Heavy Precipitation from the Wrong Direction

Yesterday, a number of locations, including the north Cascades, northeastern Washington, northern Idaho, and southern BC have received some of the heaviest precipitation they have seen in a long while, with some places getting 2-5 inches over 24 h.  Even Puget Sound folks got a respectable dampening.  And a lot of the moisture came from an unaccustomed direction...from the east rather than off the Pacific.

Here are the 24-h totals ending 8 PM Thursday for western Washington. Some folks on the western slopes of the north Cascades got over 3 inches, and .5 to 1 inch totals were widespread.  But only a few hundredths over the southern Sound.

 Taking a regional view you can see another precipitation hotspot...the eastern slopes of the Rockies, where some rain gauges were filled by over 4 inches of rain.  Lots of flooding a road washouts were reported there.

A closer view is available from a Seattle Rainwatch graph for a similar period, which shows values of 2-4 inches over the western slopes.

The WRF model 24-h precipitation total forecast ending 5 AM today (Friday) shows 2-5 inches over the north Cascades...a very good forecast.

This event was a bit complicated.  An upper level (500 hPa) low center was centered over northern Idaho (see figure) and it brought "wrap around" moisture at mid and upper level across southern BC and Alberta and then down over Washington.  You can track bands of enhanced clouds and precipitation moving around this low, approaching us from the northeast.

At the same time, in the lower atmosphere (see figure below at 850 hPa, roughly 5000 ft) the flow was northwesterly, pushing Pacific moisture up against the terrain.  This dual influx of moisture, and the lift associated with the upper low, brought copious rain to parts of the region.

For me, this rain is all good...my garden was dry and the rain will save me big bucks on my water bills. With a half-inch at least and no heat wave in sight, no watering will be necessary for dhttp://www.summer.washington.edu/summer/enroll/ays.

One final note, the models are  in agreement that Saturday looks very nice....sun and low to mid 70s.    So take advantage of it.  Conditions will deteriorate later on Sunday, but we just may squeak by that day as well.

One final thing...today is the first day of astronomical summer.  BUT NOT METEOROLOGICAL SUMMER.    Everyone knows that starts on July 12th!

For those interested, my dept is giving a course on global warming this summer....starts on Tuesday:

TM S 111 Global Warming: Understanding the Issues (5)

Includes a broad overview of the science of global warming. Discusses the causes, evidence, future projections, societal and environmental impacts, and potential solutions. Introduces the debate on global warming with a focus on scientific issues.

 Enrollment info here.