Turning Wintry

Snow has been on the ground in Fairbanks since late last week, and at this point it is unlikely to melt out, despite a warm forecast for Halloween.  (Temperatures are expected to get above freezing in the next couple of days, which is unusual for the time of year, but not extreme - it was 48°F on Halloween 4 years ago.)

Other than the great chinook and "brown Christmas" events of 1934, the latest date in the year with at least two inches of snow on the ground that subsequently melted out in Fairbanks was October 26 in 1940.  So if two inches of snow is observed at the end of October, it's almost certainly safe to remain there until spring.

Here's the history of snowpack onset date in Fairbanks; this year's presumed date of October 24 is not unusual.  1934 and 1992 were the two big outliers.

Temperatures have been dropping off statewide since I posted about "lack of cold" on the 18th, driven by rather strong troughing from the Bering Sea to the Gulf of Alaska:

Interestingly, Utqiaġvik yesterday dropped to -10°F, and the daily average temperature was below 0°F for the first time in October since 2018, and before that since 2002.  Until the mid-1990s, a daily mean temperature below 0°F in October wasn't at all unusual, occurring in more years than not, but this is only the fifth such day since 1996.

Looking back at autumn in Utqiaġvik, it's interesting to observe how little unusual warmth there has been in comparison to the past decade.  It looks like the October and September-October averages will be the coolest since 2015, but of course that's still well above the normal of the 20th century.

Halong vs Merbok

Now that ERA5 data is in from last week, we can compare ex-Typhoon Halong with other historical storms on a level playing field, i.e. with the same model reanalysis.  The most obvious comparison to begin is with ex-Typhoon Merbok from September 2022.  First, here are the ERA5 tracks and minimum MSLP of the two storms, at 3-hour intervals:

Merbok tracked much farther west but was much bigger, with more total energy, and it moved much more slowly as it reached the northern Bering Sea, prolonging the period of high wind and flooding for western Alaska.  Here's a comparison of ERA5 wind gusts at a grid point near Hooper Bay, on the far western end of the Y-K Delta, where the peak wind was almost the same in both storms (according to the model).  Notice how quickly the winds dropped off in Halong, versus the prolonged period of high winds during Merbok.

A map comparison of peak wind gust shows that Halong was worse in terms of wind across the Y-K Delta and up to Norton Sound and the western interior; but Merbok was worse for most of the southern Seward Peninsula, including of course Nome.

The small size but ferocious wind of Halong made its impacts much more akin to those of a landfalling hurricane (or typhoon), although both storms were thoroughly extratropical by the time they impacted western mainland Alaska.

Halong was so intense that ERA5 indicates all-time record high wind gusts along a fairly lengthy swath extending northeastward from Nunivak Island.

Here are storm tracks and ERA5 peak wind gusts for a couple of other historic autumn storms in the Bering Sea (but in these cases having no relation to pre-existing typhoons, as far as I know).  First, the 2011 Bering Sea "Superstorm", a really massive storm:

And the infamous storm of 1974, which was catastrophic for Nome:

It is very interesting that all four of these storms occurred during La Niña conditions, and not only that, during second-year or third-year La Niña events (i.e. the second or third consecutive La Niña winter after an El Niño).  More on this "coincidence" another time.

Lack of Cold

Things are about to change, but the absence of cold in much of Alaska has been a pronounced anomaly for weeks - recall that Fairbanks tied its record for latest first freeze.  The coldest temperature so far at the Fairbanks airport is only 26°F, which is a record for highest minimum temperature up to this date in the autumn.

The loss of early cold in recent decades is striking.  Prior to about 2000, it wasn't uncommon at all to see temperatures drop into the single digits Fahrenheit by this date, but that's only happened once in the past decade.

Anchorage is yet to see its first freeze at the airport, only the second time that has happened since 1952.  The year 2000 also seems to mark the point at which more severe cold stopped occuring by mid-October in Anchorage.

For completeness, here's the chart for Juneau.  The last three years failed to see a freeze by this date, but not this year.

The statewide temperature index shows the sustained anomalous warmth of the past 10 days or so.

This is of course linked to the mid-level circulation pattern, involving a strong ridge centered to the south of Alaska and a strong trough over Kamchatka and the western Aleutians.  Warm southwesterly winds have prevailed between the two features, and this pronounced southerly flow is what transported ex-Typhoon Halong up to western Alaska.  The temperature contrast between the trough and the ridge also played into the re-intensification of Halong as it interacted with the mid-latitude jet stream.

Halong Analog

Prompted by a question from Rick Thoman, I looked back at historical data since 1950 to search for past storms with comparable path and strength to ex-Typhoon Halong.  The task was made much easier using the ERA5-based extratropical cyclone track summaries from the University of Manitoba and NSIDC.  I searched for sub-970mb storms that passed within a box between the Y-K Delta and the Seward Peninsula (see below).

The closest analog in terms of path and ferocity of the wind - as estimated by ERA5 - was a February storm in 1951.  Here's the estimated track (a very good match for Halong) and minimum MSLP (about 10mb lower than Halong at the point of closest approach to the Delta):

And here's the model-estimated maximum 10m wind gust:

This 1951 event produced Bethel's highest sustained wind speed measurement on record, 54 knots or 62 mph.  Wind gusts weren't reported back then, but 80+ mph (as indicated by ERA5) seems entirely possible.  Halong's winds peaked at 48 mph (sustained) and 76 mph (gust) in Bethel, although the measurement techniques aren't directly comparable.

The 1951 storm warranted the following comment in the monthly climatological summary for Bethel (click to enlarge).

The big difference with the 1951 storm is that it occurred in February, so it almost certainly wasn't a redeveloping West Pacific typhoon, and the impacts would have been different for coastal areas where ice was present (but I'm not aware of ice extent information from that time).

In just a couple of days we'll have the ERA5 data for Halong, allowing for a direct comparison of the model data for these and other historical events.

Storm Catastrophe

"Absolute devastation... worst-case scenario" - words chosen no doubt carefully by the Coast Guard's Arctic commanding officer in today's briefing on the impacts of ex-Typhoon Halong.

https://www.adn.com/alaska-news/rural-alaska/2025/10/13/dozens-of-people-rescued-at-least-3-still-missing-after-storm-devastates-western-alaska/

The hardest-hit locations turned out to be on the south side of the Y-K delta, between the Kuskokwim estuary and Nunivak Island.  This is where the storm roared ashore in the early hours of yesterday morning, the extreme winds directed perpendicular to the shallow, low-lying coast.  Here's the GFS analysis from 3am.

Here are reported maximum wind gusts in mph, click to enlarge:

The 6-hourly GFS data shows the storm's evolution.

A meteorological and climatological perspective on the causes of the storm will be worthwhile in due course.  For now, here's a link for those with desire and ability to help with relief and recovery costs:

https://www.adn.com/alaska-news/rural-alaska/2025/10/13/how-to-help-residents-and-communities-after-catastrophic-western-alaska-storm/

https://alaskacf.fcsuite.com/erp/donate/create/fund?funit_id=14833

Extreme Storm Inbound

High wind and coastal flood warnings are in effect for much of Alaska's west coast tonight, accompanied by strongly worded statements from the NWS about extreme impacts caused by the re-invigorated remnants of Typhoon Halong.  The storm will hit the Yukon Delta region extremely hard, perhaps locally worse than ex-Typhoon Merbok in 2022.

Here are the latest weather model forecasts for 3am tomorrow morning.  While the expected central pressure is not quite as low as earlier indications, the wind forecast is quite extreme for a narrow zone to the south of the storm center.

The NWS graphic shows the timing of high winds for a few communities in the area. 

I calculated the horizontal pressure gradient in the hourly forecast from the GFS model, and the following image shows the zone of maximum gradient, which is approximately equivalent to the area that will see the maximum wind speeds.

The same calculation applied to ERA5 reanalysis data from ex-Merbok suggests that the peak pressure gradients were considerably less in 2022 - see below.  I think this is because Merbok was a much larger storm in terms of spatial extent; the peak winds may have been lower, but the circulation's total energy and the storm surge were enormous.

Another point of comparison is the so-called Bering Sea Superstorm of November 2011:

See the following link for the first of several brief posts on this blog about the 2011 storm:

https://ak-wx.blogspot.com/2011/11/potentially-calamitous-storm-for.html

This storm is also included in the UAF/ACCAP extreme events library.  Read about some of the impacts here:

https://uaf-accap.org/document/extreme-event-2011-bering-sea-storm

Of course Merbok also has a write-up:

https://uaf-accap.org/document/extreme-event-2022-merbok

West Coast Storms

Northwestern Alaska was heavily affected by a strong storm earlier this week, bringing a sharp reminder of the severe flooding that occurred in Kotzebue last October:

https://ak-wx.blogspot.com/2024/10/kotzebue-flood.html

https://ak-wx.blogspot.com/2024/10/flood-follow-up.html

The tide gauge at Kotzebue reached well into major flood stage, and according to Rick Thoman the peak water level matched that of last October, when damage was severe.  Evacuations were carried out in Kotzebue and Kivalina this time, and the preparations seem to have prevented a repeat of last year's major impacts.

https://www.adn.com/alaska-news/rural-alaska/2025/10/09/incoming-coastal-storm-looms-as-northwest-alaska-evacuees-return-home-amid-receding-floodwaters/

The center of the storm tracked just to the west of the Bering Strait with minimum MSLP of about 970 mb, which is very low but not record-breaking.  Here's a sequence of maps showing estimated MSLP and 10m wind speed at 6-hourly intervals from early Tuesday morning through late Wednesday; the strongest winds developed in Kotzebue Sound on Wednesday after the storm center passed to the north and the wind direction went around to the southwest.

Unfortunately a second and potentially more serious threat has now emerged with a second storm that is originating from the remnants of Typhoon Halong, a tropical cyclone that passed to the south and east of Japan in the last couple of days.  Weather models show ex-Halong becoming powerfully re-energized as it gets caught up in the North Pacific jet stream tomorrow and into Sunday.  The forecasts for Sunday morning are frankly quite alarming, with minimum MSLP near 950 mb as the storm passes near the eastern end of St Lawrence Island:

If these MSLP forecasts are correct, ex-Halong may well break 1950-present records for lowest MSLP along its track in the northern Bering Sea; ERA5 data shows records of about 956 mb from St Lawrence Island to Nome.

Needless to say, impacts up and down the west coast will be severe even if the forecast details are a little off.  The latest NWS forecast shows water levels as high as Wednesday's event in Kotzebue, and higher in Nome.

The climate context for these storms will be worthy of comment in a future post.  For now, it's interesting to note that last year's storm reminded Rick Thoman of west coast storms in 1973 and 1974; and now we again have back-to-back autumns with similar severe storms.  It's likely no coincidence that the winters of 1973-74 and 1974-75 were back-to-back La Niña winters following a strong El Niño in 1972-73; and we are in the same situation today (El Niño in 2023-24, La Niña last winter, and another one on tap for this winter).