10/15/2020, 3:12 pm EDT

Southern Company November 2020 to March 2021 Outlook

Cold risk for January Otherwise Milder/Drier Than Normal Executive summary: A La Nina winter climate is forecast across the Southeast U.S. for winter 2020-21. Historically, a La Nina winter is warmer and drier than normal in the Southeast U.S. However, due to regional climate conditions unique to the past decade, the Southeast U.S. has risk of at least some cold weather this winter season most likely in January which is forecast colder than normal for Southern Company. The unique climate conditions favor above normal North America winter snow cover which enables cold air masses to travel south to the Gulf region. In February, snow cover retreats toward Canada and the Southeast States end meteorological winter with very warm temperatures. The outlook indicates dryness for the winter season. Southern Company should plan on potential drought conditions by early next spring increasing the risk of following summer anomalous heat. Fig. 1-2: The Southern Company temperature and precipitation probabilistic forecast for the 2020-21 cold season. Climate discussion: ENSO expert Australia Bureau of Meteorology confidently forecasts a strong La Nina for winter 2020-21 (Fig. 3). Typically, a Southeast U.S. winter climate pattern during La Nina is mild and dry (Fig. 4-5). A drought condition for the next spring across the Southeast U.S. is likely to emerge. Fig. 3: The Australia Bureau of Meteorology ENSO forecast reveals an intense La Nina ahead peaking in December. Fig. 4-5: Historically, the DEC/JAN/FEB La Nina climatology favors anomalous warmth and (mostly) dry climate across the Southeast U.S. Other leading factors include a projected very warm northeast Pacific Ocean surface (Fig. 6). The area of warmth is semi-permanent and referred to as the “warm blob”. This feature has dominated the northeast Pacific Ocean since 2013-14 and is well-correlated with presence of an upper ridge pattern across or just west of the North America West Coast during wintertime and compensated for by a downstream upper trough (i.e. polar vortex). We’re not expecting a “polar vortex” winter similar to 2013-14 or 2014-15. However, the pattern is likely present during mid-winter and causes extensive snow cover to enable cold outbreaks which can infiltrate the Southeast States. Therefore the January forecast is colder than normal across the Southeast U.S. If the expanding snow cover fails, the regime is much warmer across the Southeast. Fig. 6: The ECMWF global SSTA forecast for January 2021 indicates the northeast Pacific Ocean “warm blob” and the correlating upper air pattern/risk to Southern Company. The Southern Company winter 2020-21 forecast: The outlook is based on a constructed analog which considers La Nina, the warm SSTA in the northeast Pacific and western North Atlantic basin(s). In November, there is cold risk to the Northeast U.S. due to above normal snow cover across Ontario and Quebec. A few chilly days are likely across Southern Company but mostly the chilly air stays to the north and the prevailing climate is warmer and much drier than normal (Fig. 7-8).  The December outlook is quite mild across Georgia but not quite as anomalous warm in Alabama. Early meteorological winter is mostly drier than normal. The January outlook is marginally colder than normal. Above normal number of mornings <32F is likely for January (Fig. 9). Keep in mind the cold January outlook is based on a mid-winter southern advance of snow cover across the Ohio Valley possibly touching the Ohio Valley. In February, the snow cover retreats and the Southeast U.S. is very warm to end meteorological winter. The month of March is mostly very dry with near normal system temperature. Fig. 7: The Southern Company SYSTEM temperature anomaly forecast for NOV-20 to MAR-21. Fig. 8: The Southern Company SYSTEM precipitation anomaly forecast for NOV-20 to MAR-21. Fig. 9: The Southern Company number of days <32F forecast for meteorological winter 2020-21 compared to last year for Southern Company locations. The Southern Company winter 2020-21 forecast summary: Expect a warmer than normal winter season ahead EXCEPT for mid-winter when January is marginally colder than normal. The month of February is likely to reverse very warm. The winter outlook is drier than normal and a drought pattern may emerge by early next spring. Fig. 10: The Alabama gas population weight HDD forecast for NOV-20 to MAR-21 compared to the last 3 years. Fig. 11: The Georgia gas population weight HDD forecast for NOV-20 to MAR-21 compared to the last 3 years. Addendum: The Climate Impact Company Monthly Climate Forecasts for Winter. November 2020: The projected upper air pattern pushes the “warm blob” inspired northeast Pacific upper ridge westward to the Aleutian Islands with a downstream upper trough just-off the southwest B.C. coast. East of the trough an amplified upper ridge is dominant and brings a very warm month of November to the Southwest and Interior West U.S. to the western Great Plains and Texas. In the East an un upper trough persists off the coast leaving the Mid-south, Southeast and Northeast Corridor drier-than-normal. A cold polar vortex develops over northern Canada where snow cover is above normal. In that cold air source region, there are occasional cold air masses released into the Northeast U.S. Fig. 12-13: The Climate Impact Company constructed analog November 2020 temperature and precipitation anomaly outlook December 2020: The building advections snow into northern and central Canada during November spread to Quebec and parts of New England and certainly the Great Lakes region in December. Some of the chilly Canadian air backs into the Northwest at times. Due to snow cover the Interior Northwest, Upper Midwest and Northeast U.S. are colder than normal to start meteorological winter. The “warm blob” inspired northeast Pacific ridge is just off the West Coast of North America blocking the Pacific storm track and leaving California dry. The Southwest and Florida are very warm in December. Fig. 14-15: The Climate Impact Company constructed analog December 2020 temperature and precipitation anomaly outlook January 2021: Interestingly, the “warm blob” inspired northeast Pacific ridge shifts west again – to the western Aleutian Islands while an upper trough anchors off the B.C. coast. The upper ridge over the Southwest U.S. remains. A weak upper ridge affects the Northeast States during mid-winter. The result is periods of marginally wet weather on the West Coast while most of the West stays very warm. A coolish pattern evolves over the Southeast likely caused by cold outbreaks from Canada which modify south of snow cover. New England is snowy (away from the coast) during January. Mid-south U.S. dryness persists. Fig. 16-17: The Climate Impact Company constructed analog January 2021 temperature and precipitation anomaly outlook February 2021: In February a “polar vortex” regime establishes over central to northeast Canada. The related cold – which features widespread artic air will back into Western Canada to the northern U.S. Rockies. The February chill is expansive across a widespread deep snow cover. However, as impressive as the Canadian polar vortex regime is projected a just as impressive typical of La Nina Southeast U.S. ridge pattern also develops. The result is very warm temperatures over the Southeast and the cold/warm air mass clash leads to major precipitation events in the Mid-south U.S. extending northeastward. Anytime arctic air clashes with warm air masses freezing rain and icing occurs and that weather risk is significant in February for the Ohio Valley to New England. In the West, dryness returns to California as the Pacific storm track is blocked. Fig. 18-19: The Climate Impact Company constructed analog February 2021 temperature and precipitation anomaly outlook March 2021: The March outlook is least confident for the 2020-21 cold season. Projected is an upper trough off the Northeast U.S. Coast which causes a chilly regime in the Mid-Atlantic and Northeast States. The Southwest U.S. ridge continues and an extremely warm month of March is expected for Texas and vicinity. The Ohio Valley is stormy (again). The “warm” blob inspired northeast Pacific ridge pattern is across and south of the Aleutian Islands. A downstream upper trough brings wet weather to California. Fig. 20-21: The Climate Impact Company constructed analog March 2021 temperature and precipitation anomaly outlook.