Colder Temperatures Forecast for Winter of 2001/2002
Report submitted by Jim Mihell, Sept 23, 2001
As you may recall, last year about this time, this site reported on a prediction made by NOAA (The United States National Oceanic and Atmospheric Administration) that the winter of 2000/2001 would be roughly "normal" in terms of temperature. This was good news to us skiers, as the past several years had been anything but "normal". In fact, to many, last years' winter may have seemed colder than normal, because it was so much colder than the previous few winters. Nevertheless, climatologically, when compared to pre-90s data, it was pretty much normal.
This year, NOAA has predicted a colder than normal winter for our region for 2001/2002.
Figure 1, below, shows temperature departures from normal predicted for North America for the coming winter. In this Figure, regions outlined by red lines represent regions that are predicted to be warmer than normal, while those outlined by blue lines represent regions that are predicted to be colder than normal.
For the Sault area, colder than normal winter temperatures are associated with heavier snowfall, since the cold air moving across Lake Superior enhances lake effect snow.
Figure 1: NOAA's Predicted Temperature Departures (From Normal) For Winter, 2001/2002
NOAA's seasonal forecasts are primarily based on observations of sea surface temperatures, such as the Pacific Equatorial Sea Surface Temperatures (associated with the well-known "El Nino" and "La Nina" phenomena), and the less famous "Arctic Oscillation" (AO) or "North Atlantic Oscillation" (NAO) sea currents.This year, the primary factor that is predicted to influence the winter weather for our area is the NAO current. In a nutshell, when the NAO is in what is termed a "positive" phase, winters in our area can be expected to be warmer than normal, while when it is in a "negative" phase, winters in our area can be expected to be colder than normal (all other things being equal). Just what phase the NAO is going to be in from one year to the next is not terribly predictable, however, the "positive" and "negative" phases tend to go in cycles of 2-3 decades, where either the "positive" or "negative" phase predominates. As can be seen from Figure 2, we are currently leaving a "positive" NAO phase that has predominated since the early 70s, and in fact, NOAA's scientists are predicting that this year will see a "negative" NAO event that may mark the beginning of a prolonged period of colder than normal winters for our area. Of particular interest to our area, the predominant blue spike that is clearly seen in this Figure in the late 90s was considered by many as a prelude of things to come. This prominent "negative" NAO event coincided with the winter that saw the Station Mall and Algoma Steel roofs collapse under the weight of snow.
Figure 2: Long-Term Cycle of NAO Sea Currents
Meanwhile, while Pacific sea surface temperature phenomena, such as El Nino and La Nina are thought to be unrelated to the phase of the NAO, fate would have it that a similar flip-flop in long-term sea surface temperatures in the Pacific seems to be conspiring to do the same thing, reinforcing the "negative", (i.e., "colder than normal") NAO phase. Like the NAO in the Atlantic, this shift suggests that we have entered a cool water phase in the eastern Pacific similar to what we observed several decades ago (see Figure 3).
Figure 3: Long-Term Trends in Equatorial Pacific Sea Surface Temperatures
Historical data suggests that warmer than normal water dominated in the eastern Pacific from 1925 to 1947. This favoured more La Ninas and fewer El Ninos. A cool phase, which scientists believe we have now begun, favours more La Ninas and fewer El Ninos. This scenario is generally associated with cooler temperatures and more winter snowstorms.
What does this all mean? Despite all the press that global warming has been getting lately, the general long term warming trend can easily be overridden in shorter terms by other powerful drivers of climate. In short, perhaps we should stock up on that green wax while supplies last.
For more reading, supporting a colder, snowier winter for us in 2001/2002, here are some links to climate sites:
NOAA Climate Prediction Center Seasonal Outlook for Winter 2001/2002
http://www.cpc.noaa.gov/products/predictions/90day/lead04/index.html
Why Large Scale Changes in Both the Atlantic And Pacific May Signal a Climate Shift
