The 1997 El Niño: Potential effects in Michigan - November 1997 to April 1998

Climate Prediction Center (CPC), NWS/NOAA

Updated 17 November 1997

We are currently in the midst of a strong El Niño (warm) episode, which is forecast to continue through February-April 1998. During this period the tropical ocean surface temperatures are forecast to remain comparable in magnitude and areal extent to that of 1982-83, which is considered to be the strongest warm episode of this century. In contrast to the 1982-83 El Niño, which caught the country by surprise, the present El Niño was predicted several months in advance. This improvement in climate prediction is the direct result of intensive research efforts by NOAA and its partners during the last 15 years. Part of this research effort, which is still ongoing, has been devoted to determining the effects of El Niño on temperature and precipitation patterns in the U. S. and globally. Some results of this research for your state are discussed below.

The information on state impacts is derived by looking at what has happened in those years during the past century during moderate to strong El Niño episodes. Three types of products are included. The first consists of U.S.-wide maps of average precipitation rankings during El Niño epsiodes for the November-December and January-March periods. El Niño impacts vary with season. The second product gives the change in precipitation probabilities by season. The Climate Prediction Center of NOAA makes seasonal forecasts for precipitation probabilities in three categories: the wettest 1/3; the near normal 1/3; the driest 1/3. The probability of getting any one of these three categories would be equally likely in the absence of El Niño. Probabilities of being wetter or drier than normal can be dramatically changed by El Niño. The third set of figures converts the average rankings shown earlier to per cent of normal precipitation and precipitation totals. These figures include what took place in 1982-83 as a plausible scenario as to what might happen since the present El Niño is not an average event. These two estimates give a range of precipitation totals that might be expected. However, because of the probabilistic nature of the forecasts, the range could be greater.

Historically, moderate to strong El Niño episodes have featured above normal precipitation (about 120% of normal) over the southern half of the state during November-December and drier than normal conditions over the entire state (70-90% of normal) during January-March. During the 1982-83 episode much wetter than normal conditions were observed during November-December, with excess precipitation of 2 to 5 inches over the lower peninsula. Near normal precipitation was recorded during January-March 1983.