September really kicks off the the rainy season in Yakutat, with an average September rainfall of 21.11" (536mm), However, this year not only was the 3.17" (81mm) the second lowest of record, but absolutely no rain at all fell for 20 consecutive days between September 2 and 21. This is the longest streak of no rain at all of record in Yakutat at this time of year, breaking the previous record of 17 days set September 28 through October 14, 2016.
Thunder is unusual anytime of the year in Anchorage, but when storms do happen it's mostly during the summer months. However, on September 24 there was widespread thunder in the Anchorage urban area, accompanied in many areas by gusty winds and small hail. This was the first September thunderstorm reported at the Anchorage airport since 2005 and the latest in the season since the thunderstorm of October 04, 2006.
While much of the Interior saw no snow in September, several inches fell over the higher elevations of the Yukon-Tanana uplands on the 22nd and 23rd. Eagle Summit on the Steese Highway northeast of Fairbanks, at 3600' (1100 m) had to be plowed on the morning of the 23rd as up to five inches of snow accumlated. Such snowfalls are normal at less elevations in late September.
The high temperature of 61°F (19°C) at Nome on September 30 is not only a record for the date, the previous record being 52°F (11°C) set in 1969, but is easily the warmest temperature so late in season. The previous latest date it had been this warm was September 24, 1976. Climate observations have been made in Nome with very few breaks since December 1906.
The high temperature at Seward of 76°F (24°C) on September 12 and 13 are the highest temperature of record so late in the summer. Previously, the latest date for the temperature to exceed 75F was September 10, 1910.
Several inches fell along the north side of the Brooks Range along Dalton Highway from Atigun Pass to Sag River DOT Camp on September 23rd. This is not unusual, as snow is the predominate precipitation type in this region by the last week of September, but does mark a later than average start to the snow cover season.
Ketchikan received just 10.50" (267mm) of rain during the late summer season. This is only 35% of normal and the third lowest July through September rainfall total of record. Only 1989 and 1965 had less rain during the same three months.
The temperature in Nome remained above freezing every day in September except for the 26th, when the temperature dipped to 31F (1C). The long term average for Nome is ten September days to see temperatures at or below freezing.
Recent years have seen very warm late summer and early autumn ocean surface temperatures to the Bering Sea, and as a result land areas close by have also been warm. At Cold Bay, the three mildest Septembers have occurred since 2014. This year, the average September of 51.0°F (10.6°C) was second only to the 51.2°F (10.7°C) reported in 2016.
As the days get shorter rain regularly changes to snow in the northern Interior during the second half of September, even if it's just flurries. That was not the case this year at Bettles, where there was no snow at all; the first September to record zero snow since 1997.
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