Model simulation of high-pressure ridge over Alaska in the first five days of October. (WeatherBell.com)

Alaska is experiencing some of the sunniest, warmest and driest early fall weather it has ever seen. In Anchorage, for example, temperatures have remained above normal for 32 straight days, and it’s hardly rained.

Some are “loving it,” while others — concerned about what it might signify — are terrified.

The cause is a massive area of high pressure at high altitudes, also known as a ridge, which formed over the Bering Sea in early September and drifted eastward, sprawling over the 49th state. Outside of winter, such intense high-pressure cells are synonymous with heat as they cause the air to sink, compress and warm.

Scientists who study the region’s weather have never seen a high-pressure zone like this one. “On a 2-3 week time scale, the recent ridge over the Bering Sea was one of the most intense on record, anywhere in the world, when compared to the usual climate of the region,” tweeted Richard James, a meteorologist who has documented the event on his blog.


Analysis of the statistical rarity of the massive high-pressure ridge over Alaska averaged over the last three weeks. (Tomer Burg)

On Saturday afternoon, Fairbanks’s pressure about three miles high reached its greatest intensity on record so late in the year, James wrote.

Because the oceans have warmed over the region where this high-pressure zone has formed, its strength is probably connected to climate change. While a warming climate is known to bring harmful effects to Alaska’s infrastructure, food supply and way of life, this particular weather pattern is an example of how climate change might occasionally support some beneficial effects.

Brian Brettschneider, a climatologist based in Anchorage, described the recent sunny, dry conditions as a “Goldilocks scenario” for southern Alaska. “We’ve had amazingly sunny conditions nearly all month,” he said. “The perception is that it has been the best September ever. Everyone’s loving it.”

Brettschneider explained that because of abundant water reserves around Anchorage, the long, dry period has “no downside risk.” He contrasted Alaska’s experience to that of California, where “when it doesn’t rain, it’s a big concern.”

Unusually warm, dry and sunny weather has not been confined to Anchorage, which notched its warmest September on record, but has appeared in many other parts of Alaska and eastern Siberia:

  • Fairbanks posted warmer than normal temperatures for the last 20 days of September, and Nome for the last 22 days.
  • On Sunday, King Salmon hit 71 degrees, its warmest temperature so late in the season.
  • Bethel, Alaska, failed to observe any low temperatures below freezing in September for only the fourth time on record.
  • Chukotka, Siberia, posted its warmest September on record, with an average temperature nearly 11 degrees above normal, tweeted Francois Jobard, a meteorologist in Paris.

The weather pattern has also shut down snowfall in the state. Normally, during September, interior Alaska sees its first snow, “even if it’s just flurries,” tweeted Rick Thoman, an Alaskan meteorologist who recently retired from the National Weather Service. “This year, no snow at lower elevations. For Fairbanks, this is the first September since 2010 without any snow at all.”

While the weather has proved favorable in most parts of Alaska, the lack of rain has pushed one of the state’s rainier locations, Ketchikan in Southeast Alaska, toward severe drought conditions.

“Given Southeast Alaska’s profligate use of water — for hydroelectric dams, drinking water reservoirs, fisheries, fish processing and more — anything less than normal can have widespread consequences,” the Juneau Empire explained early in the summer.

“The weather has been truly terrifying this year,” tweeted Peter Stanton, a Ketchikan resident, gazing out over clear blue skies:

In an Oct. 1 blog post, James called the warm, dry spell “extraordinary” and showed webcam images of cloudless skies all over the state.

In his analysis of the intensity of the responsible high-pressure zone, James found that it was 5.2 standard deviations above normal. “We’d expect this kind of anomaly to occur less than once every million years, on average (for this particular date window),” James wrote, under the assumptions that the climate is static (which, of course, it is not) and his analysis is correct.

On his blog, James attributed the massive high-pressure zone to typhoons in the western Pacific Ocean and “far warmer” than normal water temperatures in the Bering Sea.

When typhoons in the tropical Pacific are drawn north by the jet stream and pass in the vicinity of Japan, they help transport heat toward the North Pole, pumping up high pressure ridges like hot air injected into a balloon. At the same time, “unusual ocean warmth probably helped boost the overall warmth of the atmospheric column and build the ridge in the same area,” James wrote.

The abnormally warm ocean waters are probably linked to a loss of sea ice in the region, which has occurred as the region’s climate has warmed. The National Oceanic and Atmospheric Administration announced Monday that Arctic sea ice reached its annual minimum Sept. 23, tied for the sixth-lowest on record. Last spring, sea ice levels in the Bering Sea had fallen to their lowest level on record as enormous pulses of heat surged into the region.

More generally, as global temperatures have risen, so have atmospheric pressures. So what’s happening in Alaska is consistent with long-term trends.

While the effects of this recent high-pressure ridge over Alaska have been mostly positive, such ridges can and often do have adverse consequences, depending on where and when they set up.

Exceptionally strong high-pressure zones that formed this summer, often referred to as heat domes, spurred the “planetary heat wave,” which resulted in an onslaught of all-time-high temperature records.

In a number of places, such as Japan and Montreal, the record heat was linked to scores of fatalities.

These intensifying high-pressure zones are also the culprit for “ocean heat waves,” which scientists say are wreaking havoc on marine life.

California’s severe drought several years ago was similarly linked to a “ridiculously resilient ridge.”

The high-pressure cells not only affect the weather underneath them but also have implications for surrounding weather systems.

In fact, it was an unusually strong zone of high pressure parked to the north of Hurricane Florence that steered it into the North Carolina coast rather than out to sea.

Over the next 10 days or so, the latest abnormally potent high-pressure ridge will mean a sustained period of summerlike heat over the eastern United States. Whether that’s a positive or a negative depends on one’s perspective.

Meanwhile, the forecast for Fairbanks is for nothing but blue skies over the next five days.