SPM 05-29-2018: Atmospheric Fireworks and Heavy Rainfall for Memorial Day

Issue Date: Tuesday, May 29, 2018
Issue Time: 10:15AM MDT

Summary:

Active Memorial Day for northeast Colorado and the Urban Corridor. Thunderstorms began to fire over the mountains by early afternoon, but it wasn’t until the late afternoon that they began to move into the Urban Corridor. There was several small hail reports (up to 1 inch in diameter) over the metro area with the line of convection that moved through around 5PM. ALERT rainfall gages recorded 0.79 inches just north of Castle Pines and in Aurora for the 30 minute duration. Most other stations in the metro area recorded between 0.30-0.50 inches of rain.

Another set of storms fired along a frontal/convergence boundary further over the eastern plains. High moisture and favorable dynamics allowed numerous severe thunderstorms to form. There were several tornado and land spout reports over Kit Carson and Washington Counties, as well as in Morgan and Weld Counties. The highlight of the day was twin tornadoes in northern Kit Carson County! There was also a hail report of 1.75 inches in the same area. Overnight, thunderstorms regenerated to the west along a frontal boundary giving Kit Carson County some very heavy rainfall for the second night in a row. A CoCoRaHS station reported 3.15 inches of rainfall north of Bethune and a mesonet station reported 3.72 inches over Flagler. Radar estimates were up to 5.2 inches for the 6-hour period. If correct, this is approximately a 1 in 200 year rainfall event, and this also puts (localized) 48-hour totals at 6.7 inches!

Elsewhere across the state, the Northern Mountains and Northwest Slope got some thunderstorm activity yesterday. A SNOTEL site in Willow Park measured 0.50 inches of rain. Max 1-hour rain rates under the cores yesterday were estimated at 0.50 inches with 24-hour totals up to 1 inch. The showers picked up again early this morning on the backside of the trough.

There were two flash flood warnings issued yesterday. One over the Beaver Creek burn scar and the other over Kit Carson/Yuma County; however, there were no reports of flooding as of Tuesday morning. For rainfall estimates over your area, 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 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.