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Historic Pacific Northwest Heatwave of 2021


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A heatwave of potentially unprecedented proportions for parts of the Pacific Northwest Region, including Oregon, Washington, and British Columbia is now in its early stages of evolving. June high temperature records will likely be shattered across much of the region. Numerous all-time high temperature records will likely be challenged or broken.

On Monday, the most populated region in the Pacific Northwest could see widespread temperature anomalies more than 4 standard deviations above the normal figures. A small part of the region could experience temperatures more than 6 standard deviations above normal.

Standardized Temperature Anomalies (6/28 18z):
Pac-NW-June-HW-2021b.jpg

Select June, All-Time Records, Forecast Maximum Temperatures:

Pac-NW-June-HW-2021.jpg

Western sections of Oregon, Washington, and British Columbia, including Portland, Seattle, and Vancouver, will likely see the highest temperatures during the June 26-29 period. Elsewhere, exceptional warmth could persist into the opening days of July.

Minimum temperatures will also approach monthly and all-time lows, especially in areas affected by the Urban Heat Island (UHI) effect, namely Portland, Seattle, and Vancouver.

Climate change is increasing the frequency, magnitude, and duration of extreme heat events. One important mechanism is through wave resonance events (Mann et al., 2017). If one steps back to a larger hemispheric perspective starting near the beginning of June, one has witnessed the emergence of mega-heat domes in a "whack-a-mole" fashion in the Northern Plains, Southwest,  and northern and eastern Europe (including northwestern Russia) that led to record heat, including some monthly or all-time record high temperatures. This latest heat dome is the fourth such major event this month.

 

Updates:

Recurrent Rossby Waves, Heatwaves, and Climate Change

June 27, 2021: New Canadian National High Temperature Record

June 28, 2021: New Canadian National High Temperature Record

June 29, 2021: New Canadian National High Temperature Record

Unprecedented North American Heatwave Scorches the Pacific Northwest

Historic Nature of the Heatwave 

Attribution Study: 'Virtually Impossible' without Climate Change

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Not to steal the Pac NW's sunshine in this heat discussion...

 - it really interests me that the non-hydrostatic heights over Long Island ( ~ ) are destined/forecast to equal those astounding tropopause Tsar-bomba bulging heights in the Pac NW.  Yet we are modest in the heat genesis. 

A some of that is because the hydrostatics integration takes energy to put theta-e content into the column, thus shrinking the V.   That's not lowering distinction of the enormity of the event out west;  weather they have DP to content with or not, above 98 F it really doesn't matter if the wind is still, the sun full, and one's acclimation is temperate.  

I feel we are/have been dodging extraordinary bullets here in the east - this isn't the first time when where one of these ridges emerged here, eclipsed in recognition it may be by some, ..owing to the fact that 94/70 is ugly but not as unusual.     Playing with fire -

Here's the deal, we have a method of dying hard here.  It's called Sonoran heat release, where synoptic changes in the Pacific relay into western N America, sometimes dislodges and injects a pithy 22.5+C 850 mb, well mixing payload into one of these non-hydrostatic ridges - where by the thickness ( which is the DP integral) are thus free to expand.

We have not observed a Sonoran heat release event since 594 dm become the new 588.  

These tall heights can do a lot of damage with ‘hone grown' cumulative thermal stowing from consecutive days in their own rights - like next week’s type will be from N VA to D.E.M.   But I wonder if something special lurks this summer, as we are appearing to be in a post La Nina hang-over which tends to favor AAM/subtropical ridge robustness during warm season, and already, ..we are seeing them verify.  

One of theses times, we may hang a 25C at 850 mb over ORD with sights on BTV to PHL and Boston, and let us hope it is not timing with one of these atmospheric Tibetan Plateau sized ridges opening the garage door to park that delivery inside, because that would be like a "Hellraiser" scene at the prom if that happens.

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1 hour ago, Typhoon Tip said:

Not to steal the Pac NW's sunshine in this heat discussion...

 - it really interests me that the non-hydrostatic heights over Long Island ( ~ ) are destined/forecast to equal those astounding tropopause Tsar-bomba bulging heights in the Pac NW.  Yet we are modest in the heat genesis. 

A some of that is because the hydrostatics integration takes energy to put theta-e content into the column, thus shrinking the V.   That's not lowering distinction of the enormity of the event out west;  weather they have DP to content with or not, above 98 F it really doesn't matter if the wind is still, the sun full, and one's acclimation is temperate.  

I feel we are/have been dodging extraordinary bullets here in the east - this isn't the first time when where one of these ridges emerged here, eclipsed in recognition it may be by some, ..owing to the fact that 94/70 is ugly but not as unusual.     Playing with fire -

Here's the deal, we have a method of dying hard here.  It's called Sonoran heat release, where synoptic changes in the Pacific relay into western N America, sometimes dislodges and injects a pithy 22.5+C 850 mb, well mixing payload into one of these non-hydrostatic ridges - where by the thickness ( which is the DP integral) are thus free to expand.

We have not observed a Sonoran heat release event since 594 dm become the new 588.  

These tall heights can do a lot of damage with ‘hone grown' cumulative thermal stowing from consecutive days in their own rights - like next week’s type will be from N VA to D.E.M.   But I wonder if something special lurks this summer, as we are appearing to be in a post La Nina hang-over which tends to favor AAM/subtropical ridge robustness during warm season, and already, ..we are seeing them verify.  

One of theses times, we may hang a 25C at 850 mb over ORD with sights on BTV to PHL and Boston, and let us hope it is not timing with one of these atmospheric Tibetan Plateau sized ridges opening the garage door to park that delivery inside, because that would be like a "Hellraiser" scene at the prom if that happens.

I was enjoying the T Tip post ride until the last para. I read it several times. I felt a concerned fright not for Pinheads pain for pleasure credential analogy, but instead, thinking of the actual conditions, if the garage door delivery does play out.  As always …

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I've been impressed with the semi-constant 47-day cycle repeat since roughly last Fall in the US temperature profile. It's not exactly the same of course. Much more extreme and the cold and hot sources are in slightly different places. But the timing does line up and the look is similar when adjusting for the season. I've always figured part of the reason some heat waves and cold snaps are extreme now is that we are starting to get Spring/Fall type anomalies (+/- 20-40, instead of 10-20) in the shoulder/transitional months of Winter/Summer, when it used to be much harder for that to happen. I've had very warm highs transition to very cold highs transition at the same part of these 47 day cycles since September when near record heat (96) went to near record cold (47) in two days or so. Same thing in October. Current transition from low or mid-90s to low or mid 70s on Sunday or Monday is kind of the June version of it. Low or mid 70s would be near cold highs here for the time of year after hitting 103 earlier in the month, which is relatively close to record warmth (107 in June 1994).

Oct-29-2020Sunday-6-27

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https://www.sciencedaily.com/releases/2019/12/191209112147.htm

In a new study published today in Nature Climate Change, scientists show how specific wave patterns in the jet stream strongly increase the chance of co-occurring heatwaves in major food producing regions of Northern America, Western Europe and Asia. Their research finds that these simultaneous heatwaves significantly reduce crop production across those regions, creating the risk of multiple harvest failures and other far-reaching societal consequences, including social unrest.

Lead author, Dr Kai Kornhuber from the University of Oxford's Department of Physics and Colombia University's Earth Institute, said: "Co-occurring heatwaves will become more severe in the coming decades if greenhouse gases are not mitigated. In an interconnected world, this can lead to food price spikes and have impacts on food availability even in remote regions not directly affected by heatwaves.

"We found a 20-fold increase in the risk of simultaneous heatwaves in major crop producing regions when these global scale wind patterns are in place. Until now this was an underexplored vulnerability in the food system. We have found that during these events there actually is a global structure in the otherwise quite chaotic circulation. The bell can ring in multiple regions at once and the impacts of those specific interconnections were not quantified previously."

Western North America, Western Europe and the Caspian Sea region are particularly susceptible to these atmospheric patterns that get heat and drought locked into one place simultaneously where they then affect crops production yields.

Dr Dim Coumou, co-author from the Institute for Environmental Studies at VU Amsterdam, said: "Normally low harvests in one region are expected to be balanced out by good harvests elsewhere but these waves can cause reduced harvests in several important breadbaskets simultaneously, creating risks for global food production."

Dr Elisabeth Vogel, co-author from Melbourne University, said: "During years in which two or more summer weeks featured the amplified wave pattern, cereal crop production was reduced by more than 10% in individual regions, and by 4% when averaged across all crop regions affected by the pattern."

Dr Radley Horton, co-author from the Lamont-Doherty Earth Observatory at Colombia University, said: "If climate models are unable to reproduce these wave patterns, risk managers such as reinsurers and food security experts may face a blind spot when assessing how simultaneous heat waves and their impacts could change in a warming climate."

The scientists conclude that a thorough understanding of what drives this jet stream behaviour could ultimately improve seasonal predictions of agricultural production at the global scale and inform risk assessments of harvest failures across multiple food-producing regions.


https://www.realclimate.org/index.php/archives/2018/10/climate-change-and-extreme-summer-weather-events-the-future-is-still-in-our-hands/

In a follow-up article just published in the AAAS journal Science Advances, we look at future projections of QRA using state-of-the-art climate model simulations. It is important to note that that one cannot directly analyze QRA behavior in a climate model simulation for technical reasons. Most climate models are run at grid resolutions of a degree in latitude or more. The physics that characterizes QRA behavior of Rossby Waves faces a stiff challenge when it comes to climate models because it involves the second mathematical derivative of the jet stream wind with respect to latitude. Errors increase dramatically when you calculate a numerical first derivative from gridded fields and even more so when you calculate a second derivative. Our calculations show that the critical term mentioned above suffers from an average climate model error of more than 300% relative to observations. By contrast, the average error of the models is less than a percent when it comes to latitudinal temperature averages and still only about 30% when it comes to the latitudinal derivative of temperature.

That last quantity is especially relevant because QRA events have been shown to have a well-defined signature in terms of the latitudinal variation in temperature in the lower atmosphere. Through a well-established meteorological relationship known as the thermal wind, the magnitude of the jet stream winds is in fact largely determined by the average of that quantity over the lower atmosphere. And as we have seen above, this quantity is well captured by the models (in large part because the change in temperature with latitude and how it responds to increasing greenhouse gas concentrations depends on physics that are well understood and well represented by the climate models).

These findings, incidentally have broader implications. First of all, climate model-based studies used to assess the degree to which current extreme weather events can be attributed to climate change are likely underestimating the climate change influence. One model-based study for example suggested that climate change only doubled the likelihood of the extreme European heat wave this summer. As I commented at the time, that estimate is likely too low for it doesn’t account for the role that we happen to know, in this case, that QRA played in that event. Similarly, climate models used to project future changes in extreme weather behavior likely underestimate the impact that future climate changes could have on the incidence of persistent summer weather extremes like those we witnessed this past summer.

 

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Posted this in the other discussion not realizing this thread had been opened up, so the info is more relevant here than there ... 

We are under the heat dome big-time now, in southern BC as well as the Pac NW region. 

For BC, the all-time record highs are 44.4 C (recorded as 112 F) in July 1941 at locations in the Fraser canyon region about 150 miles northeast of Vancouver. Numerous other inland locations have recorded extremes between 42 C and that value, a few of them since we converted from F to C in the late 1970s. Canada's all-time high is just one F deg higher (113F which is 45.0 C) and that was in July 1937 in towns southeast of Regina SK. In both the 1936 and 1937 heat waves, numerous 42-44 C readings were registered and the all-time warmest top thirty (available on wikipedia) is dominated by these three events (1936, 1937, 1941) despite the warming trends recently. For whatever reason Canada has not seen any new extremes, a couple of times around 2003 and 2009 there were 42C readings. Toronto has about a dozen days with 100+ readings, the hottest were in 1936 (three at 105F) and almost all the rest between 1911 and 1953. Only 2011 contributed one to this list after 1953. There has been an increase in mean temperature at Toronto but almost all of it is with overnight lows, not daytime highs (compared to the mid-20th century, obviously all parameters increased from late 19th to early-mid 20th). 

This current heat wave appears capable of approaching those all-time record highs, will report back on the results. We are right under the heart of this 500 mb heat dome (shown at 599 dm) in south-central BC this weekend. I live about halfway up the west side of the Columbia valley where the base elevation is about 400m asl and the local peaks in the Monashee range are around 2000-2500m. My local elevation is about 1050m. The nearest reporting station (Warfield BC) is at about 700m. It can be one of the province's hottest reporting sites, Osoyoos near the US border in the Okanagan and Lytton or Lillooet in the Fraser canyon are more frequently tops. We weren't quite under the full effect of this on Friday but already it was 36 C (97 F) at Warfield. Expecting closer to 40 C today and the peak likely around Monday-Tuesday. 

(since I typed that two hours ago it has hit 41 C at Lytton BC, I also see 107F at The Dalles east of Portland OR, and numerous low 100s in WA state. About 38C or 100F at my place. This heat wave looks like it might more or less match the July 1941 event but this one has appeared earlier, one has to wonder if there could be a more severe event later in the summer). 

A/C is not all that common in our part of the world despite the fact that almost every summer there are a few sweltering days. It does tend to cool off fairly well at night here, I was out at midnight admiring the rising moon near Saturn, and it was quite comfortable, probably about 65F. If you have clear skies where you live tonight, have a look between midnight and 0200h local time, you'll see the Moon very close to Saturn and then Jupiter off to the left rising a bit later. The Moon will then be close to Jupiter on Sunday night. 


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34 minutes ago, Roger Smith said:

Posted this in the other discussion not realizing this thread had been opened up, so the info is more relevant here than there ... 

We are under the heat dome big-time now, in southern BC as well as the Pac NW region. 

For BC, the all-time record highs are 44.4 C (recorded as 112 F) in July 1941 at locations in the Fraser canyon region about 150 miles northeast of Vancouver. Numerous other inland locations have recorded extremes between 42 C and that value, a few of them since we converted from F to C in the late 1970s. Canada's all-time high is just one F deg higher (113F which is 45.0 C) and that was in July 1937 in towns southeast of Regina SK. In both the 1936 and 1937 heat waves, numerous 42-44 C readings were registered and the all-time warmest top thirty (available on wikipedia) is dominated by these three events (1936, 1937, 1941) despite the warming trends recently. For whatever reason Canada has not seen any new extremes, a couple of times around 2003 and 2009 there were 42C readings. Toronto has about a dozen days with 100+ readings, the hottest were in 1936 (three at 105F) and almost all the rest between 1911 and 1953. Only 2011 contributed one to this list after 1953. There has been an increase in mean temperature at Toronto but almost all of it is with overnight lows, not daytime highs (compared to the mid-20th century, obviously all parameters increased from late 19th to early-mid 20th). 

This current heat wave appears capable of approaching those all-time record highs, will report back on the results. We are right under the heart of this 500 mb heat dome (shown at 599 dm) in south-central BC this weekend. I live about halfway up the west side of the Columbia valley where the base elevation is about 400m asl and the local peaks in the Monashee range are around 2000-2500m. My local elevation is about 1050m. The nearest reporting station (Warfield BC) is at about 700m. It can be one of the province's hottest reporting sites, Osoyoos near the US border in the Okanagan and Lytton or Lillooet in the Fraser canyon are more frequently tops. We weren't quite under the full effect of this on Friday but already it was 36 C (97 F) at Warfield. Expecting closer to 40 C today and the peak likely around Monday-Tuesday. 

(since I typed that two hours ago it has hit 41 C at Lytton BC, I also see 107F at The Dalles east of Portland OR, and numerous low 100s in WA state. About 38C or 100F at my place. This heat wave looks like it might more or less match the July 1941 event but this one has appeared earlier, one has to wonder if there could be a more severe event later in the summer). 

A/C is not all that common in our part of the world despite the fact that almost every summer there are a few sweltering days. It does tend to cool off fairly well at night here, I was out at midnight admiring the rising moon near Saturn, and it was quite comfortable, probably about 65F. If you have clear skies where you live tonight, have a look between midnight and 0200h local time, you'll see the Moon very close to Saturn and then Jupiter off to the left rising a bit later. The Moon will then be close to Jupiter on Sunday night. 

 

Lillooet was up to 41.6C at 3 pm PDT. That’s the first 40C temperature on record there in June.

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This early onset is certainly the main feature, Don, we often count on a cloudy and unsettled June to keep the wildfire situation under control and in most years the weather gradually dries out and warms up through July in this northern extension of the interior west, so breaking all-time June records will be child's play for this late July heat wave. It ,may end up breaking the July records too.

The Fraser valley region east of Vancouver has 38-39 C readings and the dew points are oppressive for this climate, around 18 or 19 C, adding some discomfort to the humidex values. That is a heavily populated region so it's not just 100 and something in a desert with tumbleweed and a couple of houses beside a dried out lake, we're talking about millions of people between greater Vancouver and Sea-Tac taking on this 100-degree heat without much a/c and generally not all that used to it (although it does seem to happen every other year now). Also you would think there's a lot of places to go to cool off at a beach, but in a lot of places beach access is very limited around these regions, the shoreline tends to be either lined with cottages or swamp where you can't swim. And inland lakes are very small and fill up with day users very quickly. 

The current temperature at YVR (Vancouver Int'l A) is only 30 C (86 F) but it's probably closer to 35 C in most of the urban areas around Vancouver, the airport is very close to the sea and almost always has a seabreeze during heat waves. The all-time record there from late July 2009 is only 35 C. 

 

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101F at Sea-Tac at 4 pm PDT .. is that all-time for SEA? I can remember it hitting maybe 99 or 100 a few years ago. 

104F at PDX and 109F at The Dalles (which is a heat trap but still ... )

also 104F at YKA (Kamloops) which is not often within 1-2 of the heat trap locations. 

(to be fair, you couldn't design a better heat trap than the Fraser canyon, it points due south, it has bare rocky surfaces and the weather stations are at airports on south-facing benches, nobody in their right mind would live right there anyway). 

The full effects are not quite into the normal hot spots of southeast WA and eastern OR which are in the low 100s, sometimes those places like Walla Walla, Pasco and Pendleton can get into the low 110s. Probably will tomorrow. 

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57 minutes ago, Roger Smith said:

This early onset is certainly the main feature, Don, we often count on a cloudy and unsettled June to keep the wildfire situation under control and in most years the weather gradually dries out and warms up through July in this northern extension of the interior west, so breaking all-time June records will be child's play for this late July heat wave. It ,may end up breaking the July records too.

The Fraser valley region east of Vancouver has 38-39 C readings and the dew points are oppressive for this climate, around 18 or 19 C, adding some discomfort to the humidex values. That is a heavily populated region so it's not just 100 and something in a desert with tumbleweed and a couple of houses beside a dried out lake, we're talking about millions of people between greater Vancouver and Sea-Tac taking on this 100-degree heat without much a/c and generally not all that used to it (although it does seem to happen every other year now). Also you would think there's a lot of places to go to cool off at a beach, but in a lot of places beach access is very limited around these regions, the shoreline tends to be either lined with cottages or swamp where you can't swim. And inland lakes are very small and fill up with day users very quickly. 

The current temperature at YVR (Vancouver Int'l A) is only 30 C (86 F) but it's probably closer to 35 C in most of the urban areas around Vancouver, the airport is very close to the sea and almost always has a seabreeze during heat waves. The all-time record there from late July 2009 is only 35 C. 

 

This is a really high impact heat event. I saw that YVR surpassed its monthly record a short time ago. Victoria has set new monthly records for 2 consecutive days. Lillooet was at 42.2C. It will be interesting to see the final numbers when Environment Canada posts them tomorrow. Moreover, the worst is yet to come in much of BC, WA, and OR.

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3 minutes ago, Roger Smith said:

101F at Sea-Tac at 4 pm PDT .. is that all-time for SEA? I can remember it hitting maybe 99 or 100 a few years ago. 

104F at PDX and 109F at The Dalles (which is a heat trap but still ... )

also 104F at YKA (Kamloops) which is not often within 1-2 of the heat trap locations. 

(to be fair, you couldn't design a better heat trap than the Fraser canyon, it points due south, it has bare rocky surfaces and the weather stations are at airports on south-facing benches, nobody in their right mind would live right there anyway). 

The full effects are not quite into the normal hot spots of southeast WA and eastern OR which are in the low 100s, sometimes those places like Walla Walla, Pasco and Pendleton can get into the low 110s. Probably will tomorrow. 

No. That’s a new June record. The all-time high is 103. It might be matched today and should be broken tomorrow.

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Just FYI, Victoria airport is a long way north of the city and the southern part of the city is currently getting a fairly nice sea breeze cooling to about 25 or 26 C, but just a few miles inland it's 35 C at U-Vic. Same happening around Vancouver, one or two of the lighthouse stations have 25 C while in the valley it's 37-40 C. 

The one good thing here is that we don't have as high a dew point locally, the dews are 18-20 C in coastal areas and just 10 C here, so it's just scorching hot without any humidity. The sky is quite an intense shade of blue like you see in the desert southwest in heat waves, with really tiny cumulus fractus on the horizon mostly. I would not be that surprised if a roadrunner appeared outside my window. 

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Just watching local newscasts from both sides of the border, a few fires to report, nothing too serious yet, but with so many people out camping this weekend, and doing yard work, there are opportunities for fires to start and the forests are starting to dry out. Vehicle fires from overheating have been a problem. 

Lillooet BC apparently hit 43.0 C That would be 109.4 F in old money, so within 2.6 F of the all-time record there. (Just saw Don's post about Lytton at 43.3 C).

We had a week of less extreme heat before this started so everyone is partially acclimatized, I would imagine this might be the Dec 2015 of Junes in terms of annihilating previous records (inland, the anomalies were not very large at SEA or YVR before this hot spell began, Spokane is close to +5 F and will end up +6 to +7). I looked up data for June 1958 which was one of the warmer ones, nothing like this sustained, just one day around 37 C, although the first half of that month was probably about equal to this year. This is not our first June heat wave either, it was very hot here on the first three days of June, hitting 36 C several days in a row. 

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I hope we see a statistical analysis similar to the one we got for the 2020 Siberian Heatwave after this is all said and done. I'd really like to know how this stacks up statistically. I did see the tweet above regarding 500mb heights approaching a 5-sigma event implying a recurrence interval of over 4000 years.  Clearly this is an unusual event.

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2 minutes ago, bdgwx said:

I hope we see a statistical analysis similar to the one we got for the 2020 Siberian Heatwave after this is all said and done. I'd really like to know how this stacks up statistically. I did see the tweet above regarding 500mb heights approaching a 5-sigma event implying a recurrence interval of over 4000 years.  Clearly this is an unusual event.

Against what? Clearly these semantics are a bit silly when considering the acceleration of atmospheric processes.

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27 minutes ago, bdgwx said:

I hope we see a statistical analysis similar to the one we got for the 2020 Siberian Heatwave after this is all said and done. I'd really like to know how this stacks up statistically. I did see the tweet above regarding 500mb heights approaching a 5-sigma event implying a recurrence interval of over 4000 years.  Clearly this is an unusual event.

I suspect that there will be such a study as the event is virtually unprecedented and it has affected millions of people. 

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59 minutes ago, Roger Smith said:

Just watching local newscasts from both sides of the border, a few fires to report, nothing too serious yet, but with so many people out camping this weekend, and doing yard work, there are opportunities for fires to start and the forests are starting to dry out. Vehicle fires from overheating have been a problem. 

Lillooet BC apparently hit 43.0 C That would be 109.4 F in old money, so within 2.6 F of the all-time record there. (Just saw Don's post about Lytton at 43.3 C).

We had a week of less extreme heat before this started so everyone is partially acclimatized, I would imagine this might be the Dec 2015 of Junes in terms of annihilating previous records (inland, the anomalies were not very large at SEA or YVR before this hot spell began, Spokane is close to +5 F and will end up +6 to +7). I looked up data for June 1958 which was one of the warmer ones, nothing like this sustained, just one day around 37 C, although the first half of that month was probably about equal to this year. This is not our first June heat wave either, it was very hot here on the first three days of June, hitting 36 C several days in a row. 

Final figure from Lytton was 43.8C. That set a new Canadian national high temperature record for June.

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@donsutherland1and others,

 Do I think AGW is contributing to this? I strongly feel that way. The globe is ~2F warmer than it was just since the 1970s and ~3 warmer than 1900 if I’m not mistaken. And this is the fourth extreme heatwave just this month to go along with Desert SW, N Plains, and Russia as Don pointed out. But is the likely contribution to this more than, say, 2-3F? That’s impossible to know. One thing that is an additional major contributor is the widespread drought in the area (see below), likely caused largely by La Niña, combining with the very anomalous Pacific NW ridge.

  Do y’all think the AGW contribution to this heatwave is likely more than ~2-3F? Do you think that the widespread W US drought is a bigger contributor? I'm strongly suspecting it is based on the physics of air heating up more over drier soils due to their much lower specific heat levels. Would we be looking at a historic heatwave had there been no drought? I have a lot of doubt about that and also suspect that there wouldn't be as strong a ridge there without the drought. Also, note that the 3 big US heatwaves have all occurred in widespread drought regions as per the map below:

BF0539F6-2C1E-4AD6-9FEC-C61EF423A9D8.gif

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In terms of return periods of a heat wave this intense in this region, we have not yet gone past two consecutive readings of 44.4 C (112 F) at the same locations mentioned in B.C., and a check of the weather maps for those two days (July 16-17, 1941) shows something very similar, a localized 500 mb heat dome around 598 dm.

Here's a link to the historical weather chart for July 17, 1941.

https://www.wetterzentrale.de/reanalysis.php?uur=1800&var=1&nmaps=24&map=2&model=noaa&jaar=1941&maand=07&dag=17

So I went into the historical data archives for EC to check the longevity of the 1941 heat wave, finding the following (I have converted the data back to the F deg that it was originally measured in as each of the C equivalents has an uncertainty of about 0.2. The hottest period was July 12-18. 

date ____ max Lytton BC ___ max Lillooet BC

Jul 12 ___ 96 __________ 98

Jul 13 __ 100 _________ 101

Jul 14 __ 105 _________ 106

Jul 15 __ 109 _________ 109

Jul 16 __ 112 _________ 112

Jul 17 __ 112 _________ 112

Jul 18 ___ 96 __________ 92

__________________________________

Both locations had very few hot days during the summer before this heat wave set in, and returned to modified versions in mid-August with about a week in the high 90s (normal at these locations in the high 80s F). 

There was a small amount of rain at Lytton on the 16th and about a quarter inch at both locations on the 18th with the passage of weak cold fronts. This indicates to me that the 1941 heat wave produced localized nearly dry thunderstorms that were probably a forest fire hazard at the time. In terms of where the current heat wave is in its evolution, I would say around day 2 or 3 of the above, except that in the current case, it was somewhat warmer for about four days before this intense heat set in than was the case in 1941, highs for the past six days at Lytton (before Saturday) were 32.5 C (20th), 35.5 C (21st), 33.9 C (22nd), 31.6 C (23rd), 31.3 C (24th), 39.2 C (25th).

Converted to F deg those would be 91, 96, 93, 89, 88, 103 (and around 110 today). 

We'll see what the seven-day average is this time around, in 1941 it was 104.3 at both locations. 

Assuming three or four more days near 110 this time, we could be looking at an average of 106 and that could climb a bit if the exit from the heat is warmer than the 89, 88 above. 

I would say that as a climate "singularity" this is so far about equal to the 1941 event. Weather buffs will probably recognize 1941 as the year when NYC had record heat in early October (94 F the highest Oct temp on record there). The summer of 1941 was generally a hot one in eastern North America and set a few daily records although it is not in the first tier of hot summers. Some of those records were in late July with a lag of about ten days indicated from the western heat wave. It was mid to high 90s sort of heat rather than 100+ at least for the locations I could check (Toronto, NYC). 

Another parameter worth comparing is the highest minima in these BC heat waves, only about 73 F for the 1941 version. Overnight lows in the high 70s or low 80s seldom occur in this climate (r.h. too low generally, high probability of clear skies at night). The 1941 heat wave seemed to end with a spell of cloudy and warm weather as the highs dropped more than the lows, and there were thunderstorms around. 

I may check the 2003 heat wave that led to serious fire hazards around the Okanagan valley in late July and early August. From memory it was not quite this hot but more sustained for two or three weeks, and there were a few episodes of dry lightning from storm cells that fired up over the Cascades in WA and moved north into BC overnight. Those started the worst of the fires near Kelowna and Salmon Arm BC. 

Salmon don't really have arms by the way, that's a feature of Shuswap Lake. 

 

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10 hours ago, GaWx said:

@donsutherland1and others,

 Do I think AGW is contributing to this? I strongly feel that way. The globe is ~2F warmer than it was just since the 1970s and ~3 warmer than 1900 if I’m not mistaken. And this is the fourth extreme heatwave just this month to go along with Desert SW, N Plains, and Russia as Don pointed out. But is the likely contribution to this more than, say, 2-3F? That’s impossible to know. One thing that is an additional major contributor is the widespread drought in the area (see below), likely caused largely by La Niña, combining with the very anomalous Pacific NW ridge.

  Do y’all think the AGW contribution to this heatwave is likely more than ~2-3F? Do you think that the widespread W US drought is a bigger contributor? I'm strongly suspecting it is based on the physics of air heating up more over drier soils due to their much lower specific heat levels. Would we be looking at a historic heatwave had there been no drought? I have a lot of doubt about that and also suspect that there wouldn't be as strong a ridge there without the drought. Also, note that the 3 big US heatwaves have all occurred in widespread drought regions as per the map below:

BF0539F6-2C1E-4AD6-9FEC-C61EF423A9D8.gif

 

AGW and the severe multi-year drought can't fully be disentangled. While internal variability leads to drought conditions, AGW increases the probability of such outcomes through shifting precipitation patterns and greater drying of soil from higher temperatures. How much is climate change contributing?

Detailed multi-model analysis, which is utilized during attribution studies, would provide a good answer. But a rough approximation is possible from the following approach:

(Probability of an event under the current climate - Probability of an event under the baseline climate) / Probability of an event under the current climate

This formula provides a good approximation, because climate science has concluded with very high confidence that most of the recent warming has resulted from growing anthropogenic greenhouse gas forcing (actually > 100%, because a small decline in solar irradiance has made a negative contribution).

I ran some numbers for Seattle. For the baseline, I used the June-August 1951-80 period (the GISS baseline, as the Seattle-Tacoma record only goes back to 1945). For the current climate, I used the 1991-20 base period.

Probabilities:

100-degree day: 1951-80: 0.035%; 1991-20: 0.078%

Actual: 1951-80: 0%; 1991-20: 0.07%

Then using the probabilities, I got: (.0078 - .0035)/0.0078 = approximately 55%. Climate change made such events 55% more likely

For 105-degree days, the climate change contribution would be 61%

The actual probabilities could be somewhat higher, as climate change has made the kind of resonance events involved in this epic heat event more likely. @bluewaveposted a good paper on this topic earlier in the thread.

 

 

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55 minutes ago, donsutherland1 said:

 

AGW and the severe multi-year drought can't fully be disentangled. While internal variability leads to drought conditions, AGW increases the probability of such outcomes through shifting precipitation patterns and greater drying of soil from higher temperatures. How much is climate change contributing?

Detailed multi-model analysis, which is utilized during attribution studies, would provide a good answer. But a rough approximation is possible from the following approach:

(Probability of an event under the current climate - Probability of an event under the baseline climate) / Probability of an event under the current climate

This formula provides a good approximation, because climate science has concluded with very high confidence that most of the recent warming has resulted from growing anthropogenic greenhouse gas forcing (actually > 100%, because a small decline in solar irradiance has led made a negative contribution).

I ran some numbers for Seattle. For the baseline, I used the June-August 1951-80 period (the GISS baseline, as the Seattle-Tacoma record only goes back to 1945). For the current climate, I used the 1991-20 base period.

Probabilities:

100-degree day: 1951-80: 0.035%; 1991-20: 0.078%

Actual: 1951-80: 0%; 1991-20: 0.07%

Then using the probabilities, I got: (.0078 - .0035)/0.0078 = approximately 55%. Climate change made such events 55% more likely

For 105-degree days, the climate change contribution was 61%

The actual probabilities could be somewhat higher, as climate change has made the kind of resonance events involved in this epic heat event more likely. @bluewaveposted a good paper on this topic earlier in the thread.

 

 

I'm gonna add on just a bit to what Don said for this particular event. In this case, the incredibly strong Rex block that is baking BC and WA/OR had its origin in an unusually juiced episode of convection along the Meiyu/Baui front in E. Asia. Moisture transport for that event likely originated over the SW Pac and E Indian Ocean, both of which are running above normal over a very wide area (and abnormally high ocean heat content to boot), which very likely contributed to amp'ing the intensity of the event. The latent heat release from that event helped boost the N.Pac jet significantly, causing a big downstream rossby wave break and the big ridge/block. So in a way, there's even an entangling between enhanced and extreme rainfall events and this heatwave. It's just not the kind of thing that's inherently obvious until you start digging.

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 Looking at 10AM PDT readings vs 24 hours ago:

 Portland, Walla Walla, Pendleton, and Yakima are 6 F warmer.

Spokane area is 4-5 F warmer. SeaTac is 3 F warmer.

 Keep in mind that June records were already obliterated in Portland, Seattle-Tac, and other locations yesterday!

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