Saturday, July 3, 2021

Big Rain in the Northwest

A lot of rain has fallen above the Arctic Circle in northwestern Alaska this week, courtesy of strong westerly flow circulating around a deep upper-level low to the north of Alaska.  The high-quality CRN site near the Red Dog mine (940' elevation) reported a remarkable 4.0 inches of rain in the last 3 days of June:

NWS estimates (see below) suggest that more than 6 inches may have fallen in some spots, but I'm not sure if any ground-truth measurements came in that high.  Here's one list that the NWS provided:

Regardless of the highest amounts, this was a very significant rain event over a large area, including the interior North Slope.  Click to enlarge:

The 500mb analysis from Tuesday afternoon (see below) shows the strong Arctic low, and notice the contrast with the extremely strong ridge over southwestern Canada.  All-time heat records were shattered in Oregon, Washington, and British Columbia, including an outrageous 121°F in southern BC on Tuesday (by far Canada's highest observed temperature of all time).  There was certainly a dynamical connection between the two features - the ridge and the Arctic trough - and the large amplitude of the overall flow anomaly helps explain the extreme rain outcome in northwestern Alaska.

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