November 19, 2023

The Olympics Mountains Can Affect the Weather in Ellensburg and Wenatchee

 The folks living on the eastern side of the Cascades might think that the Olympic Mountains have little influence on their weather....but they would be wrong.

Consider what happened today.

A Puget Sound Convergence Zone set up, producing a band of precipitation stretching from the northeast slopes of the Olympic Mountains, across Seattle and then eastward to near Wenatchee!

Just a reminder before I go on..... Puget Sound Convergence Zones are associated with westerly or northwesterly flow that is deflected around the Olympics and which converges together to the east of the Olympics.

When low-level air converges together at low levels, the air is forced to rise, producing a band of clouds and precipitation.

This morning and into the afternoon, a convergence zone formed to the east of the Olympics, creating a cloud band that stretched for many miles,with the cloud band ending near Wenatchee (see the figure below with arrows showing the beginning and end of the convergence zone cloud band).   Interestingly, it was totally clear to the north and south of the band over western Washington... a typical occurrence by the way.

There was rain..some heavy.. within the clouds band, as shown by the radar image around 1 PM.   At higher elevations there was snow.

The high-resolution UW modeling system predicted the convergence zone band and its extension across the Cascades (see below).

The Thanksgiving Forecast

It is very nice to enjoy a walk, run, or any other outdoor activity before the holiday mean.  But unfortunately, Thanksgiving is one of the climatologically wettest and stormiest days of the year in our region.

But I have some good news:  Thanksgiving Day 2023 will be dry.   It will be partly cloudy with highs in the upper 40s over western Washington.

Thursday afternoon, a ridge of high pressure will have built over the eastern Pacific (see the weather map at 500 hPa..about 18000 ft forecast for 1 PM Thursday).  A cool, dry pattern.  I would expect low clouds in the AM, breaking up in the afternoon.  Perhaps you can get enough exercise to deserve a little more turkey or whatever you enjoy...

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