Snow Analysis

Fairbanks reached 50°F yesterday for the first time this season - a couple of weeks later than normal - and thaw season is now fully under way, with no sign of an imminent return to unusual cold.

Winter's last gasp earlier this week had a sharp bite to it in the interior and north, with overnight temperatures dropping well below zero at many locations.  Here are a few notable readings from Wednesday morning:

-24°F at the Birch Creek HADS

-16°F at the Livengood RAWS

-17°F in Bettles and Coldfoot

-27°F at the Dahl Creek HADS

-20°F at the CRN site to the east of Kaltag

It's pretty late for this kind of cold.  In Bettles, for instance, only one year (since 1951) has recorded a temperature below -15°F after April 20, and that was only marginally later in the month (April 22-25, 1966).

Accumulating snowfall is likely finished in Fairbanks, so the tentative total for the season fell just short of 100".  It was the snowiest winter since the triple-crown big snow winters of 1990-91 through 1992-93.

In view of the Fairbanks snow onslaught in February, and similar heavy snows in Anchorage and Juneau, I thought it would be worth looking at the contribution of the snowiest days and months to seasonal snow totals at all three sites.  For example, the top 10 snowiest days of each winter generally contribute about half of a winter's total snow accumulation in Fairbanks; but has this changed over time?  Fairbanks typically "nickels and dimes" its way to a substantial snowpack, but is this more true of recent years or of an earlier climate?

The answer is there hasn't been any significant change over the decades.  Click on the following chart to enlarge; it shows the seasonal snow totals in light blue, the contribution of each winter's 10 snowiest days in dark blue, and the ratio of the two totals in red.

There are slight increasing trends in snow totals in Fairbanks, and there's a hint of a decreasing trend in the "top-10-days to seasonal total" ratio, implying that heavy snow days used to contribute a bit more of the total snowfall - but the trends are nowhere near statistical significance.

Another perspective on the question is to look at the snowiest 30-day period each winter and calculate its contribution to the seasonal snow total.  Again, there's a slight decrease in the snowfall fraction attributable to the snowiest month, but it's not a significant change.

Anchorage also exhibits slight - but not significant - upward trends in snowfall, both in terms of seasonal totals and each component of the segmentation.  The snow fraction derived from top-10 days and the snowiest month haven't changed significantly over the 72 years of data in Anchorage.

A more striking result is found in Juneau, where both fractions have increased very significantly in the 82-year climate history.  The snow totals themselves haven't changed significantly, but there's clearly a substantial increase in the concentration of snowfall in the heaviest episodes, starting in 1976-77.

It seems to me that the change in Juneau must reflect the increase in winter average temperatures that also developed in the late 1970s, when the PDO phase turned positive.  In Juneau's mild climate, warmer winters have more days with rain rather than snow, and therefore the snow events make up a larger fraction of the winter's overall snowfall.  (To understand this, consider the extreme of a much warmer climate where snow is rare; 100% of the snow will occur in the top-10 snowiest days each winter.)

The surprise, perhaps, is that Juneau hasn't seen a more significant decline in total snowfall; there is a negative slope, but it's not close to statistical significance.  However, it seems possible that the inter-annual variance is increasing; many recent years have had low snow, but there have been very snowy winters too, culminating in this winter's all-time record.

Winter Storm Warnings

Winter storm warnings have been hoisted from the Yukon Delta and eastern Norton Sound to the western interior, as a decaying Bering Sea low joins forces with an Arctic trough to bring significant snowfall.  Here are snow forecast graphics from the NWS (click to enlarge):

Interestingly, however, the model forecasts have adjusted warmer for next week, with cold disappearing quickly by mid-week; warmth will quickly surge up from the southwest, replacing the cold air mass centered over northwestern Alaska.  Here are the latest 850mb temperature forecasts for late Tuesday, with cold poised to depart:

If warmer weather can stick around for the rest of the month, as seems possible, then thawing will start to make some headway.  Of course we don't want it to get too warm too quickly.

Here's a historical perspective on Fairbanks temperatures in previous years when La Niña transitioned rapidly into El Niño between winter and summer, as it is doing this year.

Interestingly, this set of "analog" years suggests that the odds most favor below-normal temperatures for 30-day periods ending late April through late May - or right around breakup season.  The median breakup date at Nenana for these 10 years is May 6, i.e. a few days later than normal.  However, not all ENSO transition years are cold around this time; two of the last three (1997 and 2009) were not, and Nenana breakup was on April 30 and May 1 in those years respectively.

Breakup Delayed

It's a bitter pill to swallow after such a harsh winter, but significantly colder than normal weather is set to return next week for much of Alaska, and there will be snow for many.  Breakup will be pushed back, and unfortunately the risk of a dynamic breakup with flooding problems is now on the rise, so to speak.

Here are ensemble-mean temperature forecasts from the latest ECMWF and GEFS models (temperature departure from normal at 850mb) for early next Wednesday:

The very good agreement at a 6-day lead time suggests that confidence is rather high.

Interior river ice thaw still has quite a way to go.  In Fairbanks, although temperatures have been above freezing by day for the last two weeks, the accumulation of daily "thaw units" has been minimal, and snowpack depth is still reported at 18".

The Tanana River ice at Nenana doesn't go out until at least 75 thawing degree days have accumulated in Fairbanks, which would equate to (for example) a week of high temperatures in the low 50s Fahrenheit and lows around freezing.  (Thawing degree days are calculated by summing the daily differences between daily mean temperatures and 32°F, for positive values only.)  And ordinarily a lot more thawing is needed - unless breakup is very late, in which case the sun's strength can get the job done without the same amount of warmth in the air.  Here's a chart to illustrate (click to enlarge):

Speaking of the sun's strength, data from the CRN site north of Fairbanks shows it has been cloudier than usual in the last 10 days, so that's another strike against breakup progress.  With Nenana ice thickness most recently measured at 51 inches, it's going to be a while.

March Climate Data

Winter 2025-26 is in the books, and it was a memorable one for many in Alaska.  The headline story, of course, was the interior cold - exemplified by the remarkably stubborn valley-level chill in Fairbanks, but experienced also more widely across the central and eastern interior.  The following figure gives a sense of where the cold was really anomalous, as in "colder than any winter in the 1991-2020 climate period":

From this perspective, interior Alaska was the most anomalously cold region on the planet for the 5-month period:

December and March were the really cold months statewide, although January and February were also below normal overall.

With November being milder, the statewide average temperature for November through March was the coldest since 2011-12, but December though March was the coldest since 1971-72.

As in Fairbanks, the greatest superlatives were reserved for March, which was truly extreme.  Six of 13 climate divisions saw their coldest March of record (1925-present), and 3 others were in the top 5 coldest.  This ranks up there with the likes of January 2012 and February 1990 for widespread record-breaking cold.

The reason for the unending supply of bitter cold was a pronounced and highly anomalous ridge over the western Bering Sea, bringing northerly flow to Alaska.  The pattern was very similar for March and for the winter as a whole:

As noted in earlier posts, eastern Bering Sea ice extent reached a record for the satellite era, peaking around March 24:

The dominance of northerly flow produced dry weather for most of the state except the North Slope and Southeast Alaska in March, and the November-March precipitation map also reflects a persistent moisture deficit from western to south-central Alaska:

Snowpack is therefore well below normal in much of south-central Alaska, and especially across the Kenai Peninsula, where the April 1 snow survey reports that many sites are ranking second lowest for snowpack.  However, the eastern interior across to the southern Yukon has well above normal snowpack.

The latest breakup outlook - updated today - highlights an expected return to below-normal temperatures, especially across the eastern interior, and that's not good news.  Unusually thick river ice and unseasonably cool weather point to a delayed breakup that may well be more dynamic (violent) when it finally occurs, especially if the ample snowpack eventually melts out in a hurry.

https://www.weather.gov/media/aprfc/BreakupProducts/ESFAK_ACR_20260410.pdf

March Record Cold

Rick Thoman has a nice blog post about the remarkable cold for many locations in March:

https://alaskaclimate.substack.com/p/record-setting-cold-march-in-alaska

With Fairbanks being near the epicenter of the cold anomaly, it's worth drawing attention to some of the remarkable highlights there.  The monthly mean temperature of -9.0°F at the airport was 19.6°F below normal, the most anomalously cold month since February 1990.  It was the coldest March on record, approximately equal to an average January in terms of mean temperature.

Rick Thoman makes the interesting point that there is actually a statistically significant trend towards greater variability in March mean temperatures from year-to-year:

Overnight minimum temperatures (mean of -26.3°F) were even more unusual at 22.9°F below normal and 5.4°F below the previous record.  Remarkably, there are not that many calendar months with such low minimum temperatures at any time during winter: only 4 months this century prior to this winter.  There are also only a couple of months in Fairbanks history with mean maximum or minimum temperatures so far outside the historical range: the extreme warmth of January 1981, and the extreme cold of September 1992.  Here's a chart of March average daily minimum temperature:

Daily maximum temperatures were not quite as extreme in terms of their monthly mean, but the overall monthly maximum of only 30°F was a record; Fairbanks has not previously been observed to stay below freezing the entire month.

The last time the temperature was above freezing at the Fairbanks airport was October 31, and that means the entire climatological "cold season" of November through March was at or below freezing (32°F was reached on January 16).  Again that is a first in Fairbanks.

Here's an interesting (to me) perspective on when the monthly mean temperature records were set in Fairbanks.  Summer and winter cold records mostly occurred around 1950-1980, but record-setting cold has occurred more recently in autumn (1990s) and March-April (2013 and this year).  Warm records clustered in 1975-1981.

Only March, April, and October have their cold records occurring after their warm records.  The February records occurred in back-to-back years in 1979 and 1980.

I'll be on the road for the next week or so, but more discussion of the March extremes will be forthcoming when all the usual climate data is available.

Juneau Seasonal Snow Record

Excessive snow has been a recurring topic here this winter, and another big headline has now emerged: Juneau has broken its seasonal snowfall record, exceeding 200 inches for the first time since records began (1948).  The previous record occurred in 1964-65.

The chart below shows that Juneau's snowfall this winter (blue line) occurred mostly in December and in the past month or so, with a lengthy spell of nearly zero snow for much of January and February.

Remarkably, Juneau's calendar month snow records have been broken for both December and March this winter.  It's the first time a single winter has broken two calendar month snowfall records at one of the "big three" cities (Juneau, Anchorage, Fairbanks).

Recall that although January was quiet in Juneau, the monthly snow record was broken in Anchorage, and last month came in second place for February snowfall in Fairbanks.  See this post for the most recent discussion of events earlier this winter:

https://ak-wx.blogspot.com/2026/02/fairbanks-snow-onslaught.html

Interestingly, although Fairbanks has had some snowy times in recent winters, a monthly record hasn't been set since 1992 (both May and September - but in different "winters").

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

Cold Won't Quit

The drumbeat of cold goes on for Alaska, and with every passing day the anomaly becomes more remarkable, especially in comparison to the climate of recent decades.  The persistence of the recent anomaly in UAF's statewide temperature index is something to behold:

The first half of March in Fairbanks was the third coldest on record, and the coldest since 1971.  Only 1°F separates it from the coldest March 1-15, in 1971.  This comes on top of the 8th coldest December-February period on record - also the coldest since 1970-71.

What would it take for March to be the coldest on record?  That would require the average temperature to be below +2°F for the rest of the month - and that did happen in 2007, but it would itself be a rare anomaly.

Here's an interesting perspective on this winter's combination of deep cold and abundant snow in December-February in Fairbanks.  For each winter, I've combined the 1930-present percentiles of the Dec-Feb average temperature and total snowfall; this winter was the 8th coldest (93rd percentile for cold) and 4th snowiest (97th percentile).  That makes a combined percentile of 95%, the second highest on record.  The record was in 1965-66, the 4th coldest and 2nd snowiest Dec-Feb period. 

The absence of percentiles above 80% after 1971-72 is very striking; this is all because of the lack of cold in the past 5 decades.

From this perspective, winter 2025-26 really has been an "old-fashioned" winter in Fairbanks.

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.