El Nino Likely to Bring A Warmer Winter and Below Normal Snowfall to Upper Michigan

Although the Pacific Ocean is far away, the distribution of water temperature across the tropical pacific can influence the weather in Upper Michigan, especially during the cold season when that water temperature anomaly typically reaches peak intensity. During the latter half of 2009, water temperatures in this part of the Pacific Ocean have risen as much as 1 to 2 degrees above normal. This so called El Nino phenomenon results in a strengthening of the upper jet stream surging into western North America, which can have important impacts on the temperature and precipitation patterns across Upper Michigan and the rest of the United States. The current El Nino is considered a moderately strong event, and the Climate Prediction Center (CPC) is forecasting this moderately strong episode to persist through this coming winter.

Since 1960, El Nino’s of similar intensity have occurred during the winters of 1965-66, 1986-87, 1991-92, 1994-95 and 2002-03. The following table summarizes the temperature departure from normal and percentage of average snowfall observed at five locations across Upper Michigan in December through March during these moderate El Nino winters. Overall, the December through March period in these five winters turned out 2 to 3 degrees warmer than usual. Snowfall tended to be about 75 percent of normal.

           4-month mean temperature    4-month
             departure from normal    percent of
Location          (degree F)       normal snowfall

Marquette NWS        +2.2                 75

Houghton             +2.1                 69

Ironwood             +2.6                 79

Iron Mountain        +1.9                 67

Newberry             +2.0                 83

All 5 stations       +2.2                 75

Since the CPC indicates this moderate strength El Nino will persist through the end of this coming winter, they are forecasting a greater than climatological chance of an above normal mean winter temperature across all of Upper Michigan. Although CPC makes no forecast for snow, past moderate El Nino winters suggest seasonal snowfall this winter will be about 75 percent of average.

However, the El Nino influence is not the only factor that impacts Upper Michigan weather. If a blocking ridge develops from northern Canada into the North Atlantic Ocean and locks a trough with arctic air in place over southeast Canada and the Great Lakes, the weather pattern can favor cold weather even in the presence of El Nino. For instance, although December 2002 was quite warm with below normal snowfall, the weather turned much colder in January through March with this blocking pattern overwhelming the El Nino influence. February 2003 averaged 6 to 8 degrees colder than normal. Snowfall in January through March 2003 was also above average. In fact, residents of Newberry endured the snowiest January on record
in 2003.

Even if the winter is mild overall with below normal total snowfall, there can be periods of intense cold and heavy snow. The shorter term variability of weather could favor for at least a couple of weeks that blocking pattern which locks arctic air into the Great Lakes. For instance, heavy snow fell across much of Upper Michigan in February through early March 1995 with as much as 74 inches of the white stuff at Houghton in February when cold Canadian airmasses frequented the Upper Great Lakes. In fact, February 1995 goes down in the record books as the second snowiest February at Houghton. But snowfall at Houghton in December 1994 and January 1995 was so much below normal when the El Nino influence repeatedly pushed mild Pacific air into the Great Lakes that total 1994-95 seasonal snowfall ended up just 82 percent of average.

Despite this uncertainty, the expected persistence of warmer water in the tropical Eastern Pacific through this winter suggests the mean 4-month temperature for December 2009 through March 2010 will be above normal. Seasonal snowfall should be below normal.

Thirty year normals used are for the period of 1971 through 2000. All climate data listed in this product are unofficial. For official data please refer to the national climatic data center at www.ncep.noaa.gov/oa/ncdc.html.

Check out www.cpc.ncep.noaa.gov for more information about the climate prediction center and their long range predictions.

Visit www.weather.gov/climate/l3mto.php to access detailed local three-month average temperature outlooks for a number of sites in Upper Michigan.


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