In the weeks leading up to the flash flood at Fort Collins, the Colorado Front Range region had experienced six weeks of predominantly hot and very dry weather. However, in the last week of July the humidity increased as moist tropical air drifted into the state from the south. On July 27, a strong cold front moved into the region from the north, triggering numerous storms over northern Colorado in the late afternoon. Storms on July 27 were small and localized, but brought torrents of rain to areas in the lower foothills just west and northwest of Fort Collins. The city of Fort Collins itself only got a light shower of rain. After dark, the moist southeasterly winds strengthened and rain continued steadily into the next morning. Along the base of the foothills it poured all morning on July 28, yet the city of Fort Collins was merely cloudy and cool morning. From the north end of Horsetooth Reservoir to the northwest of Laporte, 6-10 inches had fallen by midday on July 28. In addition, areas west and southwest of Fort Collins received 2-4 inches of rain. The rains abated during the afternoon, however high-humidity air continued in place. Around 6 p.m., heavy showers concentrated at the base of the foothills began again. Just as the rains began to diminish east and southeast of the city, the rain began to increase in intensity over the western portions of Fort Collins. Between 8:30 and 10 p.m., Fort Collins experienced the heaviest sustained rainfall on record over a urbanized area in Colorado. The rainfall set records for the largest 1-day, 3-hour, and 6-hour precipitation totals for the gage located on the Colorado State University campus, even though the storm was not centered over the campus. Rainfall rates occasionally reached 6 inches per hour over southwest Fort Collins. Thankfully the rains ended abruptly between 10 and 10:30 p.m. "Overall, 10 to 14.5 inches of rain fell over an approximately 30-hour period in a band extending along the base of the foothills from southwest Fort Collins northward to northwest of Laporte"

KUSA