Low Clouds over the Pacific

Perhaps the most important characteristic of June weather over the west side of the Northwest is the persistent low-level clouds--the cause of the annual June gloom or Junuary, as some wits like to call it.

There is a reason for the low clouds: -the NE Pacific is full of them this time of the year. Look at the visible satellite picture above (from Friday at 12:30 PM PDT). Most of the Pacific is covered in clouds. In fact, more of the Pacific has cloud cover now than during the middle of the winter! Nearly all of these clouds are stratus and stratocumulus, associated with some drizzle at best.

Even coastal California gets hit by this stuff--in fact it is worse for them than for us. Never plan a summer vacation in Monterrey if you want lots of sun.

Why so many clouds? Ironically, it has to do with high pressure. During the spring and early summer the east Pacific anticyclone (high pressure area) strengthens and moves northward and the Aleutian low attenuates. Below is the sea level pressure for yesterday at 5 PM....you can get a feel for the situation. High pressure is associated with weaker winds and sinking air.

Sinking is strongest aloft and weakens towards the surface (the air can't move through the surface). Sinking causes warming, so there is more warming aloft...this produces a stable situation with little mixing (inversion or near inversion conditions). Air near the surface thus gets moister and moisture without the mixing down of dry air aloft. Another factor is warm air moving off Asia and Alaska....as the air cools down over the warm it eventually can cool to saturation.

The result of both mechanisms: lots of low marine clouds. With higher pressure offshore (associated with the high) and lower pressure inland, the low clouds are pushed into the western lowlands. Generally you can escape them by traveling east of the Cascades, since they are quite shallow.

High pressure and cooler air on the western side and lower pressure east of the Cascades produce a bounty for some of us--strong winds and lots of wind energy downstream of gaps in the Cascades, like downstream of the Columbia Gorge or in the Ellensburg region (I have a section in my book on this).

Anyway, knowing why we have the low clouds won't get rid of them, but perhaps understanding their cause and possible benefits will make them easier to tolerate.