If you have lived in Denver or along the Front Range for a long time then you know how wild Colorado’s weather can be and how quickly it can change. If you’ve only lived in Colorado for a year, you also know that the weather here is wild. One year ago, between September 5-8, the Front Range of Colorado saw the latest readings ever of 100-degree heat followed by record snowfall.

Satellite Imagery Showing the massive Cameron Peak Fire on September 7, 2020

On September 5, 2020, Denver set its all-time record high for September, reaching 101 degrees during the afternoon. This was also the latest date a 100-degree reading has ever been observed in Denver.  Another daily record high was then tied on September 6 when Denver hit 97 degrees. September 7th was the last day of heat across the eastern plains of Colorado when Denver’s high temperature reached 93.  That tied us for the record for the number of 90-degree days for a year (73) and was also the warmest temperature ever recorded before a day of measurable snowfall. It was also the date when ash was falling from the sky in Ft. Collins due to the massive Cameron Peak wildfire.

Other cities along the Front Range also felt this extreme September heat. Boulder, Ft. Collins and Colorado Springs were also feeling record heat within a few degrees of 100 leading up to the snow. One of the main factors that limited some Front Range cities from hitting the century mark was the thick smoke blocking some of the sun’s heat.

Water Vapor Satellite loop from GOES-16. Images from CIRA-CSU RAMMB-Slider September 7-10, 2020

On Labor Day Monday, September 7, 2020, a series of cold fronts moved across our areas from the north. This dropped temperatures from the 90s during the days into the 40s at night. Afternoon highs the following day only reached into the 40s for most Front Rangers and a mix of rain and snow developed by that evening. Snow was falling across the higher elevations most of September 8th with most accumulations stacking up along the I-25 corridor from Tuesday night to Wednesday morning.

The cold front that moved through was one of the strongest cold fronts to hit the area in September. Numerous cold records were set during this event:

  • Tied earliest freeze on record (Previously set September 8th, 1962)
  • Tied record low on 9/8 (31°F, last set 1962)
  • Tied record low on 9/9 (31°F, last set 1962)
  • Record coldest maximum temperature on 9/9 (43°F). The previous record was 53°F set in 1989.
  • Tied record low on 9/10 (35°F, last set 1898)
  • Largest 2 calendar day temperature drop in September (62°F drop). The previous record was 59°F set in 1993.
  • Warmest temperature ever recorded the day before a measurable snowfall (93°F on 9/7). The previous high was 92°F on September 12, 1993.
  • Shortest number of days between a 100-degree day and measurable snowfall (3). The previous record was 38 days in 2019.
  • Number of days (2) between a record high and record low in Denver (September 6 to September 8).  Ties previous record from August 15 -17 in 1960.

It was a wild weather forecast and was a weather event that will be remembered for years to come. The snow that fell during this weather event was extremely notable and left cities covered under inches of snow. Mind you, the worst wildfires in Colorado’s history were occurring in the weeks leading up to Labor Day. Residents along the Front Range were taking pictures of ash covering cars, drivers were using headlights during the day because the thick smoke made it dark outside, there was extremely bad drought and the forecast of incoming cold and snow only seemed fitting for the wild year that was 2020.

Observed snowfall totals on September 10, 2020

Numerous snow records were set in Colorado because of this storm:

  • Tied the second earliest snowfall on record for Denver (9/8). The earliest snowfall on record is 9/3/1961.
  • Daily snowfall record set for 9/8 (1.0 inch fell). The previous record was 0.7″ in 1962.
  • Daily snowfall record tied for 9/9 (Trace). The previous record was a Trace in 1962.
  • Snapped a streak of 19 consecutive years without September snow in Denver.

Rocky Mountain National Park on September 10, 2020 – RMNP

Total snowfall accumulations were 1 to 3 inches across much of the eastern plains, 3 to 6 inches for cities along the mountains (including Boulder and the western portions of Fort Collins), and 4 to 10 inches for the mountains and foothills of the Front Range. A total of 5.6 inches of snow was measured at the NWS Boulder office, while Denver officially measured a total of 1.0 inches.  Parts of the Arkansas River Valley, the Sagre De Cristos and the Pikes Peak Region saw over half of a foot of snow accumulate.

The forecast for this week calls for near-record heat and dry conditions. No snow is in the forecast.

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