Tomorrow is going to be fascinating.
There is going to be a sudden, intense heatwave over western Washington, with temperatures jumping into the mid to upper 80s at many lowland locations.
And then much cooler on Wednesday.
This west-side heat will be associated with powerful easterly (from the east) winds over the Cascade crest and western slopes, which will provide a fire threat.
Consider the temperatures forecast by the UW high-resolution ensemble (many forecasts) prediction system for Seattle. Tomorrow afternoon, around 4 PM (red arrow), most of the forecasts are for the upper 80s!
Let me show you some forecast maps of surface temperatures.
Tomorrow morning at 5 AM, the region is relatively cool, with the warmest temperatures on the lower western slopes of the Cascades.
Why so warm WEST of the Cascades?
Because strong easterly (from the east winds) will be descending the western slopes of the Cascades and coastal mountains, and descending air warms intensely by compression.
Take a look at the surface winds at 11 AM tomorrow, with stronger winds shown by yellow and orange colors. The western slopes will be gusty!
Strong winds and dry air can dry out surface fuels and stoke windfires. In western Washington and Oregon, virtually ALL the big fires are associated with strong winds from the east.
The National Weather Service has a red-flag warning out, which indicates the potential for wildfire on the west side of the Cascades.
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Thanks so much Cliff - I'm headed out to Rainy Pass and 5 days backpacking down into Stehekin. Will delay until the 20th to keep watch before we're fully in and committed!
ReplyDeleteThe temperature differences are fascinating. Where I am in the Puyallup area as of 2pm it's 79, but 15 mins away at Thun Field it's 88. They must be getting more of the wind push? It's barely windy where i am either.
ReplyDeleteInteresting temperature difference over that short of a distance.
Deleteis the sunset cloud over the southern Olympics a pyrocumulus formation?
ReplyDeleteBear Gulch fire
DeleteI was coming here to ask the same! It looked like it from my vantage point in Beacon Hill and given the conditions today fire activity was likely quite high
DeleteBit of a general question... I always hear people question the accuracy of weather forecasts but they've always seemed pretty damn spot on in WA, including today's random 88F day. Does the PNW generally have predictable weather, more so than other parts of the world?
ReplyDeleteYes, more predictable due to the moderating of the ocean/marine layer and the obstacles, that is, mountains all around. Midwestern weather is difficult because there are no obstacles and nothing to moderate severe heat and cold as the weather systems roll.
DeleteFor PNW weather fans/nerds or even those just curious, I'd recommend Cliff's book: "The Weather of the Pacific Northwest" (second edition).
DeleteThis question is somewhat addressed near the end of page three.
"Not only is the weather different in the Northwest, but so is its prediction. [...] Pacific Northwest predictions are challenged by a sparsity of upstream surface observations, since most West Coast weather systems originate over the relatively data-poor North Pacific. Weather satellites [...] have facilitated a rapid improvement in Northwest weather forecast skill."
Other parts of the book touch on it, as well, like most of Chapter 13. Enjoy!
DJL - no it's exactly the other way around. Prediction is comparatively easy in the Midwest. There are many land-based stations "upstream" to get data from, and there are no natural obstacles such as mountain ranges to take into account. Around here, there are kinds of small-scale considerations and "micro-climates" that the terrain produces that can change the weather in a just a few miles. That can make prediction very difficult.
DeleteReplying to ag:
DeleteFrom my expierence as a lifelong Pacific Northwest resident, I would say that our weather is becoming less predictable as time goes on, but that it is generally more stable than other parts of North America (not sure about the rest of the world). Winters are typically wet but mild, springs slowly warm up and dry out as they progress, summers are dry and usually pleasant, and autumn typically starts off nice but distingrates into stormy, wet weather as it progresses. There are always exceptions to these general patterns, but by and large, our weather has been more stable than other parts of the country. Whether it stays that way remains to be seen. Yesterday saw both 80 degree heat and wicked winds at the coast. Its not normal for both to happen at the same time. This is a great example of the increasing number of oddities that are happening with our weather.
Well I spend a lot of time in MN. You'll have to explain to me why the 3-5 day forecasts here are correct upwards of 90% of the time, and in MN less than 50%, sometimes wildly off. If prediction is easy in the Midwest as you say, then the forecasters there must really be super awful. Maybe Cliff will explain why the discrepancy.
DeleteAt the same time, geographically influenced microclimates could make things a little more challenging. We see this time after time with regards to snow events.
ReplyDeleteThe convergence zone is often frustrating because we can predict when it will develop and the radar will pick it up in action. Despite this, the weather.com rain advisory can't accurately time the rain because the rain doesn't really approach from any direction.
From the VIIRS hot spot data it looks like the Bear Gulch almost doubled in size yesterday and made it up int the upper Duckabush watershed. Can you do a post on how the HDW likely came together to feed the fire so quickly? I'm personally okay with lightening started fires, but this one being stated by a firework and WA voters having no inclination at making fireworks illegal state wide (this would prevent tribes from selling them) really frustrates me.
ReplyDeleteI would love to see fireworks banned statewide for individual use. Fireworks should be left exclusivley to professionals who are trained and certified to handle them properly. While such a ban would effectivley prevent the tribes from selling them (I don't believe such a ban could be enforced on tribal land, but if no one can use them outside of tribal land, sales will fall significantly, and it won't necessarily be profitable to sell them), it is a necessary measure to ensure the safety of everyone in our state, tribal member or not. The state legislature should take this matter up in their next session.
DeleteThat explains why it was cooler than expected at Valhalla Lake yesterday afternoon. But I have a question. You have explained several times about the effect of winds from the east. That raises a question, though. The air rises before it falls. So why don't the two effects cancel out? Why doesn't the drop in temperatures going up over the mountains, render the rise in temperatures when the air descends, nugatory? The only explanation that occurs to me is Central Washington is slightly higher in elevation, so the air will drop more than it rises after summitted the Cascades. But that doesn't seem like much.
ReplyDeleteGood question....most air descending the range does not come from low levels on the other side, but from near or above crest level.
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