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

Stormy Weather

As expected, the active weather pattern and strong west/southwest flow is producing a stormy end to climatological summer, with lots of rain and wind, for much of western and northern Alaska.  Here are rainfall totals reported from automated sites in the last 72 hours (click to enlarge, and ignore zero values which are mostly false):

The 3.39" of rain at Coldfoot is consistent with a substantial response in the local river gauge, which reached a record high level:

This gauge apparently has a decades-long period of record, so it's quite remarkable to see an all-time record crest.  The list of historic crests includes both spring meltout and late summer flood events:

River gauges in Fairbanks-land are high but don't yet indicate flooding, despite some impressive rain totals in the vicinity.  Here's a list of totals as of yesterday evening, courtesy of the NWS.

The Fairbanks airport's rainfall occurred mostly on Sunday, when the daily total of 1.30" was the highest in August since 1990.  It's also worth noting that the vigorous flow aloft produced strong winds in Fairbanks on Saturday afternoon, reaching 49mph at the airport and causing power outages.

Looking ahead, it's a bit disconcerting to see more of the same: the 15-day ECMWF precipitation forecasts are wetter now than they were a week ago for the same areas of the west and north.  Both models show another 6+ inches of rain across the southern slopes of the Brooks Range, as a powerful ridge redevelops near the northern Panhandle and keeps the flow locked in from the southwest across mainland Alaska.

More Extremes

No time for details tonight, but a couple of quick notes regarding the ongoing extreme weather situation for Alaska.  First, it was southern Alaska's turn for high winds today: gusting over 60 mph in Anchorage and Palmer, 81 mph at Delta Junction (the highest in 25 years), and 90 mph out west (sustained at over 80 mph) at Cape Romanzof.

Regarding temperatures: Fairbanks spent its third straight day in the 30s Fahrenheit, and a quick look at the data suggests this is an unprecedented warm spell (at least since 1930) for the month of January.  The great thaw of early December 1934 was greater, and late February 1943 had 3 straight days with a mean temperature of 35°F or higher, but in January Fairbanks hasn't even had 2 straight days with a mean temperature of 35°F or higher.  There were only 6 individual such days from 1930 through 2024 - but Fairbanks has just seen three in a row (assuming the temperature doesn't drop off sharply before midnight tonight).

More commentary and wrap-up on this historic event in the coming days.

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:

Anchorage Wind

A reader inquired about the persistent north wind event of last week in the Anchorage area, so let's take a look at this.

First, the facts on the ground: there was indeed a very lengthy period of stiff northerly winds, lasting from early morning on Wednesday (Feb 28) through Saturday morning (March 2).  Here's a graphical look at observations from Anchorage airport, with wind speeds in mph:

Much the same sort of thing was observed up in Palmer, and with higher wind speeds, although there was a break on Thursday morning:

Remarkably, the peak wind gusts were 60mph or higher for 4 consecutive days in Palmer.  The maps below (click to enlarge) show the daily peak gusts from Feb 28 (top) to March 2 (bottom).  This was a remarkably persistent event:

Taking a quick look at historical hourly data from Anchorage airport, I see only one other event since 2000 with comparable sustained winds: it looks like a very similar event occurred at the same point on the calendar in 2017 (Feb 28 - March 3).  Here's the average MSLP for the 3 windiest days in both cases:  2017 (top) and 2024 (bottom):

Clearly the driving factor in both cases was the strong pressure gradient between low pressure in the eastern Gulf of Alaska and high pressure to the west and north.

The long duration of the event reflects the unusually persistent MSLP setup, with low pressure slow to depart or weaken in the Gulf of Alaska, and with building high pressure to the north maintaining the gradient as the low pressure eventually decayed.  Here's a sequence of MSLP analyses at 3am AKST for 5 consecutive days: February 27 through March 2.

Farther aloft, the situation was unusual, with a sharp ridge over the Bering Sea progressing slowly eastward behind a broad and deep trough over the Gulf of Alaska.  The 500mb map from Thursday afternoon shows powerful northwesterly flow in the very tight pressure gradient over southwestern Alaska, but yet the 500mb wind was out of the south at Anchorage (highlighted with the red circle below):

To me, this highlights the large degree of spin (technically "vorticity") in the atmosphere aloft, which helps explain the longevity of the low pressure in the northeastern Gulf of Alaska.  This upper trough and associated jet stream, by the way, is what brought extreme mountain snows to California over the weekend.  It was windy down there too: there's a lot of energy in this jet stream, and this is probably attributable to El Niño.

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/