Blowing Snow Climatology

First a note on the late winter cold snap that is unfolding at the moment.  Fairbanks dropped to -46°F yesterday morning and -48°F this morning, a remarkable intensity of cold for this late in the winter.  This morning's low temperature is in fact the coldest observed this late in winter since 1956, and few events can rival it.  Here are the most notable cold readings at similar dates in the 1930-present Fairbanks history, with the 1932 and 1964 events surely being the most anomalous:

Feb 20-28, 1932   -50°F or colder for 9 consecutive nights

Feb 23, 1933   -49°F

Feb 26, 1954  -50°F

March 1, 1956  -49°F; -45°F on the 8th

March 15, 1964  -46°F

Two more nights of intense cold are possible before the current chill eases.

Looking back at the past couple of weeks, there were two episodes of sustained blowing snow, which is very uncommon in the sheltered Fairbanks bowl.  Last Thursday the airport reported blowing snow for 15 straight hours, which appears to be the second longest uninterrupted duration of blowing snow observations since hourly observations began in 1948.  The record is 17 straight hours exactly 15 years earlier, in late February 2011.

Then on Tuesday another 8 hours of blowing snow was reported as the cold air moved in after the snowfall.  That takes this winter's total to 25 hours, including a brief episode in January, and the historical data shows this is close to a record - see below.

The pronounced drop-off in blowing snow from the mid-1970s through 2005 is very striking, and at first glance it's tempting to ascribe this to changes in observational practice.  However, the PDO may again be a plausible explanation, as the PDO flipped positive in 1976.  There does seem to be a correspondence between heightened frequency of blowing snow and the most negative PDO periods of 1950-1956, 1970-1975, 2008-2013, and 2021-present.

It's also interesting to observe that blowing snow is easily most common (least uncommon) in the month of February, both in terms of total number of hours and number of unique days and years when it occurs - see below.

I would welcome suggestions for why February is particularly favored for blowing snow, because the wind is not significantly higher than earlier winter months; the frequency of strong breezes (e.g. 15 knots) is barely any higher than December.

Without being an expert on snow pack properties and the physics of blowing snow, I'd suggest that the return of significant solar warming in February may be a key factor, allowing the snowpack to warm from its midwinter lows.  As for March, the stronger winds might be expected to produce still more blowing snow, but by that time the sun is often warm enough to melt the snowpack surface, forming a hard crust, and the frequency of blowing snow drops back again.  March also tends to be the driest of the winter months, so there's less new snow to blow around.

Fairbanks Snow Onslaught

Last month we were talking about record snowfall in Anchorage, and just a few weeks before that the focus was on extreme snowfall from Juneau northward in Southeast Alaska.  Attention now turns to Fairbanks, where there has been a remarkable onslaught of snow (for the interior) in the past two weeks: the NWS reports 37" in the two-week period.  Here's a season-to-date chart courtesy of xmACIS2:

The monthly snowfall of 38.5" in Fairbanks puts 2026 solidly into second place for the February total; the record is 43.1" in 1966.  The monthly total has also broken into the top 10 for all calendar months, which is remarkable given that early winter tends to be snowier than late winter.  If it were not for the snow deluge of December 2021 (50"), this would be the snowiest calendar month since 1993.

The 14-day snow total of 37.3" is competitive with the highest 2-week total in December 2021 (38.9").  Prior to that, 2-week totals of over three feet occurred in January 1937, February 1966, Nov-Dec 1970, December 1984, and December 1990.  It's not a long list.

As for snow depth, the NWS reports 38 inches on the ground in Fairbanks, and that's the highest for a date in February since 1993.  (The snow pack reached 38-40" in early March 2022 and in April 2021, but no other winter since 1993 saw these snow depths.)

Here's the culprit: a strong mid-atmosphere ridge (high pressure) near the Aleutians in the past two weeks, producing a trajectory of moist air flow clockwise around its northern perimeter.

The mid-atmosphere winds originated far to the southwest and flowed into western and central Alaska without let or hindrance: a perfect recipe for persistently wet weather in the interior.

Another unusual aspect of the recent weather in Fairbanks has been the episodes of wind and blowing snow, both yesterday and last week.  I'll have more to say about that in my next post.

La Niña Ending Soon

La Niña has made its presence known in Alaska this winter, and winter certainly isn't over yet, but major changes are afoot in the tropical Pacific Ocean.  Here's the canonical Niño3.4 SST index, which is negative (cooler than normal) during La Niña and positive in El Niño.

A region of warmer than normal SSTs is expanding quickly westward from the coast of South America, leaving equatorial cool anomalies looking anemic in the central Pacific:

Compare with the situation just six weeks earlier:

The long-range computer models expect warming to continue through spring and into summer, resulting in El Niño by summer.  This month's forecasts are more aggressive than previously, and judging from the current trend, they may not be aggressive enough.

If El Niño does develop - as seems very likely - this will be a risk factor for increased wildfire activity in Alaska this summer.  However, the statistical connection hasn't always played out in recent years; 2023 was an analogous year with El Niño developing, but Alaska's fire acreage was very low (in contrast to Canada).

In the meantime, La Niña won't relinquish her influence on high-latitude patterns immediately, and the latest forecasts suggest a strong possibility of another La Niña-like persistent statewide cold spell starting the middle of next week.  The cold plunge next week seems to be locked in: here are two leading ensemble models for next Thursday morning.

Looking farther ahead, the details are less clear on the evolution into March, but there are strong hints of a persistent ridge near the Date Line and a trough over eastern Alaska and northwestern Canada - very similar to the persistent pattern in December.

Below is an example: compare the forecast portion (left side of the graphic below the dashed line) to this December 18 post.  The blue shading near the longitude of Alaska indicates the trough that will produce the cold northerly flow; this model shows the setup lingering into mid-March.  (Note that the previous post includes an explanation on interpreting these figures.)

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).

More Anchorage Snow

Anchorage has seen another big snow event this week, occurring three weeks after the record (for January) snowstorm earlier in the month.  The new snow accumulation of 11 inches takes the January total to just over 40 inches, which is a record for the monthly total.  It's also the fifth snowiest calendar month in the modern Anchorage climate history (1953-present).

Here's a visualization of calendar month snow totals in Anchorage, with the top 10 events for the main snow months marked in red.  February has two huge outliers - 1996 and 1955 - but the most favored month for big totals is clearly December.

The climatological drop-off in January is actually rather significant; December reaches 20" over a third of the time (26 of 73 years), while January sees 20" in less than 15% of years (10 of 73, including 2026).  So this month's big snow total is a notable outlier for the time of year.

Another interesting tidbit is the preponderance of high monthly totals in recent years: 2023 saw the snowiest November, 2022 and 2023 had the 2nd and 3rd snowiest Decembers, and now we have the snowiest January.  February 2023 gets an honorable mention with the 4th snowiest February (32").  These are good times for snow lovers in Anchorage.

The statistics are at least as striking when we look at liquid equivalent precipitation in Anchorage, i.e. it's been wet in recent winters.

2022 - 2nd wettest February

2022 - wettest December

2023 - wettest November

2025 - 3rd wettest January

2026 - wettest January

What changed in 2022?  The PDO (Pacific Decadal Oscillation), for one thing:

See this 2022 post for some comments on the correlation between the PDO and Anchorage snowfall:

https://ak-wx.blogspot.com/2022/12/anchorage-snow.html