Issue Date: Friday, August 13th, 2021
Issue Time: 9:50 AM MDT
Summary:
Thursday saw early afternoon storm development along an east-west oriented surface trough/disturbance in the Central and Front Range Mountains, extending along the Palmer Ridge and Southeast Plains. The disturbance had a general southern movement, allowing for storms to fire up along it as well as ahead of it along the Southeast Mountains and Raton Ridge. Severe thunderstorms warnings were issued, along with flash flood warnings, along the I-70 corridor on the Palmer Ridge and Southeast Plains, with the main threats including high winds, large hail, and localized heavy rainfall. Warnings verified with up to 60 mph winds reported in Cheyenne Wells, and up to 1.76 inch hail reported in Vona (Kit Carson County).
A personal weather station (PWS) and trained spotter also in Vona reported over 6 inches of rain yesterday in just 3-hours. The PWS rain gauge recorded 6.05 total, with the highest rainfall rate exceeding 11 inches/hour! Streets and sidewalks in downtown Vona were reported to be under water, as well as basement flooding and damage to some homes. There were no other heavy rain reports in the small town of Vona to verify the rainfall, but the un-bias corrected gridded QPE from MetStorm in the State Precipitation Map below corroborate the very large rainfall accumulation with a small areal footprint. If verified, 6.05 inches in 3-hours amounts to a 743-year rainfall event (or just 0.13% chance of occurrence in any given year), based on Precipitation Frequency Estimates (PFE) from NOAA Atlas 14.
Later in the evening flash flood warnings were issued for the southern Denver suburbs in the Urban Corridor, as well as portions of the Hayman-Teller burn scar in the Front Range Mountains, Palmer Ridge and Eastern Plains. A late evening, almost stationary storm over the Urban Corridor produced over 1.5 inches in Littleton in a little over an hour after 11:00 pm, as seen in the time series plot below. PFEs for this area place the rainfall total between a 10 and 25-year average recurrence interval (or between 4-10% chance of occurrence in any given year).
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.
