Heat Wave Ends

This summer's only significant heat wave has now ended in Alaska, and autumn is most definitely just around the corner.  But what a heat wave it was in the past week - a very unusual spell of warm weather that completely defied the character of the rest of summer and indeed the rest of the year so far.

My last post mentioned temperature records at Juneau and Uqiaġvik, but there's more to talk about.  The heat situation escalated significantly in Juneau on Friday, when the high temperature reached a remarkable 85°F - a new record for August and the latest date with such heat by more than a month.  Previous dates with 85°F or higher at Juneau airport have all occurred between mid-June and early July.

I also overlooked a similar record in Haines on Friday: 87°F, again easily the latest date with such a high temperature.  Only once, in 2017, has Haines reached 87°F in August, and that was on the 5th of the month.

Having said all this, mid-August 2004 was a close second for late heat in both locations: Haines reached 86°F then, and Juneau saw 84°F, just one degree lower in both places.

Here's a map view of high temperatures reported on Friday (August 14) across the northern Southeast (click to enlarge):

It was also very hot in the far southeast: Klawock airport measured 88°F (marked as 87°F on the map below - a data rounding issue).  This is a new August record by a margin of 4°F at Klawock, but data only goes back to 1998.  Nearby Ketchikan saw 89°F in mid-August 1977 and 87°F in mid-August 1950, so this kind of late summer heat isn't unprecedented in this area.

Emphasizing again the nearly statewide nature of the heat wave, Kotzebue broke a high temperature record on Sunday: 75°F, compared to a previous record of 69°F on that date.  Kotzebue has rarely seen such warmth after the middle of August, with the 2004 heat wave being the most notable such event in the past.

Referring back to UAF's statewide temperature index again, the value peaked at about 9.8 on Friday and Saturday, implying a statewide anomaly higher than about 99% of all days.  The last time it was this unusually warm (compared to normal for the time of year) was January 2025.

Here's a map of the standardized 850mb temperature anomaly in the last 7 days, illustrating the Alaska-centric nature of the feature.

Contrast the 30-day anomaly from late June through late July:

Serious Warmth and Ice Decline

As advertised in recent posts, warmth has become pronounced and widespread in Alaska this week, and yesterday saw the temperature rise all the way to 70°F in Utqiaġvik - a fairly rare event, especially this late in the season.  The last time 70°F was reached in Utqiaġvik was more than two years ago (August 6, 2024), and this is only the third time it has happened in August this century (2023 and 2024 being the other years).  The latest on record for such warmth is August 24, 1979.

Far to the southeast, Juneau also set a daily record high yesterday, at 80°F.  This isn't quite as unusual, although again it is pretty late in the season; it's only been this warm this late in the season in 5 other years out of the last ~75 years of climate data.  The latest on record is - not coincidentally - August 23, 1979.

On a statewide basis, UAF's aggregated and standardized temperature index shows yesterday being the warmest day relative to normal since October last year - see below.  The latest daily index value of +9.4 indicates that yesterday was warmer than about 97% of all days in terms of standardized departure from normal - again, a fairly rare extreme.  Time will tell as to whether this month's sudden reversal from unusually cool to unusually warm will be sustained, but this is certainly a change from the persistent character of the last 8 months.

The map below shows the sea-level pressure anomaly that has prevailed in the last two weeks.  With high pressure over Alaska and low pressure near the Arctic coast of Siberia, warm southerly flow has been pulled up across the Bering Sea and into the Arctic.

The result?  Sea ice extent has been dropping very rapidly in the Chukchi Sea this month.  At the end of July it was well above normal - a significant anomaly compared to recent years - but it has now dropped to near the 1991-2020 normal.

Beaufort Sea ice has seen much less decrease and remains well above normal and close to last year's extent.  It will be very interesting to see whether or not the next few weeks see a rapid decrease like last year.

The Northern Sea Route appears to be on the verge of opening up; the NSIDC sea ice index has shown an open passage in the last few days, but the NWS ice analysis suggests there are still patches of heavy ice on both sides of Wrangel Island.  Compare the two perspectives below:

The comparison illustrates some of the uncertainty in ice cover analysis.  For NSIDC, ice extent is defined as the area with at least 15% ice coverage, and the NSIDC data shows this boundary being well north of Wrangel Island all the way across to well north of Point Barrow.  In contrast, the NWS analysis shows 4-6 tenths or higher at lower latitudes around Wrangel Island, in the mid-Chukchi Sea, and to the west of Uqiaġvik.  The two products serve different purposes and differences are to be expected, but this illustrates the challenge of characterizing the "true" state of affairs.

Peak Summer Warmth

A significant warming trend in the next several days is going to push temperatures well above normal for the time of year across much of Alaska, and especially across eastern, interior, and northern Alaska as next weekend approaches.  Here are predicted 850mb temperature anomaly maps for Friday evening:

It looks likely that this will be the warmest episode of the summer - not just relative to normal, but in absolute terms.  This is a low bar to clear, of course; Fairbanks has so far reached only 81°F this summer, and the NWS is currently indicating 82°F for Thursday.  A typical summer in Fairbanks reaches the upper 80s at some point.

It's interesting to note the absence of very warm weather in Fairbanks in mid-late August in recent years.  The chart below shows that temperatures haven't exceeded 80°F after August 10 since 2010 - a spell longer than any other in the period of record.  Mid-late August has tended to feel more autumnal in the past 15 years, but the warm spell later this week will be reminiscent of earlier times.

It is certainly unusual for the highest temperatures of summer to occur this late in the season.  In Fairbanks, the brief but intense mid-August heatwave of 2010 (91°F on the 15th - easily the latest 90°F on record) was one of the latest dates for seeing the highest temperature of the summer.  The record latest was 83°F on August 30, 1974.

It's not too late to be concerned about fire risk in areas that have been drier recently, i.e. the southeastern interior:

Wet Weather and Warm Signals

I promised a post on Arctic sea ice conditions, but first a comment is needed on more wet weather across most of western and southwestern Alaska.  NWS estimates indicate over 1.5 inches over a very wide area in the last few days.

McGrath's year-to-date precipitation is now the highest on record at nearly 15 inches.  Normal annual-total precipitation is about 18 inches in McGrath, and the typically wet months of August and September still mostly lie ahead.

Two weeks ago I noted flooding on the Yentna River (a lower tributary of the Susitna), and the gauge near Lake Creek now reports a record-high water level:

With strong low pressure and storminess in the Bering Sea, southerly flow has brought very warm weather to eastern and northern Alaska.  Notably, the Umiat RAWS reached 79°F yesterday.  There are strong signals for more warm weather in the coming weeks, and it will be interesting to see if August could end up warmer than July on a statewide average basis this year.  That hasn't happened since 1977, when August was the second warmest on record (2004 holds the record).

Considering how things have been going in Alaska since last December (see below), a change to persistent warmth would indeed be a major reversal.  It may well signal the emerging influence of the developing record El Niño, which is now shaking up weather and climate patterns all around the globe.

A Few Record Lows

Alaska's Arctic has warmed so much in recent decades that it's now a little newsworthy when a calendar-day record low temperature occurs, and this happened at Utqiaġvik on Thursday: the temperature dropped to 27°F, the lowest on record for July 30.  As a matter of fact, this is the second daily record low this summer; the 24°F on June 28 was also a record.  The previous day (June 27) also tied the daily record lowest maximum temperature (31°F); I posted a few comments on that event here:

https://ak-wx.blogspot.com/2026/06/cold-day-in-utqia.html

A chart of the annual number of daily records (set or tied) illustrates the near-complete absence of record lows in Utqiaġvik in the past 15-20 years, while record high temperatures have been very frequent:

The slight uptick in unusual cold this summer reflects the unusually abundant sea ice in the nearby Arctic waters - a significant change from the pattern of recent years.  Rick Thoman has a post up on this, and I'll follow with a few comments in a subsequent post.

Since I now have a handy computer script to create the daily record chart, below are equivalent charts for Fairbanks, Anchorage, and Juneau.  Note that I'm just using data from the current official climate sites, rather than attempting to splice together a longer period of record from different sites.  Nobody in Fairbanks will be surprised to observe that there haven't been any daily record high temperatures so far this year, whereas there were 6 record lows in March and 3 record low max temps in February.

Anchorage has set or tied record low daily max temperatures in every month this year except April and June.

Chill in the Air

Following up on my last post, Toolik Lake did indeed see snow on Sunday.  Here are a couple of webcam shots from late afternoon:

The weather observer measured a wet 4.4 inches of snow, and that's the largest "high summer" snowfall at Toolik in at least a few years.  The following chart shows daily snowfall amounts in May through September since 2022, when daily climate data begins in the GHCN database.  Note that occasional accumulating snow is not unusual in summer.

Toolik Field Station is at 2400 feet elevation next to the Haul Road on the north side of the Brooks Range:

In other news, this morning saw temperatures drop into the 30s Fahrenheit across many eastern and southern interior locations, and some of the usual cold spots suffered a freeze.  Of course summer heat is still rampant in middle latitudes far to the south, but the late July return of overnight darkness across sub-Arctic Alaska inevitably raises the risk of frost when calm and clear conditions accompany a cool air mass.  Fairbanks airport reached 40°F - the lowest July temperature since 2020 - and the nearby Goldstream Creek co-op site reported 29°F (lowest since 2022).  Several sites in the hills above Fairbanks also dropped into the upper 20s.

Perhaps the most notable report this morning was 26°F from the often-chilly Salcha RAWS; this was the lowest July temperature since 2005.

At this rate there will be color on the trees before long; although NOAA/CPC currently suggests a warmer trend (relative to normal) in the next few weeks.  Perhaps summer isn't quite over yet.

Autumn Threatens

The past 12 days or so have been significantly cooler than normal statewide, and southwestern and south-central Alaska have been very chilly and wet, as unusual low pressure has prevailed in the eastern Bering Sea.  The 500mb height anomaly over western Alaska in the last two weeks looks remarkably similar to the pattern in May:

Model-derived 850mb temperatures (about 5000 feet above sea level) recently hovered not far above record low levels for the time of year over Bristol Bay; the chart below is taken from the vicinity of Dillingham.

Rainfall has been abundant and locally excessive in southwestern and south-central Alaska:

Remarkably, Anchorage is currently tied in first place for the wettest July on record (data back to 1952), and this is the 4th year out of the last 5 to see more than 4 inches of rain in July - with a long-term median of only about 1.7 inches.  In 75 years of data, 4 of the 8 Julys with over 4" of rain have occurred since 2022.

McGrath is close to a record wet July as well, with 5.78" so far versus the 2024 record of 6.16".  Bethel's 4.49" so far this month is the highest since before 1930.

The Yentna and Talkeetna rivers are both in flood:

With all the rain and cloud recently, temperatures have trended down rather than up since early June in Anchorage:

Looking ahead, a ridge is now building over eastern Siberia, and that means cold air is dropping south over the state and will be reinforced early next week.  The latest ensemble-mean ECMWF forecast for Monday shows very unusual cold over the Brooks Range, perhaps threatening records for the month of July.  There will certainly be more snow; the Toolik Lake webcam is already showing patchy snow accumulation this morning.

Here's a lower-atmosphere temperature chart for a central Brooks Range location, with the forecast portion on the right.

Intense El Niño Under Way

I'm sure all readers of this blog are well aware that a major El Niño is expected to prevail in the coming months; the media coverage has been widespread.  However, it's worth posting a few comments of my own, including some Alaska perspective.

The first thing to observe is that this is not shaping up to be a run-of-the-mill El Niño episode; it is going to be an extremely strong event - almost certainly one of the strongest on record, and quite possibly the strongest in many decades (more than a century).  This assessment is not just a long-range forecast, because the event is already well under way: sea surface temperatures are already far above normal across the central and eastern equatorial Pacific.  Here's a recent map of the SST departure from the 1991-2020 normal:

The central Pacific Niño3.4 region is the most widely used region for tracking El Niño SSTs, and the departure from normal is already about +2.2°C:

An anomaly of +2°C is already in the upper echelon of historical El Niño events, and it's easily a record for the time of year, because El Niño's strength tends to peak in Northern Hemisphere winter.  In previous events of recent decades, the earliest the Niño3.4 anomaly reached +2.2°C was in October (1997 and 2015).

So how strong do we expect this El Niño to become?  The chart below shows a progression of forecasts from the Copernicus seasonal models in recent months.

Three things stand out in this graphic:

- The forecasts have been escalating with each update

- The forecasts have generally lagged behind the observed rate of warming in the Niño3.4 region (black line)

- The latest update, issued this month, raised the bar more significantly than in any previous update.  The multi-model predicted Niño3.4 SST anomaly now exceeds +3.5°C, far above the previous monthly-average record of +2.7°C in November 2015 (according to NOAA CPC).

Given that the planet is warming, we should arguably remove the background warming for a fair comparison with previous events.  Using the relative Niño index instead, the multi-model forecast expects a peak monthly value of +3.1°C, compared to a record of +2.7°C in January 1983; so we're still looking at a record event even after "detrending".

It's hard to overstate how significant the impacts of this El Niño will be on weather and climate patterns, especially in the tropics; droughts and floods will be directly linked to the altered atmospheric circulation.  In Alaska, the most reliable effect of a robust El Niño is to increase the strength of the Aleutian Low in winter, and especially in late winter, bringing an increased tendency for southerly and chinook winds across most of the mainland - and therefore widespread above-average temperatures (particularly in eastern Alaska).  Winter snowfall tends to be below-normal to the north of the Alaska Range.

Here's a look at monthly temperature anomalies from August through April in the last three "super" El Niño events: 1982-83 on the left, 1997-98 in the center, and 2015-16 at right.  Click to enlarge.

The only consistent feature across all three events is the tendency for late winter and spring warmth, from February through April.  Interestingly, December and January were cold across northern Alaska in two of the three winters, and October was very cold in 1982 and 1997 (5th and 7th coldest Octobers on record statewide, respectively).  2015-16 was much warmer overall than the previous two episodes, and in fact the extended cold season and spring of 2015-16 (e.g. October through May) was the warmest on record for Alaska.

Here are time series charts of Fairbanks temperatures in the three winters, relative to a modern normal:

It's an interesting question as to which of the three most recent "super" El Niños is most similar to the current one.  Based on SSTs in the tropical Pacific, recent conditions look a lot like 2015, but the negative PDO phase that continues to persist is more like 1982 than 2015 (and is certainly very unlike 1997).  Notice in the figure below the warmth east of Japan and the relatively cool waters near Alaska in 1982 and 2026.  There are a few other intriguing similarities to 1982 that I won't get into; but of course no two years are exactly alike, and this likely record-breaking El Niño will undoubtedly have some surprises in store.