Frozen Over at Dawson

A couple of interesting items came to my attention today.  First, the Yukon appears to be properly frozen over at Dawson City in the Yukon:

This is big news over there, because the lack of freeze-up next to town has been a huge problem in recent years; freeze-up has often been much delayed and sometimes hasn't occurred all winter.  I've commented on it occasionally, most recently last March:

https://ak-wx.blogspot.com/2024/03/yukon-at-dawson-still-open.html

The change this year isn't caused by colder weather - it hasn't been unusually cold - and the lack of freeze-up in recent years was generally not caused by unusual warmth.  When I have a chance, it will be worth looking at regional streamflow and precipitation data from recent months to see if anything stands out.

Here's an animation of webcam images from today, courtesy of http://dawson.meteomac.com/

On a completely different note, I ran some calculations today to establish whether the Northern Hemisphere circulation patterns have been unusually volatile this month; it sure seems like it.  The answer is yes: the following chart shows a metric of 500mb volatility for 45-90°N around the globe.

To be precise, the figure shows the area-average of the standard deviation of 500mb heights for November 1-26, expressed as a fraction of the 1991-2020 normal (which differs from place to place).  Here's a map of the departure from normal: 500mb heights have been much more variable than normal over the eastern Bering Sea and southwestern Alaska, as well as near Baffin Island and over northern Europe.

The region of high variance near Alaska largely reflects the dramatic change from this a few weeks ago:

to this last week:

The big ridge over the eastern Aleutians and southwestern Alaska about a week ago was bumping up against records for the month of November.

What could explain the volatile patterns around the higher latitudes of the Northern Hemisphere?  I think it's the unusual combination of sea surface temperature anomalies across the tropics and the mid-latitude oceans.  We have a weak La Niña, which tends to favor meandering "blocking" patterns in the high latitudes in early winter (November in particular), but we also have tremendous warmth in the northwestern North Pacific, which favors mid-latitude ridging (high pressure) and a stronger, more west-east jet stream to the north of the ridge.  These two Pacific ocean anomalies therefore currently have opposing influences on the jet stream pattern, as I see it, and volatility has resulted.

Looking ahead, as winter settles in, La Niña's influence will very much shift towards favoring a stronger jet stream with a strong polar vortex, and that in turn will tend to favor unusual cold in Alaska, particularly in the south.  This is very consistent, of course, with a negative PDO phase, which is locked in because of the warmth to the east of Japan.  Here's the SST anomaly from the past month:

In conclusion - bundle up; and happy Thanksgiving to U.S. readers.

High Wind History

After mentioning strong winds in Wednesday's post, I thought it would be interesting to look at the top high wind events of recent decades - at least according to ERA5 reanalysis data.  I did something similar for the lower 48 the other day, showing that September's Hurricane Helene ranked #5 for area of the contiguous U.S. that experienced hurricane force wind gusts.  What are the top events in Alaska's modern history?

The ERA5 data goes back to 1940, although pre-1950 the uncertainty is very high, so we won't look at anything quite that far back.  The event with the greatest land area coverage of hurricane force wind gusts (64 knots or higher), based on peak wind speed in a 3-day window, was in early 2000:

This event pops up in the Deep Cold archives, finding a mention as the date with the highest sustained wind speed (58 mph) at Delta Junction airport in the 1998-present ASOS era.

Second on the list since 1950 is a North Slope wind storm at the end of 1951.  Hourly observations from Utqiaġvik confirm a peak sustained wind speed of 56 mph (gusts not reported).

Number 3 was in February 1989: the North Slope again.  Gusts were measured to 60 knots (69 mph) at Utqiaġvik.

And in fourth place, a more recent event that brought damage and power outages to the Anchorage area:

Events #5-#8 highlight southern and especially southwestern Alaska as a hot spot for these widespread strong wind events - as we might expect with the favored Aleutian storm track.

I'm a little surprised not to see a west coast event in this list; even ex-typhoon Merbok doesn't rank anywhere near the top:

Active Weather

The weather pattern has been very energetic and changeable across Alaska in recent days, leading to sharp cold in some areas, and wind and storm damage in others.

Coastal erosion and damage occurred down in Homer over the weekend, and far to the northwest Point Hope is without power today, owing to high wind.  Winds gusted to 68mph in Point Hope yesterday, and 93mph at nearby Cape Lisburne.  Today the high winds spread across the North Slope, with Utqiaġvik gusting to 62mph and temperatures rising above freezing.

Here's this morning's 3am MSLP analysis, courtesy of Environment Canada:

Several things can be noted here: the axis of high pressure across the southern interior, associated with cold weather at the surface; the strong pressure gradient across northwestern Alaska, producing the high winds; and the extraordinarily deep low pressure system to the west of Seattle, causing severe wind damage in Washington last night.

The cold yesterday morning was notable across the interior: -40° was reached on the Yukon Flats at Beaver, and Chicken saw -42°F.  Fairbanks reached -29°F at the airport, the coldest this early since 2020 - and we have to look back to 2011 to find colder conditions this early in the season.  The Salcha RAWS reached -37°F, the coldest this early since 2011.

Cold in the Brooks Range

The past several weeks have been notably cold in the Brooks Range as a result of persistent northeasterly flow; and this has been caused by an unusual gradient between low pressure over southern Alaska and atypical high pressure over the Arctic Ocean.  Sea-level pressure has been 15mb higher than normal this month at about 80°N on the Date Line:

Here are the daily mean temperatures this autumn compared to normal at Anaktuvuk Pass, 2100 feet elevation in the heart of the Brooks Range:

From last Sunday through yesterday - six days in a row - daily average temperatures were below -15°F in Anaktuvuk Pass, which is pretty chilly for the time of year; we have to go back to 2005 to find as many days this cold in the first half of November.

It's also the first year since 2012 with an average temperature below 0°F for the first half of November, and in fact it's a notable break from the remarkably persistent warmth of 2013-2023:

The Arctic as a whole isn't noticeably cooler this year, so this seems to be a case of an unusual and persistent flow pattern bringing an unseasonably cold air mass to the region.

High-quality data from the Toolik Lake CRN site confirms the anomaly: this is also (easily) the coldest first half of November in the short history since 2017 at that location.

NWS Fairbanks expects no improvement in the short term: here's an excerpt from their latest forecast discussion.

"North Slope and Brooks Range...

- Cold temperatures (around -30F) become more widespread through Tuesday across the Arctic Plains and Brooks Range. North winds around 15 mph in the Brooks Range Sunday night into Monday morning will result in very cold wind chills near 55 below just barely short of a Cold Weather Advisory."

October Climate Data

Looking back at October, there was a lot of active weather in Alaska, especially in the second half of the month, and so it's not surprising that temperatures were highly variable.  However, the statewide average temperature (as calculated by UAF) didn't see any extremes of either sign; neither the warm nor the cold anomalies were all that unusual - see the right-hand portion of the figure below.

The "near-normal" characterization of the monthly average temperature extended to most parts of the state, with the exception of somewhat significant cool in the north-central interior and the northern Panhandle, and warmth on the North Slope.  The southern Yukon Territory was pretty chilly, however.

Warmth on the North Slope is a given these days in October, because of the lack of sea ice.  Every October since 2002 has been significantly warmer than the earlier multi-decadal normal, as illustrated so clearly in Rick Thoman's signature chart for Utqiaġvik - check out his latest post:

https://alaskaclimate.substack.com/p/alaska-october-2024-climate-summary

October precipitation was significantly above normal for the West Coast north of the Y-K Delta and across to the central and northern interior, as well as the Brooks Range.  But I'm not sure the ERA5 data (see below) fully captures the magnitude of the precipitation anomaly in the Fairbanks area, where it was the wettest October in many decades.

Not surprisingly, it was a windier month than normal for much of the state, and especially so for the West Coast.  Every month this year except February and September has been notably windier than normal for a majority of the West Coast.

The mid-atmosphere circulation pattern involved a strong ridge over and to the south of the central Aleutians, and a trough from northwestern Canada to the Gulf of Alaska.

This is very much a negative PDO pattern, with the ridge corresponding to above-normal sea surface temperatures to the east of Japan, and the Gulf of Alaska trough corresponding to cool ocean temperatures.  The warm anomaly is much more extensive and far more intense than the cool anomaly - see below.  It's interesting to see that the dividing line between warm and cold lies right along the western Aleutian chain.

Speaking of the PDO, the monthly PDO index for November was the most negative of any month since 1955.

The negative phase is being driven mostly by the extreme warmth in the northwestern Pacific, and the latest seasonal forecast models show no reprieve at all in the coming months.  Here's the NMME multi-model forecast all the way out in late spring:

And here's an ensemble of model forecasts of the PDO index:

If this forecast is correct, and I have high confidence that it is, then Alaska will continue to be strongly affected by this PDO anomaly for the foreseeable future.  We can expect an enhanced probability of unusual cold in southern Alaska this winter, and perhaps farther north as well.

More Snow in Anchorage

Anchorage is off to a remarkably snowy start to winter, with 22" reported since the beginning of the week, and a snow depth of 19" on yesterday's climate observation.  Only a handful of years have seen greater snow accumulation by this date, and none has reached a snow depth of 19" this early.  With consistent climate data back to 1953 (at the international airport), the previous earliest date with 19" or more on the ground was... last year, November 10.  Prior to that, the earliest was November 21, 1994.

This marks the third year in a row with significantly unusual heavy snow in early winter.  Last year it was the snow onslaught of November 5-13, and in 2022 the city was buried in two major events in the first half of December.

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

https://ak-wx.blogspot.com/2023/11/a-few-notes.html

https://ak-wx.blogspot.com/2022/12/anchorage-snow.html

With a snow pack of 10" in Fairbanks, this also marks the second earliest that both cities have recorded at least 10" on the ground at the same time.  The earliest was in the notorious autumn of 1992, but even then Anchorage didn't have sustained snow cover until October 27.

Here's a chart of snowfall through November 15 in Anchorage, with this year's total included through November 1.

The variability is enormous, and the change in 2020 really stands out compared to 2012-2019.  The only other period with 5 consecutive years of at least 10" in this early winter period was 1979-1983.

It seems unlikely to be coincidental that 2020 is when the PDO phase switched to negative, after 6 years of a mostly positive phase.

Here's a comparison of early winter snowfall with the PDO index in November:

There are some notable PDO extremes that coincide with snowfall extremes, e.g. high snow and negative PDO in 1955-56 and 2011, and low snow with positive PDO in 1957, 1986, 2002, 2014, and 2016.  However, the overall correlation seems to have been modest at best before the turn of the century - see below.  Since 2000, there's been a much better correlation.

One hypothesis to explain this might be that in earlier decades the positive PDO didn't prevent early winter snow, because it was still cold enough, but in recent years a positive PDO has brought greater warmth that has led to rain rather than snow.  More investigation would be required to explore this; but without doubt, the negative PDO regime is a snow-lover's friend these days in Anchorage.

Flood Follow-Up

A few different items of comment today.  First, a significant snowfall is under way across the south-central region today, signaling the start of winter proper for many valley locations in that area.  If Anchorage's snow cover hangs around in the coming weeks, it will mark an earlier than normal onset of permanent snow pack; the normal date is about November 9th.  Of course Anchorage occasionally lacks snow cover even in the depths of winter, but it's unusual, occurring most recently in 2015-16 and for a few days in late December 2019.

As for Fairbanks, the normal date for establishing permanent snow cover is October 18, and it was right on time this year.  However, the most recently reported snow depth of 10" is the highest for the date since 1992, and more fell today.  (But 11" was on the ground in September 2015.)

Looking back at last week's historic west coast storm, it's worth highlighting blog comments by Rick and Gary.  Rick Thoman confirmed that long-time Kotzebue residents reported the highest water in living memory, which is why it was such a devastating event for some in the community:

https://www.adn.com/alaska-news/rural-alaska/2024/10/26/after-flood-kotzebue-residents-take-stock-of-damaged-homes-and-property-and-take-care-of-one-another/

Although the meteorology was different, we might say this was Kotzebue's version of ex-Typhoon Merbok, which caused such havoc for coastal locations farther south about two years ago:

https://ak-wx.blogspot.com/2022/09/more-on-ex-merbok.html

The article highlighted by Gary indicates that flooding was not quite as bad this time around from Nome down to Unalakleet:

http://www.nomenugget.net/news/high-winds-cause-erosion-and-flooding-region

Rick also commented that storms in November 1973 and 1974 may be the most analogous events in the modern climate record.  Certainly the storm of November 10-11, 1973, shows a rather similar sequence of events: low pressure over the Chukchi Sea created strong winds out of the south early on the 10th, and then the winds went around to the west and blew fiercely with a strong north-south pressure gradient, pushing water into Kotzebue Sound.  Here are MSLP maps:

Compare to the recent event:

Interestingly, the wind speed itself was not particularly unusual with last week's storm, and there have been many past events with equally strong, or stronger, winds from a westerly direction in Kotzebue.  I think therefore it was the very low pressure, the large size of the storm, and the long duration of southerly fetch that allowed such a large surge to develop before the winds turned westerly and pushed the water onto the coast.

Kotzebue Flood

In yesterday's post I remarked that I hadn't yet seen specific reports of storm impacts for the west coast, but it turned out that the worst was yet to occur in the northwest, and specifically in Kotzebue:

https://www.adn.com/alaska-news/rural-alaska/2024/10/23/after-severe-flood-displaces-80-people-kotzebue-begins-recovery/

Stormy weather began way back on Saturday in Kotzebue, and the highest winds (gusts to 55 mph) occurred on Monday morning, but it wasn't until yesterday that flooding became severe as the winds went around to the west.

I think what happened here is that a prolonged and very strong southwesterly flow built up a considerable surge of water in the southern Chukchi Sea while the storm's center was at its most intense over Russia's northeastern coast on Monday.  When the circulation finally pushed east towards the North Slope on Tuesday, and the winds went around to the west in Kotzebue Sound, that elevated water rushed into the Sound and inundated the city rapidly.  The "shockingly fast" rise of the water sounds very much like a classic storm surge event that is more commonly seen in landfalling tropical cyclones.

Below is a sequence of model analysis maps showing the pressure and winds at 6 hour intervals from 10am on Monday through 10pm last night.  Judging from the severe impacts, it seems this was essentially a worse-case scenario for Kotzebue flooding.

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).