Climate Outlook for Fall and Early Winter
Contributed by Bradley McLamb
The outlook for fall and early winter is a complicated one due in part to the below-normal confidence in the evolution of the El NiÃ±o-Southern Oscillation (ENSO) during this time. Computer models have indicated for several months that an El NiÃ±o event — which features warmer-than-normal sea surface temperatures (SSTs) across the central and eastern equatorial Pacific — would develop heading into fall, and would have direct impacts on temperature and precipitation patterns across the southeastern US. However, after a period of warming during late summer in the ENSO region of the Pacific, sea surface temperatures have actually begun to cool.
Sea surface temperature anomalies for August 6, 2012 (left) and October 1, 2012 (right)
Imagery courtesy of NOAA/NESDIS
Despite the cooling of SSTs over the past two months, a weak El NiÃ±o still appears to be developing and could remain through early winter based on the general consensus of the ENSO forecast models, which would increase the likelihood of below-normal temperatures and above-normal precipitation across the Southeast throughout the period.
If El NiÃ±o conditions develop, what would it mean for North Carolina in terms of wintry precipitation? Comparing all ENSO winters since 1959 to the predictions for winter 2012-13, three winters stand out as close matches: 1969-70, 1976-77, and 2004-05. Each featured a weak El NiÃ±o with SST anomalies of approximately 0.7 to 0.8Â°C, quite similar to those predicted for the upcoming winter.
Sea surface temperature anomalies for October through March 1969-70 (top left), 1976-77 (top right) and 2004-05 (bottom)
Imagery courtesy of NCEP/NCAR
After analyzing the mean SST anomalies for these three winters, it appears the 1969-70 El NiÃ±o event is the closest match to what is forecast for the upcoming winter. The winter of 1969-70 brought below-normal precipitation and snowfall to North Carolina; however there were also several cold air outbreaks with temperatures well below-normal.
Any forecast for the upcoming season will have below-normal confidence due to the uncertainty in the equatorial Pacific. However, current information does suggest that a weak El NiÃ±o will likely remain in place through early to mid-winter, which could result in increased precipitation and below-normal temperatures for the next few months. In addition, an early season snowfall cannot be ruled out for the Southeast, and is more likely statistically-speaking when looking at the three winter cases previously mentioned, which all featured December snow.