Lakes in Southern Ohio
National Weather Service Forecast Office - Cleveland OH
Harold J. Keeney and Erik S. PytlakNational Weather Service Office - Cincinnati OH
Correlations are established between occurrences of El Niño/Southern Oscillations and climatic changes in the Ohio Valley and southern Great Lakes region of the United States. During El Niño winters, considered November to March in this study, temperatures usually averaged above normal, while precipitation averaged below normal. Using these correlations, long range weather forecasts, and activities dependent on such forecasts, can be adjusted accordingly.
The phenomenon of sudden warming of the tropical Pacific ocean off the coast of Peru is known as El Niño. This phenomenon occurs roughly every three to seven years, and was once considered a local fluctuation affecting only the coasts of Peru and Ecuador.
Today, the effects of El Niño on world climate are known to be more widespread. Although the El Niño/Southern Oscillation (ENSO) phenomenon is well documented (Trenberth, 1990), the relationship of the ENSO to mid-latitude surface temperatures and precipitation are not covered extensively in the literature (Ropelewski and Halpert, 1986).
The effects of ENSO on world climate are widespread and highly variable. The pattern of ocean temperatures in each event and how the El Niño episode evolves plays a crucial role in weather occurrences across the globe. Some global effects most frequently observed during an ENSO event are: wet conditions during the winter in the southeast United States, drought in eastern Java, southern Peru, and Australia, plus, generally warmer than normal winters in the northwest portions of the United States and Canada (Knox, 1992, Ropelewski and Halpert, 1986).
Ropelewski and Halpert in their 1986 study evaluated North American temperature and precipitation response to ENSO based on a statistical method utilizing the coherence of harmonic vectors. In that study, no clear ENSO response was found in their Mid-Atlantic region that encompasses the area of concern in this study. However, they concluded that the lack of a consistent ENSO response does not rule out the possibility of ENSO-related phenomena. The reason for the inconsistent ENSO response in the Ohio Valley and lower Great Lakes is uncertain. However, weak ENSO events could be masked by other climatic variables such as volcanic eruptions or long term wet and dry cycles (Waters, 1991).
The dynamic response of the atmosphere to an ENSO event has been addressed in many previous studies. Trenberth, in his 1990 study, concluded that the change in diabatic heating can change global general circulation patterns and associated poleward heat flux. A mid-latitude response to ENSO forcing is further supported by theoretical and modeling studies of the circulation (Hoskins and Karoly, 1981, Webster, 1981, Blackmon et al, 1983). Since poleward heat flux is most pronounced during the cool season, winter temperatures and precipitation in North America would most likely be impacted the most by any changes in the circulation pattern.
Therefore, the November-March period of El Niño years in the mid-latitudes would most likely exhibit the most significant ENSO response. Consequently, the focus of this study was primarily on this time period. Indeed, the data set for this period does seem to indicate an ENSO climatic response in the Ohio Valley and southern Great Lakes.
Climatological data covering the last eight ENSO events beginning with 1957 was collected in order to determine whether the climate of the Ohio Valley and southern Great Lakes was impacted by ENSO. Seasonal snowfall, plus temperature and precipitation departures from the mean covering November through March were studied.
Climatological data from 17 first-order FAA reporting stations in Indiana, Kentucky, Ohio, Pennsylvania and West Virginia were collected. The specific stations utilized in the study included: Akron-Canton, OH; Charleston, WV; Cleveland, OH; Cincinnati, OH; Columbus, OH; Dayton, OH; Erie, PA; Evansville, IN; Fort Wayne, IN; Huntington, WV; Indianapolis, IN; Lexington, KY; Louisville, KY; Pittsburgh, PA; South Bend, IN; Toledo, OH; and Youngstown, OH.