The 1997 El Niño: Potential effects in Virginia - 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 that featured 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 episodes for the November-December and January-March periods. El Niño impacts vary with season. Although El Niño may have an impact on Virginia precipitation, historically there has not been a consistent response. Similar U.S.-wide maps of average temperature rankings during El Niño episodes for the December-February and February-April periods follow. The second product type gives the change in temperature probabilities by season. The Climate Prediction Center of NOAA makes seasonal forecasts for temperature probabilities in three categories: the warmest 1/3; the near normal 1/3; the coldest 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 warmer or colder than normal can be dramatically changed by El Niño. The third type of figure converts the average rankings shown earlier to average temperatures and a departure from average. This estimate gives a temperature that might be expected based on historical data. However, because of the probabilistic nature of the forecasts, the range of the average temperature could be significantly warmer or colder.

Historically, moderate to strong El Niño episodes have featured an increased frequency of occurrence of near or slightly below normal temperatures over the state during February-April. During seven moderate to strong El Niño episodes temperatures averaged 1-2 degrees Fahrenheit below normal across the entire state. During five of the seven moderate to strong El Niño episodes selected, all but the most northern climate division of the state experienced February-April temperatures which were among the coolest third of the 102 years of record.