Sunday, November 6, 2022

Cold High Pressure

A strong ridge moving across the Bering Sea and western Alaska since Friday has produced very high pressure at the surface for interior and eastern Alaska, and so, like clockwork, we have cold in the valleys, with strong temperature inversions.

Here's the MSLP chart from 3am AKST this morning:

In Fairbanks the airport reported MSLP of 1050.2mb at 6am, which according to Rick Thoman is "just shy of the November record of 1051.4mb set in 2010".  Interestingly, 2010 had a number of similarities to this year in terms of global climate, including a strong La NiƱa with a negative Indian Ocean Dipole in autumn, and terrible monsoon flooding in Pakistan in late summer.  It may be no coincidence that we're seeing a similar weather event for Alaska at the moment.

Rick commented on the 2010 MSLP record at the time:

Here's an animation of the 500mb ridge progression from Friday morning to Tuesday morning (predicted):

Not surprisingly, temperatures dropped off impressively last night, with -20s seen widely in the valleys of the eastern interior.  As usual the coldest spots around Fairbanks-land were Goldstream Creek (-20°F), UAF Smith Lake (-23°F), and North Pole (-24°F).  Farther afield, the CRN site southeast of Northway reached -29°F and Chicken saw -31°F.

The morning sounding from Fairbanks shows the hefty inversion, and indeed the temperature hasn't dropped below 0°F at the higher elevations around Fairbanks (Cleary Summit, for instance).


Surprisingly, the Yukon is not yet frozen upstream at Dawson:

Below is a chart of temperatures over the last two weeks at Smith Lake on UAF's North Campus, illustrating the sharp drop-off yesterday.  Note too the difference between the blue and green lines: blue shows the temperature at 8m above ground, and green the temperature at the standard 2m above ground.  A difference of about 5°F is typical on clear, calm, cold nights, demonstrating how shallow the strong surface-based inversion is in these particularly cold locations.


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