Heat Advisory

I'm at the outset of a 10-day spell of travel, so probably won't be posting in the near future - but I wanted to comment on the news that a NWS "heat advisory" has been issued for the first time in Alaska.  This has made headlines and stirred up interest quite widely.

First, the facts: there is indeed a heat advisory in effect for a large part of interior Alaska, from the Tanana region to the Fortymile Country (including Fairbanks-land), the Yukon-Tanana uplands, and the Yukon Flats.

Details:

This is indeed the first heat advisory issued in Alaska... but that's because the Alaska region NWS offices did not issue this product at all until this year.  Special weather statements were used instead to draw attention to excessive warmth.

As for whether this event is particularly extreme - no, it's not, although it is an unusually hot spell for the region.  Fairbanks is currently expected to see 85°F on three consecutive days, and that doesn't happen in most years - although it did in both 2023 and 2024 (in July).  It's particularly unusual for June, having happened in only 6 Junes since 1930 (most recently in the very hot June of 2013).

Rick Thoman has an excellent write-up today on the same topic, including an explanation of the rationale for the NWS procedural change:

https://alaskaclimate.substack.com/p/alaskas-first-heat-advisory

May Climate Data

It finally happened - Fairbanks reached 70°F yesterday.  Based on NWS data since 1930, this is the latest on record by 4 days, although back in 1911 the university farm apparently didn't see 70°F until a day later, June 12.

It's interesting to take a look at global temperature patterns for the month of May in previous years with a "first 70°F" in June:

At least in the Northern Hemisphere, this has a lot of similarity with this year's global temperature patterns in May: note the negative PDO-like pattern in the North Pacific domain, the warmth over central Canada, warmth in western Europe and central Asia, and cold in eastern Europe.

How about the rest of summer?  It's interesting to observe that June is more likely to be warm than cold in central and northern Alaska, and that fits with the current major warm-up; Fairbanks is expected to reach the mid 80s this weekend.

But cooler than normal weather tends to return in these years in July and especially in August:

Here's the mid-atmosphere pressure pattern that produced the chilly May in Alaska this year: as noted in a previous post, a trough was locked in over the state.

The pattern shows considerable similarities to both May 2024 and May 2023, and it was the third cooler-than-normal May in a row for Alaska.  Here are my usual percentile rank maps based on (top) ground-truth observations and (bottom) ERA5 model reanalysis.

Interestingly, this was the coldest May since 2013 for the North Slope and Northeast Interior divisions, and the coldest since 2012 for the northern Panhandle division.  For the North Slope, it was the first colder-than-normal month since last July (with normal defined as the 1991-2020 average).

Perhaps a bigger story than the lack of warmth, however, was the very wet weather in much of southern and eastern Alaska, and especially in the panhandle.  For the second month in a row, the statewide average precipitation was very nearly the greatest on record for the month, and that makes four months in the last year with record or second-highest statewide monthly precipitation:

July 2024   Record wettest

January 2025   Tied record wettest

April 2025   Second wettest

May 2025   Second wettest

Rick Thoman reports that all the long-term climate sites in southern Southeast Alaska set records for May precipitation, and Juneau saw measurable precipitation on 30 of 31 days.  However, it was unusually dry in northwestern Alaska.

As is to be expected, sunshine mostly mirrored the precipitation contrasts across the state:

Finally, wind patterns showed a lot of spatial variability, according to the ERA5 data:

Late Snow in Bettles - Again

I mentioned a few days ago that the contrast between fire activity in Alaska versus Canada so far this season is very reminiscent of 2023.  Here's another facet of the similarity: Bettles briefly saw accumulating snow yesterday, just like in early June 2023:

https://ak-wx.blogspot.com/2023/06/record-late-snow-in-bettles.html

Unfortunately the climate observer in Bettles didn't (yet) report a snow depth for yesterday, so we can't say whether the maximum snow depth was measurable - but if it was, it would be the latest measurable snow on record.  Judging from webcam imagery (see below), the situation yesterday looked similar to the 2023 event; but in 2023 the light snowfall persisted (at above-freezing temperatures) for longer, and it redeveloped again the following day.

[Update June 8: the accumulation report came in at 0.4", so that confirms it's the latest measurable snowfall on record in Bettles.

End of update]

Yesterday:

2023:

Yesterday:

2023:

The NWS in Fairbanks issued a Winter Storm Warning for central Brooks Range locations above Bettles, and the warning extends through tomorrow afternoon.  It's the first WSW issued by NWS Fairbanks in June since 2018.

Anaktuvuk Pass looks to have quite a bit of fresh snow:

Update on Cold

A few follow-up notes are in order regarding the unusual chill that much of Alaska is experiencing at present.

First, the highest temperature so far in Fairbanks is still 67°F, so we can make the following chart (20°C = 68°F).  It may be the middle of next week (June 11-12) before this threshold is reached, and that would be a record for the NWS/Weather Bureau era.

Yesterday Anchorage saw a high temperature of only 48°F, which made it the coldest summer day since 1973, and only 1°F away from the coldest summer day on record (June through August).

As for the far north, it's remarkable to note that Utqiaġvik and Deadhorse have not yet exceeded the freezing mark this spring/summer - although it happened back in January.

Deadhorse has been at or below 26°F for the past 3 days, and the last time there was a single day this cold in June was back in 1974.

It's even solidly below freezing well inland: the Umiat RAWS reported a low of 19°F on Tuesday morning - with a breeze! - and it hasn't been above 29°F since late Sunday evening.  Yesterday's high temperature of 26°F is the latest on record for such cold, the previous record being 1994 (May 29).  Data from Umiat is mostly complete back to 1976, and there's some data from 1945-1954.

Other locations dropped even lower on Tuesday; a couple of USARRAY sites reported a low of 13°F.

The animation below shows that the coldest air (based on 850mb temperature) is just now passing over the North Slope and will linger over western and then southern Alaska well into next week.

Where Is Summer?

The calendar and the daylight say it's summer now, but the weather isn't quite there yet.  Anchorage has only reached 60°F three times so far, the elevated interior cold spot of Chicken is still seeing hard freezes by night, and Fairbanks hasn't yet reached 70°F.

Here's the UAF statewide temperature index: it's been on a downward trend since late winter.

The lack of a 70°F day in Fairbanks (the highest so far is 67°F) is getting to be quite unusual, especially compared to the last 20 years.  We have to go back to 2001 to find the last time May failed to reach 70°F, and the latest first occurrence in the NWS/Weather Bureau era is June 7 (1937 and 1955).  (The UAF climate record has a June 9 first occurrence in 1968, and June 12 way back in 1911.)

There's a chance 70°F will occur tomorrow, but if not then it may be another week or more until the next good chance; so the record may be in some peril.

Why so chilly?  The mid-atmosphere (500mb) flow pattern has increasingly developed into a trough over Alaska, keeping cold Arctic-sourced air over much of the state.  Back in April there was a trough over the Bering Strait region, and the kink in the jet stream has persisted and shifted east as spring has advanced.  Here's the 500mb pressure pattern for 15-day periods from the first half of April through the latter half of May.

Summer's delay may not please everyone, but it's good news for the early fire season: less than 1000 acres have burned so far statewide.  It's a big contrast to the situation in Canada, where fires are raging under hot and dry weather.  This contrast is eerily reminiscent of 2023:

https://ak-wx.blogspot.com/2023/06/almost-zero-fire.html