Record Breaking Streamflows

Flooded Clark Fork
May 2, 2018

As is clearly evident to anyone who has crossed over the Clark Fork River lately, our area streams are running high. So high in fact, that they are setting streamflow records for this time of the year. Following a winter of above average snowpack (that rivaled even 1997 & 2011) western Montana experienced near record warmth last week sending a large pulse of snowmelt raging downstream. A weekend of wet weather added to the runoff and prompted flood advisories throughout the region.

How high were the flows when compared to other years? The streamflow event was truly record breaking for late April and early May. Streams in our area typically see their highest flows from late May-early June. Below is a short list of some of the local stream gages that experienced record flows for the date of April 30th.

USGS Gage Location Flow on May 1st, 2018 (cfs) Previous record flow for May 1st (cfs)
Clark Fork near Drummond 3,480 1,700 (2012)
Little Blackfoot near Garrison 1,540 785 (1981)
Clark Fork at Turah 7,130 4,010 (2012)
Clark Fork below Missoula 29,400 25,600 (1965)
Blackfoot near Bonner 14,200 8,250 (1965)


In some locations the flows were not only historic for early May, they were some of the highest streamflow values measured in over 5 years. The low and mid elevation snowmelt in the Blackfoot Basin last week sent streamflow values in Bonner soaring to 14,500 cfs (their highest mark since 2011).

Annual Peak Streamflow for the Blackfoot River near Bonner (2011-2017)
Water Year Date Streamflow (cfs)
2011 Jun. 09, 2011 17,100
2012 Apr. 27, 2012 12,200
2013 May 14, 2013 10,200
2014 May 27, 2014 10,800
2015 Jun. 03, 2015 3,940
2016 Apr. 25, 2016 4,480
2017 May 13, 2017 9,100


Although there was a significant amount of snowpack that melted last week we still have a lot of snow left in the mountains and are still sitting above average for this time of year. With warmer weather forecast for later this week we should expect to see another bump in flows to follow.


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