 0.37 inch of precipitation.  That is an unfeasibly dry 40:1 snow to precipitation ratio.

Detractors abhor the use of automated stations for such important climate records and are quick to point out that this is but one of many examples of inconsistent measurements.  One former NWS employee said, “the NWS sold their soul to automation years ago” and as a result we are stuck with inaccurate records.

Two airports, two different climates. Read the series:

Climatology, Thornton Weather

Part 1: Do Denver weather and climate records have an asterisk attached?

Two airports, two different climates. How Denver's weather and climate records are skewed by a 12 mile move. (ThorntonWeather.com)
Two airports, two different climates. How Denver’s weather and climate records are skewed by a 12 mile move. (ThorntonWeather.com)

ThorntonWeather.com’s owner and operator used to write for a now-defunct website called Examiner. This was a national site but with locally focused content. As the Denver Weather Examiner, Tony covered a number of topics related to Denver and Colorado weather.

Among them, he was always quick to point out how Denver’s weather records were being skewed by the move of Denver’s official weather station to Denver International Airport. In 2009, he wrote a three-part series explaining why this was an issue and why it mattered.

Fifteen years later, this continues to be a problem and thus we are re-publishing the series here. While the data is not current and some of the images were lost with time, readers can still understand and appreciate the problem.

Part 1: Do Denver weather and climate records have an asterisk attached?
Originally published March 2, 2009, Examiner.

February 2009 is Denver’s least snowiest February on record.  A new record high temperature is recorded on January 21, 2009.  Record low temperatures are recorded on December 14th and 15th of last year.

These announcements are common and we all take notice when we hear them and they make for great water cooler chat topics but are these claims accurate?

In 1995 Denver finally opened its new airport out on the plains east of the city.  This new facility, 12 miles as the crow flies northeast of the old Stapleton International Airport, moved the airport from an urban environment to a rural one and more than 19 miles from the center of Denver.  Following that move, the National Weather Service (NWS) began taking some of its official measurements at the glistening new airport.  In doing so, some say Denver’s climate records have forever been altered and as such any weather record should have an asterisk attached to it.

Official Denver weather statistics were collected from the NWS’ downtown Denver office from November, 1871 to December 1949.  In January 1950 observations were moved to Stapleton International Airport where they remained until February 1995.  From March 1995 forward, Denver’s official weather has been measured at DIA.  With the move, precipitation switched to Automated Surface Observing Systems (ASOS), an automated means of making the measurement.  In a somewhat confusing twist, the measuring of snowfall remained at Stapleton until just this snow season.

Map:

http://maps.google.com/maps/ms?ie=UTF8&hl=en&msa=0&ll=39.819612,-104.886475&spn=0.337528,0.594635&z=11&msid=118280686911175493835.0004640da10c79cdcdba0

The question many are asking – Does a move of 12 miles make that much of a difference when measuring the weather?  Twelve miles is the same distance as between downtown and Golden, or downtown and Centennial or downtown and the northern edge of Thornton.  How often do we hear about heavy snow falling at I-25 and C-470 and yet downtown remains dry?  If you live in any of the outer metro area suburbs you know that what the news stations report as the weather downtown rarely is what you experience.

Twelve miles, particularly in a topographically and geographically diverse area as the Front Range would appear to make a world of difference.  That is why when you watch the evening news local meteorologists include the conditions at their local station downtown in addition to the official data at DIA.  Most local meteorologists have railed against the move and are quick to point out that the weather as measured at DIA does not reflect what Denver weather truly is.

When new records are announced, detractors point out that it isn’t fair to compare the data compiled at DIA with that which was recorded previously at Stapleton or downtown.  Just yesterday the National Weather Service announced that February 2009 was the least snowiest on record.  But was it really?  The NWS says Denver received only a trace of snow (less than 0.1 inch) but this was at DIA.  The vast majority of the metro area had at least some measurable snow during the month and Stapleton, where official records were kept for more than 40 years, had 0.8 inch of snow – a number that would push it well out of ‘least snowiest’ contention.  Many say we are comparing apples and oranges.

Empirical data shows that every meaningful statistic has been skewed by the move to DIA.  In this three part series we will take a look at how moving Denver’s official weather measurements to DIA have skewed Denver’s climate records and why it matters to you.  Tomorrow we take a look at the empirical data showing just how big of a difference 12 miles makes.  Wednesday we’ll tell you why it matters and learn about some possible solutions to the problem.

Stay tuned!

Two airports, two different climates. Read the series:

Colorado Weather, Natural Disasters, Weather History

100 years ago – Colorado’s deadliest tornado on record

Images from the Rocky Mountain News showing the devastation after a tornado struck near Thurman, Colorado on August 10, 1924.
Images from the Rocky Mountain News showing the devastation after a tornado struck near Thurman, Colorado on August 10, 1924.

The National Weather Service did a fantastic writeup about this devastating event on August 10, 1924 that claimed the lives of 11 people, 9 of which were children. It is a fascinating read. Check it out here.

From Microsoft Copilot:

The 1924 Thurman Tornado is the deadliest tornado in Colorado’s history. Here are some key details:

The tornado remains a significant event in Colorado’s weather history due to its devastating impact on the small community.

Climatology, Thornton Weather

July 2024 weather recap: Another warm one, precip comes in close to average

Thornton, Colorado's July 2024 temperature summary. (ThorntonWeather.com)
Thornton, Colorado’s July 2024 temperature summary. (ThorntonWeather.com)

Certainly, in our minds, July 2024 was a very warm one as it seemed like the 90+ degree days just kept on coming. Average temperatures did come in a good bit above normal. Precipitation wasn’t anything extraordinary and while it ended up close to average, the last half of the month was quite dry.

High pressure was the dominating force for the majority of the month with only intermittent breakdowns of the ridge. As a result, overall hot and dry conditions were the general rule. There were, however, just enough effects from some cold fronts to keep average temperatures relatively in check.

The last 10 days saw only one day with precipitation leading to dry conditions across the Colorado Front Range. This resulted in numerous wildfires in the foothills and smoke blanketing the area for several days.

Thornton’s average temperature for the month was 74.9 degrees. This was a good bit warmer than our running 18-year average for the month of 73.8 degrees. This made July 2024 the sixth warmest July over that period. Temperatures ranged from a maximum of 102 degrees on July 12th down to a low of 50.7 the morning of the 4th.

The Mile High City, as measured at Denver International Airport, came in a good bit warmer with an average mercury reading of 75.7 degrees. This was just a bit above Denver’s long term July average of 75.1 degrees. Denver set record highs on the 12th and 14th (102 and 101 degrees respectively) and tied the record high of 99 degrees on the 29th.

In terms of precipitation, Thornton received 1.74 inches during the month. Nearly half of that coming over two days on the 20th and 21st (0.80”). The total fell short of our running average for the month of 1.95 inches.

Denver’s official rainfall total for the month came in at 1.10 inches. This was well below the city’s July average of 2.14 inches.

Click here to view Thornton’s complete July 2024 climate summary report.

Thornton, Colorado's July 2024 precipitation summary. (ThorntonWeather.com)
Thornton, Colorado’s July 2024 precipitation summary. (ThorntonWeather.com)
Weather History

August 4 to August 10: This Week in Denver Weather History

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This Week in Denver Weather History

The beginning of August typically continues our monsoon season. This leads to increased chances for thunderstorms with heavy rain and the associated hazards that come with it. Our look back at this week in Denver weather history highlights the dangers of flooding, hail and lightning and even includes reference to grasshopper swarms being blown into the city.

From the National Weather Service:

3-4

In 1988…two inches of rain fell in 3 hours at both Morrison and Wheat Ridge. Thunderstorm rainfall totaled 0.80 inch overnight at Stapleton International Airport.

4

In 1889…southwest winds were sustained to 42 mph with an extreme velocity to 52 mph.

In 1924…0.01 inch of rain fell over downtown Denver. This along with the 0.01 inch of rainfall on the 10th was the only rainfall of the month…the driest August on record.

In 1963…heavy rains in the foothills above Idaho Springs caused mud and rock slides which closed U.S. Highways 6 and 40 for a time.

In 1976…hail to 1 inch diameter was reported 12 miles southwest of Denver. Hail to 3/4 inch in diameter was reported in Lakewood. Small hail…1/4 to 1/2 inch in diameter…fell at Stapleton International Airport.

In 1982…heavy rain poured through the roof of a clothing store in Aurora…causing widespread water damage. The roof was being repaired when the storm hit.

In 1983…hail up to one inch in diameter fell in Aurora where heavy rain produced street flooding.

In 1984…a Colorado state trooper was struck and injured by lightning in Northglenn.

In 1989…a microburst wind gust to 52 mph was recorded at Stapleton International Airport.

In 1997…lightning sparked a small fire in a home in Arvada… Causing minor damage. Several intersections in both Arvada and Westminster were flooded by thunderstorms producing heavy rain. Several cars were damaged by the high waters… And a number of businesses were flooded.

In 1999…flooding and flash flooding problems developed over metro Denver as slow moving thunderstorms dumped from 2 to 3.5 inches of rainfall in about 3 hours. Near the junction of I-25 and U.S. Highway 36…up to 4 feet of water flooded an auto dealership. About 45 cars were ruined. Damage estimates to the dealership alone totaled nearly a half million dollars. Sections of I-25 and U.S. 36 near the interchange were closed due to floodwaters. Floodwaters… Up to 5 feet deep…forced the evacuation of two mobile home parks in federal heights. Railroad tracks were washed out near Federal Blvd. and 64th avenue. Numerous power outages caused widespread blackouts in Thornton and Littleton. Along Massey Draw near Carr St. and Chatfield Reservoir…4 homes were flood damaged and portions of their backyards washed out. Widespread street flooding was also reported in Boulder where several buildings were flood damaged…including the University of Colorado Memorial Center.

In 2004…two golfers were shocked when lightning struck the eighth green of the golf course at Castle Pines north of Castle Rock. The two men suffered only minor injuries. Heavy thunderstorm rain from the same storm caused flash flooding. Floodwaters rushed across parts of U.S. Highway 85 near the entrance to the Castle Pines Golf Club. The traffic lanes were covered with up to 6 inches of running water.

In 2008…lightning sparked a grassfire that consumed 300 acres on the northern edge of Green Mountain…in Jefferson County. Gusty winds and very dry conditions allowed the wildfire to quickly spread and threaten several houses. Fortunately…only minor damage was reported to homes due to smoke and melted siding.

In 2018 a severe thunderstorm produced strong winds in and around Denver. A peak wind gust to 60 mph was observed near Firestone with a gust to 59 mph near Buckley Air Force Base. A peak wind gust to 40 mph from the southwest was observed at Denver International Airport.

5

In 1881…the low temperature cooled to only 76 degrees…the record high minimum temperature for the month.

In 1889…southwest winds were sustained to 42 mph.

In 1918…hail pelted the city…but was light and caused no damage. Precipitation totaled 0.25 inch. Northwest winds were sustained to 31 mph.

In 1964…lightning struck two boys in Denver while playing ball. One was treated and released from the hospital…but the other boy suffered second degree electrical shock and cardiac arrest and was hospitalized in critical condition for several days.

In 1969…two tornadoes touched down briefly in an open field southeast of Buckley Field in Aurora. No damage was reported.

In 1970…heavy rain in the Indian Hills area in the foothills west of Denver caused flash flooding…which washed out roads and damaged other property. Hail accumulated to a 3 inch depth with stones up to golf ball size; however…most of the damage was from flooding.

In 1982…2.38 inches of rain fell in an hour in Arvada… Causing minor flooding on Ralston Creek. In Westminster… 1 1/2 inches of rain fell…causing damage to streets and culverts. In addition…lightning caused some minor power outages across metro Denver.

In 1983…very heavy thunderstorms hit the southern portion of metro Denver. Heavy rainfall…as much as 2.89 inches in 38 minutes…caused widespread street flooding in southeast Denver. Two feet of water covered a section of I-25. Hail up to golf ball size accompanied the storm in Littleton and Englewood…along with 60 mph winds.

In 1984…a heavy thunderstorm drenched Littleton with up to 2.35 inches of rain in an hour…along with small hail that piled up to 2 inches deep. Flood waters were up to 4 feet deep in parts of town with many basements flooded. There were some power outages caused by lightning.

In 1990…a thunderstorm dumped 1.25 inches of rain in 12 minutes near tower and smoky hill roads in southeast Aurora. Minor street flooding was reported in the area.

In 1992…a pilot reported two funnel clouds near Cheery Creek Reservoir. Both dissipated quickly. Dime size hail fell near Franktown.

In 1994…one inch diameter hail fell near Strasburg. No damage was reported.

In 1999…a dog kennel east of Denver International Airport… Was flooded when a small dam…upstream in Elbert County… Was breached. The floodwaters…up to 4 feet deep…washed away some 6-foot fences and other small buildings. Ten of the 70 dogs boarded at the kennel drowned.

In 2002…a mail carrier was struck by lightning as he inserted a key into a multi-unit mailbox in Bailey. The shock knocked the man back against the mail truck. He suffered minor injuries. Lightning struck a residence in Commerce City. The resulting fire destroyed the roof of a detached garage and damaged much of its contents. Hail as large as 1 3/4 inches in diameter pelted Pine. One inch diameter hail fell in Arvada and southwest Denver. Heavy rain triggered a mudslide along U.S. Highway 285 near Bailey. Both lanes of traffic had to be closed until debris could be removed from the highway. Several residences in the Bailey and Glenisle areas were also flooded.

In 2004…heavy thunderstorm rainfall caused localized flash flooding in Virginia Canyon near Idaho Springs. Sections of the Virginia Canyon Road had to be closed due to the floodwaters.

In 2008…a severe thunderstorm produced large hail…up to 1 1/4 inches in diameter…northeast of Parker. Several automobiles were damaged.

6 Continue reading August 4 to August 10: This Week in Denver Weather History →

Climatology, Thornton Weather

Thornton’s August 2024 preview: Temps begin to cool, severe weather eases

Thornton's August Weather Preview
Thornton’s August Weather Preview

As summer vacations wind down and families prepare to send their kids back to school in August, Colorado weather also starts to settle down. The chances for severe weather decrease markedly during August and by the end of the month daytime temperatures are dropping quite a bit as well.

Find out more about what lies ahead with Thornton’s August weather here.

Photography, Thornton Weather

July 2024 top shots: Monthly photo slideshow

Thunderstorms move in on the evening of July 20, 2024. (David Canfield)
Thunderstorms move in on the evening of July 20, 2024. (David Canfield)

Colorado offers outdoor opportunities unlike any other state and while the summer heat settles in, photos of the amazing scenes across our state provide a view into why we love it here so much.

The weather this time of year has a pretty standard pattern of quickly warming temperatures followed by afternoon thunderstorms that can cool things down.  These storms sometimes provide a good bit of ‘excitement’ and are a prime photo subject.

  • Slideshow updated July 31, 2024

Recreationalists head outdoors and take advantage of urban, suburban and rural opportunities.  As they do, our abundant wildlife that is found just about anywhere comes into focus.

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!

Weather History

July 28 to August 3: This Week in Denver Weather History

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This Week in Denver Weather History

Monsoonal moisture oftentimes streams into Colorado this time of year leading heavy rain and dangerous lightning. Our look back at this week in Denver weather history features many flooding events caused by the moisture and even some tornadoes.

From the National Weather Service:

13-5

In 2008…a streak of 24 consecutive days of 90 degrees shattered the previous record of 18 consecutive days established in 1901 and 1874. Ironically…no new single day record high temperatures were set in the month of July. In August however…a record of 104 degrees was set on the 1st…and another record of 103 degrees was set on the 2nd. In addition…a record low min of 70 degrees was set on August 2nd.

18-2

In 1987…a streak of 16 consecutive days of 90 degrees ranked 4th on the list of hot streaks. The record of 24 consecutive days was established in the summer of 2008.

27-31

In 1956…96 percent of the total precipitation for the month of July occurred over the last five days of the month. Heavy thunderstorms produced 4.00 inches of rainfall at Stapleton Airport. This amount of precipitation in 5 days or less had been exceeded only 3 times in previous record. The last time had been in December of 1913 as snow. Considerable property damage occurred across metro Denver from flooding.

28

In 1882…intense thunderstorm lightning struck a number of places in the city…but no significant damage was reported.

In 1910…heavy thunderstorm rainfall totaled 2.21 inches in downtown Denver. Rainfall was 1.11 inches in an hour during the early afternoon.

In 1922…heavy rainfall to the south of Denver caused Cherry Creek to rise to the top of the retaining walls in the city. The creek did not flood; however…the large volume of water discharged into the South Platte River did inundate a few blocks of Globeville. Flooding also occurred along bayou creek near Franktown to the south of the city.

In 1923…thunderstorm winds were sustained to 38 mph with gusts to 52 mph.

In 1957…iridescent cirrocumulus clouds of unusual formation and brilliant color…oriented from southwest to northeast over metro Denver…were sighted by U.S. Weather Bureau observers at Stapleton Airport shortly after noon.

In 1966…heavy rains from a severe thunderstorm caused flash flooding on Deer Creek…southwest of Littleton. A child was injured when washed from a car caught in the flood waters. The flooding damaged property along the creek. Strong winds damaged several houses in suburban Littleton.

In 1970…a microburst wind gust to 52 mph was recorded at Stapleton International Airport.

In 1974…a tornado was sighted just east of Buckley Field in Aurora. No damage was reported.

In 1982…up to 2.50 inches of rain drenched an area just southwest of Denver in 30 minutes. This was the second day of heavy rain across portions of metro Denver.

In 1984…1.25 inches of rain fell in 45 minutes in Arvada. Minor flooding occurred on bear creek after a small dam broke.

In 1989…lightning killed two men in Arvada. They were taking wash from a clothesline when a bolt hit the older man…39… Killing him instantly. The bolt then traveled along the line…which was stretched between 2 tall trees…and hit his 26-year-old brother who died the next day.

In 1996…several weak tornadoes developed along a thunderstorm outflow boundary that moved into southern weld…northern Jefferson…and Adams counties. The tornadoes sighted near Bennett…Barr Lake…and in Arvada caused little damage. Strong thunderstorm winds downed several trees in the city of Denver and toppled several trees 7 miles west of Arvada where shingles were blown off several houses. Thunderstorm wind gusts reached 58 mph in Broomfield.

In 1997…a weak tornado touched down briefly in Parker… Damaging a greenhouse. Twenty pieces of the fiberglass roof were ripped away. Heavy rainfall in the foothills washed out some culverts in the Pine and Conifer areas. Heavy rainfall spread over the plains with 4 to 7 inches reportedly falling near Hudson. Several county roads were washed out between Fort Lupton and Hudson. Several basements in the area were flooded up to the ceiling. Standing water…up to 3 feet deep…was reported in some backyards. Later in the evening…a flash flood killed 5 people and injured 40 others in two mobile home parks in Fort Collins. The torrential rainfall also caused extensive damage on the Colorado state university campus. Thunderstorm rainfall totaled 0.80 inch at Denver International Airport and 1.09 inches at the site of the former Stapleton International Airport.

In 1999…heavy rainfall…up to 3 inches an hour…triggered a massive rock and mudslide along I-70 near Bakerville. The slide area was about 200 feet wide and 20 feet deep. Several other smaller slides were also reported along the highway. As a result…I-70 was closed for nearly 25 hours in both directions until the debris could be cleared from the roadway. The blockage of I-70 was one of the longest in the history of the highway in Colorado. A severe thunderstorm produced a wind gust to 64 mph at Denver International Airport. The storm also produced 1.56 inches of rain and briefly reduced the visibility to 1/4 mile.

In 2004…a severe thunderstorm produced hail as large as 1 inch in diameter in Thornton.

In 2010…a wet microburst produced very heavy rain and torrential hail in Boulder County…in the vicinities of caribou…Nederland and Eldora. Flash flooding washed out sections of County roads 126 and 128 near caribou. Several large Boulders had fallen across the roadways. Considerable flooding was reported in Nederland. Water was also observed running across County Road 130…between Eldora and Nederland. The hail had accumulated up to 8 inches deep near Eldora. Several vehicles were stuck in the ice…forcing the temporary closure of CR130 and the Lake Eldora Ski Road until snowplows could clear away the hail. Lightning strikes caused minor damage to two local businesses in Nederland. At Denver International Airport…a thunderstorm produced 0.30 inches of rain along with a peak wind gust to 38 mph.

In 2012…a tornado touched down briefly at the southeast corner of Mt. Evans near Lincoln Lake. The estimated elevation where this tornado touched down was near 12500 feet. This would make this tornado one of the highest ever observed in the U.S.

In 2014…two weak landspouts touched down; one near Ft. Lupton and the other on the southwest side of the Rocky Mountain Arsenal Wildlife Refuge. No damage was reported. A strong thunderstorm wind capsized a boat in Barr Lake. All three occupants made it to shore with no injuries.

In 2016…severe thunderstorms in western Adams and east central Jefferson Counties produced large hail near Lakewood…Golden and South Glenn. The hail ranged from 1 to 1 1/2 inches in diameter.

28-30

In 1889…dense smoke from forest fires in the mountains obscured the sun over the city for three days.

In 1971…a vigorous cold front late on the 28th produced northeast wind gusts to 39 mph and record breaking cold temperatures on the 29th and 30th. The temperature dipped to 47 degrees on the 29th and 43 degrees on the 30th… Setting record minimums for the dates. Upslope cloudiness along with rain and fog early on the 29th helped set a record low maximum temperature of 58 degrees for the date.

29

In 1878…a total eclipse of the sun was observed at 2:20 pm. From before to during the eclipse…the temperature in the sun fell from 114 degrees to 82 degrees…while the shade temperature fell from 89 degrees to 83 degrees.

In 1880…heavy thunderstorm rain and hail flooded streets and ditches.

In 25 minutes…0.76 inch of rain fell on the city along with large hail to 3/4 inch in diameter. There were no strong winds with the storm.

In 1890…a thunderstorm produced sustained west winds to 48 mph with gusts to 60 mph…but only 0.01 inch of rain.

In 1956…heavy rain and hail fell over west and north Denver.

In 1964…hail to 3/4 inch in diameter fell at Lowry Airfield.

In 1978…a small tornado was sighted just east of Parker. No damage was reported.

In 1989…heavy rain drenched all areas of the Front Range… Both in the foothills and adjacent plains. Amounts of 1 to 3 inches were general over the area. Damage was confined to a few minor road washouts and some street…basement…and crop flooding. Thunderstorm rainfall totaled 1.44 inches at Stapleton International Airport where north winds gusted to 43 mph. Lightning struck a 250 thousand dollar home near Nederland and started a fire which destroyed all of it except two garages. Lightning started a fire in a home in Evergreen. It reached the house by hitting a tree…then traveling through a metal clothesline strung between the tree and the building.

In 1995…thunderstorm winds gusted to 59 mph in Brighton. Thunderstorm winds from the south-southeast gusted to 41 mph at Denver International Airport. High temperature of 99 degrees was a new record maximum for the date in Denver.

In 1997…heavy rain caused flooding in an apartment building in Westminster. Several residents had to be evacuated from their apartments. A woman in Aspen Park received minor injuries…when lightning passed through an office window and struck her. She suffered temporary blindness for about 15 minutes.

In 2003…hail as large as 1 inch in diameter pelted Conifer… Highlands Ranch…and Franktown.

29-30

In 1997…heavy rain caused flooding and flash flooding in central portions of Adams and Arapahoe counties. Two homes were extensively damaged when water flooded the basements and adjacent pasture area in Strasburg. Water 4 to 5 feet deep had pooled in the lower lying areas of the town. A portion of quincy road was closed in Arapahoe County when 4 feet of water covered the roadway. Rainfall totaled 3.06 inches at Denver International Airport…establishing a new record for 24-hour rainfall in July. The previous record was 2.42 inches set in 1965 on the 24th and 25th.

Continue reading July 28 to August 3: This Week in Denver Weather History →

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