Dense fog to fill region Saturday

Weather Blog

PORTLAND, Ore. (KOIN) — A dense fog advisory is in effect until 11am for the Willamette Valley including surrounding communities and the Oregon coast range. Daytime highs this weekend will likely only reach the mid to upper 40s. Overnight lows near freezing mean you could run into slick patches on the road that you may not be expecting. 

Why all the widespread fog all of a sudden? Just like your homemade apple pie, the weather requires key ingredients to make the perfect storm, or in this case, the perfect pea soup. Throw in a pinch of high pressure, sinking air, lack of wind or any vertical mixing, post-rain dew point increase, clear skies, radiational cooling, temperature meets the dew point and viola!

So, will this fog clear as soon as the dense fog advisory ends? Well, no. Improve by 11am? To some extent yes. An easterly flow is in the forecast which means we can drop our dew points (aka make it drier) and mix out that stubborn fog. But don’t expect widespread clearing. This is all about microclimates. Some parts of the valley will get stuck under the inversion while PDX/Vancouver should expect a partly cloudy afternoon. For instance, when the offshore flow increases places like Salem and other valley locations to the south won’t get the same benefit. Removed from the influence of the gorge, Salem will get an increase in winds from the north. So all that suspended moisture (aka fog) will creep down the valley and essentially get stuck at the south end near Eugene/ Corvallis. At least that’s how this fog may behave in theory.

In the meantime we need something robust to really mix things up, like a giant blender in the sky. The next chance of rain and mountain snow will be Sunday afternoon through Wednesday. Tuesday through Wednesday should be especially wet. Thanksgiving Day and Friday could be our nicest days in the next seven.

This week in review:

PDX picked up 1.17″ of rain in just this last week alone. Month to date total is: 4.30″ (above normal by 0.70″). Timberline has a base of 44″ inches of snow. Mt. Hood Meadows has a base of 42″ inches. And those King Tides that lasted from last weekend into the early part of this week. Take a look at the power of water below. Netarts Bay as seen here was full and agitated like a washing machine during high tide. Look at the present left behind. A giant tree. Now, do you understand why we stress rolling logs in the surf?

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