Friday, July 5, 2013

Canyon Closure

The good news is that the triple digit streak ended yesterday.  The bad news is that Little Cottonwood Canyon is closed this morning.  Yup, no first tracks today.

Wait a minute.  It's July!  In this instance, the culprits for the canyon closure are rockslides produced by extremely heavy precipitation overnight.  Apparently Mother Nature wanted to put on her own fireworks show.  KSL reports that snowplows are out removing the debris.

Observations from the Alta-Base observing site suggest an accumulation of 1.15 inches in the one-hour period ending at 0900 UTC (0300 MDT).  Rocks were reported on the road at about 0230 MDT.

Hydrographs along Little Cottonwood Creek show a dramatic spike in streamflow during this period, with a volume exceeding that during the spring runoff.
Source: NWS
Impressive stuff.

Thanks to Trevor Alcott for his input on this post.


  1. This is the best, most comprehensive report I have seen on last night's storm! I live on Little Cottonwood Creek at 1300 east and we woke to evidence of minor flooding beyond the creek's banks.

  2. Would last night's system be classified as an MCS? It sure looked like it to me. In any case, the heavy cells that caused this flooding developed as a strong outflow boundary reached the Wasatch Range. I saw some very frequent lightning (approaching 1 flash/sec) from a cell over in that vicinity around 1:30 or 2:00 a.m., probably the one that was responsible for the flash flood.