July 27, 2020

Mid-90s Today and Significant Wildfire Threat in Eastern Washington

Today will bring 90s a significant portion of western Washington and some daily high-temperature records will be broken, with many locations getting into the low to mid-90s.  Tomorrow will be 10F cooler, but the real threat will occur later tomorrow in eastern Washington where very threatening conditions regarding wildfire initiation and growth are probable.

Let's start with a graphic I have never shown you before:  the difference in temperature between yesterday and today (for 10 AM).  Warming by 2-12 F over the eastern side of Puget Sound, but cooling along the coast.  Consider that many locations in western WA surged into the mid to upper 80s yesterday, low to mid-90sF is guaranteed for today.   On the other hand, the cooling on the coast is important reflecting lots of low clouds and beginning of the inland movement of marine air.

But now the threat.   I have spent a lot of time on wildfire meteorology lately (I have an NSF grant to work on it), and just finished the NW wildfire chapter of my NW weather book (available next March!).    A situation that has recently produced dangerous wildfire conditions in eastern Washington is the one we are about to experience. 

You start with a period of warm, dry conditions--and we have had it, with temperatures rising to 100F in eastern Washington.  Light fuels (e.g., grasses , bushes) are dry and dangerously dry fuels extend to roughly 3000 ft.  A measure of this dryness is shown by the USFS map of the Fire Potential Index (FPI), an estimation of the fire potential of deal and live fuels.   High values are found at lower elevations on the eastern slopes of the Cascades.  Still moist at higher elevations (something I confirmed while hiking yesterday).

Marine air will surge into western Washington tonight and tomorrow morning, and in doing so, will increase the low-level atmospheric pressure.  Warmth and low pressure will remain on the east side (warming produces lower pressure), and as temperatures warm tomorrow the pressure difference  across the Cascades will increase.

This increasing pressure difference will push air across the Cascades, resulting in substantial acceleration.  You can see the large pressure difference in the forecast map for 5 PM Tuesday.  The solid lines are isobars, lines of constant pressure.  You see a lot of lines across the Cascades...that is what a large pressure difference looks like.  The shading indicates temperature...very high in eastern Washington.

Dr. Brian Potter of the USDA Forecast Service devised an index called Hot-Dry-Windy that indicates dangerous areas for wildfires.  My group creates this graphic operationally, being driven by our high-resolution prediction model.   Take a look at the graphic for 5 PM tomorrow.  Some very high values (red and yellow) in areas that are quite dry. 

There is already some fires in eastern Washington (see below). 

Will there be more fires tomorrow?  That depends, of course, of whether there will be a source of human ignition (there won't be lightning).  But if a fire gets started, it could expand rapidly and dangerously...and, of course, the current fires could expand.  I just had an email exchange of Josh Clark of Washington DNR and they are fully cognizant of the dangers.   

Let's hope nothing happens.


  1. Looks like favorable conditions for fires by Wednesday night and Thursday,as high based thunderstorms are now in the forecast for much of the eastern half of Washington.

  2. Thanks for the nod, Cliff. HDW is the work of several of us, though, including Dr. Jay Charney, Dr. Alan Srock, Dr. Scott Goodrick, and Ms. Jessica McDonald - with a ton of input from NWS forecasters and other fire management personnel.

  3. The maximum temperature at my location in NW Bellingham was 84F. This is fourth day this year with a maximum temperature of 80F, or higher, and a tie for the warmest day since the maximum monthly temperature of August 2019. As an aside, with no low-level northerly flow to dry things out, it was quite muggy again today. I measured a maximum dew point of 69F (my location is relatively heavily vegetated and may not be representative of the area) which ties a reading on 7/20/20 as well as a measurement from 06/2019 for the highest dew point temperature in my period of record.

  4. There seems to be an unusual amount of particulate debris in the air around my location in NW Bellingham. It appears white and somewhat fine and accumulates on surfaces such as vehicles.

  5. Just looked at that zone forecast for SE Washington/NE Oregon…Whew boy! Sweltering on the dry side of the mountains! And then there is the wind…the fussy, particular wind, changing directions on a whim. The National Interagency Fire Center web site provides great run downs of conditions. Take a look! I know old time fire fighters who follow this site religiously. The Great Basin region (Nevada at the moment) is tackling some big fires now! But dry, desiccated conditions constitute the usual state of the high desert in late July/August…the caveat being that some years are conditioned to be more explosive than others. Working on great basin fire crews in the late 70’s, I paid my way through college. My sister was a dispatcher. I drove a pumper truck named Gangrene! I am no extraordinary specimen of a human being.. just an ordinary joe. Necessary training is imperative.. but I know for sure…if I did it, so can you…young lady out there

  6. The fire officials in Oregon have been worried since the beginning of fire season, but not because of the weather conditions. They've become worried because of budgetary constraints enacted during the virus panic and ensuing lockdowns, further exacerbated by the two month's long rioting downtown. IOW, the state budget's shot for the year, and for the foreseeable future.

  7. Cliff, I can't wait to read your book about NW weather, especially the fire weather content. When I took my first "red card" firefighter class many years ago I was fascinated by the weather section (which is pretty extensive) while most of the other students struggled to stay awake. As you know, weather is probably the most important factor in what a fire will do at any given time. Looking forward to reading your discussions about diurnal wind shifts, the Haines Index and other fire weather topics!

  8. I thought I remembered you saying that there wouldn't be a threat of wildfires this year, what has changed?

    1. Brian...no, that is not what I said. I said there is no reason to expect a worse than normal season and that the early part of the season looks favorable (low wildfire acreage). This is in fact what occurred...cliff

  9. it certainly has been hot the last few days here in Trout Lake Washington, mid 90s mostly.

  10. Cliff,

    This is very important information! I have a strong interest in forests and specifically wildfires. In another warmer state, I had the opportunity to learn about and accompany wildlife scientists into forest habitat.

    On one occasion, we had to locate bears with radio collars who had new young. It required spending significant time in the forest up and down steep vertical hills. This gave me a real appreciation of forests with a perspective toward viewing them as wildlife might. In the warmer client, the bears were not in full hibernation so they were sedated to check the baby cubs. We weighed them, checked their vitals, marveled at their long claws and their bluish eyes. Then, they were safely restored with mom and restored them to their fallen hollow tree with mom. I had always been in natural forests for recreation, but never like this. My interests in forests' welfare grew from this experience and my already established interest in wildlife.

    Of course, CA's wildfires added to my interest in wildfires. Keep up the good work. It's very important!


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