This Storm and Flooding Similar to June, 1965

Let's get a look at the scale and area affected by heavy rainfall this week.

This map shows the area and the many rivers, creeks, towns and counties where the most severe flooding has happened in the past week. Flooding occurred over a much larger area in the state last week including Colorado Springs and the west slope. The upslope weather pattern and rainfall amounts this week are similar to the week of June 14-20, 1965.  The difference is that in 1965, the most intense rainfall was centered more over the eastern plains and further south, it extended all the way to the southern border flooding both the South Platte and Arkansas River basins. Here is a summary of what happened in 1965 by NCAR.  It is quite lengthy but if you read it, the story is similar to what happened this week - rain over much of the state with intense storms that developed in different places throughout the week causing severe flooding.  Southern Douglas County had an incredible 14 inches of rain in 4 hours on June 16, 1965 that caused Plum Creek's stream flow to increase 1,000-fold from 150 cfs to 154,000 cfs in 3 hours! 14 inches in 4 hours is close to the rainfall intensity that produced the 1976 Thompson Canyon disaster that killed 144 people. Rainfall intensity this week was much lower, with 12 inches in 19 hours in the Boulder area. Boulder Creek this week saw increased stream flow of 150 cfs to about 5,000 cfs, or about a 30-fold increase.

The June, 1965 flood was the most damaging in Colorado history and considered to be one of the worst floods ever in the US. Damages were mostly in the Denver area at over $3 billion in today's dollars. This week's flood may take over the #1 spot when it's all said and done. Boulder County has a preliminary estimate of $150 million just to repair 100 to 150 miles of road and 20 to 30 bridges. The roads up Big Thompson Canyon and along the St. Vrain upstream of Lyons in Larimer County appear to be washed out and there are thousands of homes and businesses that have sustained serious flood damage.

This week was bad, and a rare storm event, but not unprecedented for the Front Range.