November 18, 2012

World Class Rain Shadow

We can be proud of living in the wettest portion of the lower 48 states as well as the area of the world's greatest annual snowfall (Mt. Baker).   But we are also world class in precipitation contrasts.
Today is a good example. Here are precipitation measurements over the 24-h ending 9 PM Sunday evening.  On the southern and southeastern sides of the Olympics they got hit by 2 to 3 inches of rain, while virtually nothing fell on much Lopez and San Juan Island.  Not much more on northern Whidbey.  In fact, the rain shadow extended as far a Bellingham!  There is some variability in the downstream extent of Olympic rainshadows and this is on the big side.

Another view of the rainshadow is the "storm total" precipitation (roughly the last two days) from the Camano Is. radar (see below).  The rain shadow...a roughly circular region downstream of the clear evident, as is the heavy precipitation southeast of the Olympics

For the next 24-h it looks like the heaviest rain will hit SW Washington, the southern WA Cascades, and NW Oregon (see graphic), although it will be respectably wet everywhere.

The NWS River Forecast Center has put out flood warnings at a number of locations (see red dots on the map below):


  1. Looking at the map of rainfall totals there are also some strange anomalies visible, especially in the South Sound region and the foothills of the Cascades - high totals next to very low totals. Wonder what is going on there.

    But we had a mostly dry day yesterday in the islands. Raining moderately this morning.

  2. Yep, Sunday brought virtually no moisture north of Bellingham at the Canadian border. Spent the afternoon outside, in fact. Heavy rain here now (Monday morning), but nothing like some other areas.


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