Monday, July 30, 2012

Partly Juicy with a Chance of Flash Floods

As anticipated (see previous post), an impressive slug of monsoon moisture drapes from the lower Colorado basin to southeastern Utah this morning, with precipitable water > 50 mm (2.5 inches) near Yuma, AZ and environs.

Check out the morning (1200 UTC) sounding from Flagstaff, AZ, which is saturated or nearly saturated from 700 to 300 mb.

Things are quiet now, but with daytime heating, slow-moving thunderstorms could erupt and produce some impressive gully washers in this area.  The NWS has a flash flood watch (area of green below) in place from noon today through this evening for an area from south of Lake Havasu to just south of Price, UT, including Zion National Park, Capital Reef National Park, Grand Staircase–Escalante National Monument, and the San Rafael Swell.

A hazardous weather outlook covers much of southern Nevada, southeast California, and northern and western Arizona where thunderstorms and isolated flash flooding is possible.

Of concern is flash flooding in dry washes and burn scars from recent wild fires.  This is not a day to be canyoneering.  There's several great videos of flash floods on the Colorado Plateau illustrating just how dangerous it can be during these floods.  Here's one by Nancy Schutt that illustrates the dramatic changes that occurred one day in Capital Reef's Grand Wash.  They were fortunate to be able to get to higher ground.

I've always wanted to storm chase on the Colorado Plateau on a day like this, viewing these types of floods from a safe place.  Alas, there is real work to do today.  

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