Issue Date: Friday, July 31st, 2020
Issue Time: 10:55AM MDT

Summary:

Some strong storms developed over Larimer, Weld, and Boulder counties along the northern Urban Corridor and Front Range, which were able to generate penny-sized hail and very heavy downpours. The heaviest rain fell near the town of Windsor with rain gages reporting up to 1.53 inches (CoCoRaHS) and two heavy rainfall reports of 1.24 and 1.45 inches. Four other CoCoRaHS rain gauges reported over 1 inch between Windsor and Greeley. Today’s QPE map picked up on the 1+ inch totals near Windsor, but may underestimate totals closer to Greeley, where less than 1 inch is indicated. A social media post indicated that some road flooding occurred in the town of Windsor. This is quite impressive as the storms had fairly quick storm motions. The outflow/moisture boundary pushed back in from the Northeast Plains, which supplied the moisture for the storms. Storms also tracked off the mountains near Fort Collins, producing up to 0.58 inches of rain just west of town. Additional storms tracked just south in northern Boulder County, which dropped up to 0.69 inches between Estes Park and Longmont. Note that CoCoRaHS sites are 24-hour rain totals, so they reflect 2 to 3 round of storms tracking over the area.

A series of severe thunderstorms also fired over the southern Front Range mountains and tracked south-southeast into Fremont, Pueblo, and Custer counties. These storms dropped up to golf ball sized hail and brief heavy rain. It’s very hard to get this large of hail during the summer with the increased freezing level height. A Flash Flood Warning was issued over the Junkins burn area in eastern Custer County, based on radar data and QPE and rain gauge estimates in the area indicate up to or just over 0.5 inches of rain fell between Canon City and Pueblo. No flooding was reported as of this morning.

Low-level clouds and persistent rain showers were present over the Northeast Plains yesterday as cool air was ushered into the area on the back side of a low pressure system that tracked through Kansas. Limited instability only allowed showers to produce around 0.5 inches of rainfall for locations near the Colorado and Nebraska border. The highest rain gauge report is 0.45 inches from a CoCoRaHS observer near the CO/NE border in eastern Sedgwick County. Better yet, the cool air and cloud cover kept temperatures ~10 degF below normal for the eastern plains. Denver only hit 80F for a high yesterday, with temperatures staying in the 70Fs farther northeast. Hope you enjoyed the cooler temperatures as highs are expected to rise into the upper 80Fs again today into Saturday.

For rainfall estimates in your area over the last 24 hours, check out our State Precipitation Map below.

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Issue Date: Thursday, July 30th, 2020
Issue Time: 10:35AM MDT

Summary:

Isolated showers and weak storms fired over the higher terrain yesterday, and storms generated gusty winds with the lack of low-level moisture. A 62 mph wind gust was reported near Grand Junction as a small storm tracked through the area, which dropped some large tree limbs on the road. Several locations across the Central Mountains and Grand Valley recorded these 60 mph wind gusts. Rain accumulations across the mountains stayed under 0.1 inch, except for Frisco, CO, where numerous showers tracked over the area during the afternoon. A CoCoRaHS observer recorded 0.14 inches of rain over the course of the day.

A couple stronger storms fired over the plains of eastern Colorado where some additional moisture was available along a convergence boundary in the area under a severe thunderstorm watch. A storm that tracked off the Front Range produced a 74 mph wind gust in Washington County just before 7PM. A train of storms created a swath of rainfall from Fort Collins east through Yuma County, which dropped up to 0.47 inches of rain between Fort Collins and Greeley according to rain gauges. QPE indicates higher rain totals over Weld/Morgan County, but no rain gauges are in this remote area to verify this small storm core estimation. A second cluster of storms fired over the Southeast Plains around sunset as this convergence boundary moved south, which produced up to 0.40 inches of rain near the CO/KS border in Prowers County according to rain gauge reports. QPE suggests similar rain totals fell northwest into Kiowa and Cheyenne counties from these storms. No flooding was reported in Colorado yesterday.

Today’s drought update shows that the rainfall over eastern and southwestern Colorado over the last week has improved drought conditions slightly. However, worsening drought conditions continued over northern Colorado, which did not see as much widespread rain. Check out the drought monitor change map below.

For rainfall estimates in your area over the last 24 hours, check out our State Precipitation Map below.

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Issue Date: Wednesday, July 29th, 2020
Issue Time: 11:00AM MDT

Summary:

Yesterday was the final day of a prolonged period of monsoon moisture generating large precipitation totals across the state (6 day event). The rainfall on Tuesday was focused on the northern and eastern parts of Colorado. The northern mountains mainly saw isolated thunderstorms bring localized heavy downpours and gusty winds. The strongest of these storms occurred over Garfield County, which dropped over 0.5 inches of rain according to the QPE map. The highest rain gauge near the area picked up 0.64 inch (CoCoRaHS). This storm went on to generate a 48 mph wind gust at the Aspen airport.

A larger cluster of thunderstorms developed just east of the Continental Divide and rolled through the Denver metro before continuing eastward over the plains of eastern Colorado. A few small storm cells prompted Flood Advisories from NWS Boulder over Boulder and Weld counties, where over 0.5 inches of rain were estimated. A CoCoRaHS observer in Lyons, CO reported 0.69 inches of rain over 30 minutes in northern Boulder County within one of the Flood Advisory areas. An ALERT gauge just south of Lyons reported 0.71 inches of rain. Western portions of Fort Collins received up to 0.67 inches of rain according to rain gauges in the area, and the heaviest rain fell over Elbert County (1.8 inches) as storms moved just east of the Urban Corridor. A few other gauges over the Palmer Ridge picked up over 1 inch as well. Flooding was not reported over these areas.

Later evening storms also fired over the Southeast Mountains before tracking southeast over the Raton Ridge and Southeast Plains. These storms brought another flash flood warning for the Spring Creek burn area, and a flash flood was reported on the southwest side of the burn area in northeast Costilla County. This is the same area that had issues on Monday. A rain gauge near the flash flood report only reported 0.38 inches of rain, and with relatively quick motion, guessing this was over a short period of time. This also indicates that flash flooding is occurring from the lower rain totals due to saturated soils from the heavy rain over the last several days. Again, this lines up with the flash flood report from Monday.

The last 6 days have been quite the rainfall eventful for Colorado. The image below shows the AHPS observed precipitation estimate over the last 7 days, which covers this rainy period. Below is a summary of some observations and rain totals from this 6-day event:

• San Juan Mountains: 6-day rain totals = 3 – 4 inches (southwest & southeast), 2-3 inches (east & north)
• Southwest Slope: 6-day rain totals = 0.25 inches (southwest) to 3 inches (southeast)
• San Luis Valley: 6-day rain totals = 0.5-1.5 (interior), 2-3 inches (western & eastern edges)
• Southeast Mountains: 6-day rain totals = 2-4 inches (highest totals along crests of Sangre De Cristo Mountains)
• Numerous debris slides across San Juan Mountains, resulting in hikers being stranded and rescued near Silverton & Telluride
• Local rivers and streams have swelled over 90th percentile flows over Southwest Slope and San Juan Mountains

For rainfall estimates in your area over the last 24 to 72 hours, check out our State Precipitation Map below.

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Issue Date: Tuesday, July 28th, 2020
Issue Time: 11AM MDT

Summary:

Heavy rain fell across southern Colorado again yesterday, including the interior San Luis Valley. Yesterday was Day 5 for those keeping track of this event. In the SLV, a CoCoRaHS station recorded a 24-hour total of 1.16 inches in Monte Vista, and two CoCoRaHS station in Alamosa were just under an inch. The airport just south of town recorded 0.26 inches.  Heavy rainfall over Blanca, CO caused a few county roads to wash out just east of Alamosa and north of San Luis around 4:30PM. A SNOTEL station located on the west side of the Sangre de Cristo Mountains in the area recorded 0.9 inches, so there was a lot of water rushing into the valley.

The southern San Juan Mountains and Southwest Slope got yet another round of heavy rainfall over saturated soils. We’ve been watching the totals closely, and it seems any higher intensity storms (>0.5 in/hr) that can form, seem to be causing mud and debris flows at this point. Such was the case again yesterday when a debris flow and mud slide were triggered just east of Telluride. QPE was estimated just under a half inch, and an observation of 0.61 inches in the area corroborated these rain rates. One of the mudflows was 35 feet wide and 3 to 5 feet deep and trapped hikers and motorists in the Bridal Veil Falls area. Thankfully, no injuries were reported. This is also why the eastern half of the San Juan Mountains are under a Low threat today.

The highest 24-hour rain gauge report was 1.77 inches from an ASOS station in western Archuleta County. Other locations across La Plata, Montezuma, and Archuleta counties, reported 0.08 to 1.61 inches of rain, indicating heavy rainfall was, once again, quite widespread. That puts the event totals (using AHPS) over the southern San Juan Mountains well over 2 inches (widespread) with more isolated totals up to 4 inches. Did a quick CoCoRaHS look for the date range. The highest 5-day total was 3.56 inches at a gauge 17 miles ENE of Dolores in the San Juan National Forest. Not surprising, local streams and creeks are running high. The following USGS gages are running at 85% or higher, and some have about as much flow as the spring runoff peak (!): San Juan River near Carracas, Los Pinos River at La Boca, McElmo Creek near the stateline and the Dolores River at Dolores (below that very high CoCoRaHS gauge). If you have any other flooding reports for the event, please let us know here: https://archive-coftb.dewberryanalytics.com/?page_id=11165

Eastern Colorado also got some heavy rainfall as storms fired from a passing vorticity max in the early afternoon. About 1.5 inches was reported in Prowers County from the storms, so the QPE may be slightly underestimated by MetStorm. A Twitter post from someone in the area showed water running like a river through their fields. This was in the same area that got heavy rainfall on Sunday, so the soils were already saturated when the heavy rain began. Lastly, two Flash Flood Warnings were issued for the Spring Creek burn area, and a CoCoRaHS on the south end of the burn area indicated 0.36 inches fell. Thankfully, no debris flows or flash flooding was reported. One more day for this 2020 monsoon event, so be sure to tune back in tomorrow to see how it wraps up!

For rainfall estimates over your neighborhood in the last 24 to 72-hours, scroll down to our State Precipitation Map below.

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