80 Degree Days in Sitka

In a summer notable for its persistent clouds and lack of sunny days, 2020 has still managed to produce two of the hottest days in the past 50 years.

When I saw the high temperature for July 2nd was 83F, I knew that 80F days in Sitka were rare, but I didn’t realize just how unusual.

By the time July 31st reached an all time record-tying high of 88F, I had done some investigation and learned that it was only the third* time since 2005 that the temperature reached at least 80F at the airport, and only the 10th day in my lifetime.

In fact, going back 50 years, there are only 15 days that made the mark.

Over the years there have been two primary weather reporting stations, one at the airport started recording in 1944, and the Magnetic Observatory was in operation from 1899-1989. In 2005 one called Sitka 1 NE started up, and I believe it’s at (or at least quite close to) the old Magnetic Observatory station.

There are differences in temperatures between the two stations related in part to the moderating effects of the ocean. (The largest consistent differences in reported highs could be expected to occur on clear days, with warmer temperatures at the airport in winter, and cooler in the summer.)

With this in mind, I took a look at the data from all three stations, going back to 1970 (with a tabular summary by decade going back to 1899).

The Past 50 Years

2010s

Although summer 2019 was warm and dry (with a record tying streak without rain at the airport), it never reached 80F. Prior to this July (2020), the last time the official temperature was at least 80F (and the only time since 2005), was July 6th, 2009 when it hit 84F.

(I was out of town the days before, and suspect that I returned that evening or the next day, so missed out on the heat, as the high on the 7th was back to a more seasonable 62F.)

During the 11 year stretch between 80 degree temperatures at the airport, there were an additional two days that topped out at 80F at Sitka 1 NE, June 23rd, 2012 (only 69F at the airport, so perhaps there was a good sea breeze?), and June 15th, 2015 (with a high of 77F at the airport).

2000s

The first 80F temperatures of the millennium were recorded June 19-20th, 2004 when the highs were 81F.

I have a specific memory of the 20th. I remember the heat felt stifling while at a picnic at Halibut Point rec that afternoon. . In my memory, I was thinking this was the day had broke the all time record and hit 89F, but clearly this was incorrect. Looking deeper, I found this had blended with another hot day later in the summer**.

Only one other year since 1970 had produced two 80F degree days, but 2004 wasn’t done yet, as August was especially remarkable for heat.

On August 10th it was 83F, and August 15th, 2004 hit 82F (originally reported as 89F**). These were in the midst of 7 of 9 days that were at least 70F, and 11 of 12 that were at least 67F.

August 2004 ended up with what was easily the warmest three week stretch (in terms of daily high temperatures) ever recorded at the airport, with the high temperature averaging 69.9F. The next closest three week stretch took place in August 1977 and its average high was more than two degrees cooler at 67.5F***.

I am a little disappointed that I only have a few photos with captions (and no journals) from a handful of days that August, but the photos I do have feature sunny conditions.

With four 80 degree days, and the general heat in August, I’m wondering what the overall weather patterns were that summer that drove the warmth, as it seems like they must have been unusual.

On August 9th, 2005 the airport reported a high of 80F (the second day of 5 in a row where highs were at least 70F). This was just a week before the Sitka 1 NE data record starts. I was in town, but have no particular memory of this day (this was before I started trying to be more consistent with weblogs, and I did not take any pictures that day).

1980s-1990s

August 12th, 1990 hit 83F and was the only day between 1976 and 2004 to break 80F at the airport. (Between 1980 and 1999 there were a couple of days that reached 79F, and a handful that topped out at 78F).

The 1980s encompassed most of my childhood, and I feel like I remember at least a couple of (what seemed to me to be very hot days), with temperatures reported in the 80s. During this time, weather data was recorded at the Magnetic Observatory (through 1989), which I believe may have been considered the official Sitka weather record at the time.

There were three days that broke 80F at the Magnetic Observatory. June 29th, 1985 was 80F (75F reported at the airport), and two days in 1980. June 5th was 86F, and August 11th, 83F.

The summer of 1980 is when I turned 5, and I’m pretty sure at least one of those days (or perhaps a blend of both) is in my memory, in the hazy sort of way that memories from early childhood sometimes are. I remember being outside in the sun, in shorts and a tank top, feeling the heat was unbearable. Attached to this memory is the recollection that the temperature had been in the 80s (84F is what stuck with me over the years).

1970s

The early part of the 1970s more regularly saw 80F degree days at the airport, with one each in 1970, 1971, 1972 and two each in 1975 and 1976 (including the just tied record of 88F on July 30th, 1976). Additionally, there was an 80F day at the Magnetic Observatory in 1974.

(It’s a little difficult to directly compare daily records between the airport and the Magnetic Observatory during this time period, the data was collected differently at each location, with airport records apparently for the calendar day, and the Magnetic Observatory daily recordings documenting the 24 hour period ending at 3pm.)

Other Notes and Questions

What does it take to get to 80F in Sitka?
Given the rarity of 80F days at Sitka overall, it’s clear the circumstances required to produce such heat are relatively unusual. I have some sense that it might depend on warm air aloft, perhaps some downsloping air movement (though it’s not clear to me how much affect that might have in Sitka), and something to prevent a sea breeze from forming and bringing in air cooled by the waters of Sitka Sound and the Gulf of Alaska. (If anyone reading this can explain what sorts of factors can result in the hottest days here, I would love to learn more!)

1970-1976 and a shift in the PDO index
In 1976 there was a shift in the Pacific Decadal Oscillation index which resulted in generally warmer temperatures throughout Alaska (though less pronounced in the summer). It’s interesting to me that in the seven years immediately preceding the shift (1970-1976) there were six days of 80F at the airport, and in the following 27 years (1977-2003) there was only one, despite a warmer baseline. Is there something associated with the PDO that makes more extreme temperatures less likely to occur despite warmer conditions overall?

Clustering of 80F days, patterns or randomness?
That said, the 1970-1976 period was unusual. Over the 70+ years of the airport records, there are a couple of other clusters of years (1950-1952; 2004-2005) where at least five 80F days were recorded, but these were driven by unusual years (two days in 1950, three in 1952; four days in 2004).

At the time, five days of at least 80F over two summers in 2004-2005 might have suggested the possibility of more regularly occurring hot days. Fifteen years on, and with the benefit of a look through the longer record, they were clearly one of a handful of clusters in the record.

80F is a nice round number (in our base-10 counting system, at least!), but ultimately an arbitrary one. It does seem to be an interesting cut-off for Sitka, but may be less so for other communities in the region (which may have a bit less influence from the cool waters of the Gulf of Alaska).

By their nature, the extreme values of data sets tend to be highly variable/noisy, with clusters that may be essentially random (but still invite our pattern-seeking minds to seek an explanation). At some point in the future, I may look at nearby temperature cutoffs, and see if things look much different (at least qualitatively).

While acknowledging the clustering could be the result of basically random processes, I wonder if there could be climatic conditions that show up on a scale of months or years which might be a factor that increases (or significantly decreases) the possibility of temperatures reaching 80F.

Differences in temperatures between nearby stations?
I’m interested by how different the reported high temperatures at different stations on some of the days. A few degrees seems pretty reasonable, but in some cases, the difference is 10-15F – I am guessing it has something to do with a marine stratus layer or sea breeze affecting the airport, but I’m not sure. Perhaps at some point I’ll investigate the temperature differences more systematically to see how much the difference varies overall.

What’s your experience with 80F in Sitka?
If you are reading this and have memories of 80F days in Sitka, please leave a comment! What do you remember about some of the hottest days in Sitka’s recorded history?

Data Sources

NOAA Regional Climate Centers xmACIS2 site – has data from all three stations used in this post.

NOAA Online Weather Data (Juneau Office of NWS) – only shows records from the airport

Zoom.earth – satellite imagery from July 31st

Notes

*The weather records show July 21-22nd, 2017 with highs of 86F at the airport. I’m quite positive these are erroneous, as the pictures I have for that day show cloudy conditions, and the Sitka 1 NE station shows highs in the lower 60s. I have emailed the folks at the weather office in Juneau about this, and will update if I learn more.

** In the August 16th, 2004 edition of the Sitka Sentinel, the official high for the 15th was reported to be 89F, breaking the all-time record of 88F, set July 30th, 1976. So apparently my memory did some blending. It may be that I came to associate my memory of the record hot weather picnic with the picture taken on June 20th. Another possibility is the picnic did take place on the 20th, but I later attached the reported record heat to that day mistakenly.

*** The Magnetic Observatory did have a three week stretch that averaged 71F in August 1923, which included 6 days in a row that reached at least 77F, with four of them hitting 80F.

While there is no way to know what 2004’s 69.9F stretch would have looked like at the Magnetic Obsrvatory, the 1977 three week period where highs averaged 67.5F at the airport is directly comparable with that period averaging 69.1F at the Magnetic Observatory. This 1.6F difference suggests 2004 was plausibly just as hot, and possibly even slightly hotter than the three weeks in August 1923.

Tables

Table of 80F day counts by Station and Month