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

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

Summary:

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.

SPM 09-29-2021: Much Needed Rainfall for Western Colorado, but Debris Flow on Pine Gulch Burn Scar

Issue Date: Wednesday, September 29th, 2021
Issue Time: 10:45 AM MDT

Summary:

Portions of the Urban Corridor and Northeast Plains woke up to some isolated showers Tuesday morning before quickly dissipating. However, the main weather story from yesterday is definitely the significant rainfall for Western Colorado. Scattered showers began to develop in the late morning in the Grand Valley and Northwest Slope associated with the late-season plume of monsoon moisture brought into the region by the cutoff low. By afternoon with the east-northeast progression of the low, there were scattered but widespread showers and thunderstorms over the Western Slopes, Grand Valley, Northern, Central, San Juan, and Southeast Mountains – even allowing for snow to fall at the highest elevations. Eventually, the eastward progression also caused enough lift for isolated shower coverage along the Palmer Ridge and Eastern Plains.

Back in the west, by early evening a trough axis moving in from Utah allowed for another round of widespread showers over the Western Slopes, Grand Valley, Northern, Central, and San Juan mountains. This provided soaking, long-duration rainfall (with some localized embedded convection) that lasted overnight and into the morning today. Rainfall totals west of the divide are impressive for late September, which is especially helpful with the drought conditions that have been plaguing the western half of the state all summer

Up to 1.30 inches was reported in Grand Junction near Colorado National Monument from a CoCoRaHS observer who also remarked:

“Rain started about 2:30 PM and was intermittent throughout the night. Heaviest rain occurred about 5:30 PM with 0.60 inches in 20 minutes causing street flooding.”

There are no precipitation frequency estimates from NOAA Atlas 14 for 20-minutes, but 0.60 inches in 30 minutes falls between a 5-year and 10-year Average Recurrence Interval (ARI) for this area, or 10-20% chance of occurring in any given year; 1.30 inches in 24-hours falls just below the 5-year ARI threshold. In addition to the heavy rain, up to 0.25 inch hail was reported nearby in Redlands, along with runoff on the roads. Other rainfall totals around Grand Junction range between 0.23 on the east side of town, and up to 0.87 in Loma and 0.69 in Fruita.

A series of arroyo and small stream flood advisories were issued north and south of Grand Junction and a flash flood warning was issued for the Pine Gulch burn area. Due to the rural nature of the burn area there are limited gauges, however West Divide Creek Station managed by CO-DWR, just southeast of the burn area, reported 1.09 inches in 24-hours, as seen in the hyetograph below. Additional gauges north of the burn area recorded between 0.58-1.53 inches of rain in 24-hours. Unfortunately, heavy rain resulted in a debris flow in De Beque, which flooded a house and rerouted Roan Creek.

A CoCoRaHS observer in Dinosaur reported 1.74 inches of rain yesterday, starting around 6:30 pm and continuing into the morning with many periods of heavy rain during the night. Precipitation Frequency Estimates for Dinosaur place 1.74 inches in 24-hours between a 10-year and 25-year ARI (or 4-10% chance in any given year). Other notable rainfall totals from Western Colorado include:

  • 1.28 in New Castle
  • 0.94-1.04 across Steamboat Springs
  • 0.86 in Parachute and Edwards, mostly from a single thunderstorm but light rain continued on/off through night
  • 0.81 in Walden
  • 0.75 in Mancos
  • 0.47-0.62 across Glenwood Springs and Carbondale
  • 0.60 in Gypsum
  • 0.53 in Cortez and Durango
  • 0.52 in Ouray

Between 0.25 and 1.04 inches of rain fell in Silverthorne and along the I-70 corridor west of the tunnels, which was helpful for moderating fire behavior from the Ptarmigan fire, but also limited firefighting efforts by grounding aircraft. As of last night, the fire has burned over 85 acres with no containment and is near residential areas. The Front Range Mountains, Urban Corridor, and Eastern Plains had much lighter precipitation accumulations yesterday – between Trace and 0.15 inches. 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.

SPM 09-28-2021: Continued Showers for Southwest Colorado, Ptarmigan Fire Ignited in Summit County

Issue Date: Tuesday, September 28th, 2021
Issue Time: 10:30 AM MDT

Summary:

The cutoff low traversing Arizona and New Mexico continued to bring late season monsoonal moisture to Southwest Colorado yesterday. There were already showers along the Colorado-New Mexico border in the in the early morning hours. The general eastward progression of the low and daytime heating then allowed for scattered, but more widespread, storm development over the Southwest Slope, San Juan Mountains, Southeast Mountains, even inching up toward the Central Mountains and southern portion of the Front Range Mountains. Showers and thunderstorms lasted well into the evening hours and overnight, however rainfall rates and total accumulation remained low enough to prevent flooding.

The following hyetograph from Red Mountain, a gauge managed by CDOT, shows the day’s steady rainfall beginning in the afternoon and continuing until just before midnight, with total of 0.26 inches of rain.
Other notable totals from CoCoRaHS observers and gauges in Southwest Colorado include:

  • 0.52 north of Durango
  • 0.52 from a USGS gauge at Mancos River near Towaoc, just north of New Mexico border
  • 0.14-0.50 in the Mancos, Dolores, Cortez region of Montezuma County
  • 0.18-0.46 across Saguache county
  • 0.35 in Pagosa Springs
  • Even Trace-0.11 in southwest Colorado Springs and 0.05-0.10 in the San Luis Valley.

For the rest of the state, the day remained dry and unseasonably warm. Highs were in the 80s and 90s across the Grand Valley, Northwest Slope, Urban Corridor, Palmer Ridge, Raton Ridge, and Eastern Plains. The Ptarmigan Fire was ignited yesterday afternoon in Summit County. The White River National Forest twitter account shared the following image of the fire above Silverthorne yesterday. Since the time of the tweet, the fire has expanded to burn around 40 acres.

No flooding was reported on Monday. 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.

SPM 09-27-2021: Late Season Monsoonal Moisture in Southwest

Issue Date: Monday, September 27th, 2021
Issue Time: 10:30 AM MDT

Summary:

Finally, some rainfall to report! As mentioned in the FTB yesterday, a late-season plume of monsoonal moisture has been circulating around a cutoff low located over Arizona, and that moisture finally creeped up into Colorado yesterday. By early afternoon, isolated showers began to form in the Southwest Slope and San Juan Mountains, and then became more widespread in the evening – expanding to the western slopes of the Southeast Mountains as well.

A combination of low rainfall rates and dry soils prevented any flooding or especially large accumulations. CoCoRaHS observers in Durango reported between 0.07-0.17 inches or rain yesterday, and nearby in Ignacio 0.30 inches was reported. Observers in Pagosa Springs reported between 0.20-0.37 inches of rain, and 0.40 inches in Chromo right above the New Mexico border. A RAWS station in Buckles, also near the New Mexico border, picked up 0.53 inches of rain between 4:00 pm and 10:00 pm yesterday, as seen in the hyetograph below.

For the rest of the state, Sunday remained hot and dry. Daily high temperatures in Eastern Colorado reached the 90s, with a high of 99 reported in Granada. Burlington reached 96 degrees, breaking a previous record of 95 set just last year. Along the Urban Corridor, Denver tied their record high minimum temperature (highest daily low temperature) of 60 degrees, previously set in 1948.

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.