A Year's Worth of Rain in One Week - Colorado Flooding

The devastating flooding along the Colorado Front Range has been headline news this week. No doubt most people have seen photos and video of the flooding and damage - they are all over social media as well as the typical news sites. If you have ever doubted the power of water the images coming out of Colorado should put those doubts to rest. The flooding extends from the Fort Collins area south to the west side of Denver.  The same rivers that bring spring meltwater out of the mountains to irrigate farms and fill community reservoirs along the Front Range are now raging torrents that have washed out roads and isolated many communities.

This image shows large portions U.S. 34 washed away at the mouth of the Big Thompson canyon

While a large area has been affected by flooding, Boulder, Colorado was the epicenter for the heaviest rain. Here are some climatological facts for Boulder rainfall to help place this in perspective

Boulder's annual precipitation averages 20.68 inches, with an average of 1.68 inches in September.
For September 1-13, the U.S. Cooperative Weather Station in Boulder has received 14.74 inches of rain. This nearly three times the previous monthly September record of 5.50 inches in 1940! This is also the wettest month ever on record for Boulder. The previous record was 9.59 inches in July 1995.

Much of Colorado has been in severe drought or worse for more than a year, and Boulder and much of the area was on track for another very dry year. Through the end of August, Boulder's precipitation for the year was 12.96 inches, which placed it in the top 30 percent of driest years in Boulder.

With the precipitation through September 13th, the total precipitation for the year so far is 27.70 inches, which now makes this year the second wettest on record. The wettest year on record is 1995 with 29.43 inches. There is no question that 2013 will eclipse this mark - the only questions are by how much and when.

Not only did the rainfall so far this month destroy the previous monthly record, but the 9.08 inches recorded on September 12 shattered the precious record of 4.80 inches measured on July 31, 1919..

Source:  National Weather Service Denver/Boulder

While the U.S. Cooperative station in Boulder is the official record, rainfall totals measured by CoCoRaHS observers were just as if not more impressive. Here are the rainfall totals of 10 inches or more for the period September 9-14.

Station No.	Station Name	Total Precip	# of Reports
CO-BO-33	Boulder 3.3 SE	18.36	6
CO-BO-72	Boulder 1.3 NW	15.45	6
CO-BO-299	Boulder 3.0 S	15.29	5
CO-BO-9	Boulder 1.4 NNW	15.05	6
CO-BO-4	Boulder 2.9 S	14.79	6
CO-BO-35	Boulder 1.5 NW	14.75	6
CO-BO-14	Boulder 1.6 S	14.71	5
CO-BO-286	Boulder 3.5 S	14.56	6
CO-BO-321	Boulder 1.7 S	14.13	5
CO-BO-337	Boulder 1.6 NW	14.06	5
CO-LR-907	Livermore 10.6 W	13.95	4
CO-BO-288	Boulder 0.5 NNE	13.88	6
CO-BO-120	Boulder 3.0 E	13.80	4
CO-AD-127	Aurora 4.2 NNW	13.74	6
CO-BO-74	Boulder 5 SE	13.72	5
CO-AD-170	Aurora 4.5 NW	13.13	5
CO-BO-234	Louisville 2.5 NW	13.01	5
CO-BO-282	Boulder 4.4 S	12.99	5
CO-BO-164	Boulder 3.0 NNW	12.79	6
CO-BO-230	Boulder 6.8 WNW	12.28	5
CO-BO-219	Riverside 2.2 NE	12.15	3
CO-AR-55	Aurora 2.9 NW	12.11	4
CO-BO-349	Boulder 1.2 N	12.10	3
CO-BO-67	Boulder 4.7 E	12.00	5
CO-BO-243	Louisville 2.6 WSW	11.91	5
CO-BO-202	Ward 4.6 NE	11.67	6
CO-AR-99	Aurora 4.1 S	11.42	6
CO-BO-135	Boulder 5.4 ESE	11.13	6
CO-DN-183	Denver 5.1 ENE	11.08	5
CO-JF-365	Golden 2.1 SW	10.99	6
CO-AR-270	Aurora 0.7 WSW	10.80	6
CO-AR-262	Aurora 2.1 W	10.78	6
CO-LR-749	Drake 4.7 SSE	10.68	3
CO-AR-281	Aurora 2.4 SW	10.62	5
CO-LR-882	Loveland 12.2 W	10.54	6
CO-BO-19	Boulder 4.6 E	10.45	5
CO-JF-63	Golden 4.8 NW	10.39	6
CO-JF-279	Pinecliffe 3.1 ESE	10.27	5
CO-LR-866	Estes Park 2.2 S	10.05	6
CO-AR-264	Aurora 3.8 S	10.03	6

Forecast surface map for 12 noon MDT Sunday, September 15

It is raining along the Foothills today, and another round of showers and thunderstorms are expected tonight through Sunday. A cold front will move into northern Colorado tomorrow. Developing easterly and northeasterly winds will force moist air to be lifted along the mountains producing convection that will linger into Monday. Dry weather will finally return to Colorado as high pressure sets up over the state.

Quantitative Precipitation Forecast for the 48-hour period ending 6:00 p.m. MDT Monday, September 16.