Heat Wave

Now that the heat has receded a bit, let's look back at events of the last few days.

First off, the most notable aspect of the heat wave must be the sustained warmth in Utqiaġvik - it's been nothing short of remarkable.  For seven days in a row, the high temperature reached between 64°F and 74°F, resulting in a weekly mean high temperature of 67.6°F.  This is well above the previous record of 65.3°F for the week ending July 15, 1993.  The weekly mean low temperature was also a record, and the overall weekly average temperature smashed the previous record by more than 3°F.

Here are the warmest non-overlapping weeks in Utqiaġvik history, with mostly complete data back to 1902:

58.3°F   Week Ending July 24, 2023

55.2°F   Week Ending August 10, 1989

54.7°F   Week Ending July 15, 1993

54.2°F   Week Ending August 20, 2012

The record-breaking anomaly was undoubtedly caused by persistent offshore flow combined with an extremely warm continental air mass.  Here's a map of the 850mb height (pressure) anomaly for the week: note the twin ridges, one to the south of the Aleutians that funneled warm air up into Alaska, and one near the Mackenzie River delta, creating another warm influx to the North Slope from western Canada.

Looking at the balloon soundings from Utqiaġvik, the 850mb temperature peaked at 14.6°C, which is the warmest since 2018, and slightly behind the warmth of June 2013.

The profound warmth of the air mass is illustrated by the very high daily minimum temperatures, with many sites seeing low temperatures in the 60s °F.  The map below shows midnight-to-midnight lows for July 24 - the warmth across the western Brooks Range was particularly notable (click to enlarge).  A couple of days earlier, the Umiat RAWS reported a daily low of 62°F, the highest on record for that site (2008-present).

In the Fairbanks area, low temperatures were in the mid-60s on Monday, and the Chatanika RAWS only dropped to 71°F.  As for daytime heat, Fairbanks did reach 90°F (see my last post) on Monday, and the Ester 5NE co-op site near Fairbanks recorded 92°F; that's the highest temperature measured in Alaska so far this year.

Rick Thoman noted that the combination of heat and humidity in Fairbanks on Monday afternoon was the worst since at least 1950: at 5pm the temperature was 88°F, and the dewpoint was 62°F.

Based on the Fairbanks airport balloon sounding data, Monday's air mass was clearly the hottest in the vicinity since the notorious heat wave of late June 2013.  The 850mb temperature reached 17.8°C (versus 18.4°C in 2013), and the 1000-500-mb thickness reached 5688m (versus 5694m in 2013).  Here's what it looked like on Monday afternoon: a deeply heated continental sounding, but with quite a bit of humidity for such a northern location.