SPM 09-04-2021: Widespread, Severe Thunderstorms for Urban Corridor, Palmer Ridge, and Eastern Plains

September 4, 2021 by ·

Issue Date: Saturday, September 4th, 2021
Issue Time: 10:05 AM MDT

Summary:

The end of the work week began with early morning showers and storms lingering around the Northeast Plains and Palmer Ridge before lifting and dissipating with the general eastward movement. However, it was not long before more widespread thunderstorm development across the state, including the necessary moisture and lift needed for some severe weather. Scattered thunderstorms began firing up in the late morning and early afternoon in the Northern, Central, and Front Range Mountains, moving eastward onto the Urban Corridor and becoming more organized. As the afternoon progressed, storms formed in the Western Slopes and Grand Valley as well. There was less available moisture for heavy rainfall west of the divide, but a different story to the east.

An early afternoon severe thunderstorm made its way across the South Denver Metro Area, causing 0.50-1.00 hail reports across a large swatch of the southern suburbs: Lakewood, Littleton, Highlands Ranch, and near Chatfield Reservoir. High winds were also reported – up to 64 mph gusts at KAPA in Centennial. Hail wasn’t just large, there was enough to blanket the ground like snow Littleton!

The Centennial Airport also received 1.62 inches of rain yesterday with most of that, 1.57 inches, falling in a single hour. Precipitation Frequency Estimates from NOAA Atlas 14 in this area put 1.57 inches in an hour to be between a 10-year and 25-year event or 4-10% chance of occurrence in any given year. Other high precipitation totals around the South Denver Metro Area include 1.64 in Highlands Ranch, 1.35 in Littleton, 1.29 in Parker, and 0.97 in Aurora.

The heavy rain and hail caused street flooding across the area, prompting response from South Metro Fire Rescues for vehicles stranded in high water.

The storms quickly moved off the Urban Corridor with eastward movement of the trough axis, forming a line of storms from the northeast corner of the state all the way to Colorado Springs in the afternoon. Fast-moving storms produced heavy rainfall across the Northeast Plains and Palmer Ridge including: 1.95 inches in Burlington, 1.40 inches in Vernon, 1.30 inches in Woodrow, 0.93 inches in Akron, and 0.71 inches south of Greeley.

A second round of thunderstorms on the Southeast Plains prompted three severe thunderstorm warnings for counties on the Colorado-Kansas border overnight. Up to 57 mph wind gusts were reported in Aroya, CO. Storms continued well into the early morning hours before moving eastward out of the state, but not before dropping impressive, and much needed, heavy rain. Rainfall totals in Southeast Colorado include: 1.95 inches in Holly, 1.94 in Timpas, 1.40 in Haswell, 1.33 in Rocky Ford, and 1.00 inch in Lamar. The 1.95 inches in Holly was likely also in just under an hour, with PF estimates placing this event between a 2-year and 5-year rainfall event (20-50% chance in any given year).

Further west, a flash flood warning was issued for the Grizzly Creek burn scar in Glenwood Canyon after 4:00 pm yesterday, which prompted an I-70 safety closure. Up to 0.60 inches of rain fell yesterday in Glenwood Springs and the surrounding area of Glenwood Canyon. Fortunately, no flooding or debris flows were reported and I-70 reopened last night.

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.

Filed Under: State Precipitation Map ·

SPM 09-03-2021: Minor Debris Flow in Grand County, Heavy Rain in Colorado Springs

September 3, 2021 by ·

Issue Date: Friday, September 3rd, 2021
Issue Time: 10:25 AM MDT

Summary:

Residual moisture left behind from widespread rainfall on Wednesday allowed for isolated showers in the Western Slopes, Grand Valley, North and Central Mountains to kick off Thursday morning. Late morning to early afternoon rainfall totals were highest in the Southwest Slope, with 24-hour accumulations around the Utah-Colorado border between 0.63-0.76 inches according to CoCoRaHS observers.

Daytime heating allowed for more widespread shower and thunderstorm development across Western and Central Colorado, and then the Front Range Mountains before spilling onto the Urban Corridor and Palmer Ridge. Most of the Urban Corridor received some rainfall yesterday, though rainfall rates and total precipitation varied, Trace – 0.20 inches were reported between Fort Collins and Castle Rock.

A Flood Advisory was issued shortly after 5:00 pm yesterday in the Northern Mountains, including a portion of the East Troublesome burn area and CO-125, after Doppler radar indicated heavy rain due to thunderstorms. A minor debris flow did occur on CO-125 yesterday in Grand County due to recent rain. CDOT crews were able to quickly clear the highway without closure and no injuries were reported. The Grand County Sherriff shared the following video on twitter taken from a Deputy traversing the debris flow. Based on the trees on the ridgeline, it is likely the debris flow occurred on the East Troublesome burn scar.

Areas along the Palmer Ridge and Eastern Plains saw heavy rain yesterday evening into the early morning hours as storms developed along a stationary frontal boundary draped across the region. Training thunderstorms produced between 0.80-1.43 inches of rain across Colorado Springs. The following time series plot of rainfall at Cottonwood Creek near Colorado Springs reported 1.43 inches of rain after 6:00 pm yesterday to 3:00 am this morning.

Eastward movement of the overnight showers and thunderstorms resulted in the Northeast Plains and Northern portion of the Southeast Plains waking up to showers this morning. 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.

Filed Under: State Precipitation Map ·

SPM 09-02-2021: Tropical Moisture Remnants Bring Widespread Storms Across the State

September 2, 2021 by ·

Issue Date: Thursday, September 2nd, 2021
Issue Time: 10:35 AM MDT

Summary:

As expected, the remnants of Hurricane Nora brought plenty of late-season monsoonal moisture and therefore widespread storm coverage to nearly all of Colorado yesterday. The western half of the state benefited from rainfall the most, beginning in the early morning hours in the Grand Valley and Western Slopes before filling in in coverage to the Northern, Central, and San Juan Mountains by early afternoon.

Heavy rain occurred in the Grand Valley, where between 0.70-1.02 inches were reported across Grand Junction. A new daily rainfall record was set at the Grand Junction Airport – 0.76 inches in 24-hours, breaking the previous record from 1937.

Some other notable rainfall totals from CoCoRaHS observers and MesoWest gauges across Western Colorado include:

  • 1.09 inches in Hesperus
  • 0.99 inches in Ignacio
  • 0.89 inches west of Glenwood Springs
  • 0.84 inches in Hotchkiss
  • 0.83 inches in  Cahone (Western Dolores County)
  • 0.80 inches in Durango and Chromo
  • 0.77 inches north of Pagosa Springs
  • 0.68 inches in Fort Garland
  • 0.67 inches in Cortez
  • 0.45-0.68 inches across Steamboat Springs and the surrounding area
  • 0.57 inches at Sand Dunes National Park
  • 0.50 inches in Crested Butte

Thankfully gentle rainfall rates helped to minimize flood potential, even with the long-duration rainfall. Additionally, up to 0.25 inches of rain fell on the Black Mountain Fire in Grand County, which helped to moderate fire activity.

By evening, the eastward progression of the low resulted in increased shower coverage over the Front Range Mountains, Southeast Mountains, and Urban Corridor, though rainfall totals were lighter due to downsloping winds and dry air closer to the surface, less than 0.25 inches was reported across the Urban Corridor.

On the Eastern Plains and Palmer Ridge, widespread convective storm coverage began in the evening, with some localized higher rainfall totals. 1.20 inches was reported in Julesburg, with 0.50-0.80 inch totals along the I-76 corridor. High winds from a severe thunderstorm in Burlington with gusts over 75 mph caused extensive wind damage: a 50 mph gust took out the ASOS station in Burlington, there are reports of downed trees and damage to power lines resulting in power outages, and damage to mobile homes and windows. The Burlington area also received up to 0.90 inches of rain according to a CoCoRaHS observer.

The eventual exit of the low-pressure system and surface trough in the early morning hours caused a clearing out for most of the Colorado, though residual moisture in Southwest Slope and Grand Valley has caused some isolated early morning showers.

Almost miraculously, no flooding was reported on Wednesday. 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.

Filed Under: State Precipitation Map ·

SPM 09-01-21: Hot, Dry, and Largely Uneventful End of August

September 1, 2021 by ·

Issue Date: Wednesday, September 1st, 2021
Issue Time: 10:20 AM MDT

Summary:

August went out uneventfully for most of Colorado with yet another hot, dry and smoky day. There was some afternoon convection in the high elevations due to daytime heating, though little if any precipitation with a lack of available moisture. With the continued heat, Colorado Springs saw a record high temperature of 94 degrees yesterday. The end of August also brings time to review the weather for the month and the end of meteorological summer (June-July-August). Along the Urban Corridor, Denver had its fifth driest August on record, but there were large differences in the spatial distribution of precipitation between the official reporting station at DIA versus Downtown Denver, which received 2.39 inches more than the airport.

Colorado Springs also had a drier than normal summer for the third year in a row, coming in 2.78 inches below average. Conversely, Pueblo received 1.4 inches more than normal for the summer months.

In the SPM below, there appears to be an area of heavy rainfall over Lincoln-Kit Carson-Cheyenne Counties. This is actually an artifact from large wind farms in the area and an overnight inversion causing the radar beam to be reflected downward, rather than above the turbines.

Finally, during the late overnight and early morning hours, showers began in the Northwest Slope, Grand Valley, and Southwest Slope as the remnants of Hurricane Nora push a late season surge of monsoonal moisture in the area. As of this morning, precipitation totals are still light, Trace – 0.10 inches, but rain will continue and pick up in intensity and coverage throughout the day (see today’s FTB for more information).

No flooding was reported on Tuesday. 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.

Filed Under: State Precipitation Map ·
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