After an astonishing outbreak of wildfire in southwestern Alaska earlier this summer, the weather has changed dramatically. The past few days have been chilly, and this morning many locations around the Bristol Bay region were in the 30s, with some close to freezing - notably 33°F at the Aleknagik CRN near Dillingham and also at Koliganek. Also worth noting is the 31°F yesterday at the CRN site on St. Paul Island; this is the first sub-freezing temperature there in July since 2012.
Chilly start to Saturday in the Bristol Bay region of SW Alaska. Some river valleys down close to freezing, and a daily record low at King Salmon of 35F (+1.7C), previous record 39F (3.9C) set in 1970. #akwx @kdlgradio @Climatologist49 pic.twitter.com/bwQKjEFr6r
— Rick Thoman (@AlaskaWx) July 23, 2022
The mean daily temperature plot from Bethel (below) shows that the cool conditions are not as unusual as the heat was in early June. Nevertheless, yesterday's high temperature of only 49°F in Bethel is right at the lower end of what's been observed historically for the time of year: the daily record low maximum temperatures (i.e. coldest daytime highs) are mostly around 49-50°F from mid-July through mid-August.
The cool weather can be attributed to a very strong mid-level low pressure system that dropped down from the Arctic. The mid-atmospheric cyclone can be traced back to the central Arctic, and arguably it is THE summertime tropospheric polar vortex that moved down to the Bering Strait. Here's a simple animation of 500mb heights at 12-hour intervals since the beginning of the month.
The vortex has been extremely strong for the time of year, and remarkably it set new records for lowest 500mb height in the month of July for quite a number of locations from the central Arctic to the Bering Strait (based on ECMWF and ERA5 data).
As for the larger significance of such an event, random variability plays a large part in the formation of a feature like this, but I'll also note that the dramatically cooler weather is finally more reminiscent of a typical La Niña pattern for summer, as noted in this ill-fated blog post from early June.
http://ak-wx.blogspot.com/2022/06/wildfire-outlook.html
[Postscript: here's a photo of snow on Big Diomede island in the Bering Strait on Monday]
July #snow in the Bering Strait: flurries on Iŋaliq (Little Diomede), Alaska Sunday evening, and then a gorgeous Monday early morning view looking west to Big Diomede, Russia. Snow in July is unusual. Photo by F. Ozenna & shared with permission. #akwx @Climatologist49 @brdemuth pic.twitter.com/6UubAruUab
— Rick Thoman (@AlaskaWx) July 18, 2022
It seems like August in July for Interior Alaska. Windy-stormy-SW flow from a large Low to the west. The local Tanana Valley Fair starts next weekend earlier than usual. That tends to create Fall weather by coincidence. I wonder if we'll get a nice pre-winter during the next two months?
ReplyDeleteThat Polar Vortex generated an extreme cold front that left damage from high winds from the south then southwest in Interior Alaska. Reported winds 2000' AGL were 50 knots plus over Fairbanks. We had a huge healthy Spruce tree broken off mid-height that cut a power line. An amazing event for July.
DeleteBlog post coming up, hopefully. Thanks for the report.
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