October 2012 Synoptic Summary

Statewide Extremes
Highest Temperature 69°F at Annette Island in southern Southeast Alaska on the 7th
Lowest Temperature -26°F at Chisana in the eastern Alaska Range on the 31st
Highest Average 44.5°F at Metlakatla in southern Southeast Alaska
Lowest Average 13.0°F at Atigun Pass, elevation 4,739 feet, in the central Brooks Range
Most Precipitation 10.28 inches at the Snettisham Power Station in central Southeast Alaska
Most snowfall reported 25.5 inches at Haines Customs, in northern Southeast Alaska

The path of incoming North Pacific low pressure systems shifted to lay over the eastern Bering Sea for a good part of October. These lows brought a series of coastal storms to the west coast of Alaska during the first week of October. By October 10, the pattern was rearranged. High pressure built over the mainland of Alaska and Siberia. This allowed a series of lows passage through Alaskan Arctic waters to the Beaufort Sea. There was heavy surf on the Arctic coast of Alaska during the second week of October. From October 8-12, the airport runway at Kaktovik, on a barrier island about 150 miles east of Prudhoe Bay, was periodically in the run up zone of the waves.

On October 12-14, low pressure reestablished over the Gulf of Alaska. North winds blew down the Chukchi and Bering Sea coasts of Alaska, and at times through the Interior. More extensive snow pack and periods of mountain blizzard developed over the Interior and the Arctic from October 15 to 20. Onshore flow brought a week of rainy weather to Southeast Alaska from October 12 to 18. Starting on October 20, southwest flow resumed over the west coast of Alaska, and brought a few days of windy weather and high surf to that region.

On October 23, a stable period of weather began as high pressure built over the Interior. Temperature inversions formed in this environment, and an air quality alert was issued for Fairbanks on October 24.

Northerly, offshore winds blew over Southeast Alaska. Westerly winds blew over the

Arctic coast at times, but with little ill effect other than some high surf that did not surge much beyond its usual run up zone. There was no substantial change in the pattern through the end of October.

The periodic southwest winds over the Bering and Chukchi Sea coasts was balanced by frequent inflow of cold air from the Yukon to the Interior. The contrast between the Arctic and the Interior could hardly have been greater at this time of year. For October as a whole, much of the Arctic was from 8°F to 12°F above normal. At the same time, nearly all the Interior was colder than normal. Barrow's overall October temperatures were 10.3°F above normal. This was by far the warmest October at Barrow on record.

Above normal precipitation in the west and especially in the Arctic reflected the frequent inflow of Pacific maritime air from far beyond the Aleutians. There was also above normal precipitation – mostly in the form of snow – in the eastern and central Alaska Range. There was a small area of precipitation only 50 percent of normal midway along the Yukon River between Manley Hot Springs and Galena.

The real unusual feature of Alaska weather in October was caused by prolonged dry north winds over Southeast Alaska from October 23 onward. Such offshore winds rarely last more than a few days in Southeast Alaska, especially in late autumn. There was a large area where precipitation was only half as much as normal. This area included all of Southeast Alaska and the north coast of the Gulf of Alaska.

A remarkable period of record cold and dry October weather began throughout Southeast Alaska on October 26. Nearly every weather station in the region observed some record low October temperatures from October 26 to 31. Some of the new records were well beyond the previous marks. Precipitation and overall temperatures in Southeast Alaska for the month of October as a whole were below normal everywhere, sometimes by a lot. Temperatures over the length of the Inside Passage reached the teens and lower 20s on October 29 through 31.

Freeze up was well underway on many Interior and Arctic rivers in Alaska by mid October. The first ice on the Tanana and Chena Rivers near Fairbanks appeared suddenly on October 12. At the end of October, river ice in the Interior was typically three to seven inches thick and lake ice was mostly from eight to ten inches thick. This was thicker than it was at the same time in the year before.

At sea, gale force winds blew over Alaska waters for 28 days in October. The largest storm of the month was a 970 millibar (28.64 inches) low which crossed the eastern Aleutians on October 3 and moved slowly north to reach Bering Strait two days later. Due to both the strength of the wind as well as its long duration over the eastern Bering Sea, rough seas rose throughout the region until beginning to subside on October 6.

In the first week of October, the Beaufort and Chukchi Seas were completely free of ice over waters as much as 1,000 miles from the Arctic shoreline of Alaska. The edge of the ice pack then advanced during all of the second week of October, The advance accelerated rapidly during the second half of October. By October 24, shore ice had formed on all of the Alaska Arctic coast east of Point Lay. On October 31, the ice in the Chukchi Sea had reappeared within 100 miles of Barrow. In spite of the record low ice coverage in the Arctic Ocean in September, the waters off Point Barrow were not ice free very long in 2012.

Sea surface water temperatures were within 2°F of normal in the eastern Gulf of Alaska. In the western Gulf of Alaska and in most of the Aleutian Islands, sea surface temperatures were from 2°F to 5°F below normal. In the eastern Bering Sea waters, sea surface temperatures were typically 4°F to 8°F colder than normal, especially for those waters over the edge of the continental shelf.

Alaskan volcanoes were inactive during October. However, some volcanic ash did appear in the sky on October 30. A lack of snow cover and strong winds over the site of the 1912 Novarupta eruption on the Alaska Peninsula lofted ash about 4,000 feet up, and carried it across Shelikof Strait to Kodiak Island. No earthquakes of any significance occurred in or near Alaska during October. Several good aurora displays were observed in the first nights of October following a coronal mass ejection late in September.