I was asked to write a spring outlook for the North Dakota Climate bulletin which covers our past winter season in the state of North Dakota. I am posting my thoughts here as well:
The North American continent during the winter of 2009-2010 was dominated by two principle players; an El Nino in the central Pacific Ocean and a strong negative Arctic Oscillation. An El Nino occurs when the waters of the equatorial Pacific are warmer than normal. This extra heat energy into the atmosphere tends to enhance the sub-tropical jet stream making the southern tier of the United States cooler and wetter than normal, whereas the polar jet stream that impacts North Dakota tends to shift into southern Canada bringing above average winter temperatures and below average precipitation (snowfall) to the state.
Although the southern tier of the United States generally saw winter weather typical of most El Ninos, North Dakota and other northern states did not. Although in a complex atmosphere there are always numerous unknown reasons that could be players, one reason this area finished colder than would otherwise be expected could be blamed on a phenomenon referred to as the Arctic Oscillation (AO). The AO is a climate pattern characterized by winds circulating counterclockwise around the arctic. When the AO is in its positive phase, a ring of stronger winds circulating around the North Pole tends to keep the coldest air in the higher latitudes. In the negative phase of the AO, this belt of winds becomes weaker allowing arctic air to more readily move southward bringing bitterly cold air to the state.
In recent months the Arctic Oscillation has been strongly negative several times which not only impacted our weather, but also conditions throughout the lower 48 states. The Arctic Oscillation can impact seasons besides winter; it was a strong negative AO that helped produce the cold summers in 2004 and 2009 and could also be a player during the spring of 2010.
According to research being done by Rob Kupec a meteorologist at WDAY-TV in Fargo, ND as well as a graduate student at North Dakota State University, spring seasons in North Dakota when an El Nino is still present, like this year, tend to finish with slightly warmer than normal spring seasons. But a three-month average often means little if the warmer conditions come in March or early April before the planting season begins. Also, if the warmer Pacific Ocean does not fade by May, wetter than average conditions often arrive during the spring planting season.
These factors as well as the Arctic Oscillation continuing to be a player seems to be increasing the odds for the latter half of the spring being cooler and wetter than normal during the beginning of the growing season after the warmer than average start to the season.
The North Dakota State climate Office has links to the National Weather Service’s local 3-month temperature outlooks for the upper coming year. Those outlooks can be found here:
The latest spring outlook from the Climate Prediction Center is giving equal chances for the spring season to be either average, above average or below average for both precipitation and temperatures throughout the state and considering the wide weather fluctuations we will likely experience in the coming weeks, that seems to be a valid analysis.
Those outlooks can be found at http://www.cpc.ncep.noaa.gov/products/predictions/.