Spring's progress continues to be rather fitful this year in Alaska. Much of the state has been unusually wet for the time of year in recent weeks, and temperatures have become decidedly cooler than normal again in much of the south. A very vigorous Bering Sea trough is to blame, along with substantially cooler than normal water temperatures in the eastern Bering Sea - the latter being a lingering reflection of the expansive winter sea ice. Here's a recent SST anomaly map:
Interestingly, the PDO index is drifting into more negative territory again, despite the fact that El Niño is developing rapidly in the equatorial Pacific.
The 30-day precipitation anomaly map shows a widespread and significant wet signal across Alaska - see below (NWS data, estimated). Of course, it's usually a rather dry time of year, so the actual amounts are not enormous in most interior and valley locations; but it's a notable statistical anomaly. Anchorage, for example, is running at record wet so far for the April-May period, with just over 3 inches of liquid-equivalent precipitation. The record for the two-month total is 3.29" in 2019.
A temperature chart from Homer illustrates how warmth has been generally lacking in recent weeks. This morning was especially chilly, with many locations near or below freezing across the Kenai Peninsula and farther afield.
Yesterday morning Fairbanks also dropped to 32°F, the latest freeze at the airport in 18 years.
A notable exception to the cool weather pattern has been in the Arctic northwest; Kotzebue was extremely warm for the time of year last weekend, breaking daily record high temperatures.
Here's the 500mb height (mid-atmosphere pressure) anomaly in the last 14 days, expressed in terms of standard deviations departure from normal:
And the 850mb temperature anomaly:
Clear skies and calm winds produced a widespread freeze across eastern and northern Alaska this morning, with the temperature dropping into the 20s in most locations. Fairbanks airport reached 29°F, which is a little unusual in the modern climate for this late in the season; other than last year, it hasn't happened after May 10 since 2013. The low temperature in Chicken was 19°F, which is the first time below 20°F this late in the season since 2014.
Farther north, accumulating snow fell in Fort Yukon yesterday morning. The accumulation was probably less than an inch, given that the snowfall rate was light, but temperatures were below freezing, and it was falling for over three hours. Snowfall measurements haven't been available from Fort Yukon for many years, but historical data shows an inch of snow as late as mid-June in 1971, and as early as late August in 1961. It's a short summer in the northern interior.
Farther north still, the North Slope is still locked in with wintry weather. The high temperature in Utqiaġvik yesterday was only 13°F, and that's a little more notable: we have to go back to 2007 to find a colder day this late in the season. Utqiaġvik temperatures have been oscillating between above and below the 1991-2020 normal so far this year:
The contrast between North Slope winter and interior spring made me wonder when the seasonal contrast between the two regions is greatest. It is indeed in spring: the following chart shows the difference between normal temperatures in Utqiaġvik versus the average of Bettles, McGrath, and Fairbanks.
The Arctic coast doesn't begin climbing out of winter cold until nearly April, but the interior has gained a lot of warmth by then, and the temperature contrast peaks in late April. Of course, the interior cools off much more quickly in autumn, and the valley-level interior becomes briefly colder than Utqiaġvik in November.
Looking back at April, it was a cloudy and wet month for most areas except the North Slope and Southeast. With precipitation well below normal in the usually wet Southeast, the state-average precipitation was not much above normal, but the southwest and southern interior were unusually damp for the time of year.
The broad swath of wet weather was caused by strong westerly flow to the north of a robust Gulf of Alaska ridge, and downstream of the ridge the dry anomaly was inevitable over Southeast Alaska.
Statewide mean temperatures in April were very close to the modern normal, with equally balanced ups and downs during the month. The Aleutians were significantly warmer than normal, although not to the extent of some recent years (2016, 2020).
Cloud cover was well above normal for most of the state. The combination of cloudy and damp weather certainly wasn't a bad thing in terms of wildfire risk as we advance quickly toward fire season.
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/
Notwithstanding very abundant sea ice in the eastern Bering Sea this winter, Arctic-wide sea ice is now vying with 2019 for record-low extent at this time of year; it has been running near the bottom of the "pack" (pun intended) since November. The following chart provides a comparison to 2019 (the previous record low at this date), 2012 (the year of the record low in September), and last year.
Deficits relative to the 1981-2010 normal are widespread across the marginal seas of the Arctic:
It's an interesting question as to whether the developing big El Niño episode will have a positive or negative effect on Arctic sea ice this summer. Several of the strongest El Niño events of recent decades developed in parallel with substantial year-on-year declines in Arctic sea ice extent, so the risk of another major drawdown would seem to be elevated. Here's a scatterplot of year-on-year change in September ice extent versus the June-August Niño3.4 SST anomaly; the notable recent years are 2023, 2015, 2002, and 1997 (lower right quadrant).
However, it's equally clear that there is actually not much correlation overall between year-on-year ice change and the phase of ENSO during summer. In particular, pre-1997 El Niño events didn't have a consistent relationship with ice changes, and many stronger La Nina summers show modest ice declines rather than gains.
For a bigger picture, here's the correlation of June-August detrended SSTs with the year-on-year ice change:
The colors indicate the SST anomalies that would normally be associated with an increase of sea ice. Clearly, the North Atlantic and North Pacific have more correlation than the tropical Pacific, but this doesn't imply causation; the SST patterns revealed here may simply reflect the impact of circulation patterns that affect sea ice extent. Nevertheless, it's interesting to observe that a negative PDO pattern (like recent years) tends to favor higher sea ice extent, and that's confirmed in a scatterplot - although the correlation is not statistically significant:
The atmospheric anomalies themselves show a greater connection with sea ice change, of course; but those anomalies are relatively unpredictable at seasonal time scales. A positive Arctic Oscillation, for example, slows the summer ice melt, whereas a negative AO phase tends to bring a reduction in ice extent.
ENSO does tend to be inversely correlated with the AO phase in summer, so it's more likely than not that we'll have a negative AO pattern this summer, i.e. more high pressure over the Arctic (and favoring warm and dry conditions in much of Alaska). This points toward greater sea ice loss, as in other recent El Niño summers; but time will tell if this year fits the same pattern.
