Big El Niño Coming

Most readers are probably well aware that El Niño is on the way for next winter; the forecasts have been well-publicized.  Normally one would be wise to take El Niño forecasts with a grain of salt at this time of year, because there is a notorious "spring barrier" of predictability in Northern Hemisphere spring, but in this case the signals are so strong and coherent that there's little doubt of the outcome.

The most compelling evidence that a major El Niño is about to emerge can be seen in the profile of subsurface temperature anomalies in the equatorial Pacific.  The figure below is a couple of weeks out of date, but it shows a very intense warm anomaly below the surface, and this is migrating eastward and upward.  As the warmth continues to emerge at the surface, East Pacific equatorial surface water temperatures will become much warmer than normal, consistent with a strong El Niño signature.

The warmth produced by the subsurface anomaly will add to the substantial surface warming that has already occurred in the last few months, so it seems inevitable that the equatorial SST anomalies are going to become quite extreme in the next few months.  The canonical Niño3.4 SST index is already near 1°C above normal, although this includes a contribution of about 0.5°C from long-term warming in recent decades:

Here's a chart showing the recent progression of Niño3.4 SST anomaly forecasts from ECMWF's seasonal model.  The red line is the latest forecast; the model has been adjusting warmer with every run in recent months.

If the forecast is correct, the Niño3.4 anomaly may approach +3°C by autumn, with the modern record being +2.7°C in November 2015 (relative to a 1991-2020 baseline).

What does this mean for Alaska?  We'll discuss prospects for next winter another time, but for summer the history of past years with strong El Niño conditions (see below) suggests a heightened probability of above-normal temperatures, driven by relatively high pressure (ridging) from Alaska to the Canadian Arctic.  The top analog years also show dry summer conditions in Southeast Alaska and hints of dryness in southern interior and western Alaska.  Note that this is based simply on the 10 years since 1950 with the most positive Multivariate ENSO Index in June through August.

However, not all El Niños are created equal, and analog years show a lot of variability.  To illustrate this, here are temperature percentile maps for six summers when a robust El Niño developed by autumn following La Niña-like conditions the previous winter.  Where possible, I've used a preceding 30-year baseline for a fair comparison across the decades.

More recently, 2015 produced a very strong El Niño, but that episode didn't emerge from a cool phase in the previous winter.  There was also a robust El Niño in 2023, although its oceanic warm signature was inflated by unusual global warmth.

Not surprisingly, temperatures from the northern Gulf Coast to southwestern Alaska tend to be linked to the PDO phase, which was positive in 1957, 1986, (especially) 1997, and 2015, but negative in 1965, 1972, and 2023.  Elsewhere, variability is large among the analog years, although there isn't much cool to be found in northern and western - or southeastern - Alaska.

Similar maps for precipitation are included below.

It's difficult to pick out any consistent moisture signals on the maps, but interestingly ground-truth data from Fairbanks shows that none of the top 6 El Niño analog years had above-normal rainfall for May through September.  Click the figure below to enlarge (2014 is included only to show the record wettest summer):

Juneau also shows distinct indications of a (relatively) dry summer when El Niño develops in a similar way:

Summer rainfall can go either way in Anchorage, however:

For a more comprehensive look at all the seasonal climate guidance for this summer, I highly recommend tuning in to Rick Thoman's briefing on May 22:

https://uaf-accap.org/event/may2026-climate-outlook/

Summer Review

I've been meaning to post a few comments on the climate patterns and anomalies during summer - better late than never, I trust.  On a statewide basis it was a fairly warm and fairly dry summer, but neither aspect was highly unusual in terms of the state averages: according to NOAA it was the 10th warmest summer in the last 30 years (warmer than 2024 but cooler than 2023), and statewide precipitation was the fifth lowest in 30 years (driest since 2019).

However, regional differences were significant, especially for precipitation.  The summer was much drier than normal along the central and eastern Gulf Coast, but much wetter than normal for most of western Alaska as well as the northern interior and western Brooks Range.  Here are the ERA5 (top) and NOAA (bottom) percentile rank graphics for the three-month period:

Here's a chart of accumulated precipitation at Yakutat, to illustrate the dryness (click to enlarge).  The June through August period was the second driest on record, following 2007, with total rainfall amounting to only 37% of the long-term median (9.6" versus 25.8").

Precipitation deficits were very pronounced in July along the northern Gulf Coast, but August really exacerbated the drought (relative to normal) and also set up the big contrast with excessive rainfall in northwestern Alaska:

We covered the late August stormy pattern for western and northern Alaska here, and the August 500mb height anomaly highlights the pressure gradient across western Alaska: the ridge over southern Alaska deflected the jet stream northward into western and northern Alaska.

In terms of sunshine and wind, it was a very poor summer for the Y-K Delta region, with all three months bearing part of the blame.  However, only June was cooler than normal in the southwest.  Eastern and northern Alaska were generally sunnier and less windy than normal, although not in August.

Looking back at lightning and wildfire activity, both were above the long-term median, but lightning much more so.  For a time in late June and early July, lightning strike counts were running second only to 2015 (with data back to 2012), and the seasonal total ended up in 4th place, similar to 2019 and 2022.  In contrast, wildfire acreage ended very close to 1 million acres, which is about twice the long-term median but well below 2019, 2022, and of course 2015.

It seems likely that Alaska's very wet spring was largely responsible for the relatively subdued fire season.  The statewide average for the April-May total precipitation was easily the highest on record, with both April and May ranking in second place statewide; and importantly, the wet anomaly included large parts of the fire-prone interior.

 

May was also cooler than normal, and June was only a little warmer than normal in the interior.  This is a big contrast with, say, the enormous warmth of May 2015 that dried out the state in advance of that huge fire season.

Here's a map to illustrate the distribution of lightning activity relative to normal.  There was far more lightning than normal in northern Alaska, and the more typically active southern interior also had more lightning than normal.

A plot of actual strike count density shows that the bulk of the activity occurred across the interior, as always, but it was very unusual to see the high strike counts extending so far north into the Brooks Range.

I suspect that the combination of fairly high temperatures and high humidity in the northern interior was part of the reason for the very active lightning season there (warm, humid air is fuel for thunderstorms).  Here's a map of dewpoint percentile relative to the 30-year climate:

From a broader climate perspective, widespread and extremely unusual warmth in the North Pacific this summer is one of the biggest stories in climate science at the moment.  June-August sea surface temperature anomalies were as much as 3°C above normal in the northwestern Pacific, leading Japan to have its third record-hot summer in a row.

Remarkably, the August area-average SST reached 20°C for the Pacific basin north of 30°N, according to NOAA's ERSST data.  The acceleration of warming in the past few years is quite something:

I'm out of time for this post, but I'll append below the rest of my August climate percentile maps for the sake of completeness.

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.