Warm West, Cool East in the Pacific Northwest

Today was one of those unusual late spring/summer days when it was warmer over the interior of western Washington than over portions of eastern Washington.  The highs today (shown below) were in the upper 80s in the central and southern Sound and around Vancouver BC, with 90s over the western slopes of the north Cascades, while Spokane and vicinity were in the mid-70s.  Go eastward into Idaho and western Montana and 50s-60s dominated.  Downright chilly.

The reason for this contrast is apparent in the upper level (500 hPa, about 18,000 ft) weather map for 11 AM today, shown below.  A ridge of high pressure is offshore, while an usually strong low center is position over southern Idaho.  The high pressure provides warm, sinking air in the middle troposphere, and the combination of ridge and trough resulted in northeasterly flow aloft above the Cascades--which contributes to warming over the western slopes.

The low center was associated with cool temperatures and extensive clouds from eastern WA to the east, with substantial precipitation.   The MODIS visible satellite image around noon shows the clouds associated with the upper low--you can see the circular distortion of the clouds.
Along the coast, marine stratus hugged the shore.

A radar image during mid-afternoon shows the precipitation extending into far eastern Washington and northern Oregon.

The ridge will move eastward during the next few days and western Washington will have two more warm days, marine air pushing in on Thursday.  Then for the next week we will enjoy typical late June weather, with some clouds and highs in the lower 70s.    Perfection.



from Cliff Mass Weather and Climate Blog https://ift.tt/2yktKC0