Localized Strong Winds & High Fire Danger Imminent

Update 3:35 PM Monday: Red Flag Warning EXTENDED until late Thursday night. Wind advisory in effect for the brown shaded areas until 11 AM Tuesday for wind gusts up to 50 mph. Low level smoke still possible this evening.

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Update 9:30 AM Monday: Widespread haze is possible across the Puget Sound region this afternoon as winds shift. Be prepared & stay tuned!

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Extremely dangerous fire weather conditions are imminent in Western Washington. Find all the details in this blog. I will have updates as this weather event unfolds.

A Red Flag Warning is in effect for the pink shaded area. 

You can click HERE for the alert, or find it below.

The warning outlines the two main upcoming weather threats (gusty winds and very dry air). We'll take a deeper look at these conditions in this blog!

Winds will begin to increase Monday afternoon with a north to south pressure difference across Puget Sound. Below is the UW model forecast for 5 PM Monday. Pressure lines show a difference from north to south through the Puget Sound area. Rule of thumb: closer lines=higher difference in pressure.

Look at how close the lines are in central Idaho and Wyoming...that is the very strong Plains cold front that is causing the winds here. (Denver will go from 95/sunny to 30s/snowing in 48 hrs.).

Winds Monday afternoon-evening will be from the north, with gusts of 20-40 mph, strongest over water.

By Monday night, the pressure difference becomes very strong across the Cascades, switching from north-south earlier in the day. The increase in this pressure difference continues into Tuesday morning. Look at the very strong pressure difference across the Cascades! (See how close the lines of pressure are near the mountains).

This strong pressure difference will cause strong winds to be pushed from east to west through gaps in the Cascades Monday night to Tuesday morning.

Before we get to wind speeds, we need to establish where gaps in the terrain are.

I have made arrows at main gaps in the Cascades. When winds flow out of them, they are extremely localized. We will be focusing on the gap with the blue arrow. This is the largest of the Cascade gaps, and it is called the Stampede Gap. It stretches roughly from Stevens Pass to Mount Rainier. Besides the narrow Columbia River Gorge (southernmost arrow), this is the most wind-prone gap in the Cascades.

Remember the strong pressure difference across the Cascades? Now, we'll see how it pushes winds out through the Stampede Gap in easterly wind events.

 

I made this map showing three "wind zones" from what forecast models predict for Monday night & Tuesday morning. Since wind direction is named by the direction the winds come from, we will call these three zones SE (right zone), E (middle zone), and NE (left zone). Here's the forecast for these zones.

SE Zone (Enumclaw, Buckley, Black Diamond, Ravensdale):

Gusts 40-60 mph from 9 PM Monday-12 PM Tuesday

E Zone (Northern Puyallup, Sumner, Edgewood/Milton, Auburn, Federal Way, Bonney Lake, Fife, Kent, Des Moines, Vashon Island):

Gusts 35-50 mph from 9 PM Monday-12 PM Tuesday

NE Zone (Tacoma, University Place, Lakewood, Gig Harbor):

Gusts 30-45 mph from 10 PM Monday-9 AM Tuesday

These are quite strong winds for September. Since trees are still fully loaded and winds from these directions are abnormal, there is a chance of power outages. Be sure to charge your devices!

Remember, since these are gap winds, they will be very localized. Someone in South Hill will not have the same strength of winds as someone in Federal Way. (Areas like South Hill and Graham will have winds gusting 15-25 mph).

In addition to winds, it will be very dry in Western Washington. Even once winds have decreased Tuesday evening, downslope flow out of Eastern WA will continue to bring dry air to our area. Very low humidity will combine with winds to create critical fire weather this week. Take a look at this forecast model showing humidity at 5 PM on Tuesday.

When the Red Flag Warning says humidity of 10-20%, that's probably going to happen. Here, the model shows humidity around 15-25% in the Puget Sound area.

Any fires that start will spread rapidly. It is important to be very careful with anything that could start a fire. Find out about burn bans and regulations here: https://burnportal.dnr.wa.gov/

Due to the winds, temperatures will peak in the mid 80s on Monday and Tuesday. Remember that if you're outside of the valleys, temperatures will be a couple degrees cooler than those in the valley. Also...the "heat of the day" won't last as long now, because it is getting closer to fall and the daylight is decreasing. 

After wind subsides on Tuesday, humidity will remain low (below 30% for multiple days), and temperatures will skyrocket to the low-mid 90s on Wednesday and Thursday. Upper 80s expected on Friday. Interesting note...due to strong offshore flow, temperatures at the ocean beaches of WA & OR will jump to the 80s and low 90s in some spots. That's really rare!

Remember to take this fire weather setup seriously. Be very mindful of things that can spark fires. Large wildfires have happened in Western WA before, and it can happen again. The local NWS office described this event as a "once in 30 years" fire weather setup.