Issue Date: 8/12/2015
Issue Time: 9:05AM
Summary:
Precipitable water values were incredibly high on the Tuesday, ranging from 1.05 to 1.45 inches across the state. Though atmospheric dynamics were not overly favorable, there was enough instability to generate scattered to even widespread thunderstorms mainly over the higher terrain and areas adjacent to the mountains. Storm coverage was highest over the Southwest Slope, Raton Ridge, Palmer Ridge and the Urban Corridor. Some of the more impressive rain totals were:
- 4 Urban Drainage and Flood Control District ALERT gages picked up 1.0 to 1.1 inches in less than one hour. The highest 5 minute rain totals were ~0.45 inches in Aurora (this translates to an hourly rain rate of 5.4 inches!)
- An observer in Fremont County recorded 1.24 inches in about 25 minutes
- In the evening, a broken line of heavy rainfall produced a quick +/- 1 inch of rain in Ouray and San Miguel counties
Overall, however, one limiting factor to rain accumulation was that the downpours only lasted 30-45 minutes. In addition to heavy rainfall, a few hail reports were received: one in Fremont County of 1 inch hail, and another in Montrose County of “slightly larger than pea sized hail”.
Meanwhile, a robust Denver Cyclone was observed during the afternoon north of the Palmer Ridge. Such a circulation is typically characterized by a very sharp wind shift right along I-25 from Denver northward. To the west downsloping and drier northwesterly winds usually limit heavy rainfall chances. To the east, extra convergence, and vorticity (spin) can result in a flare-up of heavy rainfall producing storms, hail and even tornadoes. Such was the case yesterday. Around 4pm, a funnel was spotted over Aurora. In the map below, we show yesterday after surface observations (from the MesoWest archive), showing the distinct wind shift, which was consistent with the funnel’s location. It is also interesting to note that the heavy rainfall noted above occurred just east of this boundary.
No official flooding reports were received yesterday. For an estimate of 24-hour rainfall that occurred in your area, please check out our radar based map below.
