Issue Date: Thursday, August 19th, 2021
Issue Time: 9:35 AM MDT

Summary:

As forecasted, a plume of monsoonal moisture rotating around a low-pressure to the west entered the western half of Colorado yesterday, bringing widespread, heavy, long-duration rain to the Northwest and Southwest Slopes, Grand Valley, and even western portions of the Northern and Central Mountains. Afternoon thunderstorms produced an initial surge of heavy rainfall and even small hail, followed by waves of showers lasting overnight and well into the early morning. This prompted flood advisories and ultimately flood warnings for the Pine Gulch and Grizzly Creek burn scars, as well as a portion of the Cameron Peak scar.

Due to the rural nature of the Pine Gulch burn area, there are limited observations. However, a total of 1.04 inches was recorded from a MesoWest gage in Demaree, just west of the burn scar. The time series plot below shows rain beginning around 6:00 pm and continuing until 6:00 am this morning. To the south, observations in Grand Junction range from 0.49-0.78 inches from CoCoRaHS observers across town – similarly, rainfall totals are from afternoon storms and continuing showers overnight into morning.

Observers in Glenwood Springs reported just about 0.5 inches of rain yesterday, however nearby Glenwood Canyon and the Grizzly Creek burn scar received over an inch and half of rain yesterday and overnight. The plot below of No Name Creek shows an accumulation of 1.44 inches, with continuous rainfall starting in the early afternoon and continuing through this morning.

The flash flood warning issued for Glenwood Canyon prompted a safety closure of I-70 (after just reopening partially within the week). CDOT shared the following information on twitter describing their approach to I-70 closures based on flood watches and warnings.

What happens during a Flash Flood Warning? CDOT crews at the 2 closure points will close I-70. The @CSP_News will sweep the area to ensure there are no motorists or members of the public in the area. Crews will continue to monitor the mudslide area.

— Colorado Department of Transportation (CDOT) (@ColoradoDOT) August 18, 2021

Unrelated to any burn scars, but due to heavy rain – an early morning debris flow occurred north of Craig, closing CO-13 in the Northwest Slope. Between 0.34-0.37 inches were reported in Craig from CoCoRaHS and COOP observers, though there are very little observations along Highway 13 where the debris flow occurred. However, a personal weather station north of Craig and east of CO-13 recorded 0.25 inches of rain yesterday, and already an additional 0.30 this morning from rain beginning before 7:00 pm last night and continuing through morning. CO-13 remains closed with no estimated time for reopening, according to the following tweet from CDOT.

#CO13 northbound/southbound: Road closed between County Road 73 and County Road 38. Closed during ongoing slide cleanup MP 111-115. No est. reopen time. https://t.co/WIJBWjWZNI

— Colorado Department of Transportation (CDOT) (@ColoradoDOT) August 19, 2021

Other notable precipitation totals from CoCoRaHS observers in Western Colorado yesterday include:

• 1.59 inches in Dove Creek, right on the Utah Border
• 0.76 inches in Dolores
• 0.74 inches in Rockwood
• 0.71 inches in Cortez
• 0.56 inches in Montrose
• 0.39 inches in Ridgeway
• 0.34 inches in Durango
• 0.32 inches in Pagosa Springs

Elsewhere, an evening thunderstorm produced modest rainfall in Greeley and along the I-76 corridor, but the most of Eastern Colorado stayed dry. For rainfall estimates in your area, check out the State Precipitation Map below.

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Issue Date: Wednesday, August 18th, 2021
Issue Time: 9:15 AM MDT

Summary:

As discussed in yesterday’s FTB, Tuesday was an overall calm day before the incoming pattern change. Scattered afternoon showers developed in the high elevations of the Northern, Central, and Front Range mountains before spilling onto the Urban Corridor, while the Eastern Plains and the southern half of Colorado remained largely dry.

In the Northern and Front Range Mountains, early afternoon flood advisories issued turned to a flash flood warning for portions of the Cameron Peak burn scar and nearby locations in Larimer County. A RAWS station on the southern extent of the burn scar recorded 0.18 inches in an hour, as seen in the precipitation accumulation time series plot below. Thankfully, no flooding was reported.

As storms moved eastward off the mountains, limited available moisture dampened precipitation accumulations from thunderstorms. According to CoCoRaHS and MesoWest observations across the area, only Trace – 0.11 inches of rain fell. Instead, the main phenomena observed were high winds. Thunderstorm wind gusts exceeding 50 mph were reported across the Urban Corridor and adjacent Northeast Plains, from Keenseburg to Castle Rock– including a 63 mph wind gust recorded at KAPA-Centennial Airport.

No flooding was reported on Tuesday. For rainfall estimates in your area, including antecedent conditions, check out the State Precipitation Map below.

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Issue Date: Tuesday, August 17th, 2021
Issue Time: 9:40 AM MDT

Summary:

Monday saw another day of afternoon showers and thunderstorms in the Southwest Slope, the only region in the state with notable, widespread precipitation. Some of the higher totals include:

• 0.43 inches from CoCoRaHS observer in Mancos, who indicated heavy rain from 3:10 to 4:20 pm
• 0.25 inches from CoCoRaHS observer north of Durango, also from an afternoon storm
• 0.38 inches at Groundhog Reservoir (time series plot below), which corroborate both CoCoRaHS observations with most of the rain falling in the 3:00 pm hour

Elsewhere in Colorado, scattered showers fired up in the high elevations of the Northern and Central Mountains as the afternoon progressed. Pockets of higher accumulations were observed for areas lucky enough to be under a convective cell, though most of the mountains stayed dry. Small areas of the East Troublesome and Cameron Peak burn scars had flash flood warnings issued yesterday afternoon.  Meteorologist Chris Bianchi shared the following radar reflectively loop on twitter showing the isolated, flash flood-warned cells near each burn scar (green polygons). Up to 0.25 inches total fell in the small areas, based on gridded QPE from MetStormLive.

Small slivers of the East Troublesome and Cameron Peak burn scars are flash flood-warned. #9wx #COwx pic.twitter.com/0nZrgJbY5r

— Chris Bianchi (@BianchiWeather) August 16, 2021

No flooding was reported on Monday. For rainfall estimates in your area, check out the State Precipitation Map below.

Click Here For Map Overview

Issue Date: Monday, August 16th, 2021
Issue Time: 9:30 AM MDT

Summary:

Those on the Northeast Plains woke up yesterday to an early morning line of thunderstorms moving southeast between the I-76 and I-70 corridors. As discussed in yesterday’s FTB, this was unusual for anywhere in Colorado this time of year, but it was indicative of the moisture available for showers and thunderstorms throughout the day. By early afternoon, widespread storms began to fire up along the high elevations of the Northern, Central, San Juan, Southeast and Front Range Mountains, before expanding into the Southwest Slope, Palmer Ridge, and Southeast Plains by evening.

Along the Urban Corridor, the Colorado Springs area received between 0.10-0.77 inches of rainfall across town, according to various observation networks, thanks to an initial strong afternoon thunderstorm and then lingering light precipitation though the evening.

In the Central Mountains, two flash flood warnings were issued after heavy rain was indicated over Poncha Pass and Chalk Cliffs in Chaffee County. A MesoWest station in Poncha Springs reported 0.24 inches of precipitation, as seen in the time series plot below. The heaviest rain fell in a short period between 3:00 and 6:00 pm. Nearby in Salida, a PWS reported 0.25 inches for the day. Thankfully no flooding was reported on Poncha Pass, the Decker burn scar, or the Chalk Cliffs – one of the most debris-flow prone areas of the state.

Afternoon storms also prompted a flood advisory to be issued for Grand Lake and some of the East Troublesome burn area. Two MesoWest stations around Grand Lake both picked up 0.22 inches in a short period just before 3 pm, however no flooding was reported in Grand Lake as well.

Still, forecasted rain, thunderstorms, and the potential for debris flows resulted in preventative measures taken by CDOT. A long stretch of I-70 was briefly closed between Dotsero and Rifle, including Glenwood Canyon; and CO-5/Mount Evans Road remains closed after “adverse weather” prompted a safety closure. No flooding has been reported in Glenwood Canyon from the Grizzly Creek scar or along Mount Evans Road.

On the southwest slope, high winds were reported in Montrose and Cortez overnight and into the early morning after rounds of thunderstorms. A CoCoRaHS observer in Hesperus (La Plata County) reported 0.87 inches of precipitation from several rounds of storms, including pea-sized hail. The Durango area received between 0.25-0.55 inches as well.

For rainfall estimates in your area, check out the State Precipitation Map below.

Click Here For Map Overview