SPM 06-27-2020: Heavy Rainfall and Severe Weather Return

Issue Date: Saturday, June 27th, 2020
Issue Time: 10AM MDT

Summary:

Boy did it rain yesterday! The 10- to 30-minute totals from storms were quite impressive as low-level moisture returned behind a cold front and paired with shortwaves moving through the flow at peak heating. Although storms were moving at a moderate pace it did not keep them from dumping buckets of rain. That was to be expected with dew points in the 50Fs over the adjacent eastern plains. Enhance convergence along the Palmer Ridge helped enhance rain rates and produce a brief funnel cloud (spotter network). I don’t love the QPE below as I think it underestimates some of the localized totals yesterday, so I’m going to focus on totals produced by rainfall gages.

First, over the Denver Metro area, the Lakewood area had a couple rounds of rainfall. The highest ALERT gage recorded 1.69 inches (Upper Sloan Detention Pond) for the 24-hour period. Of the 1.69 inches, 1.20 inches fell in a span of 10 minutes – that translate to between a 100- and 200-year rainfall at the 10-minute duration! The Willow Creek gage just south of Castle Rock was also impressive, which was the same storm that later produced a Tornado Warning near the Springs. In a 30-minute span, there was 1.48 inches of rainfall, which is about a 1 in 25-year event. NWS Boulder issued a handful of Flood Advisories for the storms and one Flash Flood Warning.

Further south, over the USAF Academy, a gage recorded about the same for the same storm, 1.57 inches (1.42 inches in less than an hour). From 4:10 to 4:30PM, 0.75 inches of rain were recorded, and a Flash Flood Warning was issued at 4:35PM. Along with heavy rainfall, the storm produced golf ball sized hail (1.75 inches) and stalled cars on Voyager Parkway due to high water. As storms rolled east, the produced strong winds (55 mph), which caused damage in Yuma and Kit Carson Counties. Storms that moved into Logan County produced not only 50-mph winds but also baseball sized hail that knocked out car windows (2.75 inch)! All storms over eastern Colorado produced spikes in small streams, but no gulch or small streams reported flooding as of this morning.

Back to the west, gusty outflow winds were the main hazard as the low-levels were quite dry. A 63-mph gust was recorded in Mesa County, and this same storm produced ½ inch hail in Grand Junction. Radar estimated another 0.20 inches of rain or so for the area. That puts 48-hour totals around a half inch for the area.

For precipitation estimates over your area in the last 24-hours, scroll down to 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 24-hour, 48-hour and 72-hour total precipitation contain bias corrections that are not disaggregated into the hourly estimates, so there will likely be some differences. 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.