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02/21/2019, 3:18 pm EST

North America Season 1-3 Ahead Outlook

Outlooks for spring, summer and autumn 2019 Summary: The Climate Impact Company season 1-3 ahead climate forecasts are updated and valid for spring, summer and autumn 2019. The outlook is based on presence of weak El Nino, regional warm SSTA off each coast and the soil moisture regime ahead of the warm season. The spring outlook is confidently projecting a warmer-than-normal pattern in the West while Texas and Louisiana are wetter-than-normal. The entire U.S. is projected warmer-than-normal during summer with hottest risk in Texas, the Northeast and Northwest. Most of the U.S. is warmer than normal in the U.S. Climate discussion: The outlooks are generated by a constructed analog. Given the uniqueness of climate in recent years added methodologies include incorporation of optimum climate normal (OCN) and influence of unique regional SSTA regions. A constructed analog is simply the current ENSO regime retrogressed 12 months to find similar character in the Nino34 SSTA. Given the change in the long-term cycles of ENSO, Pacific decadal oscillation (PDO) and Atlantic multi-decadal oscillation (AMO) in the 1990’s analog years are generally selected from the past 2-3 decades only. OCN is the 10-15 year climatology rather than the conventional 30-year climatology given the steady annual warming of the global climate. Regional SSTA have become an important predictor for portions of continents often with residual downstream affects. Large areas of warm SSTA tend to support warming subtropical ridging while cool SSTA regions support presence of a cool semi-permanent upper trough. The current global SSTA pattern (Fig. 1) indicates 5 regions which will have influence on the U.S. climate. Of course, ENSO leads the charge although direct impacts on North America climate during the warm season by an ENSO regime are not nearly as strong as during winter. ENSO is trending into El Nino now and all dynamic/statistical models, on average keep a weak El Nino going for much of 2019 (Fig. 2). Regional warm SSTA are located in the Gulf of Alaska and southwest of California. The question is whether these warm zones spread into one-another signaling warm phase of the PDO for 2019. Dynamic models increase the warming but further diagnostic evidence is required to increase confidence on that call. For now, CIC projects a weak +PDO for 2019. Presence of this feature increases risk of a western North America upper ridge pattern. Off the East Coast of the U.S. a semi-permanent warm SSTA zone continues and is expected to remain in-place for 2019. Influence on North America climate is increased risk of an upper ridge across the Southeast/East U.S. or just offshore. The ridge is held in-place by an expected semi-permanent upper trough over a cool pool south of Greenland. The constructed analog forecast is based on the presence of warm SSTA off each coast of the U.S. and weak El Nino to project the season 1-3 ahead climate. The analog years indicating presence of weak El Nino through the warm season coupled with warm SSTA off the west coast of North America and East Coast of the U.S. include 2005 and 2015. Also considered in the warm season forecast is the influence of soil moisture. Currently, a large portion of the Central and East U.S. is observing soil moisture in the 95 to 99 percent wettest in the 1895-2019 climatology (Fig. 3). Historically, taking from the past 2-3 decades of climatology (for JAN/FEB) the super wet late winter soil moisture condition across the U.S. is similar to 2016, 2010, 2005 and 1998. Interestingly, each of these analog years found an El Nino-driven climate to produce the wet soil regimes and later that year El Nino was gone and La Nina was developing. A La Nina later in 2019 is not out of the question. Combining the group of analog years (above) 2005 is weighted twice and 2015 once to produce the base analog forecast. 2016, 2010 and 1998 are eliminated due to the strong La Nina that developed and not expected in 2019. As previously indicated OCN is also averaged with the analog years. Fig. 1: The global SSTA weekly analysis by NCDC/PSD and regions having influence on the North America climate for 2019. Fig. 2: A collection of dynamic and statistical ENSO phase forecast models using Nino34 SSTA indicates weak El Nino ahead. Fig. 3: The daily soil moisture anomaly observations based on ranking using the 1895-2019 climatology is indicated. DEC/JAN/FEB 2018-19 verification: Most winter outlooks were biased cool in the South U.S. due to an anticipated weak El Nino episode. Other factors outweighed the influence of ENSO on the U.S. climate pattern during winter especially an unusually strong polar vortex delivering historic cold to the Midwest and West U.S. in February. The warm SSTA off the Southeast U.S. coast biased the southeast quarter of the nation very warm. The combination of strong upper level features including the February polar vortex combined with persistent warmer than normal ocean water either side of the continent also lead to a wet/white winter leaving U.S. soil moisture abundantly wet as meteorological winter concludes. The winter 2018-19 temperature anomalies so far (Fig. 4) are more representative of a La Nina climate compared to an El Nino climate (Fig. 5-6). Fig. 4-6: The Dec. 1, 2018 to Feb. 19, 2019 U.S. temperature anomalies compared to winter El Nino and La Nina temperature composites. MAR/APR/MAY 2019: Forecast confidence INCREASES as weak El Nino is more confidently forecast and the influence of late season snow cover and wet U.S. soils causes the outlook to be less anomalous warm than previously issued. That’s the trend the constructed analog should present. During spring the clear warm zone is the West U.S. despite the cold/snowy end to meteorological winter. Occasionally, the warmth stretches across the central Plains. Canada and the Northeast U.S. are adjusted cooler to near normal. The Gulf region is temperate with above normal cloudiness and rainfall expected most obvious over Texas. Wet weather also affects British Columbia. Fig. 7-8: Climate Impact Company constructed analog climate forecast for meteorological spring 2019. Previous forecast below. JUN/JUL/AUG 2019: Forecast confidence is about average. The concern is that the Great Plains, Midwest to Appalachian region could be cooler due to the wet soils in this area entering the summer season. Anomalous heat in the Northwest is confidently forecast and a fairly significant warmer change. The East U.S. remains hotter than normal although less extreme than previously indicated. The slightly less hot outlook is likely caused by widespread wet soils entering the summer season. Not quite as hot but the East is likely very humid this summer season. The precipitation outlook favors anomalous dry climate across the western Great Plains and Texas plus Florida. The dryness in Texas suggests at some point during summer the heat could become extreme. The only wet zone is confined to the southwest Tennessee Valley. The East-central U.S. forecast is not nearly as wet as previously indicated. Fig. 9-10: Climate Impact Company constructed analog climate forecast for meteorological summer 2019. Previous forecast below. SEP/OCT/NOV 2019: The autumn outlook is warmer than normal except temperate in the Southeast U.S. Forecast confidence on the temperature outlook is above average while the precipitation outlook is clearly made with below normal confidence. Of interest is where the wet anomalies are in regard to potential tropical cyclone activity which is off the East Coast and Mexico. Fig. 11-12: Climate Impact Company constructed analog climate forecast for meteorological autumn 2019.