SPM 08-22-2017: Slow Moving Storms Increase Flood Risk

Issue Date: Tuesday, August 22, 2017
Issue Time: 10:30AM MDT


Monsoon moisture was on the increase again yesterday. The upper-level low pressure system over California paired with a broad high pressure center over Texas helped advect more moist air into the state. Storms favored the San Juan Mountains, southern Front Range and Southeast Mountains for the stronger thunderstorms. Slow steering winds under the ridge as well as Precipitable Water (PW) values near 0.8 inches helped increase the precipitation totals from the prior two days.

Over La Plata County, there was a storm report of heavy rain near Durango with 1.24 inches falling in 30-minutes. A SNOTEL site in the Southern San Juan Mountains near this area recorded 1.4 inches with 0.8 inches falling in an hour. Over the Front Range and Southeast Mountains, a CoCoRaHS station near Westcliffe recorded 0.7 inches. There were two Flash Flood Warnings over the Junkins and Hayden Pass Burn Scars, but no flooding was reported as of this morning. These burn scars will need to be monitored closely throughout the week as daily rainfall is expected. As the storms slowly moved south, a USGS precipitation gage reached 0.63 inches over Delhi, CO with radar total estimates just over 1.5 inches. There were no reports of flooding yesterday.

For the solar eclipse yesterday, mostly clear skies were found around the state with exception to a few places over the Southeast Plains. As many of you probably noticed, temperatures dropped off quite a bit during the event. The decrease in irradiance caused as much as a 5F drop in temperature during the hour of the eclipse. The temperatures quickly rebounded within the next hour.

To see how much rain fell in your area, scroll down 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 6AM of the date shown in the bottom right corner. Also shown optionally are fire burn areas since 2012. The home button in the top left corner resets the map to the original zoom.

Note: We have identified a possible underestimation in QPE over the southwest part of the state. We are working to on this issue, and will provide an update as soon as possible.