SPM 10-03-2018: Rosa Brings a Surge of Late Season Subtropical Moisture to Western Colorado

Issue Date: Wednesday, October 3rd, 2018
Issue Time: 09:55 AM MDT


The main axis of subtropical moisture moved into western Colorado yesterday, which brought beneficial, widespread rainfall to the western slope. Rainfall began during the early morning hours over the San Juan and Central Mountains and moved north throughout the day. As storms moved to the north, they became more isolated in nature and higher totals were confined to the mountains. A second set of showers moved into the southwest corner during the evening hours, but limited instability kept storms more isolated and less convective in nature than forecast. Storm motion was fairly quick and with more stratiform rainfall, rather than convective rainfall, the ground was able to soak up most of the moisture.

The western slope is experiencing either extreme or exceptional drought conditions, so yesterday’s boost of moisture helped make some headway with the drought after a very dry September. Totals over western Colorado were generally in the 0.25 to 0.5 inch range with higher totals over steeper terrains. Radar rainfall estimates were just over 1.5 inches in northern Delta County with totals just over 1 inch in the San Juan Mountains. The largest CoCoRaHS observation for the day was over Gunnison County near Crested Butte, which was 1.32 inches. The Columbus Basin SNOTEL site near Lewis Mountain (north of Hesperus, CO) recorded 1.9 inches for the 24-hour period. Thankfully, 1-hour rain rates yesterday were less than 0.5 inches, so there was not much of a flood threat even for recent burn scars. Flooding was not reported on Tuesday.

To see how much rain fell over your neighborhood yesterday, 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 fire burn areas (post 2012), which are updated throughout the season to include new burn areas. The home button in the top left corner resets the map to the original zoom.