Snow and Ice Update

Snow cover extent has been relatively stagnant across Alaska in the past two weeks, with somewhat less than half of the state's land area under snow cover.  At valley-level across the interior, snow cover has only been established across northern and eastern areas, and temperatures were warm enough last week to eliminate snow in parts of Alaska's upper Yukon region.  Compare NSIDC snow cover estimates from the latest date and one week earlier:

Here's a chart of snow extent so far this season (heavy black line) compared to previous years in the past couple of decades.  The early October advance of snow cover across the north and east pushed snow extent above normal for the time of year, but we're now very close to normal for the date:

Fairbanks received 2 inches of snow yesterday, and the NWS expects a substantial storm from Fairbanks eastward and southward in the next few days:

Given the date on the calendar, and assuming the forecast is approximately correct, it seems likely this will represent the establishment of the permanent winter snow cover for a wide area.

The sea ice situation is more unusual, as sea ice has expanded very rapidly from the seasonal minimum on Alaska's side of the Arctic.  The NWS and NSIDC analysis maps already show only a narrow band of ice-free waters to the north of the Beaufort Sea coast, and the combined Chukchi/Beaufort ice extent is the greatest for this date since 2001 - and almost exactly equal to the 1981-2010 average.

The chart below illustrates the rapid recovery from well below normal to above-normal ice extent in the past month.  Remarkably, the ice growth from September 15 to October 17 is the greatest in the satellite era (1979-present).

On the Russian side of the basin, however, sea ice is far below normal - for example, the Kara Sea is tracking near record lows, with essentially no seasonal ice growth yet (same as last year).

The explanation for the contrast lies partly in the weather pattern: low pressure and cold on the Pacific side of the Arctic Ocean in the past month, and a positive Arctic Oscillation that has brought very warm air from the Atlantic domain into western and Arctic Russia.

September Climate Data

With September climate data now available, let's look back at the predominant weather patterns for the month.  The monthly-mean circulation anomaly was quite similar to August, with a high-pressure ridge retaining a strong influence across southern Alaska.  In contrast, low pressure was dominant over the Arctic Ocean, and the Arctic Oscillation was virtually tied with 1975 as the most positive on record in the month of September.  The mid-atmosphere height (pressure) anomaly shows the strong north-south gradient:

The corollary of a strong pressure gradient is, of course, strong wind, and the enhanced westerly flow brought abundant moisture and frequent rainfall to central and northern Alaska.  Again the pattern showed similarities to August, and much drier than normal conditions continued from the Kenai Peninsula to Southeast Alaska.

The monthly precipitation total in Fairbanks was the highest for September since 1925, and as noted in Rick's comments, some rivers saw their highest measured flow on record for so late in the season.

Check out the contrast in sunshine fortunes across the state: western Alaska and the northern interior were extremely cloudy, but southeastern regions were much sunnier than usual.

Despite the broad similarity in the pattern, temperatures were not as overwhelmingly warm in September as in August; the flow direction across central and northern Alaska had more of a southerly component in August.  The figures below highlight a strong north-south gradient that fits with the pressure gradient and the enhanced westerly flow.

Warmth in southern Alaska was amplified by ongoing high sea surface temperatures across the North Pacific to the south of Alaska, and especially to the south of the Aleutians.  Although the core region of unusual warmth is quite a long way from mainland Alaska, southwesterly winds commonly track from the Aleutian region up into southern Alaska, making the oceanic warm anomaly a "source region" for unseasonably warm air.

As for Arctic sea ice, the minimum ice extent on September 12 was the 10th lowest in the satellite-era period of record.  Seasonal meltout was less than might have been anticipated at the start of summer, owing to a relatively cool summer with persistent low pressure across the high Arctic Ocean.  For this reason, the NSIDC describes the melt season as "unusual in the extreme".  My impression, however, is that much of the ice that qualified for "ice extent" (based on the 15% area threshold) on the eastern side of the pole was very tenuous, and a different weather pattern could easily have produced a large drop in extent.  Here's a map of estimated ice concentration just a few days before the date of the seasonal minimum:

Compare the eastern hemisphere coverage to the NSIDC "ice extent" map from the same date:

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.

Arctic Sea Ice Update

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.

Sea Ice Follow-Up

Following up on Saturday's post, I searched the NSIDC sea ice index data (since late 1978) for historical dates with comparable ice extent in the southeastern Bering Sea, and specifically reaching the north shore of Unimak Island.  The only date that came up was in early March 1984.  Compare the ice coverage back then with yesterday's map:

The latest NWS analysis shows a higher-resolution estimate of the state of affairs (click to enlarge):

Here's a satellite view from yesterday, courtesy of UAF.  Notice that dense ice is packed along the north shore of Unimak Island, but there is more open water just to the north.

The previous day's image (Sunday) shows a magnificent clear-sky view of the Bering Sea ice cover:

For more comments, check out Rick Thoman's latest blog post, where he shows that 1976 likely had higher ice extent in the southeastern Bering Sea, based on ERA5 estimates.  It will be interesting to compare the ERA5 data between the two years once the reanalysis is available for recent days.

https://alaskaclimate.substack.com/p/alaska-style-march-madness

Record Sea Ice

The remarkable cold spell of the past few weeks has produced a major southward expansion of sea ice in the eastern Bering Sea.  Here's the latest NWS sea ice analysis (click to enlarge):

The analysis shows that the north side of the Alaska Peninsula is entirely iced in, and some ice has reached Unimak Island.  Perhaps not surprisingly, Cold Bay saw a daily record low temperature on Thursday: -3°F.  Only two other dates in Cold Bay (since 1950) saw temperatures this low so late in the season (in 2012 and 1976).

Looking at NSIDC sea ice data back to 1978, the ice extent to the east of 170°W is the greatest on record for any date, exceeding the March 2012 record as of yesterday's analysis.  The recovery from the last 12 seasons of relatively low maximum ice extent is sudden and impressive.  (But note that Arctic-wide sea ice remains far below normal - actually the lowest on record at this time!)

It's an interesting question as to the last time sea ice was observed along the north shore of Unimak Island.  Ice is not too uncommon historically in Isanotski Strait (False Pass) to the east of the island, and the following site indicates that ice "rarely" reaches Unimak Pass to the west, but I'm not sure that has happened since 1978.  I'll dig into the NSIDC data a bit more to look for a firm answer.

https://unimak.us/climate.shtml

Sea Ice Update

The extreme cold over southern Yukon is making headlines at the moment - and deservedly so, given how persistent it is - but for balanced perspective it's also worth considering the remarkable warmth in the Arctic in recent months.  Rick Thoman notes in his latest post that Arctic sea ice extent is running at a record low for the time of year, as it has been since late November:

https://alaskaclimate.substack.com/p/winter-solstice-2025-arctic-sea-ice

Zack Labe's splendid graphic highlights the anomaly:

The largest deficits are found to the east and north of Svalbard, where ice-free waters extend to nearly 85°N, according to the NSIDC analysis.  This is pretty remarkable in late December:

It might be counter-intuitive given the preponderance of cold in Alaska, but Bering Sea ice is also below normal, mostly because of ice deficits in the central and western Bering Sea.  There is pretty good ice cover to the east of St Lawrence Island:

The warm anomaly in the Arctic has been ongoing since the height of summer.  Of course most recent years have been warmer than earlier decades, but the latter half of 2025 has been particularly unusual:

Beaufort Sea Ice

Although Arctic-wide sea ice extent is running very low this summer - with big deficits on the Russian side of the basin - surprisingly there is much more ice than normal in the Beaufort Sea.  The following figure illustrates the striking contrast from recent years:

We have to go back to 2006 to find more sea ice in the Beaufort Sea at this date, and the ice extent is even higher than the median for the 1980s.  Rick Thoman pointed out this fact on his site, and he also notes that a considerable amount of multi-year ice has made it into the Beaufort Sea.  The following image from NSIDC is a few weeks old, but it clearly shows a zone of older ice stretching from the Canadian high Arctic to the Beaufort Sea.

The anomaly in the Beaufort Sea stands in huge contrast to the rest of the Arctic.  This figure from Zack Labe shows the rank of each regional basin's ice extent relative to other years in the satellite era.

The Chukchi Sea also has more ice than most recent years, although in the case of the Chukchi the ice is not as extensive as last year.

The NSIDC sea ice index shows the ice deficit on the other side of the pole, with nearly all ice gone in the Kara Sea already. 

Taking a look at the weather pattern from recent months, there has been high pressure centered over the Beaufort Sea, but this in itself is not unusual.  The second figure below shows the departure from normal MSLP since May 1, and the more anomalous aspect is the low pressure near Greenland (positive AO/NAO phase):

The effect of the pressure pattern has been to generate unusual northerly winds from near the pole to the western Canadian Arctic; the figure below shows the departure from normal of the vector wind.  I suspect this has helped to shift the highest concentration of ice onto the Canadian side and also accelerate the Beaufort Gyre, sending old ice westward into the Beaufort Sea.