January Climate Data

Looking back at Alaska climate data for January, the month was a story of two dramatically different halves, with the prolonged mid-winter cold snap ending (on a statewide basis) right at the month's midpoint.  It's worth recalling again just how persistent the cold was for that period of six weeks ending January 15; here's the UAF statewide temperature index since November 1st:

The contrast in the mid-atmosphere pressure pattern could hardly be greater between the first and second halves of the month.  The first half of January saw a strong trough planted right over the state, but this reversed to a high pressure ridge for the second half:

Owing to the dramatic turn-around, the monthly average temperature wasn't all that unusual, only 3.5°F below normal, and even the coldest climate division (Bristol Bay) was considerably warmer than January 2020 (and even more so than January 2012).  Southeast Alaska was warmer than normal, as unusual cold only lasted through the first few days of the month there.

Amazingly, the December 31st record 50-inch snowpack in Juneau melted out completely by the middle of January, with 30 inches disappearing in a rainy second week of the month.  All of Southeast Alaska and the eastern half of the state at large was considerably wetter than normal, while the west coast and western interior were dry, along with most of the Alaska Peninsula.

The dryness across the Seward Peninsula and interior northwest compounded a lack of snow from earlier in the winter (see figures below), and snowpack was far below normal by February 1 for places like Nome, Kotzebue, and Ambler - at least according to ERA5 data.

The ERA5 temperature map above shows that unusual cold was widespread over the eastern half of the Bering Sea, and so it's no surprise that sea ice expanded more quickly than normal, nearly reaching St Paul Island by the end of the month.

Sea ice did in fact reach St Paul Island a few days later, according to the NWS analysis:

Nevertheless, on a monthly basis, January Bering Sea ice extent was about 12% below the 1991-2020 normal, because of deficits in the western half of the basin.  The basin-wide total was in line with the past several years, and seems to have stabilized (for now) well above the 2015-2018 lows.

Alaska Landslide Inventory

Back in November a study was published that looked at historical news reports to create a new inventory of landslides in Alaska dating back to 1883.  Many other inventories have been produced over the years for specific purposes, but this approach focuses on the human exposure to landslides.

https://link.springer.com/article/10.1007/s10346-025-02663-z

As one would expect from increased population and better reporting, the number of reported landslides has increased tremendously over time, although the number of landslide-caused fatalities has not increased (largely because of the 1936 Juneau landslide).   The authors argue that a major part of the increase in landslide numbers is related to warming of the climate, which is hypothesized to cause a higher frequency of freeze-thaw events, rain-on-snow events, and rainfall extremes.

Extreme rainfall events in mid-high latitude areas are often produced by "atmospheric rivers", and there's a lot of interest among climate scientists in historical and future trends in these events.  To cite one example, the following study indicates that mid-latitude atmospheric rivers have become more frequent in Northern Hemisphere winter (as defined by moisture transport in the ERA5 reanalysis data).

https://www.nature.com/articles/s41612-025-01191-w

The following figure from the paper (click to enlarge) shows a region of increased frequency in the Gulf of Alaska, adjacent to landslide-prone Southeast Alaska.

Extreme precipitation events have increased widely across southern and southeastern Alaska, according to this data:

Just for fun, I pulled out the ERA5 precipitation amounts for each landslide identified by Darrow and Jacobs as having been triggered by excessive rain.  The chart below shows the rain excess above normal for the 7 days ending on the landslide date, at the ERA5 grid cell closest to the landslide location.

Of course, ERA5 is thoroughly incapable of reproducing local rainfall variations in complex terrain, which is no doubt a critical factor in many cases, so this analysis is very crude.  Nevertheless, it's mildly interesting that the fraction of events with a rain excess above +4 inches more than doubled from pre-1990 (10%) to post-1990 (22%).

One other comment - the increase in atmospheric river events near southern Alaska in recent decades is related to a greater frequency and persistence of La Niña-like (and negative PDO-like) anomalies in the Pacific, with increased warming in the tropical West Pacific:

https://www.science.org/doi/epdf/10.1126/sciadv.adq0604

Cold and Snow Correlation

Last week I alluded to the linkage between the Pacific Decadal Oscillation and seasonal snowfall in Anchorage, with a negative PDO phase often producing increased snow relative to normal.  Of course the PDO also influences seasonal temperature variations - a negative PDO typically brings colder conditions to Alaska, especially in the south.

These twin correlations imply that seasonal mean temperature and snowfall are also correlated to each other in Anchorage: increased snowfall tends to accompany cold.  Here's a chart illustrating this relationship in the last half-century.

I thought it would be interesting to look at the snow/temperature relationship elsewhere around the state.  I started by examining ERA5 reanalysis data, but it's not particularly helpful: it actually suggests a positive correlation in the Anchorage area, presumably because the model's resolution is inadequate (i.e. the results reflect the influence of conditions at higher elevation).

However, one region where the model likely gives a good picture of the low-elevation snow/temperature relationship is in Arctic Alaska.  In the far north, warmer conditions are favorable for increased winter snow, simply because of increased availability of moisture.  This is supported by data from Utqiaġvik up until measurements ceased in 2019: warmer winters tend to be more snowy.

However, historical data from Kotzebue and Nome do not have a positive correlation, despite what the model says.

How about the interior?  The relationships are weak, with little correlation, although there's a suggestion that the warmest winters tend not to be very snowy in McGrath and Fairbanks (especially the latter).  Particularly for Fairbanks, this presumably reflects the drier weather that occurs when the pattern favors warm downsloping/chinook winds from the south and southeast.

Data from Bethel suggests a hint of a negative correlation like Anchorage: more often than not, colder-than-average winters are also snowy.

Turning to Southeast Alaska, Juneau shows a robust negative correlation, as we would expect for a much warmer climate where unusually warm winters tend to be more rainy than snowy.

These charts probably give a good sense of how seasonal snowfall is likely to trend over time if Alaska's climate continues to warm in future decades.  Broadly speaking, we would expect winter snow accumulation to diminish in the low-elevation south and to increase in the Arctic, while the interior may remain relatively unchanged.  But of course large annual and decadal variability will continue, and there may be long-term circulation changes (e.g. related to the PDO) that have significant impacts on long-term trends.

I'll be happy to add charts for other locations upon request (if the data is adequate).