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10/16/2018, 5:02 am EDT

Month 1-3 Ahead U.S. Climate Forecast Valid NOV-18 to JAN-19

Weak El Nino Modoki still in the forecast BUT a roaring stronger conventional El Nino likely to emerge by late winter. Winter forecasts are trending warmer. Executive summary: The winter forecast dilemma is whether to bias the upcoming El Nino forecast for winter 2018-19 toward a Modoki event when equatorial East Pacific warming is biased toward the Dateline OR a full-tilt conventional El Nino when Pacific warming is centered farther east. The difference in the U.S. climate pattern is HUGE! If the Modoki style pattern emerges the West will be warmer/drier while Southeast/East is stormy and colder. The conventional El Nino is simple…anomalous warmth much of the U.S. Previously, the Climate Impact Company forecast was biased toward the Modoki solution which favors a warm start to winter but goes cold in the East in January and February as El Nino warming shifts toward the Dateline. The forecast trend is more in the direction of the warmer conventional El Nino. In the updated forecast the December forecast is adjusted somewhat warmer and is warmer than normal for most of the U.S. The previous forecast of cold across the East in January is eased back. The Climate Impact Company winter outlook was quite cold in February. The adjusted winter outlook issued in later October is likely to ease that cold February signature. In summary, a weak El Nino Modoki-style remains in the forecast into mid-winter. However, the trend is for a more conventional El Nino which could be quite strong yielding a milder end to winter 2018-19. Heating degree day discussion: The 2018-19 cold season gas population weight HDD forecast for the U.S. is adjusted a little colder for November although directly in-between the 30-year and 10-year normal and colder than the last 2 years. The December outlook is adjusted warmer from 817 to 804 which is also in-between the 30-year and 10-year normal. December 2018 will not be as chilly as last year. The mid-winter forecast is adjusted warmer from 986 to 968 which is slightly warmer than the 30-year normal and much colder than the 10-year normal. If El Nino is more conventional the January forecast could be somewhat warmer. The February forecast is anticipating the warmer El Nino influence going from 811 to 792 HDD with additional warmer changes possible. A warmer revision is expected if conventional El Nino evolves in early 2019. The March outlook is adjusted warmer from 615 to 593.   NOV 2018 DEC 2018 JAN 2019 FEB 2019 MAR 2019 Forecast 533 804 968 782 593 Previous 527 817 986 811 615 Last Year 535 875 958 702 662 2016-17 461 863 839 600 604 2015-16 486 640 937 711 495 30-Year 589 885 991 793 649 10-Year 490 766 867 757 540  Table 1: The CIC gas population weight HDD forecast for the U.S. cold season compared to both the 10-year and 30-year normal table. Fig. 1: The CIC gas population weight HDD forecast for the U.S. cold season compared to both the 10-year and 30-year normal graph. November 2018: The late autumn outlook is adjusted colder in the Great Lakes to Ohio Valley region due to the influence of near to above normal snow cover near and to the north-northeast of this region. The anomalous warm pattern is adjusted slightly farther west with strongest warm anomaly over the northwest Great Plains. The Gulf States to the East Coast is adjusted wetter and Texas is cooler due to persistent cloudiness (and rain). Dryness in the West expands and includes all of California. Fig. 2-5: The Climate Impact Company month ahead forecast for November 2018. The previous forecast is below. December 2018: Early winter looks warm as El Nino onset becomes established. Mild Pacific influence is dominant. The forecast is adjusted warmer and the core of that warmth becomes established over the Upper Midwest assuring any early season snow melt is likely to dissipate. The Southeast/East Coast storm track remains firm with much above normal precipitation in Louisiana to Alabama. California is in the face of the El Nino Pacific storm track and observes a stormy early winter. Fig. 6-9: The Climate Impact Company 2 months ahead forecast for December 2018. The previous forecast is below. January 2019: The previous outlook was quite cold in the East fearing El Nino Modoki which typically produces a warm West U.S. ridge and downstream cold trough in the East. However, signs of a more conventional El Nino are increasing and the mid-winter forecast is adjusted less cold in the East and additional warmer adjustments are increasingly possible. Fig. 10-13: The Climate Impact Company 2 months ahead forecast for January 2019. The previous forecast is below.