Summer Review

I've been meaning to post a few comments on the climate patterns and anomalies during summer - better late than never, I trust.  On a statewide basis it was a fairly warm and fairly dry summer, but neither aspect was highly unusual in terms of the state averages: according to NOAA it was the 10th warmest summer in the last 30 years (warmer than 2024 but cooler than 2023), and statewide precipitation was the fifth lowest in 30 years (driest since 2019).

However, regional differences were significant, especially for precipitation.  The summer was much drier than normal along the central and eastern Gulf Coast, but much wetter than normal for most of western Alaska as well as the northern interior and western Brooks Range.  Here are the ERA5 (top) and NOAA (bottom) percentile rank graphics for the three-month period:

Here's a chart of accumulated precipitation at Yakutat, to illustrate the dryness (click to enlarge).  The June through August period was the second driest on record, following 2007, with total rainfall amounting to only 37% of the long-term median (9.6" versus 25.8").

Precipitation deficits were very pronounced in July along the northern Gulf Coast, but August really exacerbated the drought (relative to normal) and also set up the big contrast with excessive rainfall in northwestern Alaska:

We covered the late August stormy pattern for western and northern Alaska here, and the August 500mb height anomaly highlights the pressure gradient across western Alaska: the ridge over southern Alaska deflected the jet stream northward into western and northern Alaska.

In terms of sunshine and wind, it was a very poor summer for the Y-K Delta region, with all three months bearing part of the blame.  However, only June was cooler than normal in the southwest.  Eastern and northern Alaska were generally sunnier and less windy than normal, although not in August.

Looking back at lightning and wildfire activity, both were above the long-term median, but lightning much more so.  For a time in late June and early July, lightning strike counts were running second only to 2015 (with data back to 2012), and the seasonal total ended up in 4th place, similar to 2019 and 2022.  In contrast, wildfire acreage ended very close to 1 million acres, which is about twice the long-term median but well below 2019, 2022, and of course 2015.

It seems likely that Alaska's very wet spring was largely responsible for the relatively subdued fire season.  The statewide average for the April-May total precipitation was easily the highest on record, with both April and May ranking in second place statewide; and importantly, the wet anomaly included large parts of the fire-prone interior.

 

May was also cooler than normal, and June was only a little warmer than normal in the interior.  This is a big contrast with, say, the enormous warmth of May 2015 that dried out the state in advance of that huge fire season.

Here's a map to illustrate the distribution of lightning activity relative to normal.  There was far more lightning than normal in northern Alaska, and the more typically active southern interior also had more lightning than normal.

A plot of actual strike count density shows that the bulk of the activity occurred across the interior, as always, but it was very unusual to see the high strike counts extending so far north into the Brooks Range.

I suspect that the combination of fairly high temperatures and high humidity in the northern interior was part of the reason for the very active lightning season there (warm, humid air is fuel for thunderstorms).  Here's a map of dewpoint percentile relative to the 30-year climate:

From a broader climate perspective, widespread and extremely unusual warmth in the North Pacific this summer is one of the biggest stories in climate science at the moment.  June-August sea surface temperature anomalies were as much as 3°C above normal in the northwestern Pacific, leading Japan to have its third record-hot summer in a row.

Remarkably, the August area-average SST reached 20°C for the Pacific basin north of 30°N, according to NOAA's ERSST data.  The acceleration of warming in the past few years is quite something:

I'm out of time for this post, but I'll append below the rest of my August climate percentile maps for the sake of completeness.