The Meteorology (and More) of the Grass Fires of Eastern Washington

There have been a number of grass fires in a limited area of eastern Washington, roughly between the Tri-Cities and Vantage.   Generally burning in unpopulated rangeland comprised of grasses, sage, and shrub-like vegetation, the fires have done little damage, even though they have burned tens of thousands of acres.    Strong winds play an important role in these fires, as do the nature of the "fuels."   As we shall see, climate change has play little role in such fires, but human modification of vegetation and provision of ignition sources have been critical.

The current Northwest fire map (below) shows no activity in forested areas, but three fires in grass/rangeland:   the Cold Creek fire west of Kennewick, the Juniper Wind tower fire, near the Gorge, and Round Butte Fire in eastern Oregon.  And earlier this month, the Powerline Fire started near Mattawa, just to the north of the Cold Creek blaze, and is now over.

We can use MODIS satellite imagery that considers a combination of wavelengths to show burn scar areas (see below).    You can see the Columbia River.  The bottom arrow points to the Cold Creek Fire, the top arrow to the Powerline Fire, which was started by a motorcycle.

These fires started in grasses and low shrubs--the pictures below shows examples, the first near the Powerline fire, the second by the Cold Creek blaze.

Now a big problem is that the landscapes above are full of a highly flammable, non-native species called Cheatgrass---also known as grassoline.  And flammable native species like sage.

Below is a government map of the distribution of cheatgrass.   The Columbia Basin is covered by the stuff!  During the past several decades, Cheatgrass, a non-native invader, has covered eastern WA, displacing the native (and less flammable) bunchgrass.  Cheatgrass dies and dries out early in the summer, leaving highly flammable fuel.

In any normal summer, the dead fuels of grasses and small bushes dry out very quickly--one does not need above average temperatures or below normal precipitation.   In fact, this water year  (since October 1, 2018) was one of BELOW NORMAL temperature and ABOVE NORMAL precipitation over the Columbia Basin, something shown by the two figures below from the Western Climate Center.   Clearly, there is no global warming component to this.

So we start with landscape with flammable grasses and low bushes, that are dried out without the help of any special heat or lack of moisture.   Then we add human ignition sources--such a cigarettes thrown from cars, motorcycles and off-road vehicles, fireworks, and for the case of the Juniper Fire, a wind turbine that ignited and melted down--starting a fire in the grass below (see image).

Here is a youtube video of the burning turbine and you can see the grass situation as well.


But there is on more thing:  wind.  The areas of the fires are often windy--in fact, that is why the wind turbines are there.     The region from Ellensburg to the Tri-Cities often gets strong northwesterly winds coming across the Cascades.  That is illustrated by a forecast wind speed for 5 PM yesterday (Monday, see below).  The yellow and oranges indicate stronger wind.

During the summer, strong winds descend the eastern Cascades during the late afternoon and evening hours, and the winds are strongest downstream of a weaknesses in the Cascades known as Stampede Gap.  This results in the most powerful winds in a zone from Ellensburg towards the Tri Cities.   To get a good feel for this, below is the average wind speed at 80 m above ground level for Washington.  You see the red area....the windiest place in the state? Guess what?  Most of the grass fires we have seen lately are in or near this area.

The winds in the Ellensburg/Vantage/Mattawa, Tri-Cities area are strongest in the summer, when eastern WA is warmest and when there is strong pressure difference across the mountains.

So we have a dry area with lots of flammable grasses and shrubs, loads of human activities ready to ignite fires, and plenty of wind in the summer.   Sounds like purgatory.  This is a worsening problem due to the invasive grasses and increasing human ignition sources (new one:  burning wind turbines). 
And the situation is made worse by increasing human habitation and building near the flammable rangeland.  That issue is not one for an atmospheric scientist to deal with.