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12/11/2018, 3:30 pm EST

U.S. Month 1-3 Ahead Climate Outlook

Changeable JAN/FEB outlook but anomalous cold most dominant Executive summary: The open Norwegian Sea north of Europe warms the polar atmosphere causing the polar vortex to split and depart the northern latitudes. The blocking pattern favors returning cold and snow to the East U.S. Warming from El Nino will battle this pattern so expect a lot of volatility. Climate discussion: The strongest positive phase of the arctic oscillation on record was observed in 2018. +AO indicates the polar vortex is stronger than normal and located far north, near the North Pole. As summer ended and autumn began the far northern latitudes cool due to rapidly diminishing sunlight. The stronger than normal polar vortex made the atmosphere colder than normal. The cold polar vortex generating chilly air across the open water just south of the polar ice cap in the northern latitudes produced a lot of snow spreading south across Canada leading to the second-most anomalous snow cover for the month of October on record. Once vast snow cover across Canada developed the North American continent cooled (relative to normal) leaving the warmest environment in the northern latitudes across the Norwegian Sea to the north of Europe. The warmth across this open ocean area lead to anomalous high pressure blocking in the far northern latitudes forcing the polar vortex to split with one center shifting south over North America and causing the already plentiful snow cover to shift farther south in November leading to the snowiest late autumn in the 1967-2018 record. In December, Pacific warmth inspired by Madden Julian oscillation and an emerging El Nino cause the U.S. to lose the impressive snow cover. Can the cold pattern regenerate? New snow cover will be needed to do so. Fig. 1-2: Since June the polar vortex has been near the North Pole and creating early season chill to cause expansive snow cover (left). In November the polar vortex spilt and shifted south expanding snow and cold (right). Fig. 3-4: The record North America snow cover (left) and 15-day warm-up ahead (right) likely to melt a lot of the record snow cover. Heating degree day discussion: The CIC population weight HDD forecast for the NOV-18 to MAR-19 cold season is adjusted sharply colder for January from 952 to 985 which is very close to the 30-year normal. February remains very close to the 30-year normal. Each month is much colder than the 10-year normal. The December forecast was adjusted slightly warmer from 850 to 848.   NOV 2018 DEC 2018 JAN 2019 FEB 2019 MAR 2019 Forecast 637 848 985 786 607 Previous 637 850 952 788 618 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. 5: The CIC gas population weight HDD forecast for the U.S. cold season compared to the 10-year normal. Forecast discussion: The forecast is based on an ENSO-analog featuring a high confidence weak-to-moderate El Nino for meteorological winter 2018-19 and followed by at least some decay of El Nino beginning in March (Fig. 4). Fig. 6: CIC ENSO analog forecast using Nino34 SSTA. January 2019: The outlook is adjusted colder anticipating a cold start and end to the month with a warm-up in-between. A pattern featuring both warm and cold extremes. However, mid-winter snow cover increases enhancing cold risk. The storm track lay across the Southern U.S. to the Mid-Atlantic States featuring southern latitude snow events. Fig. 7-8: The Climate Impact Company month ahead forecast for January 2019.  February 2019: The outlook remains cold in the East anticipating above normal snow cover. New England coastal snow storms are expected. The West-central U.S. is adjusted for more snow and rain. Fig. 9-10: The Climate Impact Company 2 months ahead forecast for February 2019.  March 2019: Mature El Nino brings a warm climate pattern across the northern states while the South U.S. is cooler than normal. Storminess reigns in New England while the western Plains to Texas are also wetter than normal. Fig. 11-12: The preliminary Climate Impact Company 3 months ahead forecast for March 2019.