The West Comes Unglued!

Hydrometeorological insanity prevails over the western U.S. as the monsoon goes out with a bang rather than a whimper.  A good rule of thumb for meteorology is to beware when the atmosphere is in outlier mode, and that is certainly the case this week as a monsoon trough amplified over the southwest and ridging built over the northwest, leading to a pronounced high-over-low pattern over western North America.  These features, along with the abundant moisture and the development of crest-level easterly to southeasterly flow across much of Utah and Colorado can be seen in the 0600 UTC (0000 MDT) analysis for last night.

0600 UTC (0000 MDT) 12 September 2013 Analysis of 700-mb geopotential height (contours), wind (barbs), and relative humidity (color filled at 10% increments beginning at 70%).

Let's start in southern Utah where a flood warning now extends over a huge chunk of terrain from the high plateaus running down the central part of the state to the Colorado and Green Rivers to the east.

Source: NWS

Reports to the NWS for Monday morning through yesterday evening include 3.95 inches at Buck Flat on the Aquarius Plateau north of Escalante, 2.85 inches in Escalante, 2.73 inches at Bryce Canyon, 2.13 inches at Bullfrog Marina, 2.95 inches in Zion National Park, 2.91 inches in Capitol Reef National Park, and 2.77 inches in Caineville.  To put those numbers into perspective, the average September rainfall at most of those sites varies from about 0.66 to 1.25 inches.  

The net impact of all this rain has been tremendous stream flows.  The Dirty Devil near Hanksville topped out at almost 10,000 cubic feet per second (cfs).  Note that on Sunday, the flow was around 30 cfs.  

Source: USGS

The hydrology of the western US is snow dominated, but in this case, all of this rain and runoff appears to be having a small but measurable impact on reservoir storage, with a slight uptake in the level of Lake Powell.

Source: http://lakepowell.water-data.com

And it doesn't stop there.  Incredible rains hit the foothills above Boulder, Colorado last night with more than 6 inches observed at the National Center for Atmospheric Research.

Source: NCAR

At least 1 is dead and at the University of Colorado some students have been evacuated and classes have been cancelled.  

All of this and I haven't even discussed the modest downslope wind event along some portions of the Wasatch Front (gusts to 47 mph at Centerville and 45 mph at the University of Utah).

Yup, this is quite an event.  And it isn't over yet.