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10/23/2018, 6:08 pm EST

Southern Company Winter 2018-19 Outlook

Highlight: Weak-to-moderate El Nino Winter Executive summary: The Climate Impact Company winter 2018-19 outlook features CLASSIC EL NINO WETTER-THAN-NORMAL climate for most of the cold season while temperatures are forecast warmer-than-normal on the front end of winter, near normal in January and COLDER-THAN-NORMAL in February. There is near normal risk of a few days of extreme cold during mid-winter. El Nino intensity is forecast weak-to-moderate. If El Nino is stronger than forecast the temperature outlook will be about the same although less risk of extremes while the precipitation outlook is wetter. After an El Nino winter no drought will be present over the Southeast U.S. next spring. The Climate Impact Company Winter 2018-19 Outlook Climate discussion: El Nino onset is forecast to arrive in November. An El Nino winter season ahead is certain. Less certain is the intensity of El Nino. Climate Impact Company is forecasting weak-to-moderate intensity of El Nino governing the winter climate forecast for Southern Company. The intensity of El Nino is important. The weaker El Nino episode forecast for the next 3-4 months implies that at times forecast factors other than El Nino southern oscillation (ENSO) will affect the Southeast U.S. climate. These factors include Madden Julian (MJO) oscillation or “Mojo” as referred to by the media due to the tendency of MJO episodes to produce extreme weather. Also possible given the weaker El Nino are stratospheric warming events which lead to high latitude arctic air development which can release into the Southeast U.S. If the El Nino is stronger than forecast the MJO is likely silent and influence of cold outbreaks from the northern latitudes into the Southeast U.S. suppressed. The weak-to-moderate El Nino means a wetter than normal winter season with near normal temperature but susceptibility to at least a couple cold outbreaks. A stronger El Nino would produce a wetter climate and less extreme cold risk. Fig. 1: The International Research Institute for Climate and Society collection of all ENSO phase forecasts through summer 2019. Fig. 2-3: Temperature and precipitation climatology of meteorological winter (DEC/JAN/FEB) across the U.S. Fig. 4: El Nino warming in the equatorial East Pacific is NOT impressive. Fig. 5: Immense subsurface warming in the East Pacific has been reluctant to reach the surface. Forecast: The Southern Company System cold season 2018-19 outlook is based on an ENSO analog, persistence and regional forecast factors. The analog years are 1994-95, 2006-07, 2009-10 and 2014-15. A brief description of what to expect each month of the cold season follows. November 2018: Forecast confidence is ABOVE average that a wet fetch out of the Gulf of Mexico will bring a wetter than normal late autumn to the Southeast U.S. Due to the wet pattern temperatures are generally suppressed averaging close to normal. December 2018: Despite onset in November the El Nino peak intensity follows soon after and causes a mild month across the U.S. to start meteorological winter. Forecast confidence is ABOVE average that typical El Nino storminess brings a wetter than normal December. There is minimal risk of any extreme cold. January 2019: In January there is susceptibility to 1 or 2 cold outbreaks mainly spawned by low latitude El Nino style storms. Temperatures average near to below normal for the month but expect a few mornings to drop into the teens. Precipitation is near to wetter than normal. Some snow is possible across northern sections. Forecast confidence is AVERAGE. February 2019: Late meteorological winter is CAUTIOUSLY forecast colder than normal in the East U.S. If El Nino is stronger the cold prediction for February will fail. The Southeast turns colder and drier to finish winter. March 2019: Forecast confidence is BELOW average. If El Nino continues with intensity the drier forecast for March will be wetter. Temperatures continue to average near normal for early spring. Fig. 6: The Southern Company System forecast temperature anomalies for the 2018-19 cold season. Fig. 7: The Southern Company System forecast precipitation anomalies for the 2018-19 cold season. Fig. 8: The Alabama gas population weight heating degree day forecast compared to the 30-year normal and past 3 winter seasons. Fig. 9: The Georgia gas population weight heating degree day forecast compared to the 30-year normal and past 3 winter seasons. Fig. 10: The projected number of days when minimum temperature is below 32F for each month of meteorological winter compared to observed values last winter. Fig. 11: The probability of minimum temperature in-between 13F and 20F forecast for December 2018. Fig. 12: The probability of minimum temperature in-between 13F and 20F forecast for January 2019. Fig. 13: The probability of minimum temperature in-between 13F and 20F forecast for February 2019. Fig. 14: The Climate Impact Company original winter 2017-18 system temperature anomaly forecast compared to verification. Fig. 15: The Climate Impact Company original winter 2017-18 system precipitation anomaly forecast compared to verification.