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Why Alaska's winter weather has been extreme but not abnormalSnow, wind and rain has been the rule so far this winter across much of Southcentral Alaska. Anchorage residents have been treated to generous snowfall, with plenty of strong winds along the western slopes of the Chugach. North Gulf of Alaska coast residents have been contending with copious snowfall since early December. With so much active weather over the past several months, many people wonder what’s going on. A look at the weather across the North Pacific and Gulf of Alaska this winter indicates that November was cold over most of the region as a slight eastward shift in the storm track allowed cooler arctic air to press farther south. Numerous storms tracked through the northern Gulf, which produced above-normal snowfall from Cook Inlet east. In December, most storms tracked through the central Bering and moved up the west coast. This occurred as a persistent high-pressure ridge dominated the eastern Gulf and western Canada. This pattern generated a strong pressure field along the northern Gulf and, consequently, windstorms along the slopes of the western Chugach Mountains. These systems carried moisture from the North Pacific. During the last week of December, the storm track shifted as the high pressure over the Gulf and Western Canada moved east. This allowed storms to move back into the Gulf, which they’ve done with a vengeance. There only were a few days between Dec. 22 and Jan. 12 without snow or rain along the North Gulf of Alaska coast. A particularly stormy winter, so farAre these normal weather patterns? Typically, patterns across Alaska persist for 10 to 15 days and before switching. A warm period of clouds, snow or rain might switch to a dry, cool period (we’re heading into one). Although the National Weather Service does not keep tabs on the number of storms that move through the region, December through early January was a stormy stretch, with the storms lingering longer than normal. Nevertheless, this is not what we would consider abnormal or extreme weather for this part of the world. Let’s look at other snowy winters in Southcentral Alaska for comparison. In recent decades, it was snowy in Valdez during the winters of 1989-1990, 1991-1992, and 1994-1995. This latter winter was also very snowy in Anchorage (third snowiest). The 1989-1990 weather pattern was similar this winter, while both 1991-1992 and 1994-1995 were subtly different. It’s important to keep in mind that different weather patterns can produce similar weather. This results from the rich nature of weather; for much of the year, it’s in flux. How does this fit in with the 10-15 day persistent patterns noted above? The only time the weather pattern is the same day-to-day is during high-pressure periods. Otherwise storms regularly move into the eastern Bering or Gulf -- and then onshore. In late December and early January, there were short breaks between storms that otherwise made for a three-week period of continuous storms. (Persistent) natural variabilityReturning to our original question, is this winter’s weather across Southcentral abnormal? There is no getting around the fact that the storm track has been persistent -- but not abnormal. Rather, it's well within the range of what meteorologists call natural variability. What's that? Think of it as the broad spectrum of weather patterns that occur over a period of time. A simplistic example in the short-term is the difference between the high and low daily temperatures. The temperature does not stay the same because of various factors -- heating by the sun, sea breezes, cloud cover, etc. The same factors, plus the temperature of North Pacific surface water, generate weather across the region. What impact is our current La Niña having? La Niña’s are defined as cooler-than-normal water in the central and eastern Tropical Pacific. This can produce large impacts over much of the Pacific basin. Typically, La Niñas favor a storm track that brings many storms into the Pacific Northwest -- which has not occurred so far this winter. Last winter was also a La Niña winter, and the Pacific Northwest’s rain and snow was normal, with considerable rain and snow moving down into the Sierra Mountains.
It is all fine and dandy talking about past weather. How about informing us if this pattern is going to continue throughout the rest of the winter? |
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