July 08, 2021

Cooler Air in Western Washington Means Strong Winds and Wildfire Threat in Eastern Washington

 It is perhaps ironic that when cool, cloudy air floods western Washington as it did yesterday, winds surge in eastern Washington, leading to the potential of rapid wildfire growth.

The visible satellite image this morning shows the situation. 

Cool, dense, cloudy marine air has inundated western Washington and extends up the river valleys to the crest.    If you look closely, you can also see smoke from the British Columbia fires extending over northeast Washington.


Yesterday, an upper-level trough (or low) moved through (see graphic at the 500hPa pressure level, about 18,000 ft), resulting in the energetic influx of marine air.  


Looking at the observations above Seattle Tacoma Airport (time on x-axis, height on the y-axis), you can see major cooling in the temperatures (red lines in C) and a dramatic shift to moderate southerly winds below about 5000 ft.


The Cascades blocked most of the low-level cool air so that eastern Washington stayed warm.   This sets up a pressure difference across the Cascades with cool, dense air to the west resulting in high pressure compared to the warmer eastern Washington.  This is apparent in the sea-level pressure forecast for 5 PM Wednesday shown below (lines indicate pressure, shading shows temperatures in the lower atmosphere, yellow is colder).


The large pressure difference over the Cascades resulting in air accelerating over and down the crest and across the eastern slopes of the Cascades.

The maximum gusts observed yesterday along the eastern slopes of the Cascades (shown below) surged above 40 mph in many locations to a high of 56 mph north of Wenatchee.


And such winds were well forecast by the UW WRF weather prediction model (wind gusts at 11 AM Wednesday in knots shown below).


Such strong, gusty winds descending the eastern slopes of the Cascades can greatly enhance wildfires, causing them to blow up and spread quickly.  The greatest danger is when the approaching trough initiates thunderstorms, with lightning starting fires, followed by strong winds that encourage fire growth.

Yesterday we were lucky, there was no lightning over the eastern slopes of the central Cascades, but there was a large grass fire of concern:  the Batterman Road fire, which has spread to over 14,000 acres and is 50% contained.


Not much change during the next week in our weather.  No rain in Washington, showers in BC, and no heatwave in sight.

9 comments:

  1. We are now heading into the warmest time of year here in Western Washington....so nice to see things are settling down, but the avg temps during the last two weeks of July, and the first wo weeks of August, means that we will see a few days of streaky-hotter weather-like 80s and upper 70s...the avg temp during the upcoming summer stretch being 78 degrees...and this is our NW "secret"--really nice, comfortable summer weather...it almost compensates for the other 8-9 months of cloudy. mediocre weather!...I love it.

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  2. I shot a timelapse of Mt Rainier from the SE yesterday evening and could have sworn there was a little bit of smoke flowing around the upper peak area. I've seen similar smoke behavior around Mt St Helens a few times.

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  3. So- if the spring is wet, they warn us about enhanced fire danger because of more vegetation.

    If spring is dry, they warn us about enhanced fire danger because of dry vegetation.

    What type of set-up gives low fire danger- and why don't "they" (meaning the media and/or the government) ever talk about it? "They" love to scare us. Trouble is, if you cry "wolf" too often, it loses it's intended effect. "They" should tell us when fire danger is low or moderate. Or doesn't that happen anymore?

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    Replies
    1. Probably due to the fact that summer is almost ALWAYS devoid of rain for either situation and the end result is always a parched landscape.

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  4. "They" love to scare us.

    I think it's a sign of the times (and not a good one). "They" have a need to feel important, and creating drama is how they do it.

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  5. So the average warming of the oceans increasing each year is just bs then? I ask this not knowing what to believe, and not challenging your info...

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    Replies
    1. No...overall the oceans are warming. I never said otherwise. But it is not uniform. For example, the western oceans warm more rapidly than the eastern oceans (like off our shore). The slowly warming pacific contributes to our slow warming here in the Northwest.

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  6. that would be a relief for us in Eastern WA if we could get a little more spillover with no fires. Also, are you going to challenge this ridiculous attribution study? They constrained the "impact area" to cherry pick it. https://www.nature.com/articles/d41586-021-01869-0?utm_source=Nature+Briefing&utm_campaign=7ecba51a80-briefing-dy-20210709&utm_medium=email&utm_term=0_c9dfd39373-7ecba51a80-44781177

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  7. This is a fascinating topic. The Pacific's effects are fascinating. The overnight low that I recorded this morning was just 49.8 F (coolest in weeks), and the 24 hr high just 84.7 F.

    With the exception of that truly odd heatwave, here (just west of the crest) we've been enjoying a very pleasant summer so far. I distinctly recall 1976 being a sizzler in comparison. Having 'watched the weather' for almost fifty years here, this seems very faithful to the Mediterranean pattern and the flora and fauna seem to be doing quite well even in the coastal lowlands.

    A few years ago, a "scientific study" was made of aerial photographs of ag areas here. This year, just like then, the grain at the top of hayfields looked yellow and gold from the air, but at ground level it was obvious that the plants were still quite green and not suffering at all. The 'analysts' conclusion (their report) belied reality. I've thought about driving around to take photographs that show what conditions really are.

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

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