DENVER — It's not very often that it rains on the Front Range non-stop for two days. The September 2013 rainfall event may have crossed your mind during this week's soaker, so here's a comparison of the two events.
Meteorology
- MAY 2023 STORM: Mid-Latitude Cyclone
A cold front moved across northeastern Colorado on Tuesday night causing an outbreak of severe weather.
That preceded a shortwave trough in the Polar Jet stream which spawned a mid-latitude cyclone that dove into the Great Basin and slid across the southern end of Colorado on Wednesday.
In the afternoon, there was severe weather with several small tornadoes and 4" hail. Then rain showers lasted on the Front Range from Wednesday night to Friday morning.
- SEPTEMBER 2013 STORM: Mid-Latitude Cyclone
On Sept. 9, 2013, a cold front moved across the state bringing locally heavy rain to parts of northeast Colorado.
That was followed by a trough that spawned a similar mid-latitude cyclone to the May 2023 storm. Widespread and heavy rain showers developed on the afternoon of Sep. 11 and lasted until the morning of Sep. 13.
After about a 24-hour break in the rain, showers redeveloped on Sep.14 and lasted until late the next day.
Duration
- MAY 2023 STORM: 48 hours. The first severe thunderstorm hit the Front Range at about 2 p.m. on Wednesday, and there was rain non-stop after that until Friday afternoon.
- SEPTEMBER 2013 STORM: 48 hours. While the 2013 storm was really a weeklong event, most of the rain fell in that system also fell over a 48-hour period from the afternoon of Sep. 10 to the early morning hours of Sep. 13.
Total Rain
- MAY 2023 STORM: 3 to 8 inches. There were some totals on the Front Range in the two-inch range and a few over eight inches, but the general spread was between 3-8"
- SEPTEMBER 2013 STORM: 6 to 18 inches. There were some spots that were in the 2-4" range and a few over 20".
Rainfall Rate
- MAY 2023 STORM: 0.5" per hour. This storm has much lighter rainfall rates than the 2013 storm. There were brief times in localized spots that saw faster rates, but in general, the rain fell at rates less than a half inch per hour.
- SEPTEMBER 2013 STORM: 2.0" per hour. The rates varied throughout the event but there were several instances of rates above 2.0" per hour.
One Day Highest Total
- MAY 2023 STORM: 5.30" on May 11 in Castle Rock. So far, the highest unconfirmed 24-hour total from this event.
- SEPTEMBER 2013 STORM: 11.85" on Sept. 12 in Ft. Carson broke the all-time record for 24-hour rainfall total.
Location
- MAY 2023 STORM: Denver Metro and Palmer Divide. The bullseye for this storm was on flatter ground.
- SEPTEMBER 2013 STORM: This biggest rain totals with this storm was focused in the foothills of Larimer, Boulder and Jefferson counties. The steeper terrain increased the speed of the flood water and made it move even faster.
Precipitation Type
- MAY 2023 STORM: Mostly rain and hail below 8,000ft. Quite a bit of snow in the higher elevations. Snow helped minimize the flash flood potential because it has to melt before it becomes water.
- SEPTEMBER 2013 STORM: All rain and hail.
Timing
- MAY 2023 STORM: Streams and rivers were just nearing peak snowmelt flow which usually happens in the last week of May or first week of June.
- SEPTEMBER 2013 STORM: Streams and rivers were starting to diminish after a hot and dry summer on the Front Range. If this storm would have happened in late May, it would have likely been much worse.
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