SPM 09-30-2021: Widespread, Soaking Rainfall for Much of Colorado

Issue Date: Thursday, September 30th, 2021
Issue Time: 10:35 AM MDT


Wednesday was another wet day for much of Colorado. It started off with morning showers and thunderstorms, including snow at high elevations, for the Grand Valley, Western Slopes, Central, and Northern Mountains associated with the eastward progression of a strong shortwave trough. Another morning of heavy rain combined with high accumulations yesterday resulted in several western locations experiencing flooding and debris flows.

A Flash Flood Warning was issued for the Grizzly Creek burn area before 9 am, indicating that flash flooding was already occurring in Glenwood Canyon due to heavy rain and thunderstorms, as per emergency managers. I-70 was closed by CDOT in both directions after the warning was issued – CDOT also confirmed a mud flow in the canyon, as seen in the tweets below.

A USGS gauge at Deadman’s Creek Met Station Near Glenwood Springs, reported 0.98 inches of rain yesterday and 2.33 inches in the last two days. CoCoRaHS observers around Glenwood Springs reported 0.62-0.73 inches of rain as well yesterday. A Flood Advisory was also issued for Fruita at 12:24 pm, with the language of the advisory indicating that minor flooding was also occurring due to heavy rainfall in the Little Salt Wash Creek.

On the flip side, the Ptarmigan Fire in the Central Mountains benefited from the late morning/early afternoon rainfall. The following is an excerpt from a last night’s news release:

The rain has not extinguished the fire, but it has helped reduce fire activity, which allowed firefighters to make good progress building containment lines on the southern and western flanks today. Weather limited the use of helicopters today.
Fire officials currently estimate the Ptarmigan Fire to be between 85 and 100 acres with no containment. The cause remains under investigation.

Rainfall totals around Silverthorne were less impressive, but the I-70 corridor received up to 0.39 inches of rain yesterday.

While storms dissipated from the west in the early afternoon, showers also began to pick up along the Front Range Mountains and spill into the Urban Corridor. A widespread north-south line of storms covered most of the urban corridor, bringing isolated heavy rainfall and minor runoff and street flooding. Small stream flood advisories were issued for Larimer County, including portions of Cameron Peak burn area, and Boulder County for the Calwood burn area. Both burn scars had moderate threats forecasted in the FBF yesterday, but thankfully no flooding was reported. 24-hour rainfall totals across the Urban Corridor range from less than 0.10 inches in Fort Collins and Loveland, 0.44 inches in Boulder, 0.65 in Lakewood, and 0.84 inches in Castle Rock.

Back west, another round of thunderstorms picked up again for Grand Valley and Southwest Slope in the evening. A debris flow was reported by a NWS employee in Whitewater, Southeast of Grand Junction after 5:00 pm indicating “6 to 8 inches of water and mud flowing across driveway”. Up to 0.25 inch hail was also reported from evening thunderstorms nearby in Skyway. Rainfall totals across the Grand Valley vary from 1.33 inches in Glade Park, 1.08 in Redlands, 0.33-0.68 in Grand Junction, and 0.58 in Palisade and Cedaredge. In the Southwest Slope, Montrose received 0.64 inches of rain, 0.41 in Ridgeway, 0.35 in Rico, and 0.25 in Ignacio.

The Southeast Mountains, Raton Ridge, and Southeast Plains had their turn for rainfall in the late evening, which lasted well into the overnight hours. A series of special weather statements for 50 mph winds, small hail, and frequent lightning (sub-severe thunderstorms) were issued by the Pueblo WFO yesterday evening for strong storms in Southeast Mountains and Southeast Plains. Hail up to 0.88 inches was reported in Aguilar. Some notable rainfall totals in the Southeast Mountains and Plains include:

  • 1.27 in Colorado City
  • 1.00 in Crowley
  • 0.97 in Cedarwood
  • 0.87 in Ordway (who remarked that things were so dry before this rain there was still hardly any mud)
  • 0.84 in Walsenburg
  • 0.72 in Rocky Ford

This morning US141 closed in both directions from a rock slide between Naturita and 15 miles south of Gateway – tweet from CDOT below. Due to the very rural location in this part of the state, there are few gauges to verify how much rain fell over the area. A MesoWest gauge at Nucla received 0.05 inches yesterday, which isn’t much. However, MetStormLive QPE in the State Precipitation Map below indicates up to 0.25 inches fell across the area.

The only portions of the state that remained overall dry yesterday were the San Luis Valley and Northeast Plains. For rainfall estimates in your area, check out the State Precipitation Map below.

Click Here For Map Overview

The map below shows radar-estimated, rainfall gage-adjusted Quantitative Precipitation Estimates (QPE) across Colorado. The map is updated daily during the operational season (May 1 – Sep 30) by 11AM. The following six layers are currently available: 24-hour, 48-hour and 72-hour total precipitation, as well as maximum 1-hour, 2-hour and 6-hour precipitation over the past 24 hour period (to estimate where flash flooding may have occurred). The accumulation ending time is 7AM of the date shown in the bottom right corner. Also shown optionally are vulnerable fire burn areas (post 2012), which are updated throughout the season to include new, vulnerable burn areas. The home button in the top left corner resets the map to the original zoom.

Note: The 24-hour, 48-hour and 72-hour total precipitation do not contain bias corrections today due to errors in the CoCoRaHS data. This means there may be underestimations in QPE over the southwest and southeast corners of the state.