Scott A. Yuknis High impact weather forecasts, climate assessment and prediction. 14 Boatwright s Loop Plymouth, MA 02360 Phone/Fax 508.927.4610 Cell: 508.813.3499 ClimateImpact@comcast.net Climate Impact Company Summer 2018 Outlook for Southern Company Valid: May to September 2017 Issued: Tuesday, March 27, 2017 Executive summary: The Climate Impact Company summer 2018 outlook for Southern Company shows marginally anomalous warm temperature and a dry start to summer ending wetter than normal. The caveat is hotter. Summer 2018 Southern Company Temperature/Precipitation Forecast 1
Climate discussion: We are VERY concerned about EXTREMES regarding the 2018 summer outlook for Southern Company. The frequency of extremes is increasing during recent climate. During the last 12 months Birmingham, AL has unusually warm and cold periods (Fig. 1) including 14 days when precipitation has totaled more than 1.5 in. (Fig. 2). Fig. 1-2: Temperature extremes and many heavy rain days have been observed the past 12 months in Birmingham, AL. The Southern Company 2018 Summer Forecast is based on ENSO analogs using their consensus for the operational forecast but also identifying the cold/hot and wet/dry extremes as outlier or CAVEAT forecasts. The analog years used to generate the Southern Company forecast for the summer 2018 season are 1996, 2001, 2006, 2009 and 2012 favoring the trend toward weak El Nino (2006, 2009 and 2012) for mid-to-late summer. The analog 2
years represent a climate transition out of La Nina and into neutral ENSO into mid-2018 and a potential trend toward weak E Nino by late summer. The ENSO analog calculation is based on operational Nino index (ONI) which is a running 3-month average of the Nino34 SSTA most common for ENSO phase assessment (Fig. 3). Fig. 3: The Southern Company Summer 2018 Forecast is driven by ENSO analog years. A transition of the Nin34 SSTA index out of La Nina this spring and toward weak El Nino next autumn is favored. The late summer/early autumn projection is made with low confidence. Currently, global SSTA is mixed warm and cool in the middle latitudes with a lingering La Nina signature in the eastern equatorial Pacific Ocean (Fig. 4). The NOAA/NMME global SSTA forecast model indicates neutral ENSO and warming of the North Pacific and North Atlantic for JUN/JUL/AUG 2018 (Fig. 5). The SSTA forecast favors the warmer possibilities for the Southeast U.S. Neutral ENSO is a confident summertime forecast. Of potential (significant) added influence to the Southern Company Summer 2018 Forecast is the warmer than normal North Atlantic basin identified by the warm phase of the Atlantic multi-decadal oscillation (+AMO). On its own, +AMO increases risk 3
of summertime drought in the Southeast U.S. while also raising the risk of hurricane activity. A low certainty part of the forecast is can +AMO-induced drought risk be offset by risk of heavy rainfall due to an inland-moving tropical cyclone. Fig. 4: Current global SSTA analysis reveals a mix of warm and cool anomalies across the North Pacific and North Atlantic characteristic of a changeable mid-latitude climate while La Nina lingers in the equatorial East Pacific. Fig. 5: The NOAA/NMME global SSTA forecast for JUN/JUL/AUG 2018 indicates a warm-up for the North Pacific and North Atlantic basins while ENSO is neutral. 4
Soil moisture is a significant contribution summertime climate. Currently, drought conditions are affecting the Southeast U.S. (Fig. 6). Dry conditions in the Southeast U.S. are typical of a wintertime La Nina climate. La Nina weakens during the 2018 warm season. However, to reverse drought in the Southeast U.S. a wintertime El Nino is required OR remnants of inlandmoving tropical cyclones. Therefore the Southeast drought is likely to continue this summer season only changing of a tropical cyclone moves inland in the region. Fig. 6: The NOAA/USDA soil moisture analysis across the Southeast U.S. reveals a drought condition unlikely to change during summer unless a tropical cyclone moves inland. Forecast discussion: Based on the analog years mentioned a consensus forecast is displayed and the outlook for Southern Company is based on these charts. Of added important interest is the potential extreme. Given 5
presence of drought in the Southeast U.S. there is risk of a hotter than forecast regime. Using the analog years the warmest potential solution is also indicated as the caveat forecast to the operational outlook. 1. May 2018: A warmer than normal pattern is expected across the Southeast U.S. The hottest anomalies are across the Southwest U.S. beneath an upper level ridge pattern. The occasional upper trough pattern, producing showers is across the East and will produce wetter than normal weather across the east/south Georgia drought region in May. Fig. 7-8: Climate Impact Company constructed analog forecast for temperature and precipitation anomalies for May 2018 is indicated. 2. June 2017: The largescale drought across the Southwest U.S. continues to attract anomalous heat beneath high pressure ridging. The downstream effect is occasional presence of an upper trough producing a wet start to meteorological summer in the Northeast. Trailing the Northeast upper trough is occasional cool air masses which reach the Southeast States. At other times heat surging eastward from the Southwest U.S. source region is also present. The combination of the two opposing thermal regimes causes a normally warm start to summer in the Southeast U.S. The rainfall outlook is confidently drier than normal possibly causing Southeast drought to strengthen leading to a potentially hotter CAVEAT forecast. 6
Fig. 9-11: Climate Impact Company constructed analog forecast for temperature and precipitation anomalies for June 2018 is indicated. The warm extreme caveat forecast for the Southeast is added. 3. July 2017: The mid-summer outlook finds sprawling anomalous heat extending from the Southwest U.S. drought region throughout the West and into the Great Plains and Texas. Once again the susceptibility to wet weather suppressing mid-summer heat is in the eastern half of the nation although Georgia looks dry. There is potential for a tropical episode to affect the northwest Gulf States with the inland moving system dragging rains northeastward toward the Appalachian Spine. Due to the generally dry climate the Southeast CAVEAT forecast is potentially hotter. 7
Fig. 12-14: Climate Impact Company constructed analog forecast for temperature and precipitation anomalies for July 2018 is indicated. The warm extreme caveat forecast for the Southeast is added. 4. August 2017: The August forecast is made with low confidence due to uncertainty in a developing cool pattern over the North-Central U.S. The wet weather is caused by presence of an upper trough likely to invite tropical moisture out of the Gulf of Mexico causing wetter than normal climate across the Southeast U.S. The wetter regime suppresses late summer heat. If the rains fail a hotter CAVEAT forecast prevails. 8
Fig. 15-17: Climate Impact Company constructed analog forecast for temperature and precipitation anomalies for August 2018 is indicated. The warm extreme caveat forecast for the Southeast is added. 5. September: The late summer forecast widens heat suppressing rainfall stretching from Texas to the Ohio Valley. The rainfall is not likely associated with inland moving tropical cyclones. The Southeast U.S. is temperate with wet weather in Alabama. 9
Fig. 18-19: Climate Impact Company constructed analog forecast for temperature and precipitation anomalies for September 2018 is indicated. 6. Meteorological summer (JUN/JUL/AUG 2018): The Climate Impact Company meteorological summer temperature and precipitation outlook indicates hotter than normal conditions across the western half of the U.S., dryness in the Great Plains and a wet regime in the Northwest U.S. The NOAA forecast is similar except hotter in the Southeast U.S. with less widespread dryness sin the Central States. Fig. 20-21: Climate Impact Company constructed analog forecast for temperature and precipitation anomalies for meteorological summer 2018 is indicated. 10
Fig. 22-23: The NOAA Climate Prediction Center summertime 2018 probabilistic temperature and precipitation outlook are indicated. Southern Company forecast: The Southern Company Summer 2018 Forecast charts indicate a warmer and slightly wetter than normal month of May followed by borderline warmer than normal and anomalous dry months of June and July (Fig. 24-25). A wetter regime is expected in August and September suppressing anomalous heat. The Alabama and Georgia monthly CDD forecasts for summer 2018 are very close to the 30-year normal and somewhat less hot than the last 3 years (Fig. 26-27). The CAVEAT forecast is hotter and closer to the mean value of the past 3 summer seasons. The extreme heat forecast is also indicated (Fig. 28-29). The 2017 outlook was warmer than normal each month of summer while observed temperature was much more volatile averging near or cooler than normal in May, June and August and hotter than normal in July and September (Fig. 30). The precipitation outlook was drier than for July and August, near normal early summer and wette rthan normal in September (Fig. 31). Observed values were generally somewhat wette rthan normal. 11
Fig. 24: The Southern Company warm season SYSTEM departure from normal temperature for each month is indicated. Fig. 25: The Southern Company warm season SYSTEM departure from normal precipitation for each month is indicated. 12
Fig. 26: The Alabama gas home cooling CDD forecast for each month of the warm season compared to normal and the past 3 years. Fig. 27: The Georgia gas home cooling CDD forecast for each month of the warm season compared to normal and the past 3 years. 13
Fig. 28: The Southern Company forecast of days with maximum temperature exceeding 90F for the summer season compared to last year. Fig. 29: The Southern Company forecast of days with maximum temperature exceeding 95F for the summer season compared to last year. 14
Fig. 30: The Climate Impact Company original temperature anomaly forecast for summer 2017 versus observed values. Fig. 31: The Climate Impact Company original precipitation anomaly forecast for summer 2017 versus observed values. 15