End in Sight to Historic Colorado Flooding

By , Expert Senior Meteorologist
September 18, 2013; 6:16 AM ET
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Some good news is in store for flood-ravaged Colorado this week. The weather pattern responsible for the tremendous and deadly flooding is moving away.

The mechanism responsible for bringing once-in-100-year rainfall rates to parts of Colorado was breaking off this week. In some cases, the rainfall rates exceeded a 100-year event.

Boulder, Colo., has received nearly 10 inches of rain since Sept. 8, 2013, which is 26 times the normal rainfall for the past week. Some locations have received nearly double this amount.

While there will still be spotty drenching thunderstorms over central Colorado this week, the activity will be far less persistent and much less concentrated compared to last week, thanks to dry air filtering in from the West.

The spotty storms can still cause incidents of flash flooding, but most streams and rivers over Colorado will recede over time this week. However, the runoff will work downstream into the other rivers over the Plains, such as the Platte River in Nebraska, where some areas could face record flooding.

While it will take a couple of days, incidents of flash flooding over Colorado become more isolated in nature as the week progresses.

Even though the rain will diminish, many roads will remain closed due to damage from washouts and debris flows.

According to Chief Meteorologist Elliot Abrams, "The persistent flow of tropical moisture is shifting away as a large area of high pressure moves farther to the east."

A band of tropical moisture over the interior West in recent weeks was being squeezed over Colorado last week. Meanwhile, circulation around high pressure over the Midwest was forcing additional moist air uphill over the Front Range and foothills of the Rockies.

"It is possible that a lack of organized tropical systems moving into the South Central and Southeastern United States so far this season may be partially to blame for the surge of heavy rain over the Rockies," Abrams said.

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Large tropical storms and hurricanes tend to draw in moisture, near their center. The air becomes drier some distance away, suppressing rainfall and thunderstorms.

Moving forward, another zone of heavy rainfall will be setting up late this week into this weekend. This time, however, the rain will be centered over Texas and the southern Plains.

While much of the South Central U.S. needs rainfall, there is the potential for an excessive amount in some locations that could lead to flooding.

According to the National Weather Service in Boulder Colo., multiple rainfall records have been set at Boulder, as a result of the week-long deluge. As of Monday, 29.65 inches of rain fell for 2013 thus far, breaking the old record of 29.43 inches set in 1995. The rain thus far in September, which has tallied 16.69 inches, broke the rainfall record for any month of 9.59 inches set in May 1995. The old monthly rainfall for September of 5.50 inches was shattered. Records at the Boulder observation site date back to 1893.

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