The Bear Gulch Fire in the southeast Olympic Mountains really revved up yesterday morning and afternoon.
Four days ago, it was smoldering, with only minimal smoke (see below, arrow points to the fire).
Yesterday, during the late morning and afternoon, it really started to increase:
And today, the plume of smoke was impressive, stretching hundreds of miles into Canada.
Just after sunset from Seattle last night, looking towards the Olympics, one could clearly see the smoke plume from the fire.
In fact, my last blog, made before the blow-up, gave the reason: the sudden development of strong, dry easterly winds over the region.
I have spent a great deal of time studying western Washington and Oregon wildfires, and a major finding was that virtually all the big, westside blow-ups are associated with strong, dry easterly (from the east winds).
In fact, I just wrote a paper on the subject that was just published (here).
Yesterday morning, there was a surge of such easterly flow as transient high pressure built into eastern Washington, and a thermal low moved northward up the coast. High pressure to the east and lower pressure to the west drive easterly flow since air tends to go from high to low pressure near terrain.
You can see the development of the easterly flow in the lower atmosphere by looking at the weather observations from planes landing and taking off from SeaTac (see plot of winds and temperatures below). Time is on the x-axis in UTC and increases to the left. (16 /12) is yesterday at 5 AM. The Y-axis is height in pressure. 850 is about 5000 ft. Wind barbs are shown (blue) as well as temperature (red lines, °C).
The easterly winds really increased (to about 30 knots) yesterday morning.
Warm air. Dry air. Strong winds. All very favorable for fire.
Fortunately, the winds weakened yesterday and reversed, so the fire should decline substantially now. No hot weather is predicted over the next week, and rain will come in late Saturday.
We are going to make the transition to fall weather, and there is probably no going back.
PS: one more fun fact about yesterday. Several stations away from the mountains experienced an unusually large diurnal range: the difference between high and low temperatures in one day.
47 to 88 F at Olympia: 41F difference! Several other locations were like that. Why do you think that mountains work against such large daily temperature differences? Leave your answers in the comments.
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Mountains block massive continental cold fronts from deep in the Canadian Arctic. These are known to crash temperatures by 50 degrees or more in places like Denver.
ReplyDeleteThis is certainly not the whole story, but it's a piece of it.
Adiabatic expansion/compression (lordy, I remember something from Atmospheric Thermodynamics (in the ME Engineering Dept, small seminar class)). Look at the direction of the winds HP to LP (Chinook). I'm guessing dryer air with lower enthalpy (sort of heat content capacity) lead to larger extremes. Similar to how high deserts have large temperature swings, no buffer. I could quickly write 10 pages on this humidity issue in areas that got reservoirs causing localized evaporation and increased heat content of the atmosphere due to higher water vapor content (humidity).
ReplyDeleteBurned acreage from Bear Gulch jumped some 30% in the last few days with a new arm extending north into Jefferson Co.
ReplyDeleteRegarding why mountains may work against large diurnal temperature differences: I think they can work both for and against, depending upon one's proximity to them, the current season and pattern, and whether one is located on the leeward or windward side.
Here, easterly flow brings in dry, hot daytime highs, but overnight lows remain somewhat unaffected or are even lower (dry air usually means clear skies and heat loss to space). The mountains work against large diurnal differences for the most part during summer, keeping the hot, dry air from the desert away from us, mostly.
While in the winter, I think we'd see more diurnal variation without the mountains, as the winter systems would pass over more quickly without dumping as much rain (low clouds forced to rise over the mountain range). And if we received flow from the east or from the north in the winter, the lack of mountains would allow more frigid air into our area.
I'm also not a scientist, so I may be completely wrong! :)
Hey Cliff I read this article in the NYT today. It says wildfire smoke will kills thousands by mid century with Seattle being the front line for deaths.
ReplyDeletehttps://www.nytimes.com/2025/09/18/climate/wildfire-smoke-health-deaths.html?smid=nytcore-ios-share&referringSource=articleShare
Later on if you have to time to blog about this, I’d love to hear how your research supports/rejects their arguments. Thanks and love your blog!!!
I wonder if smoke from the Bear Gulch fire, with the change in wind direction, is why Mount Rainier is swaddled in smoke this morning.
ReplyDeletehttps://crystalmountainresort.roundshot.co/summit/#/
I know there's been a different fire closer by and to the east, but this smoke seems much greater than that fire produced previously.
When I was 18, I went to Wyoming for a backpack in the Wind River Mountains. We arrived in Pinedale, 7300 feet elevation, in mid August. It was about 78 degrees. Next morning at 5:30, there was frost on the sagebrush! A 50 degree range- I was impressed. I think high valleys have MORE temperature range, compared to sea-level, because of intense sunlight by day, followed by more radiational cooling at night, because of the thin, dry air.
ReplyDeleteBut if the MOUNTAINS have smaller range, I can only imagine that it is at intermediate elevations during an inversion, on slopes, where there is less sky exposure, so less cooling, while the low-level inversion forms by radiational cooling in the valleys. By day, I imagine that the intense sunlight heats the open high meadows (and rocks) more than it heats the valleys. But I would not have predicted less temperature variation compared to humid low elevation areas like the Southeast, where humidity holds in the heat of the day.
While the easterly flow created warmer, drier conditions over the Bear Gulch fire on September 16, it appeared from the direction the smoke moved, toward the north and northeast in the afternoon, that the wind flow was more from the south and southwest at the time the fire was taking off. Looking at the Jefferson Cr. RAWS information, the easterly flow in the morning hours up to early afternoon was quite light, then the wind switched to southwest and became stronger in the afternoon, while the humidity continued quite low. So fire spread did not seem to be associated with strong easterly winds, but increased south to southwest winds in the afternoon along with continued low humidity. The spread was probably also enhanced by the fact that the fuels were still very dry despite recent rains, which were lighter in this area, and possibly also due to a higher Haines index value that afternoon.
ReplyDeletewxman... you are missing an essential point. There was substantial directional shear at the time, with easterly winds at lower levels turning to more southerly aloft. Look at the winds above seatac...you will see this. You also have to consider that the Jefferson Creek RAWS is in a valley and would not get the strong easterlies as the fire site...cliff
DeleteThank you for the post. I know this area well, having hiked nearly every trail and way-trail within the fire's perimeter over the last few years (Six Ridge is the only one I've missed). The old-growth stands and alpine zones beyond the logged area around the lake were some of the best in the Olympics.
ReplyDeleteBeyond the weather, I've often suspected a correlation between the size of fires here and their point of origin. The two largest fires, the Bear Gulch and the 1950s Forks Fire, both started in logged areas at low elevations and spread uphill—which makes sense, as heat rises. In contrast, lightning tends to strike higher elevations near the peaks, like the fires in 2023, which often results in smaller fires.
I hope the media decides to discuss the specific cause of the Bear Gulch fire—fireworks—rather than relying on 'climate change' clickbait to sell ads. It seems far more productive for Washington voters to push their legislators for a statewide fireworks ban, a tangible action, than it is to try and convince climate change deniers to use fewer fossil fuels
Loco G.... I think you are right about the origin. Started low in a logged area with lots of debris and flammable grasses. Then moved uphill...which is favorable on south-facing slopes...cliff
DeleteIt seems that mountains tend to limit large diurnal temperature ranges because at higher elevations, daily maximum temperatures are usually much lower than at lower elevations - particularly during the warmer part of the year from mid spring to early fall. At the same time, daily minimum temperatures at higher elevations, while colder than at lower elevations, are often not as cold, relatively, compared with how much warmer daily maximum temperatures tend to be.
ReplyDeleteOverall, the higher above sea level you go, the less the average diurnal temperature range tends to be because air temperatures in the troposphere are primarily a result of the heating and cooling of Earth’s surface, though this is a general rule/rule of thumb which doesn’t always hold true due to topography and land cover.
Excellent work keeping an eye on this fire, Professor Mass! It is remarkable how much it has grown just in the past week. I am relieved that it is currently staying in remote, mountainous terrain and not making its way down to lower elevations, and I hope it stays that way so long as it continues to burn. I of course hope that our hardworking firefighters are able to get a handle on it, and that fall rains come soon to put it out.
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