Colorado’s biggest storms can happen anytime, CU-Boulder-NOAA study finds
5/20/2015
Kelly Mahoney
People tend to think of weather in terms of seasons being drier or wetter
than others, but according to a new study extreme precipitation events of rain,
hail or snow can happen anywhere and anytime of the year in Colorado, says
atmospheric scientist Kelly Mahoney, lead author of the study.
CUT 1 “Colorado’s extreme precipitation can occur in any season and, really,
at all elevations across the state. So trying to assign extreme events to a
certain season isn’t necessarily a good thing to do here in Colorado. (:12) Very
big storms can happen during any season and for those reasons it’s important
for decision makers to understand that impacts such as flooding are a nearly
year-round risk across the state.” (:24)
Mahoney is a scientist with the Cooperative Institute for Research in
Environmental Science, a partnership between CU-Boulder and NOAA.
She says the study was done to improve the understanding of the state’s
extreme event climatology.
CUT 2 “Because even in regions where you think you have a strong seasonal
signal the data actually show that the heavy precipitation events can happen
outside of this sort of expected time. (:10) And that sort of logic is what we
were kind of speaking to in this paper. That we really don’t obey the law of
averages in Colorado when you come to the extremes.” (:18)
Researchers found that the central mountains, along the crest of the
Continental Divide, defied assumptions that the biggest storm events would
happen during the winter, says Mahoney.
CUT 3 “Along the spine of the Continental Divide there’s really no clear
pattern. The common belief—based on sort of historical averages—is that
winter storms at the state’s highest elevations will produce big snow events.
And that’s not necessarily what we found. (:15) Instead, high-elevation intense
events have occurred during all months of the year there – again in those
one-day totals - including the summer, which is interesting, because the
precipitation at that time of the year is more likely to be rain and therefore
more of a flood risk.” (:29)
And the September 2013 flooding along the Front Range, says Mahoney, is
more evidence that big storms can happen out of season.
CUT 4 “After the September 2013 floods the sort of knee jerk reaction from a
lot of people was, ‘Whoa! This happened in September. September is not a
wet month for the Front Range.’ And that’s true when you look at seasonal
averages. (:13) However, when you look at those precipitation ingredients
coming together, September actually makes a lot of sense for our heavy oneday totals. So while it wasn’t typical, it certainly wasn’t unprecedented. There
have been other past events in September.” (:28)
For the study, researchers selected precipitation data from 130 weather
observation stations throughout Colorado that had a record of at least 30
years of daily data between 1950 and 2010. At each station, the 10 largest
daily rain totals were identified and used to characterize Colorado’s extreme
precipitation by season.
The study also includes researchers from Scripps Institution of Oceanography,
Colorado State University and the U.S. Geological Survey.
For more detailed information on the study go to
-CU-