Historic Winter Rain

Extraordinary and historic winter rain has been occurring today across a large swath of interior Alaska extending all the way up to the Yukon Flats and the southern edge of the Brooks Range.

This blog has documented many instances of winter rain in Fairbanks, but this is something else.  In data extending back to 1948 (albeit with one missing decade from 1964-1974), Fort Yukon has only reported plain rain (i.e. with a temperature above freezing) in November through February on two occasions, and that briefly: a single report of light rain and 33°F on January 22, 1962, and a report of light rain with 35°F on Christmas Eve, 1985.  But today it rained from 4:15am through 10:30am, and then it began again at 3pm; it's still ongoing as of 6pm, and the temperature has been as high as 39°F.

Rain has also been reported in Bettles, Fairbanks, Tanana, and of course points to the southwest, where the moisture is coming from.  The following map shows 12-hour precipitation totals (inches) as of 5:30pm, and it appears these represent mostly or entirely rain, at least at lower elevations.  Click to enlarge:

Two of the sites with higher totals are the Livengood (1.24") and Chalkyitsik (1.06") RAWS, and the hourly observations look very plausible:

Webcam images from Chalkyitsik show that it certainly wasn't snowing, and snow can be seen melting off a roof in the course of 3 hours (lower right, click to enlarge):

Incredibly, it was simply a rainy day across the central and northeastern interior.  And NWS Fairbanks expects it to continue; they say "an additional 0.5 inches is expected to fall through Sunday" (in Fairbanks).

What can explain such an amazing departure from normal?  Here are the 500mb and MSLP charts from 3am this morning:

These show a very pronounced pressure gradient and intense southwesterly flow between the deep trough over far eastern Russia and a powerful ridge over the northeastern Pacific.  Warmth and moisture have been transported quickly to interior Alaska from deep in the subtropics.  We also see that the flow aloft is oriented from southwest to northwest, rather than south to north, so the moisture makes it into the interior without hindrance from the southern coastal mountains and Alaska Range.

Winds across the North Slope have been extraordinary in their own right: here are the peak wind gusts in mph.

And maximum temperatures across the interior:

In the Fairbanks region, the international airport reached 42°F, Eielson reached 46°F, and Nenana saw 44°F.

For future reference, here are several surface observation maps showing snapshots of weather conditions throughout the day (two or three purple dots to the left of the station indicate rain):

Warm Weather Follow-Up

Following up on snow conditions in southwestern Alaska, there hasn't been any clear weather lately to reassess snow cover from satellite, but FAA webcam images now show very little snow for most or all low-elevation locations in the southwestern mainland to the south of the Yukon River.

Sparse or no snow extends at least as far north as Holy Cross and Crooked Creek; but Sleetmute still has snow cover, as does (much farther inland) McGrath:

The warmth in Bethel has been quite pervasive since early December, and the average temperature since December 1 is the sixth highest on record; 1979 holds the record.  2018 (second place) was quite a bit warmer than this winter so far.

The Kuskokwim 300 race has been postponed because of the poor trail conditions:

https://www.kyuk.org/kuskokwim-300/2025-01-17/postponed-kuskokwim-300-receives-support-from-mushers-vets-and-volunteers

However, the latest CPC forecast does suggest a change is on the way:

Also noteworthy is extreme warmth on the North Slope this week; early Sunday saw 41°F at Umiat, which ties the record for January.  Temperatures above +40°F were observed from Cape Lisburne in the far west to the easternmost extent of the North Slope - click to enlarge:

Where is all the cold air?  Down south is where: New Orleans had a foot of snow today.

Snow and Ice Update

Rick Thoman wrote about mid-January snow conditions at his site today, and I think it's worth amplifying some of the information here.  Snowpack is now very poor in western and southwestern Alaska, as there has been some very warm weather - notably so last weekend, but again today it is substantially above freezing over much of the southwest, with rain in some places.  The first map below is several days out of date, being based on ERA5 data, but it shows a more extensive area of very low snowpack than the map I posted on New Year's Eve (second map below):

The satellite image below, taken on Wednesday, shows that there is (or was) still snow on the ground across the Y-K Delta region, but it seems it's a minimal snowpack.  Click to enlarge:

On the plus side, it seems that there's been enough snow at elevation to improve the snowpack a bit in south-central Alaska, although it's still well below normal along the northern Gulf coast:

As for sea ice, the latest NWS analysis lines up nicely with the satellite image, with ice coverage extending just south of Nunivak Island.

The NSIDC analysis (showing regions of 15% sea ice concentration or more) is similar, and it reflects a modest deficit for the Bering Sea compared to the 1981-2010 normal.  Arctic-wide, sea ice extent is running very close to a record low, and it's notable that there are no areas with significantly above-normal ice for the time of year.

Major Thaw

December was very warm in Alaska (relative to normal), but January is shaping up to be even warmer; records have been falling in the past week, and the Climate Prediction Center is showing very high probabilities of unusual warmth in the 6-10 and 8-14 day forecasts.  All the cold air has gone south:

Yesterday was extraordinary: widespread temperatures above 40°F in southern Alaska, and as high as 53°F at Nenana; this is only 1°F shy of the January record (54°F in 2009).  The Fairbanks area reached the mid to upper 40s.  Here are 24-hour maximum temperatures ending at midnight last night (note that the plotted 54°F at Nenana is a rounding error - it was 53°F):

For the second time this month, Anchorage saw a daily minimum temperature of 36°F yesterday, tying the January record both times.  But of more immediate concern were the high winds, which caused considerable disruption and damage across south-central Alaska:

https://www.adn.com/nation-world/2025/01/13/anchorage-schools-closed-due-to-weather-related-problems/

Wind speeds exceeding 50mph were widespread not only in the Anchorage bowl but across much of southern Alaska, with much higher gusts in places.  Here are the 24-hour peak gusts (mph) ending at midnight:

The cause of the wild weather is no big surprise: a very large trough over the Bering Sea and a strong low pressure system moving into the Y-K Delta region yesterday.  There was also a strong ridge over British Columbia, enhancing the east-west pressure gradient across southern Alaska.  Here are the surface and 500mb height charts from 3pm AKST yesterday, courtesy of Environment Canada:

December Climate Data

It always takes a week or so for complete climate monitoring data to become available for the previous month, but now we're in a position to look back at the main climate anomalies from last month and for 2024 as a whole.

December was an unusual month in terms of the circulation pattern over the North Pacific and Alaska: a strong mid-atmosphere trough was dominant across the North Pacific from Japan to the waters south of Alaska, but to the north a very broad ridge prevailed from Siberia to central Canada.

This pattern reflects a strongly positive phase of the Pacific-North American (PNA) pattern (see here for explanation), and this is reliably and strongly associated with unusual warmth in Alaska at this time of year.  Hence temperatures were well above normal nearly everywhere, and it was a top-10 warm December for the state as a whole.

The NCEI data shows the Northwest Gulf division with its warmest December on record, but Kodiak airport actually came in at 6th warmest, with December 2014 still holding the record.

The December pattern was substantially inverse of what is typical for La Niña; here's the average 500mb height anomaly for 10 Decembers with strong La Niña:

But of course, La Niña is not particularly strong this winter; it only recently gained enough amplitude to be officially classified as such by NOAA:

https://www.climate.gov/news-features/blogs/enso/january-2025-update-la-nina-here

December precipitation was a mixed bag.  The major anomaly was the wet pattern for much of the Gulf coast, and especially the lower Alaska Peninsula to Kodiak Island and the southern Kenai Peninsula.  Kodiak reported its 2nd wettest December on record.  Southeast was fairly wet too, a big change from autumn.

As for wind, ERA5 data shows a return to above-normal wind for western Alaska as well as the northern interior.

Here's the situation in terms of sea surface temperatures: still very warm from Japan to the region south of Aleutians, although the persistent trough produced a lot of cooling near and south of 40°N (and warming closer to Alaska):

Looking back at annual-average data for 2024, temperatures were modestly warmer than normal, as a result of 8 months above the 30-year normal and 4 months below (January, May, July, August).  December was the most anomalously warm month, although June was very unusual too.

According to NCEI, the statewide annual mean temperature was 28.9°F, which marks the 5th consecutive year below 29°F after the run of very warm years from 2014-2019.  It seems likely that this reprieve is related to the persistence of La Niña and the negative PDO phase in recent years; this winter is the 4th La Niña winter out of the last 5 years (although last winter was a strong El Niño).

2024 annual precipitation and annual-mean wind speed were more anomalous than the year's average temperature; ERA5 data shows much of western and northern Alaska with much above normal precipitation and wind speed.  NCEI data shows drier conditions in southwestern and south-central Alaska, but I'm not sure how accurate that is; Anchorage certainly had a wet year.  Both data sources show a notably dry year in the southern Alaska Panhandle.

Cold Snap

Clear and calm conditions allowed a few thermometers to register -50°F today, the first time that benchmark has been reached in Alaska this winter.  Umiat saw -52°F, locations on the Yukon Flats were very close to -50°F, and Chicken reached -51°F.

Only one winter in recent decades - 2015/16 - failed to see -50°F somewhere in Alaska at some point in the winter.  The last 3 winters all produced -60°F or lower at Chicken.

This morning's sea-level pressure analysis shows sprawling high pressure across northern Alaska and a strong anticyclone over the Arctic waters to the north.

As is typical under these circumstances, surface air temperatures are far lower than temperatures aloft.  The soundings below show the vertical temperature profile at Utqiaġvik and Fairbanks from this afternoon.