Record Rain and Snow

Fairbanks schools and borough offices are closed for the second day today, as record-breaking rain and wet snow has produced difficult travel conditions in the area.  The airport's two-day liquid-equivalent precipitation total of 2.28" is within the top 10 for any time of year (1930-present), and of course most of the heaviest precipitation events occur in the warm season in Fairbanks.  Only two cold season events have seen higher two-day totals: the Christmas storm of 2021 (2.45", blog post here) and January 19-20, 1937 (which was actually a three-day event totaling 3.21"). 

More superlatives: yesterday's calendar day precipitation total of 1.99" is the third largest of any day since 1930 in Fairbanks, the only wetter days being July 27, 2003, and August 12, 1967 (the great Fairbanks flood).  And according to Rick Thoman, the peak 24-hour total (Sunday evening through Monday evening) of 2.07" is the highest on record for the cold season, and the first to exceed 2".  The previous cold season record for 24 hours was 1.93" in the 2021 storm, and before that 1.84" in 1937.

Higher amounts were reported elsewhere: a CoCoRaHS site near the airport measured 2.96" in the two days, and the Keystone Ridge site came in at 3.27".

At least half of the precipitation fell as plain rain, according to the airport ASOS data, and owing to temperatures persistently below 20°F late last week, the cold ground led to lots of ice formation.  There's a window for some thaw today, but temperatures will drop back below freezing tonight and stay there, so some of that ice is going to be around all winter, unfortunately.  It's a theme we've seen repeatedly from winter rain events in Fairbanks in recent years.

Here's a snapshot of the atmosphere's vertical profile at 4pm AKDT yesterday; it was still raining at the airport, but rain had switched back to snow on Keystone Ridge:

Check out the wind speeds aloft: over 150 mph at 34,000 feet.  The southwesterly flow direction through much of the lower and middle atmosphere is what brought the moisture into the central interior without it being squeezed out by the Alaska Range to the south.

As for storm impacts elsewhere in Alaska, the west coast has been very windy, strong winds affected south-central areas yesterday, and Bering Sea coastal flooding has undoubtedly been significant, but I haven't seen detailed reports yet.

Far to the west over Chukotka's Arctic coast, the storm's central pressure bottomed out at around 956 mb according to Environment Canada.  As noted in Friday's post, this is very likely an October record for that location, but we'll have to wait a few days for the ERA5 data to be sure.  Here's the surface analysis from 4am AKDT yesterday.

Big Storm Coming

Weather warnings have been hoisted for Alaska's west coast as well as the central and northwestern interior, as a major storm is set to develop over Russia's Kamchatka peninsula tomorrow and then move northeastward, bringing impacts to Alaska starting on Sunday.  According to weather models, it's going to be a big one - potentially one of the strongest on record for the time of year over far eastern Russia.

The storm is developing along a frontal boundary to the north of Japan, as cold air pushes east from Siberia and encounters very warm conditions over the northwestern Pacific.  It's been notably cold in recent days in eastern Siberia, with the notoriously cold town of Verkhoyansk dropping below -30°C (-22°F) the last three nights.

Here's a look at projected MSLP and precipitation from Sunday afternoon through Monday afternoon, according to the leading ECMWF model.

The expected minimum MSLP of 957mb over far eastern Russia on Sunday afternoon would be a record low for October in that inland location, although sub-950mb MSLP has occurred before over the Gulf of Anadyr (based on ERA5 data):

The NWS discussion says it well: "It doesn`t matter how you slice it, this storm will have some extreme values associated with it from a climatological standpoint, as the upper jet streak of 180 knots, the precipitable water values near record levels for this time of year, and total precip amounts (for this time of year) are pretty much off the charts in terms of anomaly/return intervals."

Snowfall is expected to be "extreme" and/or "epic" (to quote the NWS) for western and south-central Brooks Range locations.

The upper-level forecast charts show the very powerful jet stream that will move across western and northern Alaska:

And the 500mb charts highlight the extreme contrast between warmth and ridging to the south, and the cold trough to the northwest.

Batten down the hatches!  It's going to be a wild few days for western and northern Alaska.

In the meantime, here are a couple of webcam photos from Koyuk today, showing freeze-up on the river as it flows into Norton Bay:

 

Overnight temperatures were well below 0°F last night in the hills to the north of Fairbanks, as well as the Yukon Flats and other northern interior spots.  The Beaver RAWS reached -16°F, and Bettles saw -8°F.  This kind of cold isn't usually seen until late October or early November, although of course it varies; in the past Bettles has been this cold as early as October 5th (1958) or, more recently, October 15th (2008).

Stormy Weather

The last few days have brought wild weather to large parts of Alaska, courtesy of a very powerful upper-level trough and associated low pressure system over the northern Gulf Coast.  Anchorage received measurable snow for 7 days in a row, with a total of almost 20", and that's enough to put them in first place for season-to-date snowfall at this point in the year.

Not surprisingly, the surface pressure analysis on Tuesday afternoon looked very similar to that from about a month ago, when Anchorage received its really big snow storm: the low center was a hundred miles or so to the southeast of the city.

Compare to the November 9 map posted here:

https://ak-wx.blogspot.com/2023/11/south-coast-snowstorm.html

The 500mb map from the same time on (this) Tuesday afternoon shows the mid-atmosphere trough in all its glory:

The eastward "tilt" of the trough at lower latitude is characteristic of particularly strong storm systems with a lot of upper-level "energy".  The sub-500 dm height at Anchorage (499dm to be precise) is notably low: about a third of winters in recent decades haven't seen a 500mb height that low all winter.

Here's an estimate of 3-day total liquid-equivalent precipitation, and the second map below indicates the estimated return frequency: over 5 years in parts of the higher terrain from the northern Panhandle up towards the Alaska Range.

The Fairbanks area received a significant snowfall, with a surprisingly large precipitation total of 0.54" (liquid equivalent) in the last 2 days (Tuesday and Wednesday).  I say "surprisingly" because temperatures were fairly low, only peaking at 10°F and 7°F on the two days respectively, and the snow:water ratio was an unusually low 11:1.  About 50% of winters in Fairbanks don't see a single 2-day precipitation event as large as this - although it has become more common in recent years.

Finally, the big pressure gradients associated with the broader circulation anomaly also generated big winds, especially for the West Coast, where the winds were northerly and created blizzard conditions.  Here are peak wind gusts (mph) for Monday and Tuesday.

Sadly the weather appears to have been a contributing factor in the deaths of two Nome residents on Sunday night:

https://www.adn.com/alaska-news/rural-alaska/2023/12/13/missing-nome-snowmachiners-found-dead-troopers-say/

How to Eliminate Cold

The reprieve won't last long, but a very powerful Bering Sea storm has dramatically swept away the cold air that dominated the state in the past few weeks.  It was an extraordinary transformation: check out the sequence of daily temperature maps below, showing Friday through yesterday.

Rick Thoman notes the extraordinarily rapid change in the statewide daily temperature index:

How fast did the weather change over Alaska? The Alaska Statewide Temperature Index, one of our ACCAP tools, showed its largest one day change (Saturday to Sunday) in over a decade. Details about the index at https://t.co/eph70nSIeM. #akwx @IARC_Alaska H/T @Climatologist49 pic.twitter.com/k0ZlaUNkN6

— Rick Thoman (@AlaskaWx) December 6, 2021

The storm was a nasty one along the Bering Sea coast, with very high winds.  Here are some of the peak gusts, courtesy of NWS:

The following article describes some of the impacts on coastal communities.  Rick notes that sea ice was sufficient to prevent serious coastal flooding, which illustrates a major upside of the recent cold weather.

http://www.thearcticsounder.com/article/2149wind_gusts_in_northwest_alaska_pushed_away

Here's the NWS sea ice analysis from Friday.

Below are the 500mb and surface analysis maps from 3 am yesterday morning (December 6), courtesy of Environment Canada.  MSLP of 958 mb was reported on Sunday afternoon on St. Lawrence Island (at both Gambell and Savoonga), and that appears to be close to the all-time record for the area (about 955 mb according to 1950-present ERA5 data).

This powerful storm may come as a bit of a surprise in a strong La Niña, because just a few weeks ago I discussed the fact that the Aleutian Low tends to be weaker during La Niña.  However, another very interesting aspect of La Niña winters is that daily variability tends to be higher, so the weather patterns near Alaska tend to be more volatile.  I explored this topic a few times in past years, so search for "ENSO variance" if you're interested; or check out the following post.

https://ak-wx.blogspot.com/2015/09/enso-height-patterns.html

Arctic Trough

The weather has been wild in western, southwestern, and south-central Alaska in the past few days, as an upper-level trough has deepened over the eastern Bering Sea and western Alaska.  This feature, and the associated cold air, bears some relation to the Arctic vortex that delivered last week's interior cold snap; it appears that a lobe of the Arctic air mass settled down over western Alaska, and the clash with North Pacific warmth farther south set up a stormy situation yesterday.

Here's the 500mb chart from 3pm yesterday, showing a very sharp trough over western Alaska.  The eastward kink at the southern end is very indicative of a strong surface-level cyclone.  Click to enlarge:

The surface analysis from 3am today (see below) shows the path of the 972-973mb surface pressure center, which tracked right up Cook Inlet yesterday evening.

The impacts on the south-central population were substantial: about 10" of snow in Anchorage, 21" in Girdwood, and a closed Seward Highway.  Very sadly, the storm also led to the loss of a crabbing vessel near Kodiak Island:

https://www.adn.com/alaska-news/2020/01/01/coast-guard-searching-for-crabbing-vessel-scandies-rose-west-of-kodiak/

From a meteorological perspective, one of the most striking aspects of yesterday's events was the intense temperature contrast across the system.  While Bethel was shivering in windy sub-zero conditions, Anchorage saw a record high of 46°F before the cold air arrived in the evening.  The difference in daily high temperatures between Anchorage and Bethel was a remarkable 56°F, and this is nearly the greatest on record (59°F on Dec 23, 2004).

The map below illustrates the situation at noon: 46°F in Anchorage, 39°F and raining at McKinley Park, but with very cold air advancing from the west.  Notice the 21°F and windy at Akhiok on Kodiak Island; the waters west of the island would have been very rough, and icing may have been a significant issue.

Here's the situation 8 hours later: down to 0°F at McKinley Park and 18°F in Homer.

The frontal passage was especially striking at McKinley Park, where the temperature dropped from 39°F to 10°F in just 15 minutes as the wind direction changed from southerly to northerly.

Anchorage also saw a sudden temperature drop in early evening: 15°F in less than an hour.

One bright side of this cold blast over western Alaska and the Bering Sea is that sea ice growth will be vigorous; but that may be "cold comfort" for residents of the west.  Bethel has seen a daily average wind chill below -30°F for all but one of the last seven days, and up in the northwest, Kivalina is this evening enduring its second 60+mph ground blizzard in 48 hours.  Sounds like real winter.

West Coast Storm

Earlier this week a strong storm moved through the northern Bering Sea and the Bering Strait, bringing strong winds to western Alaska and breaking up sea ice that was already weakened from unseasonably warm weather in the past few weeks.  According to NSIDC analysis, Bering Sea ice extent peaked at 567,000 km² just a few days after my last update and has dropped by one-third in the 18 days since.  Here's a comparison of ice maps from the peak (Jan 26th) and today.

The most recent storm seemed like a strong one, with sustained wind speeds of over 50mph on St. Lawrence Island; and the balloon sounding from Nome on Tuesday morning reported a wind speed of 49mph at ground level.  However, the minimum central pressure of the storm was only about 980mb when it reached Alaska, which isn't particularly low by Bering Sea standards.

The chart below shows the typical monthly extremes in MSLP for a latitude/longitude box centered on the west coast of Alaska (depicted on the map underneath).  The months of October through February all typically bring at least one storm with minimum MSLP of 975mb or lower somewhere in this region; so the latest instance was a fairly run-of-the-mill storm.  What is not normal, however, is the lack of sea ice; only last year had significantly less ice on this date in the modern satellite record (but mid-February 1985 had about the same amount).

West Coast Storms

Just a quick update this morning to note the stormy conditions in western Alaska; blizzard warnings are in place from Point Hope south across the Seward Peninsula to the Stebbins/St Michael area.  As the weather service discussion put it yesterday, a "very active weather pattern continues to hammer western Alaska".  The effects on the coastline are being exacerbated by the remarkable absence of sea ice even far up in the northwest; and the slow growth of sea ice is also related to the storminess, as noted by Rick Thoman yesterday:

Sea ice in the Chukchi & Bering Seas very slow to grow this autumn, due in part to ongoing storminess. Combined extent for Nov 17 is 46% below 2006-16 median & Bering Sea ice is 84% (!) below median. Data from @NSIDC & @NWSAlaska #akwx #Arctic @Climatologist49 @ZLabe @DaveSnider pic.twitter.com/RtzPvmYXMW

— Rick Thoman (@AlaskaWx) November 18, 2017

This morning's surface observations show an interesting wind contrast between St Michael and Unalakleet, a distance of only 47 miles, as shown on the map below; the wind direction is completely opposite at the two locations.

The wind contrast highlights the location of a strong front that is moving east across Norton Sound and southwestern Alaska.  It's analyzed as a cold front on the Environment Canada map (9pm AKST), which seems ironic as the surface conditions behind it are warmer than to the east of the front, but that's what you get in the wild world of western Alaska weather.

The sequence of maps below (note the timestamps on the top right) show how the wind at St Michael went round from southeast to southwest as temperatures rose, but meanwhile the temperature fell a couple of degrees in Unalakleet as cold interior air moved over the Nulato Hills.  Note too the rising temperature in Fairbanks as high clouds moved in aloft; the coldest conditions have shifted east to the Yukon Territory.

[Update Sunday 6pm]

I find it interesting to note that the wind continued to veer around to the northwest and eventually north and northeast in St Michael today, and as this happened the temperature dropped sharply.  So in the space of less than 18 hours, the wind (a stiff breeze throughout) at St Michael rotated through three-quarters of the compass, while less than 50 miles away at Unalakleet the wind remained virtually unchanged throughout.  Fascinating!

[Update Wednesday 6pm]

Here's a map showing peak wind gusts for the 24 hours ending 6pm yesterday (Tuesday November 21).  This is an entirely different storm from the one discussed above.  Stormy times in western Alaska!