June 23, 2015

The Wildfire Risk is Rising: How Bad Will it Be?

With warmer than normal temperatures and lack of rain, the land surface and vegetation of our region are drying rapidly.  As a result, the risk of wildfires is rising:  but how bad will it be?

In May a few media outlets were hawking an early and severe wildfire season here in the Northwest, due to low snowpack and low river levels., neither of which have a large impact on wildfires in our region.  Well, we are now at the start of the traditional wildfire season and the reality is that there have been LESS fires and LESS acreage burned than normal in our region.  As I write this, there is one moderate-size fire burning in Washington State (600 acre fire in the Olympics), and the fires in the western U.S. have burned less area and were fewer in number than normal (for proof of this check out this website by the National Interagency Fire Center).

Why less fires than usual?   First, precipitation was only a bit below normal during the past winter/spring.   There is no precipitation drought, but a snow drought, with precipitation falling as rain rather than snow in the mountains.  Thus, eastern Washington started the warm season with near normal soil moisture and normally moist vegetation.

Second, May was unusually wet in parts of eastern Washington and Oregon, keeping the surfaces moist, even though temperatures were above normal.

Third, there has been a dearth of lightning the past month.  This is VERY important because most fires are caused by lightning around here.

But the situation is changing rapidly now and becoming more threatening...the details of which I will describe below

Before we look ahead, it is useful to consider the fire climatology in our region (see below). Lightning fires are dominant over human caused.  Lightning can produce the big surges of fires that can overwhelm fire-fighting resources.   You see the one large spike in human-caused fires?   That is July 4th!  Peak wildfire season is in August.

So lightning is a critical element in controlling the frequency of wildfires.   Thus, you can have hot, dry years that produce few major fires if there isn't much lightning.

To get a major wildfire season you need the surface to be dry, and particularly for vegetation (dead or alive) to be dry and ready to burn.   You dry the surface with a combination of lack of precipitation and warm temperatures/sunshine.   Why warm temperatures and sun?  Because they cause water to evaporate from the surface.

Around here summers are generally dry, except for occasional thunderstorms, which are generally found over and east of the Cascade crest.  So temperature is the key element in drying things out.

We thus come to the first problem:  temperatures have been MUCH warmer than normal during the past month.  To show this, here is the departure from normal of maximum temperatures during the last 30 days. Wow.   Six to ten degrees above normal in much of eastern Oregon an Washington, as well as western Oregon.

This warmth, plus precipitation at or slightly below normal (which is NOT much even during normal years) has caused the surface to dry.   As a result, various soil moisture indices have indicated rapid declines of soil moisture.  For example, the popular Palmer Drought Severity Index (PDSI) shows moderate to severe drought conditions in the upper soil layers over eastern Washington and California.
The U.S. Forest Service reports the estimated moisture content of various types of "fuels".   Here is the estimates of moisture content of the bigger branches and debris (1000-hr fuels).  Low moisture content east of the Cascade crest and northern CA.

So the surface conditions are drier than normal, with the Forest Service folks estimated we are about 2-3 weeks ahead of normal (early to mid July conditions).   Unusual amounts of grass over grew in eastern Washington in May due to the wet conditions that month.  That grass has now dried out and has become a fire threat.   That is why there were a series of fast burning grass fires in eastern Washington during their warm spell last week.   They were put out quickly and did little damage...but they are a warning.

So lets look into the future using the state-of-the-art prediction tools at our disposal.  First, there is a threatening situation during the next week.   Over the weekend, temperatures are going to warm rapidly as a huge ridge of high pressure builds over the region.  Here is the latest forecasts by weather.com for Wenatchee.  For Friday through Wednesday, the highs will be above 105.  Not good. The surface will be toasty dry.

What about lightning?    The latest UW WRF MODEL forecast suggests that starting this weekend the potential for thunderstorms will increase dramatically.   To show this, here are forecasts of something call CAPE (Convective Available Potential Energy)....a measure of the amount of instability in the atmosphere.. for several times starting Friday afternoon.  Instability is needed for thunderstorms.  Substantial numbers of thunderstorms are possible from Friday through Tuesday.

Friday afternoon, lighting could strike the Oregon Cascades and northern CA.

 More on Saturday afternoon, with the risk spreading into eastern WA
 Monday evening....a regional threat

The bottom line is that with very dry conditions in place,  multiple lightning-caused fires are quite possible.  Fire folks need to get ready.

But what about the rest of the summer?   Our seasonal forecast models (like the NOAA CFSv2) can give us some insights.  The temperature forecast for July though September is for much warmer than normal conditions  from northern CA into British Columbia (see below)   This implies drying conditions.  Not good.
Precipitation?   Wetter than normal over the Rockies, with moisture  extending into eastern Oregon (see below). No precipitation signal over eastern WA.  This precipitation will be mainly for thunderstorms, which means lots of lightning over the Rockies, Sierra, and southern Cascades. 

 Where it has been very wet (the Rockies), the fire risk might be reduced by the moisture.  But the places on the western periphery (like the southern Oregon and northern CA Cascades) might be hit by a lot of lightning--and it will be dry there.   And these thunderstorms might drift into eastern Washington.   Substantial threat.
The predicted soil moisture from this model (again for July-Sept) is below normal over the Pacific Northwest. A bad omen.
Based on the above (and other) seasonal forecasts, there appears to be a particularly large wildfire risk this summer, particularly over northern CA and Oregon.    The risk is also high over Washington State.    Dry conditions will exist...the big question is lightning.  The amount of lightning will control the outcome.   Using our high-resolution forecasts, government officials can get a pretty good idea of fire risk days ahead of time regarding lightning and get resources ready to deal with fires quickly.

It is important to note that lightning caused fires are a natural part of the ecology of the region, NECESSARY for the  life cycle of several of our local plant species.   And the extreme warmth this year is probably the result of natural variability--not human-caused global warming.  The real problem is that our civilization has injected population into a natural fire-prone environment and thus some folks are at risk, forcing us to intervene to stop fires in many locations.

Washington State now has a statewide burn ban in effect---a very good idea.  Considering the risk, perhaps they should go further, such as a total fireworks ban, including the sales of all fireworks.  The burn ban does not extend to Federal lands--is that possible?  This would be a good idea, as would clearing brush/grass around structures in fire-endangered areas.

We are dealing with the conditions of 2070 this summer and it will be necessary to use more extensive methods than normal to reduce human-caused fires.   Control of lightning is in other hands.


  1. A few random, non-scientific observations after a week exploring eastern Oregon. Most of the areas I visited in the NE had fire danger posted as "low" or "moderate." The only "high" signs I saw were near Bend.

    The Wallowas appear to have a good snowpack, with many of the trails still snowed in. Steens mountain still has some snow, thought not much.

    The various shallow lakes near Hart Mountain were in dire shape though...almost completely dry. These lakes show a lot of variability depending on the season and weather, but still, I'd think they'd be in better shape this time of year.

    - Douglas

  2. I found your comment "low snowpack and low river levels, neither of which have a large impact on wildfires in our region" interesting. Up in BC, these two factors play an instrumental role in determining river levels which impact surrounding soil moisture content. Also interesting is the difference between BC's & Washington's fire seasons so far. BC saw 5 times the amount of lightning this May compared to the previous 13 years. Add to that the lower than normal precip amounts and the warmer than normal conditions and we've seen a very active and early start to the forest fire season. In fact, as of June 18th, 60,000 hectares have already burnt compared to the summer average of 15,000ha and it's only June! Lots of folks concerned north of the border...

  3. Cliff, I have to disagree with some of your assertions that the PNW wildfire season is below average so far. The NIFC statistics are for fires at a national level, not a local level. Right now, there is one large (over 400 acres) lighting caused fire burning in Olympic National Park. The local fire department I work for saw 25 natural vegetation fires last week, and we average about 125 in an entire year. Yesterday's observed Energy Release Component values (34) for our area were in about the 90th seasonal percentile and nearly 4 times the average value for this date (9). So, while the worst may be yet to come, we are already seeing conditions in Western Washington more typical of late July or early August.

  4. If you want to see our possible future look to Alaska. Over 150 fires were started just this last weekend in the state.

  5. In Re the burn ban on federal land:

    States can't dictate what happens in federal land in their borders. It would take the BLM/NFS imposing a ban on their respective lands to do it. But that doesn't mean the state can't push for it. The respective state- level people in charge should contact their federal equivalent and advocate for a ban. Given how much of the land in the Northwest (particularly in the Rockies) is federally governed, it might be worth it to impose.

    Source: Am a lawyer

  6. I agree totally about the fireworks. Unfortunately the Native American -operated firework stands are up and running in full force and one can hear fireworks going off sometimes at all hours on the weekend already.

    In California and southern Oregon homeowners are aware of the need for fire buffers between vegetation and structures. Here less so but still necessary in these conditions. Those living in suburban forested environments would be well advised to clear between their homes and the trees that surround them.

  7. So, the Queets fire is not a major fire yet, I guess, at just 650 acres? NPS has closed the trail at mile 12 (out of 16). How comfortable should I feel hiking 6-8 miles up the Queets this weekend? (I am thinking not very and looking for another place to go)

  8. wff255,
    The Interagency totals are dominated by western fires and the stats show that to date this year is less than normal...even with all the fires in AK. Right now, there is one significant fire in the state (Olympics,which grew to 650 acres) and we had a number of brush fires. My point is that we are about to start the major fires season with very warm temperatures and lightning...cliff

  9. Spokane County sources would counter the "less than normal" statement. I'm thinking many of these brush and wildland fires were municple/county incidents. http://www.krem.com/story/news/local/wildfire/2015/06/23/early-wildfire-season-explodes-with-313-fires/29190211/

  10. What do you think about the prediction of thundershowers this Saturday & early Sunday.

    Will it be mostly be in the Cascade mountain areas?

    John Gowdy

  11. Alligator...there is a strong possibility of thunderstorm over the weekend...that is a big part of the threat..cliff

  12. raincoatmusic
    Where are those statistics coming from? Whole year, to date? I prefer to use official major stats from Federal agencies.. There have been a lot of brush fires, mainly man-caused. The snowpack business makes no sense...the fires are NOT in the mountains...cliff

  13. I was up in the North Fork Teanaway area last Saturday. It was insane. Areas that are nearly always still very snowy are bare... that's not news. What was surprising, though, was that July/August wildflowers were in full bloom the third week of June and it was HOT up there! The river was way down which does seem to matter when it comes to keeping fuels moist. I hope it's not bad this year but I won't be surprised if it is. I agree that natural fires are necessary for lifecycles and forest renewal but those pesky people build houses everywhere! It would be a shame if firefighters die protecting structures built in known high-risk areas. Just like the coastlines, especially the Atlantic seaboard, we need to stop building in these very dangerous places, even though they are beautiful when conditions are benign.

  14. Cliff: I was in the Wenatchee area last week. The grass growth is exceptionally thick but had not quite reached the explosive dry level yet. I suspect it will by the end of the week. That late wet spell in eastern Washington may have delayed the onset, but at that same time made the situation worse. Tricky business predicting fire seasons, but what has happened thus far in BC should be a warning - they have already gone through 80% of their fire budget for the year (CBC).

  15. Question - should i believe the forecast from Weather.com or Accuweather.com? Accuweather shows lower temps over the next 10 days and I so want that...

  16. Why would river levels matter for wildfires? Unless the fire is literally in the river bed or flood plain. Once a fire is a few hundred yards away from a major river would it really make one iota of a difference? The lower snow pack is definitely a cause of concern as the ground and fuels will dry faster due to lack of snow melt permeating into the ground. Lower snowpack means less soil moisture .


Please make sure your comments are civil. Name calling and personal attacks are not appropriate.

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