February Climate Data

Climate data is available for last month, and NOAA/NCEI rates the statewide monthly average temperature at +4.0°F, or 4.7°F below normal, making it the third month in a row to be noticeably colder than the modern (1991-2020) normal.

Interestingly, it's the first time since 1998-99 that all three months of climatological winter (Dec-Feb) were more than 3°F below the 1991-2020 normal; and it's only the second time that has happened since 1975-76.  This highlights that persistence and repetitiveness have been the significant aspects of the cold, more so (in general) than intensity.  The Dec-Feb average temperature was only the coldest since 2019-20 (when January and February, but not December, were extremely cold).

Here are my usual ERA5 percentile maps for the last three months individually:

It was only the peripheral areas of the southwest, northwest, and southeast that escaped being colder than normal for the three-month mean, although Southeast Alaska was cold only in December. 

The mid-atmosphere pressure pattern was a classic for cold in Alaska, both in February and for DJF as a whole - see below.  The key feature is above-normal pressure (500mb height) over the Aleutians and Bering Sea, i.e. the semi-permanent Aleutian Low was weaker than normal.  When the Aleutian Low is strong, it pumps warm air up into Alaska from the southwest (common during El Niño), but when it's weak, colder northerly flows are able to intrude more often than normal (typical of La Niña, as this winter).

 

Liquid-equivalent precipitation was well above normal in February to the north of the Alaska Range, and also in most of Southeast Alaska, but the northern Gulf coast and southwestern Alaska were drier than normal.  This was quite like the December pattern, so the Dec-Feb precipitation anomaly map is similar.  However, it should be noted that local details are obscured in these maps; Anchorage DJF precipitation was actually well above normal because of the record snowfall in January.

The snowpack situation is a mixed bag, according to ERA5 model estimates: poor across much of southern Alaska, and very poor across the Seward Peninsula and parts of the northern interior, but fair to good from the Y-K Delta to the eastern interior.  Considering how much snow has fallen at times in the three big cities, the lack of more widespread deep snowpack is notable.

As for wind, February was a relatively windy month for much of the state, and especially for the interior and north, as vigorous intrusions of cold air made their way south and east.

On the plus side, relatively clear skies allowed plenty of returning sunshine in February for southwestern and south-central Alaska.

Looking ahead, a rapid transition into El Niño is looking more and more likely in the coming months, and some of the long-range models are now showing a very strong El Niño, perhaps even rivaling some of the strongest of recent decades.  East-central equatorial Pacific SSTs are already poking above normal (see below), so from this standpoint La Niña is already over.  However, La Niña-like weather patterns will likely continue for some time, and there's no sign of an imminent end to the cold weather pattern that is currently entrenched across Alaska. 

Statewide Cold

The widespread cold of the last week in Alaska has been really exceptional for this late in the winter.  Only a quick glance at UAF's statewide temperature index is needed to confirm this - see the chart below.  The index has been nearly pegged at the bottom of the scale since last Wednesday.

Recall that the index scale is designed to indicate the departure from normal in terms of frequency, so an index value near -10 corresponds to near-record cold for the time of year (compared to the 1991-2020 climate).

The calculation behind the UAF index is actually the average standardized temperature anomaly across 25 observing sites, taking into account the reduced climatological variance at more maritime locations and the greater variance in the interior.  Last Friday (Feb 27), the average anomaly was 3.1 standard deviations below normal, which is the lowest daily value since the remarkable cold snap of April 2021.  Prior to that, the only dates in the past 20 years with such anomalous statewide cold were in April and May 2013 - the year of the record late breakup at Nenana.

If we only look at December through February, it's interesting to note that only ONE other event since 1991 produced a daily statewide anomaly below -3 SD, and that was early February 1999.  The cold back in December and early January this winter didn't reach anywhere near the same intensity, peaking at only 2.3 SD below normal on January 3 (the persistence of the cold was a more unusual aspect on a statewide basis).

Therefore in the context of normal Alaska climate at the end of February, the last week has been very extreme, a rare cold outlier.

Fairbanks exemplifies this: the low temperature of -49°F on Sunday was the coldest in March since 1911, and it tied the monthly record for the 1930-present era.  It's also the first time since 1932 that 5 consecutive nights have dropped below -45°F after mid-February.  In fact, until this winter such a string of cold nights hadn't happened at all since the New Year's cold snap of 1999-2000.

More on this winter's achievements in Fairbanks in a subsequent post.

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