The Most Dangerous Day for Washington Wildfires for the Remainder of the Year

When it comes to rapid wildfire spread and growth,  strong winds are essential.

Virtually all major periods of rapid wildfire growth are associated with gusty winds.

It was clear that today would be a risky period on the eastern slopes of the Cascades.

Why?  Because we had some moderate fires going on the eastern slopes and strong westerly winds were forecast to push over and down the Cascades.

The Labor Mountain Fire Today

Before today, three lightning-initiated fires had been burning on the eastern Cascade slopes (see map):  the Wildcat fire east of Mt. Rainier, the Labor Mountain fire south of Leavenworth, and the Lower Sugerloaf Fire to the northeast of Leavenworth.

The visible satellite imagery this morning, around 9 A.M., clearly showed smoke from the fires, with the Labor Mountain fire being the most active (see below).

The satellite image of the heat emission from the fires confirmed that this fire was modestly active at 8 AM (the red dot shows the fire).

But when today's front approached from the west, cooler air flooded into western Washington, causing the pressure to rise.  This created a large pressure difference across the Cascades, forcing rapidly increasing westerly winds (winds from the west) down the eastern slopes of the mountains.

The UW WRF model predicted this change.  Consider the predicted winds near the surface over the central Cascades (below).  At  8 AM, the westerly winds were predicted to be modest, with the strongest near Ellensburg.

Huge strengthening by 2 PM

And the fire temperature observed from satellite around 1 PM clearly showed the fires increasing rapidly in response.

Surface observations documented the winds accelerating.  For example, the nearby Dry Creek USDA RAWS site showed the winds surging to around 40 mph.

A map of the maximum gusts today through 6 PM shows several locations with gusts over 30 mph east of the Cascade crest.

The great danger of the wind-driven Labor Mountain fire resulted in evacuation notices for those west of the fire (see below).

As of 8 PM, winds have started to decline, but fire-maintained gusts will continue for much of the night.

Good news.  In a few days, the fire danger for the whole region will recede as a series of wet Pacific fronts move in.