Grass Fires in Eastern Washington: Strong Winds and Human Ignition

June is the beginning of the grass wildfire season over the lowlands of eastern Washington.

By June, the extensive grass and range vegetation of the Columbia Basin has dried out and "seasoned" sufficiently to burn.  Also in June, strong westerly (from the west) winds can develop as weak Pacific weather systems move through.

Dry range vegetation, strong winds, and an ignition source are the ingredients for a large, fast-spreading fire. 

All of this has happened over the past few days, producing several significant grass and range fires, including the one at Juniper Dunes (13,000 acres!).   

The map below shows some of the recent fires.

Here is a satellite image of the Juniper Dune fire from two days ago.   Pretty impressive looking.

The grass fires are now history, but you can see the burned (brown) areas in today's visible satellite image.

So why the fires?  

The fuel moisture of small dead fuels was under 11% and thus flammable (see below).

Looking at the 100-hr dead fuel moisture (for larger dead debris) over the Columbia Basin (below), shows that fuel moisture (solid red line) dropped below normal with our short heat wave (the gray band shows the normal range of fuel moisture).  

Light dead fuels, such as grasses and small-diameter debris, can dry out within hours under the right conditions.

And then there are the winds resulting from the passage of a weak trough aloft.  To illustrate, here are the gusts yesterday---at several locations they exceeded 50 mph!

The strong winds are critical for the rapid expansion of such prairie fires.

It appears that these fires were initiated by careless humans, which is true of most eastern Washington grass fires.

Not All Daily Temperature Records Are the Same

Yesterday, the temperature at SeaTac Airport rose to 89F,  beating the all-time daily record for the date (86F)!

Today, even if the temperature is the same today, it won't break any records.

How could this be?

It turns out that not all records are equal.

Let me explain.

Below is a plot of observed temperatures (blue bars), average temperature range (brown band),  and record highs (red) and lows (blue) for June at Boeing Field in Seattle.

Look carefully at the record highs.   A large variation of record highs in June from 81F to 104F!  Generally around 90F.   

So why the variability?    

It turns out that to get the really high temperatures in western Washington, the atmosphere needs to organize itself in a very specific way, generally with a strong upper-level ridge and offshore-directed flow at low levels.

And on some days, by the luck of the draw, the atmosphere gets the right setup for maximal heat. After many years, the needed flow pattern occurs, and the temperature climbs to record levels.

Global warming plays very little role in these records---the key is getting the right atmospheric flow situation.

Would you like me to prove this to you?

Here is a plot of the highest maximum temperature each year between June 7 and June 21 since 1950 at Olympic Airport (a less urbanized location than SeaTac).   No apparent upward trend.

Turning back to SeaTac, below is a plot of the highest temperature on June 14th at that location (below).  

2025 was the warmest year on record for that date.  But note!  There is no trend in the record temperatures for that date over the entire period of record.

In fact, the highest temperatures on June 14th are trending down!  (brown line).  

So the global warming claims for the origin of such records should be taken with a large grain of salt.