SPM 09-12-2019: Widespread Rainfall and Thunderstorms as the Fall-like Trough Moved Across the State

Issue Date: Thursday, September 12th, 2019
Issue Time: 9:42AM MDT


The main axis of the trough slid through the state yesterday, which started showers and thunderstorms early over western Colorado. The most measurable rain was to the north where better moisture was located. Lower 1-hour rain rates were realized due to lack of instability, but persistent showers allowed for some higher totals over the Flat Tops and Northern Mountains. MetStorm indicates just over 0.5 inches fell over the area with some lighter rain over the entire Northwest Slope. This is very much needed with drought conditions quickly worsening. Observations were as high as 0.45 inches over central Routt County with a CoCoRaHS over Rangely, CO recording the same. A RAWS site between Oil Spring Mountain Wilderness Area and Rangely recorded 0.53 inches. Further south, totals dropped off a bit. North of Durango 0.14 inches were recorded near the 416 burn area at a RAWS station, and a CoCoRaHS recorded 0.25 inches for the same area. Stronger thunderstorms also produced some hail (1 inch near Silt) and gusty winds (shingles were blown off a roof near Silt). With the jet overhead, non-thunderstorm wind gusts were also reported in the 45-55 mph range.

Daytime heating allowed more instability to build as the trough and cold front approached eastern Colorado. A Severe Thunderstorm Watch was issued for the northeast quadrant of the state during the late afternoon/early evening. Severe Thunderstorms produced some wild hail with the freezing level starting to drop. Hail up to 1.75 inches was reported over the far Northeast Plains with hail up to 1.5 inches in Greeley and 1.25 inches near Boulder. As forecast, storms also produced some strong winds with a gust of 61mph measured in Logan County near Crook. As far as rainfall totals, an ALERT station near Longmont recorded 0.25 inches. Up to 0.46 inches fell over the High Park burn area, but flooding was not report. A CoCoRaHS station outside of Greeley in Kersey had 0.63 inches for the 24-hour period. MetStorm indicates up to 1 inch fell in the storm cores with max 1-hour rain rates just under 0.75 inches. Weaker thunderstorms were also present over Kiowa and Cheyenne County that formed along the surface low’s convergence boundary. Hail (up to 1.5 inches) was reported with totals as high as 0.5 inches.

Flooding was not reported with the faster storm motions. To see estimated precipitation totals 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 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.

Note: The 24-hour, 48-hour and 72-hour total precipitation do not contain bias corrections today due to errors in the CoCoRaHS data. This means there may be underestimations in QPE over the southwest and southeast corners of the state.