The long term average winter (defined as the months of December through February) temperature for Bismarck is 12.8 degrees, with January being the coldest at 8.9 degrees. In spite of this, temperatures are highly variable from year to year and even from day to day in North Dakota. So, average temperatures do not really tell the whole story. As an example, the coldest winter on record for Bismarck was a bone chilling -0.4 degrees during the 1886-1887 winter. Conversely, the warmest winter on record was 25.9 degrees, which occurred during the 1930-1931 winter. Note that these temperatures represent the average of the high and low temperatures.
As for snowfall, anywhere from 15.5 to 20.8 inches of snow occur during a typical winter (December through February). The average snowfall is 19.9 inches. However, this is highly variable from year to year. For example the Figure below shows that last winter we set the record with a total of 58.0 inches. In contrast, as little as 2.8 inches occurred during the 1900-1901 winter.
The long term average winter (defined as the months of December through February) temperature for Williston is 12.7 degrees, with January being the coldest at 9.0 degrees. In spite of this, temperatures are highly variable from year to year and even from day to day in North Dakota. So, average temperatures do not really tell the whole story. As an example, the coldest winter on record for Williston was a bone chilling -0.1 degrees during the 1935-1936 winter. Conversely, the warmest winter on record was 26.5 degrees, which occurred during the 1930-1931 winter. Note that these temperatures represent the average of the high and low temperatures.
As for snowfall, anywhere from 13.2 to 18.3 inches of snow occur during a typical winter (December through February). The average snowfall is 18.0 inches. However, this is highly variable from year to year. For example the Figure below shows that last winter we set the record with a total of 48.6 inches. In contrast, as little as 0.7 inches occurred during the 1930-1931 winter.
Winter 2009-2010 Outlook for Western and Central North Dakota
So what will the winter be like this year in North Dakota? Well, it appears the main player that will dictate temperatures and precipitation across the Northern Plains this winter will be the presence of a moderate El Niño. El Niño is considered to be the positive phase of the El Niño Southern Oscillation (ENSO). It is known for abnormally warm central and eastern tropical Pacific waters. This warm pool of water, normally confined to the western Pacific, alters the preferred placement of thunderstorm activity in the tropical Pacific. Thunderstorms can be thought of as the bridge between the ocean and the atmosphere. So, as thunderstorms develop over the warmer than average waters in the central and eastern tropical Pacific, when they otherwise would not, they significantly alter the atmospheric circulation, which in turn affects the seasonal weather patterns across much of the Northern Hemisphere. The figure below (courtesy of NOAA's Climate Prediction Center) shows the current conditions in the tropical Pacific. The reddish colors represent warmer than average sea surface temperatures. Note the orange and red colors straddling the equator in the Pacific. This is indicative of El Niño.
A second player to consider this winter is the phase of the Pacific Decadal Oscillation (PDO). The PDO is an ENSO-like oscillation in sea surface temperatures. However, there are two key differences between the two. First, the primary signal in sea surface temperatures is found in the Northern Pacific Basin. Secondly, the PDO has a period of variability of about 50-70 years, whereas the ENSO has a period of variability of 3 to 7 years. There are two different phases of the PDO; the positive and the negative phase. The figure below illustrates the differences in sea surface temperatures between the two phases. During the positive phase, colder than average western and central north Pacific waters are present, while warmer than average conditions are found in the eastern Pacific Ocean waters. Just the opposite is true during the negative phase.
Lately there has been research that suggests that the phase of the PDO can alter the effects of El Niño events. Specifically, it has been suggested that during the positive phase of the PDO, El Niño events tend to have a stronger impact on the average winter weather pattern across the United States, bringing very warm and dry conditions to the Northern Plains. However during the negative phase of the PDO, El Niño events tend to show a weaker influence on the seasonal weather pattern. While the PDO was in the positive phase during the 80s and 90s, more recently the PDO has shown signs of being in the negative phase.
Figure reproduced from: http://tao.atmos.washington.edu/pdo/
As mentioned above, El Niño events tend to bring much of the northern United States warmer and dryer than average conditions. So that means it is going to be a warm and dry winter right? Most likely this will be the case at least to some degree. So the next question is how warm and dry will the winter be? To answer these questions let’s look at some of the past years in which El Niño conditions were present. The tables below display the average monthly and seasonal departures from average for temperature and snowfall at Bismarck for past years in which El Niño conditions were present. The difference between the top two and bottom two tables are that the top (bottom) tables display El Niño events that occurred during the positive (negative) phase of the Pacific Decadal Oscillation (PDO). Notice that during the positive phase of the PDO monthly temperatures during the winter are consistently above average. In fact, in most cases they are much above average, especially during February. Of these 10 particular El Nino events, 8 of them produced winter that were much warmer than average, while the remaining two were near average. Differences arise during the negative phase of the PDO. Notice that although there is still a tendency to see above average conditions, the anomalies are reduced. The most interesting result is during the month of February. During the positive phase of the PDO the month of February was on average over 10 degrees above average, with all ten events producing much above average conditions. Conversely, during the negative phase of the PDO, El Niño events produced near average to slightly below average conditions overall, with 7 of the 11 events being below average. Overall, this indicates that during February a significant weather pattern change occurs during these negative PDO El Nino events, allowing cooler conditions to overspread the Northern Plains. This same behavior is not observed during positive PDO El Niño’s.
Although snowfall is quite variable during El Nino events, on average, they tend to produce below average snowfall during the winter. This is especially true during the positive PDO El Nino events during the months of December and January.
So, what does this mean for the winter of 2009-2010? Well overall it appears temperatures will be above average, especially during December and January. Now this does not mean that temperatures will be above average every day during these months. It simply means that the monthly average temperatures will be above average. During February, the weather pattern could change allowing colder air to spill in across the region, bringing below average temperatures for the month. This has been observed during several previous events, as mentioned above. It is important to keep in mind that even if the winter turns out to be warmer than average, there will likely be extreme day to day variability, with periods of cold and snowy weather. This is typical of North Dakota winters. We just might not see as much cold and snow as is normally expected.
*Note that this information is based on local research and does not represent the official forecast for western and central North Dakota.
The Official Forecast
The official forecast for the winter (defined as the months of December through February) issued by NOAAs Climate Prediction Center (CPC) is shown below. They are forecasting an enhanced chance of warmer than average conditions (eg., 40% chance for above average temperatures, 33% chance of near average conditions and 27% chance of below average conditions) for western and central North Dakota. For precipitation, CPC is forecasting equal chances for either above, below or near average for the area.