June 18, 2018

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.


  1. The humidity has been running a little higher than normal in these parts too. Temperatures in the 80s with dew points in the 50s is near perfection. It’s been fun to see some cumulus congestus in the afternoons with this weak instability.

  2. Perfection in the PNW is actually 54F!

  3. It's only been five days since we had rain in Glacier, WA - and the farmers in the valley are loving it (the axiom about "making hay while the sun shines" is spot-on). The Cedar Waxwings were back only two days earlier than last year, and a very robust crop of butterflies are browsing flowers/flowerbeds. We have had some days in the mid-to-high 80's, but I've been keeping track of overnight lows for a year, and we have yet to have an overnight low reach 60'F, which is actually rather interesting to me as snow has remained on some pockets of shade on mountain ridges (about 4,000 ft) without melting-out entirely for a couple of years. Given the lows, I expect that the Mt Baker glaciers are stable (if not advancing), but don't know for certain. The DOT crews say that digging out Artist's Point at the ski area is a big job this year; snow depth was 25 feet when they started.

    All that said - it's far more an "average" year than a dry one. Short warm spells - wonderful, and oh-so welcome.


Please make sure your comments are civil. Name calling and personal attacks are not appropriate.

Rain without Clouds, the Upcoming Cooling, and Strong Leeside Winds: All in My New Podcast

The radar image this morning at 5:30 AM showed rain...some heavy... offshore. As shown in the satellite image at the same time, much of that...