SPM 06-26-2020: Storms Produce Strong Wind Gusts and Brief, Heavy Rainfall

Issue Date: Friday, June 26th, 2020
Issue Time: 10:20AM MDT

Summary:

Storm coverage increased yesterday as some mid-level dynamics and moderate mid-level moisture moved into the state. With the majority of the moisture in the mid to upper levels of the atmosphere, there was a large, dry boundary layer (lower level of the atmosphere). This promoted strong outflow winds from storms and some evaporation of rainfall before it reach the surface – those actually go hand in hand. Additionally, storm movement was a bit quicker and pulse-like storms prevented heavy rainfall for lasting more than a few minutes. So once again, QPE from Stage IV, MRMS, and MetStrom looked a little bit different.

It looks like MRMS/Stage IV slightly overestimated totals and MetStrom slightly underestimated totals. This is typically what we’ve seen from these products lately on marginal rainfall days. This was further examined by looking at a WxUnderground station in Genoa, CO where a storm core passed directly overhead. The station recorded 0.51 inches, but and MRMS showed 0.75 inches. Stage IV was slightly lower, but still overestimated. Looking at MetStorm below, it looks like bias corrected 24-hour value was slightly underestimated. Totals from MetStorm were closer to reality over that area without the bias correction (see max 2-hr). There are still plenty of reasons that the bias correction has helped improve MetStorm, so the pros outweigh the cons the majority of the time. QPE is not a perfect science, but this illustrates that the truth is often a blend of the solutions, the dry sub-layer can cause issues in estimations over CO, and the importance of rainfall gages to calibrate the QPE. Please consider joining the CoCoRaHS network if you live in a rural area – https://www.cocorahs.org/application.aspx

Anyway, back to the storms yesterday. There several wind gusts reported over the northern portion of the state (especially west). Gusts from outflow boundaries were recorded between 45 and 65 mph. A strong thunderstorm over Grand Junction produced minor street flooding where QPE was estimated around 0.25 inches. CoCoRaHS in the area of flooding showed between 0.15 and 0.20 inches. Hail in Prowers County reached up to 1.25 inches in diameter. NWS Pueblo issued a Flash Flood Warning for this storm where radar indicated up to 2 inches of rain and MRMS estimated 2.50 inches. QPE was estimated closer to a half inch, which was confirmed by another range gage in the area that recorded 0.26 inches. Flash Flood Warnings were also issued for the Spring Creek and Decker burn area. Rain totals up to a half inch were estimated by MetStorm, but flooding was not reported as of this morning.

For precipitation estimates in your neighborhood over the last 24 to 72-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.