Heating Up

After a summer that has generally been on the cooler and wetter side for many in Alaska so far (except in areas close to Canada), things are heating up.

Much of the North Slope has been well into the 70s and even low 80s Fahrenheit in the past few days, with Umiat reaching 82°F yesterday, and Utqiaġvik reached a rare 74°F on Wednesday: the warmest since 2009.  Rick Thoman also noted that Wednesday's daily mean temperature of 63.5°F tied the highest on record in Utqiaġvik, with only one previous day matching that level of warmth: July 13, 1993, when the all-time high temperature of 79°F was recorded.

A heat wave is also now unfolding for the interior, with both Fairbanks and Eagle predicted to reach 90°F tomorrow, according to the NWS.  This would be the first 90°F reading in Fairbanks since 2017; there have only been 36 such days in the 93 years of Weather Bureau/NWS data.  (Eagle already reached 91°F earlier this month, on the 7th.)

It's actually fairly late in the summer for Fairbanks to see this kind of heat: in the past, 80% of the 90°F days have occurred before July 15.  The latest on record was August 15 (2010), and the earliest was May 28 (1947).  The median date is June 25, which is a little before the early July seasonal peak in average temperature: it's more common to get very dry and warm weather earlier in the summer rather than later, when clouds and humidity are more abundant.

Here's a view of all 90+°F days in the Fairbanks climate record since 1930.  No trend in frequency is immediately evident, although it's slightly notable that the past 30 years have seen only a handful of such days.

The location of the official climate observing site has changed over time, so it's interesting also to look at data from the UAF farm.  It seems that before about 1970, 90°F was observed in fewer years, but when it did happen there were typically two or more days with such heat.  However, this is probably related to the time of observation, which seems to have typically been around 5pm in the earlier years - and therefore close to the time of maximum warmth, allowing the highest temperature to be recorded as the max for two consecutive days.

Here's the upper-air setup for the impending heat wave: a strong ridge near the Alaska-Canada border by Sunday afternoon, with associated clear skies, subsidence, and widespread high airmass temperatures for much of northern, central, and eastern Alaska.