June Chill, May Climate

Yesterday NOAA/NCEI came out with their climate statistics for May, and it was the sixth consecutive month with a statewide mean temperature below the 1991-2020 normal in Alaska (although April was only marginally below).  It was also the third consecutive May with a cool anomaly relative to recent decades:

Significantly above-normal temperatures have been rather scarce in most areas in recent months, and Rick Thoman noted that many interior locations had their lowest May maximum temperature since 2000.  The statewide temperature index barely rose above normal at any time in the month, although the first few days of June turned much warmer.

As if to re-emphasize the cool theme, a very notable cold front swept across the interior and north yesterday, ushering in a very chilly air mass for the time of year.  Here's an enhanced satellite image showing the frontal cloud band at 3:20pm AKDT.  Blue colors across the North Slope and high terrain indicate snow cover, and sea ice is visible in Kotzebue Sound and along the northern Arctic coastline.

The 500mb analysis from about the same time yesterday shows the connection to a very strong mid-atmosphere cyclone over the Arctic Ocean.  Judging from ERA5 data, it appears to be one of the strongest - if not actually the strongest - on record for the month of June in this region.

Temperatures this morning were near or below freezing widely across the interior, with hard freezes across the northwest and Brooks Range.  The NWS (courtesy of Rick Thoman) noted that the wind chill of 13°F in Kotzebue at 5am was the lowest on record for this late in the spring.  Here are a couple of zoomed-in maps of minimum temperatures across the Arctic northeast and interior/Arctic northwest.

Looking back in more detail at the month of May, NOAA's data indicates that the Bristol Bay climate division saw its coldest May since 2001.  However, the coarse climate division perspective completely obscures the fact that it was notably warmer than normal in Alaska's northwest; Kotzebue had its warmest May since 2020.

The mid-atmosphere pressure pattern responsible for this odd outcome is illustrated below.  A robust trough over Alaska brought chilly and wet conditions to most of the state, but the setup was conducive to above-normal sunshine over the northern Bering Sea and southern Chukchi Sea, and it seems that helped boost temperatures in the northwest.  I think there was also an element of chinook/downslope warming over the Seward Peninsula and near Kotzebue Sound, as winds from the northeast passed over the Brooks Range and then warmed on their way back down to sea level.

Winds were stronger than normal across the North Slope and much of the interior and south of Alaska:

Courtesy of the wonderful toolset at the Iowa Environmental Mesonet, here's a comparison of the May 2026 wind rose (top) compared to the long-term normal wind rose for May (bottom) in Utqiaġvik:

While easterly or east-northeasterly winds are always heavily favored in Utqiaġvik at this time of year, the regime was even more persistent, and with stronger winds, than normal this year (compare the frequency of winds in the 15-20 mph category).

For the climatological spring season as a whole (March through May), statewide average temperatures were the lowest since 2013, mostly because of March.  In the south it was the coldest spring since 1972 in the NCEI data from Bristol Bay to the mid-Panhandle, including Anchorage (and since 1974 in Juneau).

Wet and cloudy were also major themes from South-Central to the northern interior; but the bright side, of course, is that an early start to fire season was avoided.