Saturday, September 10, 2022

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:

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.


  1. I'm not convinced that this years weather situation (extreme anomalies) will release Fairbanks from the "new wet regime." Seems to me Anchorage lost it's drier, sheltered benefit of being in the rainshadow of the Chugach mountains from prevailing storms from the SE. Meanwhile, northeastern interior appeared to be in a rainshadow pocket through much of August. Either way that was one heck of a switch that happened from early to late summer. I didn't see a mention of the polar vortex but have been wondering if something like that or a trade wind pattern assisted the extreme transition in conditions.

    1. Thanks for the comment. I'm inclined to agree - a return to wet seems likely sooner or later for Fairbanks - but the summer was very anomalous on the dry side, so it's certainly a notable, if short-lived, change.

      Good query on the cause of the transition, I think it originated in the tropics. Will see if I can put up a few comments on that.