Climate Watch

By Rick Thoman Alaska Climate Specialist Alaska Center for Climate Assessment and Policy International Arctic Research Center/University of Alaska Fairbanks

NOAA’s Climate Prediction Center’s April outlook calls for an increased chance of above normal temperatures for western Alaska but favors neither above nor below normal precipitation.

The main factors for the outlook are the continuing but weakening El Niño and the near average sea ice extent in the Bering Sea in March. Over the past 117 years, temperatures in Nome have ranged from 60°F during the exceptionally warm April 1940 to a low of -30°F reached last year, as well as in 1968 and 1918.

April, along with March, is the on average the driest month of the year, and total precipitation (melted snow plus rain) has exceeded two inches only three times since 1907. Most precipitation during April falls as snow, but at low elevation significant rain does occur on occasion, especially in the second half of the month.

Days lengthen rapidly in April, and by the end of the month there’s still a hint of twilight on the northern horizon during the early morning hours. The longer days and higher sun are the primary contributors to April marking the transition to the western Alaska’s warm season, when eastern Norton Sound is typically warmer than the Bering Strait and St. Lawrence Island.

In the west, snow covered sea ice and tundra remain effective at reflecting back incoming sunshine to space, while in the east snowmelt and the edges of the boreal forest create a darker surface that more effectively absorbs the sun’s warmth.

Unsurprisingly, Nome falls in between, with temperatures rising more in April than in the Bering Strait but not as much as on the eastern Norton Sound coast.