Saturday, September 14, 2013

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 NameTotal Precip# of Reports
 CO-BO-33 Boulder 3.3 SE18.366
 CO-BO-72 Boulder 1.3 NW15.456
 CO-BO-299 Boulder 3.0 S15.295
 CO-BO-9 Boulder 1.4 NNW15.056
 CO-BO-4 Boulder 2.9 S14.796
 CO-BO-35 Boulder 1.5 NW14.756
 CO-BO-14 Boulder 1.6 S14.715
 CO-BO-286 Boulder 3.5 S14.566
 CO-BO-321 Boulder 1.7 S14.135
 CO-BO-337 Boulder 1.6 NW14.065
 CO-LR-907 Livermore 10.6 W13.954
 CO-BO-288 Boulder 0.5 NNE13.886
 CO-BO-120 Boulder 3.0 E13.804
 CO-AD-127 Aurora 4.2 NNW13.746
 CO-BO-74 Boulder 5 SE13.725
 CO-AD-170 Aurora 4.5 NW13.135
 CO-BO-234 Louisville 2.5 NW13.015
 CO-BO-282 Boulder 4.4 S12.995
 CO-BO-164 Boulder 3.0 NNW12.796
 CO-BO-230 Boulder 6.8 WNW12.285
 CO-BO-219 Riverside 2.2 NE12.153
 CO-AR-55 Aurora 2.9 NW12.114
 CO-BO-349 Boulder 1.2 N12.103
 CO-BO-67 Boulder 4.7 E12.005
 CO-BO-243 Louisville 2.6 WSW11.915
 CO-BO-202 Ward 4.6 NE11.676
 CO-AR-99 Aurora 4.1 S11.426
 CO-BO-135 Boulder 5.4 ESE11.136
 CO-DN-183 Denver 5.1 ENE11.085
 CO-JF-365 Golden 2.1 SW10.996
 CO-AR-270 Aurora 0.7 WSW10.806
 CO-AR-262 Aurora 2.1 W10.786
 CO-LR-749 Drake 4.7 SSE10.683
 CO-AR-281 Aurora 2.4 SW10.625
 CO-LR-882 Loveland 12.2 W10.546
 CO-BO-19 Boulder 4.6 E10.455
 CO-JF-63 Golden 4.8 NW10.396
 CO-JF-279 Pinecliffe 3.1 ESE10.275
 CO-LR-866 Estes Park 2.2 S10.056
 CO-AR-264 Aurora 3.8 S10.036

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.

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