August and Summer Review

Now that August climate data is complete, it's time to pen a few comments on the unusual summer of 2026.

First of all, it's interesting to observe that August was the warmest month of summer statewide, and that's rare: it has only happened twice in the last century, in 1941 and 1959 (according to NOAA/NCEI data).  Here's this summer's daily statewide temperature index from UAF (note that this is an index based on departures from normal, not absolute temperatures):

In 102 years of data, June has been the warmest month of the year in Alaska five times, including a tie with July in 2024.  July is the warmest month in over 90% of years.  Of course, this breakdown varies with region.  Fairbanks more often sees June as the warmest month, and has never had August as the warmest month, but southern maritime locations more often see peak warmth in August (e.g. over 75% of years in Cold Bay).

August was also the first warmer-than-normal month statewide since last November, breaking a streak of 8 consecutive below-normal months (although April was essentially normal) - based on the 1991-2020 normal.  The last time 8 months in a row were cooler than normal was in 2012, not long before the sudden reversal (which proved enduring) to persistent warmth in early summer 2013.

Here's the mid-atmosphere pressure map from August, showing that high-pressure ridging became a prominent feature across all of southern Alaska.

The ridge was fostered by, and also acted to reinforce, much above normal sea surface temperatures from the Sea of Japan to the waters south of the Aleutians.  This is basically a negative PDO signal, although the warm pool is shifted slightly north compared to its classical position.

August warmth was most anomalous in northern and eastern Alaska: the North Slope was very warm indeed, and NCEI ranks the Southeast Interior division as the 5th warmest on record (but not as warm as 2023).

August rainfall was feast or famine, so to speak, with a sharp contrast between very damp conditions in the western interior and much drier weather to the south and east of Fairbanks.  It was also very dry in the Aleutians, courtesy of the North Pacific ridge.

Sadly, the very warm and dry conditions in the southeastern interior allowed a damaging fire to occur in Tok.  To quote Rick Thoman, "More than 40 homes in Tok were damaged or destroyed by the fire, making it one of the most destructive fires in terms of societal impacts in Alaska history".

The Tok fire illustrates the adage more often used in hurricane preparedness: "it only takes one".  It's no comfort to those affected, but the statewide seasonal wildfire activity was far below normal this summer - only 89,000 acres burned, the lowest total since 1995.

The very inactive fire season is in some ways a surprise, because despite the overall cool weather in June and July, there was a lot of lightning for a 3-week period in late June and early July.

Here are some maps to illustrate the spatial distribution of this season's lightning and its departure from normal.  The southeastern interior saw less lightning than normal, but a much larger area from the Y-K Delta to the western and northern interior was significantly more active than normal.

The Lower Yukon fire monitoring zone was the most unusually active region in Alaska, with a new seasonal record for total lightning strikes (data since 2012).

On the inactive side, the upper Tanana River region saw the most significant lightning deficit compared to normal:

The lack of significant fire growth in the wake of the June-July lightning onslaught can be mainly attributed to the wet spring, along with a notably cool May, preventing fuels from becoming very dry before the onset of lightning season.  Of course the absence of really warm weather in June and July helped a lot too.

As one example of the "missing warmth" in Alaska's interior, Fairbanks only reached 81°F for the highest temperature of the summer; this has only happened a few other times in the period of record.  The normal summer peak temperature in Fairbanks in recent decades is 88°F.  In contrast, southeast Alaska reached unusually high temperatures in mid-August, and the period of record does not show any other year with such a contrast (i.e. peak summer temperatures around 5°F warmer in Southeast than in Fairbanks).

Wrapping up the discussion with some maps of the overall summer climate anomalies, we see that southern Alaska and the central interior were generally cooler than the 30-year normal, but not dramatically so in most locations.

A more significant anomaly is seen in the summer's total rainfall, which was well above normal in the southwestern mainland and far below normal in southeast Alaska.

NCEI's data shows the central and northern panhandle regions with the second lowest summer rainfall in the last 30 years (3rd percentile on my map) - 2004 was considerably drier.  However, summers drier than this year occurred with some regularity prior to 1995, so the drought isn't quite as remarkable on a long-term basis.  Here's a chart for the central panhandle division:

Summer sunshine was most abundant (relative to normal) in the extremities of Alaska - west, north, southwest, and southeast.

It's interesting to see the unusual combination of sunnier and wetter than normal in western Alaska; this happened because June (long daylight hours) was much sunnier than normal, and August (typically wetter) was much wetter than normal - and these two months dominated the respective seasonal anomalies.

Finally, for completeness - July was windy in southern Alaska, and August was windy in the southwestern mainland, but all three months were notably less windy than normal on the North Slope.  With less breeze than normal, the mosquito season may have been an especially bad one for the long-suffering residents of the far noth. 

August Changes

It's been a very chilly few days in the central and eastern interior, with an upper-level trough creating cloud and rain for many.  The high temperature in Fairbanks on Friday was only 52°F, a very low value for this point in August, and yesterday Delta Junction and Northway reached only 46°F and 47°F respectively.  This is the most anomalously cool weather since mid-June.

August is an interesting month for climatologists, because in the far north it is, in some ways, more like an autumn month than a summer month.  This contrasts sharply with its character farther south in the mid-latitude and sub-tropics, where summer drags on or even reaches its zenith of heat and humidity in August (just ask the poor residents of Houston, Texas).

The accelerated timetable of seasonal change in the high latitudes is of course directly tied to the much greater loss of solar heating by this time of year.  At 30°N the sun loses only a small fraction of its power from June to August, and the difference can be imperceptible to many; but the percentage decline is very much larger in the Arctic.

Here's a figure showing the loss of solar radiation from June to August.  Note that this includes the effect of increased cloud cover for many northern areas in late summer, so it's not all attributable to the sinking sun; but the north-south difference is clear.

With solar heating rapidly being lost, the effect on temperatures is inevitable; August is much cooler than July across nearly all Arctic and sub-Arctic land areas.  But the map below immediately reveals another very interesting aspect of August: the northern oceans (except for the ice-covered Arctic Ocean) continue to warm up despite the loss of solar heating.  This is because the heat capacity and vertical transport/mixing of heat are so much greater at the ocean surface than at the land surface: the August sun, weaker as it is, still outweighs the loss of heat from the ocean surface for a time (the air temperature over the northern extratropical oceans typically peaks in the second half of August).

With the distribution of land and ocean being what it is in the Northern Hemisphere, the effect of these seasonal changes is to substantially increase the overall north-south gradient of temperature at about 60°N in August.  And this in turn provides the driving force for a significant increase in westerly winds at that latitude (except farther south in the northwestern Pacific, and a bit farther north in Europe).  Here's a map of the July-August change in westerly winds at 250 mb, which is approximately the level of the jet stream.

The increased energy in the westerly flow causes more disturbed and cloudy weather around the high latitudes, and there's a substantial increase in precipitation compared to July across the North Pacific and North Atlantic - see below.  Interestingly the increase in precipitation doesn't extend to northern land areas in general, and some regions become significantly drier in August; this is at least partly because of the decrease in temperature over land, i.e. cooler air holds less moisture, but over the oceans the warmer water provides more moisture and more rainfall for maritime areas.

Below are zoomed-in versions of the July-August temperature and precipitation change maps for Alaska.  The drop-off in temperature is most pronounced across northern Alaska, and it's minimal along the Gulf Coast, with its heavy maritime influence.

Most of western and southern Alaska are distinctly wetter in August than in July, and it's a large difference for the northeastern Gulf Coast.  Yakutat is a classic example: August produces about 80% more rainfall than July on average.  However, the eastern interior and (according to ERA5 data) parts of the Brooks Range are drier in August.  Northway, for example, sees about 30% less rain in August than in July.

I've used data from the most recent 30-year period for the maps above, so it's interesting to see if the same trends were evident in the previous 30-year window.  The answer is, "essentially yes" - see below.

I also find it interesting to note that August is also considerably cooler than June over much of northern Alaska.  Unlike the comparison to July, this is not universally true across northern land areas, and in fact northern Alaska shows the largest temperature drop from June to August of any high-latitude location.

Finally, the nClimDiv data from NOAA/NCEI gives a good sense of how August temperature and precipitation have changed in the past several decades in relation to June and July.  The following charts show 30-year running mean values on a statewide basis. 

Interestingly, August has warmed up a lot less than either June or July on a statewide basis, and apparently it's only in recent decades that August has become cooler than June.  This is supported by ERA5 data (see below): the August-minus-June analysis for 1965-1994 shows much less pronounced cooling in the northern interior, and southern Alaska apparently used to be more significantly warmer than June.

A more detailed analysis of ground-truth station data and atmospheric circulation patterns would be required to confirm and understand this subtle change in early versus late summer temperatures.

August and Summer 2022 Climate Data

Climate data is in for August, so let's take a look back at summer 2022 in Alaska.  It will long be remembered for the extraordinary reversal in fortunes with respect to rainfall: after the driest June on record statewide (1925-present), the combined July-August precipitation was the third highest on record, and only 2% below the 1998 record.  This is based on the NOAA/NCEI climate division (NClimDiv) data, which also indicates that July-August was the wettest on record for the northwestern Gulf of Alaska and Cook Inlet divisions (see here for a map of the divisions).

The June dryness exacerbated the moisture deficits from a dry April and May, and of course this was a major reason for the big wildfire season: over 3 million acres burned, the 5th highest in recent decades (only 1990, 2004, 2005, and 2015 were worse).  If it wasn't for the big change in July, the fire acreage would have been much higher still.

The extraordinary contrast between early summer and late summer is illustrated by the following chart, showing the ratio of statewide July-August precipitation to April-June precipitation.  (These statewide numbers from NCEI are area-averages.)  Amazingly, this year's July-August precipitation was nearly 300% of April-June, whereas the highest ratio in all previous years was 180%.  What an extreme climate anomaly!  The distribution isn't Gaussian, but this year's number represents a 6.3 standard deviation departure from the 1925-2021 mean.

Regionally, the contrast was even more extreme in the Cook Inlet division (see below): we're talking about a 10.3 standard deviation departure from the prior distribution.  April-June was easily the driest on record, and then July-August was easily the wettest on record.  In the past century there has been nothing remotely close to this kind of change from extremely dry to extremely wet at this time of year.  I'll have to look into whether anything similar can be identified in the history at any other time of year.

Here are the monthly precipitation rank maps for June through August relative to the past 30 years.  Note that the June and July numbers differ slightly from the maps I posted in earlier monthly summaries (here and here), because NCEI revises the data over time.

For the traditional climatological summer season of June-August, most of the state was considerably wetter than normal, although August did not make up for earlier deficits in the eastern interior.  This includes Fairbanks: the June-August total of only 2.43" is the lowest since 2004 and the 6th lowest since 1930.  It's also a big change from most of the past decade, and it may signal an end to the "new wet regime" that I discussed earlier this year:

https://ak-wx.blogspot.com/2022/03/precipitation-changes.html

ERA5 reanalysis data shows more detail on the persistent dryness in the eastern interior and also supports the fact that August's wet weather did not extend to far southeastern Alaska.

 

 

The contrast in seasonal rainfall totals could hardly have been greater from south to north across the Alaska Range - see below.  Clearly the July-August flow regime, which was produced by a trough over western Alaska, involved downsloping flow from the southwest across the eastern interior, and therefore not much rainfall relief.
 

How about temperature?  The persistent flow regime produced a more striking west-east contrast in August than in July, with temperatures dropping significantly below normal over parts of the eastern Bering Sea and the eastern Aleutians, while eastern Alaska was distinctly warmer than normal.

For the season as a whole, it was a notably warm summer in southern mainland Alaska, although in the southwest this was all because of June.  The North Slope was apparently cooler than normal, but as usual I don't trust the colder result from the NClimDiv data.  Utqiaġvik was slightly warmer than the 30-year normal, and Umiat was warmer than the 2008-2020 average.

The very active, mobile weather pattern also produced a much winder than normal August in the Bering Sea and most of southern Alaska, and it was one of the windiest summers on record across the Bering and southern Chukchi Seas.

Like the wind and rain, the lack of August sunshine in southern Alaska was very unusual, but that's small consolation for the people who suffered through it.  For the interior, August was much less sunny than June and July, but it was still a very sunny summer overall, compared to normal.

I'll finish with the summer average dewpoint and near-surface soil moisture, as estimated by the ERA5 model.  The western interior had very low humidity in both June and July, and this no doubt contributed to the aggressive fire activity, even though July ended up being fairly wet.  As for the overall low soil moisture in southern Alaska, this reflects the extreme magnitude of the anomaly in June.