Cooling Off, and July Climate Data

It's beginning to feel a lot like autumn already for much of Alaska, as temperatures have dipped below the declining seasonal normal in the past few days.  Sub-freezing temperatures occurred in many of the colder spots of the central and eastern interior this morning, including in the Fairbanks area: 27°F at Goldstream Creek and 31°F at the Creamers Field SNOTEL site.  The early chill will hasten the arrival of autumn colors in the next couple of weeks.

I've been too busy to post my usual monthly climate update in recent days, but better late than never - here's a look back at climate anomalies in the month of July.  It was a fairly warm month overall, and significantly drier than normal on a statewide basis, which marks a big contrast with last year's record wet July.  Warmth was widespread (except for Southeast), but the dryness was most significant along and north of the Gulf Coast from Cook Inlet to the far northern Panhandle.  Here are percentile rank maps from NCEI (top) and ERA5 reanalysis (bottom):

As usual, the NCEI and ERA5 maps differ significantly for precipitation, with ERA5 showing much wetter conditions from the western interior to the Alaska Peninsula and Kodiak Island; and ERA5 also highlights the unusually sunny and dry conditions across the North Slope.

One of the most significant events during the month was the heatwave focused on northwestern Alaska early in the month.  Rick Thoman comments a bit more on this in his blog:

https://alaskaclimate.substack.com/p/july-2025-arctic-and-alaska-climate

Wind was above normal in the zone of wet and cloudy weather across the southwest.  This region of poor weather seems to have been caused by a frontal zone along the eastern side of the (quasi-permanent) Bering Sea trough; as the second figure below illustrates, there was a subtle north-south ridge axis over Alaska, blocking the westerly flow.  The more significant upper-level feature was a ridge over the East Siberian and Alaskan Arctic Ocean, and that was a key player in the northern heat wave:

https://ak-wx.blogspot.com/2025/07/northern-heat.html

Regional lightning activity was not far from normal for the month overall, based on lightning strike counts that include northwestern Canada; but it was more active in parts of the Alaskan interior, and especially north-central areas.  As is typical, most of this activity occurred early in the month, including well over 10,000 strikes on the 7th.  It appears this is the first year (2012-present) with over 10,000 cloud-to-ground lightning strikes on 5 different days during summer, based on data collected by the Alaska Lightning Detection Network.  I'll have more to say about this summer's lightning and wildfire activity in a subsequent post.

AI Weather Forecasting

Back in March of 2024, I mentioned the new AI weather model developed by the world-leading European forecast center (ECMWF), and it's exciting now to be able to comment on a major recent upgrade to the ECMWF's AI forecasting technology.  In short, ECMWF has released a new version of their AI system (AIFS) that produces an ensemble of outcomes, similar to the ensemble output from traditional physics-based models.

https://www.ecmwf.int/en/about/media-centre/news/2025/ecmwfs-ensemble-ai-forecasts-become-operational

In many respects, this latest AI system is now significantly better than the ECMWF's own IFS (Integrated Forecasting System), the traditional physics-based model that has been developed over decades, and that grinds out its forecasts on large supercomputers.  In contrast, the AIFS is "data-driven", meaning it learns from the historical data with no computational constraint from the laws of physics; and its realtime forecasts run extremely quickly with a tiny fraction of the computing resources.

Here's a chart to illustrate the realtime performance of AIFS forecasts initialized from December 2024 through June 2025:

The AIFS-ENS model (black line) has the highest correlation of 30-90°N 500mb height anomalies, and for lead times beyond about a week it's dramatically better than the first AIFS version that had only a single ensemble member.

It's interesting to have a look at where on the globe the superior performance is to be found.  The maps below show the improvement of AIFS over the traditional IFS ensemble, measured in terms of the percentage change in variance explained for 500mb height at various lead times.  For instance, if the correlation coefficient improves from 0.8 to 0.85, that's a 13% improvement in variance explained.  Interestingly, the improvement seems to emerge first in the tropics at only 2-3 days into the forecasts, and then the higher latitude forecasts start to benefit - especially over the North Pacific and North America - after 4-5 days.

The spatial signals become very noisy at longer lead times because of the rather small sample size, but averaging the results across all longitudes reveals that the high latitudes see the most improvement beyond 7 days:

The significant improvement in the Arctic will be very encouraging for Alaska forecasters, because weather predictability is lowest in the high latitudes to begin with.  Redoing the first figure above for 60-90°N, we see a nice boost beyond 10 days (see below).  To be precise, the anomaly correlation at day 15 goes from +0.21 (IFS) to +0.27 (AIFS-ENS), and while that's still too low to be useful, it represents a 57% gain in variance explained.

It can't be overstated how remarkable it is to see performance gains like this from such young technology; presumably there is room for considerably more improvement in the years ahead.

Finally, readers may ask where the AIFS-ENS forecasts can be viewed?  Unfortunately, I'm not aware of any free websites that provide AIFS-ENS maps that include Alaska, with the exception of ECMWF's own site, and that's not particularly user-friendly:

https://charts.ecmwf.int/?facets=%7B%22Range%22%3A%5B%22Medium%20%2815%20days%29%22%5D%2C%22Type%22%3A%5B%22Forecasts%22%5D%2C%22Component%22%3A%5B%22Surface%22%2C%22Atmosphere%22%5D%2C%22Product%20type%22%3A%5B%22AIFS%20Ensemble%20forecast%22%5D%7D

I expect in due course the AIFS-ENS data will be added to sites like Tropical Tidbits, so check back there (under "Ensemble") occasionally.

Beaufort Sea Ice

Although Arctic-wide sea ice extent is running very low this summer - with big deficits on the Russian side of the basin - surprisingly there is much more ice than normal in the Beaufort Sea.  The following figure illustrates the striking contrast from recent years:

We have to go back to 2006 to find more sea ice in the Beaufort Sea at this date, and the ice extent is even higher than the median for the 1980s.  Rick Thoman pointed out this fact on his site, and he also notes that a considerable amount of multi-year ice has made it into the Beaufort Sea.  The following image from NSIDC is a few weeks old, but it clearly shows a zone of older ice stretching from the Canadian high Arctic to the Beaufort Sea.

The anomaly in the Beaufort Sea stands in huge contrast to the rest of the Arctic.  This figure from Zack Labe shows the rank of each regional basin's ice extent relative to other years in the satellite era.

The Chukchi Sea also has more ice than most recent years, although in the case of the Chukchi the ice is not as extensive as last year.

The NSIDC sea ice index shows the ice deficit on the other side of the pole, with nearly all ice gone in the Kara Sea already. 

Taking a look at the weather pattern from recent months, there has been high pressure centered over the Beaufort Sea, but this in itself is not unusual.  The second figure below shows the departure from normal MSLP since May 1, and the more anomalous aspect is the low pressure near Greenland (positive AO/NAO phase):

The effect of the pressure pattern has been to generate unusual northerly winds from near the pole to the western Canadian Arctic; the figure below shows the departure from normal of the vector wind.  I suspect this has helped to shift the highest concentration of ice onto the Canadian side and also accelerate the Beaufort Gyre, sending old ice westward into the Beaufort Sea.

Weather Update

Alaska's interior weather has been relatively more favorable for fire suppression in the past couple of weeks, but nevertheless fire acreage has continue to move up at a rather steady pace, and is nearing the million acre mark.  This puts the 2025 season squarely in the above-normal category for acres burned; the long-term median is about half a million acres burned per year.

According to NWS estimates, there has been above-normal rainfall across a swath of the interior in the past two weeks, but southeastern and northwestern interior areas have been much drier.  With a fairly strong warm signal in the 6-10 day forecast, it seems there's still a risk for fire activity to ramp up again, although of course summer will be waning fast in just a few weeks.

The cumulative lightning chart shows the drop-off in thunderstorm activity since July 8: this year has dropped to 6th place for ground lightning strikes (2012-present data).

It's interesting to note the bifurcation in cumulative strikes as of late July: based on the very limited history since 2012, it seems there is a bi-modal distribution of either "active" or "inactive" years up to this time of year.  2025 certainly qualifies as unusually active after the lightning onslaught in June.  Here are the annual year-to-date lightning strike counts as of July 20:

A map comparison of July (so far) versus June lightning strike density shows the decline this month, with much-reduced activity for most areas except for central locations from near Bettles down towards Minchumina. 

June Climate Data

June was an interesting month for global climate, and Alaska's weather reflected the larger-scale patterns that unfolded.

One of the most striking aspects was that unusually strong ridges developed in the mid-latitudes of the Northern Hemisphere - particularly across the North Pacific from Japan to the US West Coast, and across the North Atlantic and southern Europe.  Record heat waves occurred in western Europe and Japan, and it was the hottest June on record in both regions.

In contrast to the mid-latitude ridging, the atmospheric pressure was generally lower than normal in the Arctic, and especially from eastern Russia to the Bering Sea and across the northern North Atlantic and northern Europe.  This "see-saw" of MSLP is typical of the Arctic Oscillation, and June characterized a positive AO phase.

The Arctic Oscillation typically refers to conditions in the troposphere and is not always directly linked to the stratospheric flow above, but in this case the circulation anomaly extended well up into the stratosphere.  In the lower stratosphere, for example at 100mb pressure, there was a similar ring of above-normal heights (pressure) in the mid-latitudes and low heights near Greenland:

In tandem with the pressure anomaly, the 100mb circumpolar westerly winds at 60°N were the strongest on record for June.  Think of it as a vortex of counter-clockwise rotating air aloft that was moving faster than ever observed before (in June) up at about 50-60,000 feet.

What relevance does this have for Alaska?  Well, the low pressure over the Bering Sea involved unusual storminess, so it was a very windy, cloudy, and wet June for Aleutian and Bering Sea communities.  Also, with southern Alaska located squarely in the zone of enhanced westerly winds to the north of the Pacific ridge, the wet weather traveled eastward across the Gulf Coast to the northern Panhandle.  It was also unusually cool in southern and especially Southeast Alaska, with warm air unable to migrate up from the south.  Here are my usual monthly percentile rank maps based on NCEI data (top two maps) and ERA5 data (maps below):

One might expect that low pressure in the Arctic (positive AO phase) would also produce windy and perhaps wet weather for Arctic Alaska, but in fact the classical positive AO setup at this time of year tends to allow a localized ridge to the north of Alaska, and that's what we saw in June (see the first map in this article).  As a result, the North Slope was mostly calm, sunny, and generally warm and dry.  Sunny, warm, and calm conditions also extended over most of the northern and eastern interior - but this refers to monthly averages, and there was also a tremendous amount of lightning during the month.  Here's a map of lightning strikes during the month, showing very widespread activity:

With over 93,000 ground strikes, this was the second most active June recorded by the ALDN (2012-present); the most active June was in 2015, with about 103,000 strikes; but that year the activity was concentrated farther south, and especially in the southwestern interior:

I'll be doing more analysis of this year's lightning activity in a subsequent post.

It's also worth commenting on North Pacific SSTs, which have reached extreme levels of unusual warmth from Japan eastward in recent days (responding to the strong ridge across the North Pacific).  Check out the development of extreme warmth between early June and early July:

This is an enormous marine heat wave, perhaps the most expansive and anomalous on record in recent decades; I'll have to do some objective analysis to quantify this.  The warmth in this region is characteristic of a negative PDO phase, and so the PDO index has plummeted to record negative values in recent days (see below).  We might say this is also part of the reason for the cool June in southern Alaska.

More Heat and Lightning

[Update July 10]

Rick Thoman pointed out that a SNOTEL site near Kobuk reached 93°F on Saturday, a remarkable temperature for this typically (slightly) more maritime area in the northwestern interior.  (Note that SNOTEL thermometers are more reliable than the warm-biased RAWS instruments.)

But it was back down to 30°F yesterday morning - that's quite a change.  Click to enlarge:

[end of update]

The second big heat wave of the summer for central and northern Alaska came to an end with a tremendous amount of lightning in the past couple of days.  The ALDN recorded over 12,000 cloud-to-ground lightning strikes in the 24 hour period ending at 6am today, with several regions of strong activity:

Yesterday was the 5th day this summer with over 10,000 ground strikes recorded, and this is the most of any summer in the modern ALDN history since 2012 (note that this calculation includes northwestern Canada to the west of 129°W).  Previously the record was 4 such days in both 2016 and 2017; but some summers don't see a single day this active - for example, the peak lightning day last summer was 6500 strikes on June 23.

In terms of total year-to-date strikes, 2025 remains in second place behind 2015.

Many new fires will have been started by this latest round of lightning, but the weather is now much cooler and more humid, which will greatly aid fire control efforts.  There are two substantial fires between Fairbanks and Nenana, collectively called the Nenana Ridge Complex, with expansive evacuation orders in place.  These fires have been burning since around June 20.

Looking back at the heat wave, it peaked over the holiday weekend, and was focused over the northern and northwestern interior, as well as the Brooks Range.  After seeing its latest measurable snow on record (again) only 4 weeks earlier, Bettles reached 90°F on Saturday, and that's only the second 90°F this century at Bettles - the other was in 2019.  Bettles is now running in second place for number of 80°F and 85°F days this summer (15 and 8 respectively).  What a turn-around from the cold start to summer:

Up at Anaktuvuk Pass, the temperature reached or exceeded 80°F for 4 days in a row, which is quite extraordinary for the location (2100' elevation at 68°N).  Even a single 80°F day is very unusual up there, but the count has now reached 6 days this summer; the previous record from recent decades (since the mid-1980s) is just 2 such days in 2016.

Northern Heat

The heat is back for interior Alaska, and this time with a focus on the north, especially the northwest.  A strong high pressure ridge has set up squarely over the North Slope and will intensify even a bit more into tomorrow morning before fading.  Here's the 500mb analysis from 4pm AKDT yesterday, courtesy of Environment Canada:

Mid to high 80s Fahrenheit have been reported from many sites around the northwestern interior and the southern slopes of the Brooks Range, but most of these are RAWS sites that are known to run hot on sunny summer days.  There was a credible 88°F at Huslia airport, however, on Wednesday.

More significantly, I think, there was a daily minimum temperature of 72°F at an elevated RAWS site about 40 miles north of Kotzebue, i.e. well above the Arctic Circle.  I think there's no reason to believe this temperature is too high, as there is no solar insolation in the early morning hours: the "midnight" sun is blocked by terrain to the north.

Click to enlarge the following map (July 3 minimum temperatures):

It is rare to see a 70+ daily minimum in Alaska, but this site's elevated location is quite prone to warm summer "nights" under similar heatwave conditions: 71°F daily minima were reported in 2013 and 2019.

It's harder to prevent "overnight" cooling in valley locations, so for example the record warmest daily minimum in Fairbanks is 70°F in 2013.  (The university farm reported a low of 76°F on June 26, 1915 - the same day as Fort Yukon's infamous 100°F - but that 76°F seems implausible because the Fairbanks observer also recorded "hail the size of marbles", which would surely have cooled the air more significantly.)

Here's a contender for perhaps the highest low-elevation daily minimum in Alaska: 72°F at Umiat in late June 1982.