Climate Watch
By Rick Thoman Alaska Climate Specialist Alaska Center for Climate Assessment and Policy International Arctic Research Center/University of Alaska Fairbanks
An important factor for Alaska’s seasonal climate during the cold season is what is happening in the equatorial Pacific, because small changes in ocean surface temperatures there can modify the dominant location of the jet stream across the Pacific Ocean.
In turn, this can change the prevailing storm track near Alaska. El Nino is the name given when persistently warmerthan-normal ocean surface temperatures are found near the equator south and southeast of Hawai’i. The flip side of El Nino is La Nina, when significantly cooler-than-average temperatures are found in this same area (this was the case for the past three winters).
It turns out that in Alaska, the most consistent impacts during El Nino winters are found from about Anchorage and Fairbanks eastward, while there is more variability across El Ninos in western Alaska and the Aleutians. In coming weeks we’ll examine how El Nino winters have played out in Nome in regard to temperatures and precipitation.
This week, we’ll look at seasonal– September through June– snowfall during the 16 El Nino winters over the past 50 years. In the graphic I’ve plotted total snowfall during El Nino seasons relative to the average during non-El Nino winters. At first glance it appears that El Nino tilts the odds toward less snow than non-El Nino winters. But looking more closely, notice that the first eight El Nino, from 1976-77 through 1991-92 all had seasonal totals at or below the average for non-El Nino winters. But the eight El Nino winters since then appear to tell a different story, with basically even split between above and below average snowfall totals. This is not too surprising: El Nino is an important factor in our winter weather but it is not the only one, and the changes in sea ice and the large-scale warming of the global oceans are also important factors, and as we know, these features are quite different now than in the 1970s and 80s.
My take-away is that El Nino is not a useful predictor for seasonal snowfall for Nome. Next week we’ll see if El Nino is useful for constructing seasonal temperature outlooks in western Alaska.