North Slope Accident

Many readers will have heard that an oil field accident occurred on the North Slope on Friday, as a very large mobile oil drilling rig tipped over and was destroyed.  According to the following article, "Several people with North Slope experience have said the rig likely tipped due to being moved in warm 30 degree weather, which would have caused the road to be softer".

https://alaskalandmine.com/landmines/doyon-26-largest-land-drilling-rig-in-north-america-tipped-over-and-caught-fire-on-north-slope/

Here's a temperature chart for nearby Deadhorse, showing the temperature rising to 31°F on Friday.

Is it reasonable to believe that the road (presumably an ice road build on top of the tundra) became soft even though the temperature did not rise above freezing?

Yes - the properties of ice change significantly with temperature, and liquid water can be found in tundra soils at temperatures well below freezing.  The closer to the melting point, the softer the ice, and the greater the proportion of liquid.

Here's Google's Gemini (AI) response to a query about this situation.  We could quibble about a couple of details in the response, but it nicely lays out the issue that seems to explain the accident.

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In the context of the January 2026 incident on Alaska's North Slope, the "softening" of the road is a result of the unique mechanical properties of frozen water and permafrost near their phase-change threshold.

1. The "Warm Ice" Effect

Ice is not a static material; its strength is highly dependent on its temperature. As ice approaches its melting point (32°F / 0°C), it undergoes a process called pre-melting.

Reduced Compressive Strength: Engineering data shows that the compressive strength of ice at 30°F is significantly lower than at 0°F. At colder temperatures, ice is brittle and rigid. Near 30°F, it becomes more "plastic" or ductile, meaning it deforms under heavy loads rather than holding its shape.

Liquid Water Films: At 30°F, microscopic films of liquid water begin to form between ice crystals (intergranular boundaries). This acts as a lubricant, allowing the ice grains to slide past each other more easily, which reduces the overall load-bearing capacity of an ice road or frozen tundra.

2. Permafrost and Unfrozen Water Content

The soil in the Arctic (permafrost) is not just frozen dirt; it is a matrix of minerals, organics, and ice.

Unfrozen Water Content (UWC): Even below 32°F, a portion of the water in the soil remains liquid due to salts, pressure, and surface tension within soil pores. As the temperature rises from 0°F toward 30°F, the percentage of liquid water in the soil increases exponentially.

Loss of Shear Strength: Research from the US Army Cold Regions Research and Engineering Laboratory (CRREL) indicates that the shear strength of frozen soil drops dramatically as it warms toward the freezing point. At 30°F, the soil may still look frozen, but its ability to support the massive, concentrated weight of a mobile drilling rig (which can weigh several million pounds) is severely compromised.

3. Impact on Ice Road Infrastructure

On the North Slope, "roads" used to move rigs are often built by packing snow and freezing water over the tundra.

Creep Deformity: Under the immense weight of a drilling rig, ice and frozen soil undergo "creep"—a slow, permanent deformation. The rate of creep increases significantly as temperatures rise toward 30°F.

The "Punch-Through" Risk: If a rig is moved during a "warm" spell, the road may suffer from localized failure. If one side of the road yields or "squishes" even a few inches more than the other due to uneven softening, the high center of gravity on a tall drilling rig can cause it to tip past its point of recovery.

Evidence in Industry Practice

The Alaska Department of Natural Resources (DNR) and North Slope operators (like ConocoPhillips or Hilcorp) monitor soil temperatures strictly.

Standard Operating Procedures: Most North Slope permits require a minimum "frost depth" and a maximum surface temperature before heavy equipment can move.

Historical Precedent: The "January Thaw" or "Warm Spells" are well-known hazards in Arctic logistics. Moving a rig at 30°F is considered high-risk because the margin of safety provided by the "structural rigidity" of deep-frozen ground is largely lost.

Conclusion: Even though 30°F is below freezing, it represents the "danger zone" for Arctic engineering. The combination of increased unfrozen water content in the soil and the increased plasticity of ice makes the ground "soft" enough to fail under the extreme pressures exerted by heavy industrial machinery.

Cold Revisited

Now that the weather has calmed down, it's a good time to look back at a couple of aspects of the cold spell in Fairbanks.

First, I've been meaning to compare the cold to previous episodes on various time scales.  From a historical standpoint, the most significant aspect of the cold snap was arguably its long duration, rather than its extreme intensity at any given time.  The widely-cited headline statistic is certainly the most notable: the temperature at the airport stayed below 0°F for 32 consecutive days, the most in over a century.  The record is 41 such days in 1917-18.

In terms of individual days, the daily maximum temperature of -46°F at the airport on January 4th was the lowest since 1977; even the cold snaps of 1989 and 1999-2000 didn't have a day that cold.

A lot more statistics could be compiled, but Rick Thoman saved me a lot of work with this summary (click to enlarge);

A curious aspect of the cold spell was that the international airport was colder than any other reporting site in the Fairbanks area except for North Pole.  This is unusual: the two longstanding co-op sites in the Goldstream Valley ("Ester 5NE" and "Goldstream Creek") are typically significantly colder than the airport.  The discrepancy was large enough that a question has been nagging at me: is it possible that the airport thermometer has been running too cold, so that the cold snap wasn't actually quite as severe as reported?

To illustrate the issue, here's a look at the joint distribution of daily mean temperatures from Fairbanks airport and Goldstream Creek since 2012, for the date window from December 1 through January 15:

Based on data from 2012-2024, Goldstream Creek is typically colder than the airport on more than 75% of days in December and January, but the chart shows that most of the coldest days in the recent cold spell were colder at the airport.  The airport's cold "advantage" emerged in mid-December as the cold snap deepened:

I decided to dig into this further by calculating the 2012-2024 December average temperature difference between the airport and several other valley-level sites around the area, and then examining how these differences vary from year to year.  The idea is to see if last month's cold anomaly at the airport is outside the bounds of usual variability.

The following figure shows the result of my calculations.  Points above the horizontal zero line indicate Decembers that were relatively warmer at the airport compared to the usual difference for the site indicated; for example, in December 2021 the airport was warmer than would normally be expected based on any of the other sites (yet that month wasn't particularly warm overall).  And in 2025, the airport was colder than expected.

The result confirms the unusual situation last month, but it also reveals that there's quite a lot of variability from year to year (e.g. 2021), so the fact that the airport was colder doesn't necessarily indicate a problem with the thermometer.

Interestingly, the temperature differences between the airport and Goldstream Creek show the least variability from year to year between 2012 and 2024.  In other words, Goldstream Creek has the most similar temperature variations to the airport, and the most consistent temperature differences.  However, last month the difference was way off, and this is what drew my attention to the topic.

Honing in on Goldstream Creek, then, the same calculation with temperature differences relative to other sites shows that December 2025 stands out as an apparently significant outlier - more so than using the airport as the reference point.

My conclusion is that if something is awry with the temperature measurements, then it's more likely at the Goldstream Creek co-op than at the airport; Goldstream may have been running too warm.  Consider that since 2012, the Goldstream Creek has never had fewer days reaching -40° than the airport in a winter; but this winter the airport has 21 such days, while Goldstream has only 13.

Of course, it's also possible that the Goldstream valley was actually less cold than would normally be expected for legitimate meteorological reasons.  Perhaps drainage flows from the hills into that valley kept the winds up a little bit, and this would explain why the nearby Ester 5NE site was also warmer than would be expected.

Big Changes Underway

Dramatically warmer conditions are on their way north and will bring major relief from western and interior Alaska's deep freeze in the next couple of days.  Huge temperature rises are expected as temperatures recover all the way up to or even above the freezing mark in places.  Strong winds and blizzard conditions will occur in the mountains, heavy snows will be widespread outside of the chinook zones, and unfortunately it will be so warm that some places see freezing rain and ice accretion.  If it's not one thing, it's another when it comes to Alaska's winter climate.

As if to put an exclamation point on the recent cold spell, Tanana reached -58°F yesterday.  Meanwhile, the cold has been unrelenting in the past week in southwestern Alaska; today is the 9th straight day with a daily high temperature below -10°F in Bethel, and that hasn't happened since January 2012 (Bethel's coldest month on record).

In Fairbanks, today is the 32nd consecutive day with a daily high temperature below 0°F, and that's a record for the NWS/Weather Bureau era.  However, a longer stretch of 41 such days was measured at the University's Experiment Farm in 1917-18 (Nov 24 - Jan 3).  December 1917 had an overall average temperature of -33°F at the farm, more than 10°F colder than last month.

Looking back at last month as a whole, it was the coldest December statewide since 1980, according to NOAA/NCEI, and it was the first calendar month to be more than 10°F below the 1991-2020 normal since January 2020.  However, the cold was only really anomalous from the eastern interior to northern Southeast Alaska.  Here's one perspective based on ERA5 data, showing some areas within the coldest 5% of Decembers since 1950.

NCEI data shows the interior divisions in the coldest 10% since 1925, and the central and northern Panhandle divisions were the third coldest on record, trailing only 1964 and 1933 (the latter being by far the coldest).

Here's the culprit for the cold: a very strong and persistent ridge over the Bering Sea, as illustrated by the mid-atmosphere pressure (500mb height) anomaly.

Compare the monthly mean 500mb height (below, top) to the long-term normal (below, bottom).  Under normal circumstances there is a trough over the Bering Sea and the mid-atmosphere flow is directed from the southwest, preventing excessive cold in Alaska.  Last month the flow was mainly from the north and northwest, and Arctic and Siberian air was imported across eastern Alaska.  Moreover, the pattern produced relatively clear skies, allowing for ample cooling during the mid-winter dark.

It's a far-off memory now, but much of southern Alaska from Yakutat westward was drier than normal in December.  Southeast was much wetter, with Juneau northward seeing extreme snows at the end of the month.

Nobody in South-Central will be surprised to learn that the month was also much windier than normal for most of southern Alaska, owing to powerful episodes of cold flow from the north.  It's an interesting fact that windy Decembers across southern Alaska are more typically very warm across the state, with strong westerly or southerly flow; but last month was more akin to December 2012 or December 1964, with strong northerly winds instead.

Looking farther afield at sea surface temperatures across the North Pacific, it's interesting to see that there is still a lot of unusual warmth to the south of Alaska as well as in the southern and western Bering Sea.

However, the North Pacific basin as a whole has certainly cooled off quite a bit (relative to normal) since summer.  The following post from mid-November noted the cooling trend emerging during autumn, and at that time I speculated:

"Given that La Niña will prevail during at least the first part of this winter, the disappearance of the positive NPM [i.e. cooler North Pacific] probably means a greater chance of cold in Alaska..."  

https://ak-wx.blogspot.com/2025/11/autumn-climate-data.html

It's going to be interesting to see whether the second half of winter takes on a very different character, or if further cold episodes develop even as La Niña begins to weaken.

More Snow and Cold

Back on December 18, I commented that the extreme cold then affecting northwestern Canada and far eastern Alaska looked likely to shift westward in the coming weeks, and that trend has played out nicely.  Not only had Fairbanks "not seen the worst of it yet", but severe cold has now developed in southwestern and south-central Alaska.

This morning was remarkably cold for many locations across the south and southwest; here's a selection of minimum temperatures since midnight last night (click to enlarge):

The -33°F in Bethel and the -12°F in Homer are both the coldest since 2012, and the astonishing -35°F in Kenai is the coldest since February 1999.  Today's high temperature in Homer has been only +1°F, which is also the lowest since 1999.

Anchorage airport (-17°F this morning) was colder (-21°F) in 2024, but the high temperature so far today is only -6°F.  January 7, 2009 was the only day this century with a colder maximum temperature (-9°F).

As for snowfall, Anchorage received a hefty dump on Monday and Tuesday this week, with 19 inches in the two days.  This is the highest 2-day snowfall since March 2002, and the 5th highest on record (data back to 1953).  It's also a record for highest 2-day snowfall in January, the previous record being just 2 years ago; prior to that the greatest 2-day total in January was only 13.7" (in 1987).

The combination of cold and snow in the past week is extremely anomalous for Anchorage.  For instance, the temperature rose to only 18°F during the snow storm earlier this week, and that makes it the largest 2-day snow with a 2-day high temperature below 20°F; the previous was 16.6" with a high of 14°F, again in January of 2024.

Here's a scatterplot of weekly temperature and snowfall for Anchorage in winter; I've highlighted the latest week and the very analogous week in 2024.

Anchorage has had weeks in the past with either more snow or lower temperatures, but the combination of cold and snow right now is virtually outside the bounds of the historical climate, just as it was 2 years ago.

The interesting thing about the 2024/2026 similarity is that 2023-24 was a strong El Niño winter, but this winter we're in a La Niña.  As I've commented before, this winter resembles a "traditional" La Niña for Alaska, whereas 2023-24 was quite atypical for El Niño.

CPC's latest 6-10 day forecast indicates that the cold is likely to continue shifting westward in the coming days, and Southeast will likely continue to warm up as the flow orientation changes.  There's a lot of uncertainty after the middle of the month, however, and I wouldn't be at all surprised to see a new round of cold across northwestern Canada for the second half of January.

Why So Cold?

First, before discussing again the extreme interior cold, I would be remiss not to mention the remarkable snowfall in northern Southeast Alaska during the final days of December.  Driven by a persistent influx of moisture aloft, and a very cold air mass locked in at the surface by high pressure to the north, extreme snow accumulations occurred from Juneau northward.  Juneau airport measured a snow depth of 50 inches on the 31st, easily the highest on record (data back to 1949).

Reported multi-day totals in late December were widely near or above 40" at sea-level locations: click to enlarge the following.

Rick Thoman has lots more detail in his post on the event:

https://alaskaclimate.substack.com/p/southeast-alaska-extreme-snowfall

Now back to the headline topic: the generational cold snap that will come to at least a temporary end tomorrow for the central and eastern interior.  Yesterday's high temperature of -44°F in Fairbanks, and the daily mean temperature of -46.5°F, were the lowest values since New Year's Eve 1999; it has been 26 years since this intensity of cold occurred in Fairbanks.  Today's high temperature may be as low as -46°F, the coldest since December 13, 1977.  [Update: it was.]

Here's another remarkable statistic: the 9 straight days (and counting) with a low temperature of -46°F or lower hasn't occurred since December 1975 in Fairbanks.  If it's still -46°F at midnight tonight, we'll have to look back to December 1961 to find an equally long streak of 10 such days.  [Update: the streak reached 10 days.]

Of course, there have been other harsh cold spells since 1975, but none with quite the sustained intensity of this one.  January 1989 is top of the list, with 12 days having lows below -45°F, but the streak was broken by one slightly milder day in the middle (-40°).  The New Year's cold snap of 1999-2000 saw 7 days with -45°F or lower; and early January 2009 produced 8 such days.

What do all these cold snaps have in common (1961, 1975, 1989, 1999, 2009)?  Like this winter, all occurred during La Niña in the tropical Pacific.  La Niña hasn't always produced extreme cold in Alaska, especially in recent years, but extreme cold is much less likely without it.

The more immediate cause of the astonishing cold spell is a sustained confluence of the ingredients that are required for deep cold in interior Alaska, i.e. a cold air mass, clear skies, minimal solar heating, and calm winds.

The first ingredient is the starting point: the circulation pattern has persistently transported cold air from the north and northwest into Alaska, and this pattern has involved a ridge (high pressure) over the Bering Sea and a trough (low pressure) over eastern Alaska and northwestern Canada.

Here are a couple of simple animations to illustrate the flow pattern in the last week: 500mb height (i.e. mid-atmosphere pressure) in the top animation, and 850mb temperature anomaly (about 4000 feet above sea level) in the lower.  Notice the persistent ridge over the Aleutians and Bering Sea, with northerly or northwesterly flow over central Alaska.

The following figure shows the resulting temperatures in and above Fairbanks: the black line shows 850mb temperature, and the blue line shows surface temperature.

The feature to notice here is that while temperatures aloft (850mb) have certainly been cold in the past 10 days, they haven't been that much colder than earlier in December; but surface temperatures have bottomed out, reflecting a strong and sustained temperature inversion.  This occurs when heat energy is persistently lost to space under clear skies (with no real solar heating by day), and when calm winds prevent less-cold air aloft from mixing with the severely cold surface layer.  Yesterday the Fairbanks airport reported zero wind for well over 24 hours, and the sky was clear above the ground-level ice fog, so there was nothing to disturb the cooling process or provide a warming influence.

This exact confluence of circumstances is obviously rare, particularly in terms of the longevity of the event.  And thinking in terms of the ingredients for cold, it seems the key aspect that has been especially unusual and has allowed this event to become so severe is the absence of wind since December 27.  The cold air aloft has not been particularly unusual or extreme; clear skies are not especially rare in Fairbanks; but typically the active jet stream pattern that brings deep cold to Alaska also tends to produce significant pressure gradients across the state, leading to episodes of wind that preclude or break up a strong inversion.  In other words, I suggest that prolonged calm is unusual when the circulation pattern favors cold.  An example (admittedly extreme) of a more typical style of cold was the northerly blast about a month ago:

https://ak-wx.blogspot.com/2025/12/cold-outbreak.html

It will be worth digging into this idea further in a future post: what distinguishes a "normal" cold pattern from one that includes strong inversions and therefore severe valley-level cold?  And how did the pattern manage to persist so long in this case?

These and other questions will be fuel for fruitful comment once all the data is available for a full post-mortem.