Serious Warmth and Ice Decline

As advertised in recent posts, warmth has become pronounced and widespread in Alaska this week, and yesterday saw the temperature rise all the way to 70°F in Utqiaġvik - a fairly rare event, especially this late in the season.  The last time 70°F was reached in Utqiaġvik was more than two years ago (August 6, 2024), and this is only the third time it has happened in August this century (2023 and 2024 being the other years).  The latest on record for such warmth is August 24, 1979.

Far to the southeast, Juneau also set a daily record high yesterday, at 80°F.  This isn't quite as unusual, although again it is pretty late in the season; it's only been this warm this late in the season in 5 other years out of the last ~75 years of climate data.  The latest on record is - not coincidentally - August 23, 1979.

On a statewide basis, UAF's aggregated and standardized temperature index shows yesterday being the warmest day relative to normal since October last year - see below.  The latest daily index value of +9.4 indicates that yesterday was warmer than about 97% of all days in terms of standardized departure from normal - again, a fairly rare extreme.  Time will tell as to whether this month's sudden reversal from unusually cool to unusually warm will be sustained, but this is certainly a change from the persistent character of the last 8 months.

The map below shows the sea-level pressure anomaly that has prevailed in the last two weeks.  With high pressure over Alaska and low pressure near the Arctic coast of Siberia, warm southerly flow has been pulled up across the Bering Sea and into the Arctic.

The result?  Sea ice extent has been dropping very rapidly in the Chukchi Sea this month.  At the end of July it was well above normal - a significant anomaly compared to recent years - but it has now dropped to near the 1991-2020 normal.

Beaufort Sea ice has seen much less decrease and remains well above normal and close to last year's extent.  It will be very interesting to see whether or not the next few weeks see a rapid decrease like last year.

The Northern Sea Route appears to be on the verge of opening up; the NSIDC sea ice index has shown an open passage in the last few days, but the NWS ice analysis suggests there are still patches of heavy ice on both sides of Wrangel Island.  Compare the two perspectives below:

The comparison illustrates some of the uncertainty in ice cover analysis.  For NSIDC, ice extent is defined as the area with at least 15% ice coverage, and the NSIDC data shows this boundary being well north of Wrangel Island all the way across to well north of Point Barrow.  In contrast, the NWS analysis shows 4-6 tenths or higher at lower latitudes around Wrangel Island, in the mid-Chukchi Sea, and to the west of Uqiaġvik.  The two products serve different purposes and differences are to be expected, but this illustrates the challenge of characterizing the "true" state of affairs.