Record Cold November in Places

With very unusual cold persisting in southwestern Alaska, and even colder conditions arriving in the next few days, some spots with longstanding climate histories appear likely to break their records for coldest November.

For example, assuming the NWS forecast is correct for the rest of the month, King Salmon will end up with a monthly mean temperature of about +4°F, compared to the 1963 record of +8.4°F (data since 1942).  With such a large margin of difference, it seems very unlikely that the record won't be broken - as noted by Rick Thoman.  Temperatures in recent days have been colder than anything seen last winter, and are not too far off the coldest that is typically seen throughout an average winter at this location.

Looking at data from Bethel, which has a period of record back to 1923, it looks like November 1939 was colder than November 1963 in the region, but the NWS forecast suggests Bethel still has a chance of breaking the record.  Currently it seems the monthly average may end near 0°F, with the 1939 record standing at +0.1°F.  This is quite a bit colder than the average January in Bethel (only 5 Januarys have averaged below 0°F since 1976).

How about Cold Bay, with data back to 1950?  The November 1963 record is 28.4°F, and we're currently looking at 28.1°F for this month's average.

Anchorage currently looks unlikely to break its monthly record of 9.4°F, set in 1955.

If records are broken at several sites, this would be the first winter month since January 2012 with widespread monthly cold records at longstanding climate sites in Alaska.  March 2017 saw record-breaking cold in Haines, and April 2013 was record cold in the interior, but other than that warmth has been the oft-repeated theme.

Cold Descends - Thank La Niña

It's been a very cold week for the time of year in western and southern Alaska, and the eastern interior is now seeing its first real cold of the season, with an impressive -44°F at Northway this Saturday morning.  Chicken also saw -44°F last night.  Here are a few of the coldest readings in the past several days:

Tuesday Nov 16

Bettles   -35°F

Wiseman   -35°F

Denali Visitor Center   -28°F

Wednesday Nov 17

Norutak Lake RAWS   -32°F

Kaltag   -31°F

Unalakleet -31°F

Thursday Nov 18

Selawik 28E  -31°F

Ruby 44ESE  -29°F

Friday Nov 19

North Pole 1N  -34°F

Tok #2  -34°F

Wednesday morning's -31°F at Unalakleet on the Bering Sea coast is really impressive, with an easterly breeze making it feel even colder.  Unalakleet climate data is patchy after 1977, and non-existent after 1997, but there is good data from 1944-1977, and the earliest -30°F in all those years was November 22.

The upper-air observations from Fairbanks reported an 850mb temperature of -25.3°C on Wednesday morning, which is the earliest -25°C at 850mb since the remarkable pre-Thanksgiving cold snap of 2011.  On that occasion, Fairbanks saw -41°F on the 17th, and the 850mb temperature reached -30°C on the 21st.  Read about it here and in other posts from that month.

In terms of departure from normal, the greatest temperature anomalies have been in the southwest.  Here's a simple animation of approximate daily departures from normal in the last week (based on model data):

The southwestern mainland is where cold is most reliably seen in Alaska during strong La Niña winters, as illustrated by the map below; this shows that all of the 10 strongest La Niña's since 1950 produced below-trend December-February temperatures in southwestern mainland Alaska.

The intensity of the current La Niña is admittedly up for debate, because it depends on how intensity is defined, but these days I prefer to watch the Multivariate ENSO Index, which uses five different variables to measure the phase of ENSO.  The map above shows results for the 10 most negative MEI values in November through March, and the current MEI is running at about 7th most negative since 1950.

Why does La Niña tend to bring cold to Alaska?  The answer is that La Niña involves a westward shift in the semi-permanent zone of frequent heavy rainfall over the western equatorial Pacific and the Maritime Continent, and this has predictable impacts on the atmospheric circulation at higher latitudes over the North Pacific.

The two maps below show the 200mb (jet stream level) wind during strong La Niña winters (top) and strong El Niño winters (bottom).  While the jet stream maximum near Japan remains basically the same - the basic north-south temperature gradient doesn't change that much - there's a major difference in how far east the jet extends, and this is linked to the longitude of peak tropical rainfall (westward for La Niña, eastward for El Niño).  In particular, the jet stream is stronger across the central and eastern North Pacific during El Niño.

The jet stream differences are connected to subtle but important shifts in the average circulation near Alaska: compare the 500mb maps below (mid-atmosphere level, La Niña top, El Niño bottom).  There's always a trough over northeastern Asia on average during winter because of the basic temperature gradient (it's always cold in winter in Siberia), but La Niña keeps the trough focused near the Sea of Okhotsk, while El Niño brings the trough farther east and strengthens it in association with the stronger North Pacific jet stream.  

The difference between the two states is easier to see if we look at anomaly maps, i.e. departure from normal:

During La Niña, the tendency for above-normal height (pressure) near the Aleutians - which is equivalent to a weakening of the usual trough - means that cold northerly flow has a better chance of reaching Alaska.  The average flow aloft still has a southerly component (which is why Alaska isn't as cold as it could be in winter, considering its latitude), but the southerly component is lessened compared to normal.  The maps below show average wind at 500mb (La Niña top, El Niño bottom)

Also, and I believe this is significant, La Niña's weaker trough means a higher frequency of clear skies and calm winds, which strongly promotes surface cooling; I suspect Alaska gets more cooling out of La Niña that we would expect from upper-air temperatures alone.  It would be worth examining this idea a bit more for a subsequent post.  Here's the average MSLP in the two contrasting patterns: lots more storminess from the Aleutians to the Gulf of Alaska in El Niño winters (bottom).

As an aside, El Niño's impacts on Alaska aren't the opposite of La Niña's effects; the climate response is non-linear and asymmetrical.  Unusual warmth in El Niño is traditionally confined to the southeastern half of Alaska (see below), although the last major El Niño in 2015-16 was an exception, with extraordinary warmth across most of the state.

October Climate Anomalies

First, a brief follow-up on the last post: we ended up with 15 consecutive days without Nome being warmer than Fairbanks, which is quite amazing for the time of year.  Based on 90 years of climate data, the record for a sequence of such days ending in November is only 7 days, which occurred in 1956.  There were 10 such days leading up to Christmas in 1959.

Something like normalcy has now returned for Fairbanks, as much colder air arrived aloft over the interior, allowing surface temperatures to drop to more seasonable levels.  It's still cold in Nome, though - and notably cold around the northwestern interior: quite a number of locations dropped into the -20s there this morning.

The Tanana River at Nenana looks to be mostly frozen over - at last.

Looking back at October, here are the climate division temperature and precipitation ranks, courtesy of NOAA/NCEI:

Below is Rick Thoman's temperature anomaly map for the month.  Notice that the cold departures in the southeast, though small in absolute terms, amounted to one of the colder Octobers in the last 30 years (compare with the map above).

The large warm anomalies in the northern interior are interesting, and it's good to see that this quite localized feature is reflected in the ERA5 data:

Enhanced cloud cover seems to have had something to do with this warm anomaly, and this in turn was related to unusual low pressure from Alaska to northwestern Canada, and an extensive trough from eastern Russia to the northeastern Pacific: see below.  It was a very unusual circulation pattern with really exceptional, record-breaking warmth over much of central and eastern Canada; the northern interior warmth in Alaska was right on the western edge of the continental-scale anomaly.

Here are the ERA5 maps for some other variables:

Finally, given that we're talking about October, it's worth checking in on Utqiaġvik, where the loss of sea ice has so profoundly changed the temperature climate for the month.  This October was a little cooler than in the last 5 years, but still way above the norm from earlier decades.

Utqiaġvik October average temp of 23.7F (-4.6C) makes this a typical October for the 21st century. For the 20th century (post 1919), this would have been 4th warmest. Dramatic change the result of #seaice loss. #akwx #Arctic @Climatologist49 @ajatnuvuk @CinderBDT907 @bertaglenn pic.twitter.com/dM0e3gbLcn

— Rick Thoman (@AlaskaWx) November 1, 2021

Cold West, Warm East

The recent weather pattern, with a persistent trough over far eastern Russia and the Bering Sea, has allowed winter to make an appearance over western Alaska, while central and eastern areas have been much warmer.  The contrast reached an extreme last weekend, as deep southerly flow and a major chinook brought excessive warmth to the eastern interior.

Remarkably, it has been almost two weeks since Fairbanks had a daily mean temperature lower than Nome, and this is very unusual indeed for the time of year.  Typically the interior cools off much more quickly in late autumn than the west coast, owing to the strong maritime influence in the west and the lack of ice in the Bering Sea.  Because of this, early November is the time of year when Nome is most likely to be warmer than Fairbanks, i.e. the opposite of what's happening this year.

In the first half of November, Nome is warmer than Fairbanks on 87% of all days, according to the 1930-2020 history, and in recent years this percentage has risen still higher, as the Bering Sea has been so warm.  For instance, in the past decade only 12 days between Nov 1 and Nov 15 have been as cold or colder in Nome than Fairbanks, i.e. 8% of all days in that window; and yet we are currently standing at 12 such days in a row.  Here's a chart of daily mean temperatures, and their 1981-2010 normals, in the two locations since September 1.

The freeze-up situation reflects the unusual contrast: there has been lots of ice on the Yukon out west for days now, but the Tanana River still shows mostly open water.  Here's a webcam photo of the Yukon at Grayling from more than a week ago, versus the Nenana webcam today:

The notorious cold spot of Chicken has only dropped to -4°F so far this season, a far cry from last year, when -40° was reached more than once in early November.  Looking at a map of the lowest temperatures since October 1 (click to enlarge images below) shows many locations yet to see 0°F or even single digits Fahrenheit from Nenana to Fairbanks and in the Yukon-Tanana uplands.

Here are a few 500mb maps to illustrate the circulation pattern, including the remarkable chinook last weekend.  Note the persistent trough over far eastern Russia: an anchor point for the cold air mass that has been entrenched over western Alaska.

3am AKST Oct 26:

3am AKST Oct 31:

3am AKST Nov 5:

Disappearing Halloween Snow

Rick Thoman pointed out today on Twitter that this Sunday will - in all likelihood - be the 5th Halloween in the past 6 years to have less than an inch of snow on the ground in Fairbanks.  For a span of 75 years - 1941 through 2015 - only one year managed the same feat.  (Incidentally, that year was 1962, which bears more than a passing resemblance to this year in terms of alignment of various aspects of the global climate system.  Interesting.)

The disappearance of Fairbanks snowcover at Halloween is consistent with a downward trend in October 31 snow depth that seems to have started more than two decades ago; it's been 24 years since more than 6 inches was on the ground, but prior to 2000 about a third of all years had at least that much snow.

Here's Rick's excellent graphic:

Total October snowfall in Fairbanks also shows the same kind of decline.  Before 2009 it was quite normal to have 10" or more of snowfall in October; this happened in nearly 50% of all years.  But amazingly it hasn't happened for the last 13 consecutive years.  Based on the 1930-2008 climate, and assuming each year is independent of the last, the chance of less than 10" happening 13 straight times is less than 1 in 1000.  So this appears to be a highly statistically significant change.

Interestingly the ERA5 reanalysis captures the preponderance of low snow accumulations in October over the last 12 years; the map below uses a 1951-2010 median as the baseline "normal".  According to this data, the anomaly has been most significant over the Bering Sea, but it extends across southern Alaska to the Canada's west coast and northwestern regions.

The lack of October snow does not principally reflect dry weather, at least not in the Bering Sea region; ERA5 actually shows more wet than dry weather in this area, and since 2009 Fairbanks has seen above-median liquid-equivalent precipitation in 5 of 13 years, including 4 very wet Octobers (2012, 2017, 2019, and this year).

Rising temperatures are a much more plausible explanation for the loss of snow; the ERA5 map below uses a 1951-2010 average for the climatological baseline.  In Fairbanks, all but 2 of the last 12 Octobers have been warmer than the 1930-2008 mean, and more than half have been over 5°F warmer than the old normal.

Alaska isn't the only place to have seen a paucity of October snow in the past decade or so.  Here's the ERA5 map for a global domain: note the similar low-snow signal from eastern Canada across the northern North Atlantic and in much of Russia.

Changing Ice

A couple of items of follow-up today.  First, all semblance of similarity to the early cold of 1992 has long since been lost this autumn in Fairbanks, with above-normal temperatures persisting now for more than two weeks, and a near-record high of 48°F yesterday.  It was the highest temperature for more than a month, which in itself is quite remarkable at this time of year, when the seasonal normal is dropping so quickly.  There's been no meaningful drop in this year's daily mean temperatures since late September.

The warmth has pushed back freeze-up of rivers; the Tanana is mostly ice-free at Nenana, as is the Yukon River across the border at Dawson, and the Salcha shows plenty of open water (photo below from Thursday, courtesy of Twitter user NateoftheNorth).

Second topic: following up on my post last week on a very different facet of the cryosphere - Arctic sea ice - I proceeded to examine both the opening and closing dates of the Northeast Passage in the past two decades, and the chart below is the result of this effort.  This is based on the NSIDC sea ice index images, which show the estimated daily location of ice concentration above 15%.

The note for 2013 highlights the fact that there was well over a month of open passage to the north of Severnaya Zemlya, but the near-shore route adjacent to the mainland (Taymyr Peninsula) was closed for nearly the entire season.  The more northerly route is pretty far north (north of 80°N) and I'm unsure if this would be considered an open Northeast Passage, but I allowed it for the chart.

Besides the striking trend towards a more navigable route, it's interesting to see the difference between this year and last.  This is largely the result of contrasting weather patterns, with 2020 having exceptionally warm conditions across the Arctic Ocean, but summer 2021 being relatively (but not extremely) cool and cloudy.  Obviously the window for open navigation is sensitive to the details of where the ice is located, with Severnaya Zemlya being - as this year - the most common bottleneck; Arctic-wide sea ice was not that much higher this summer than in recent years.

Sea Ice Update

It's been a while since I posted anything on Arctic sea ice, but it's worth looking back at the melt season now that freeze-up is well under way.  It was a relatively cool and cloudy summer with lower pressure than normal across the Arctic Ocean, and sea ice melt was somewhat reduced compared to the past decade or so.  Here's the September sea ice extent, courtesy of NSIDC: this year's seasonal ice minimum was notably higher than the lowest values of the modern era, but of course still much lower than earlier decades.

On a regional basis, sea ice melted out extremely early this year in the Laptev Sea, but the summer weather pattern - with an unusual trough of low pressure to the north of Alaska - allowed ice to last much longer than in recent years in the Chukchi and Beaufort Seas.  NSIDC's write-up also notes that last winter saw increased transport of old, thick ice into the Beaufort Sea, and that ice is resistant to summer melt.  Here's a paper on last winter's unusual ice transport.

Rick Thoman nicely illustrated the recovery in Chukchi Sea ice as follows:

It's also interesting to note that the Northeast Passage appears to have been open for only about five weeks this year, which is a huge change from last year.  Judging from daily ice extent images from NSIDC, August 22 - September 27 was the window in which there was an opening in the ice next to Russia's Taymyr Peninsula.  Last year the window for open navigation was approximately July 15 - October 29, or well over three months!

Looking back at recent years, the last time the Northeast Passage closed up as early as this year was 2013, and all other years since 2007 saw open water along the entire route into October.  2007 was the last year in which there was no opening all summer, again judging from the NSIDC images (which can be found here).

Here's my estimate of the closing dates for the Northeast Passage, i.e. the last date with an open route from the Atlantic to the Pacific near the coast of Russia, based on NSIDC sea ice extent (defined as ice concentration greater than 15%).

2021  Sep 27

2020  Oct 29

2019  Oct 16

2018  Oct 20

2017  Oct 5

2016  Oct 18

2015  Oct 14

2014  Oct 5

2013  Sep 27

2012  Oct 14

2011  Oct 10

2010  Oct 2

2009  Oct 9

2008  Oct 3

September Climate Anomalies

First, to follow up on the last post - the answer is no, the snow didn't survive in Fairbanks - at least not at the official snow monitoring site, which I believe is now at the university farm (location of the longest-running continuous climate record in Alaska).

Several days with daytime temperatures in the low 40s, and a lot of rain, doomed the early attempt at establishing snow cover.  The first 10 days of the month have now seen 1.28" of liquid-equivalent precipitation in Fairbanks, which is the 4th highest on record; and the top two spots are held by 2017 and 2019, so this is the 3rd time in 5 years with a very wet start to the month.

Looking back at September, here are the temperature and precipitation rank maps from NOAA/NCEI's climate division data: most of the state was in the lower tercile of the 1991-2020 distribution, and areas from Bristol Bay to south-central were much colder than normal.

Here's Rick Thoman's usual graphic showing the absolute temperature anomalies: note the remarkable -5.5°F anomaly at King Salmon.

And here's the ERA5 view of the month: it was yet another cloudy month in the northwest, but unlike during summer the winds were relatively light across western Alaska.

As an aside, I previously noted that the NCEI data seemed much too cold for the North Slope in July, but the value has been adjusted since then, and the latest result for July is much more reasonable - see below.  So it seems we should treat NCEI's preliminary monthly numbers with some caution.