Executive summary: The Climate Impact Company winter 2023-24 forecast is issued. The outlook for DEC/JAN/FEB 2023-24 is warmer than normal in the East and near to colder than normal in the West-central U.S. An energetic storm track is forecast for the Southeast/East U.S. while California and Texas are drier than normal. The forecast trend is colder West-central States and drier in California. The outlook is based on the presence of an El Nino climate and influences of warm SSTA in the North Atlantic mid-latitudes and a marine heatwave in the Northeast Pacific. An El Nino winter typically floods Canada with mild Pacific air lowering the risk of arctic air development. Extreme cold risk during winter 2023-24 is below normal. Fig. 1-2: The Climate Impact Company constructed analog winter 2023-24 temperature and precipitation anomaly outlook. Climate: A complete description of climate factors generating the winter 2023-24 outlook is in the season 1-3 ahead climate discussion. A summary of leading predictors follows. ENSO: El Nino developed in June 2023 and has steadily intensified since that time. However, the attendant El Nino climate is much slower to form. Oceanic El Nino peaks during mid-winter. Once meteorological winter arrives, a full-tilt El Nino climate is underway. AMO/PDO: The North Atlantic basin observed the warmest year on record and the anomalous warm surface is likely to continue during the winter season. Consequently, record-strength positive phase Atlantic multi-decadal oscillation (+AMO) is ongoing. In the Northeast Pacific, a large marine heatwave (MHW) is present. MHW NEP23A is forecast to stay just offshore the West Coast. Waters southwest of California are cool. Described is a persistent negative cool phase of the Pacific decadal oscillation (-PDO). The tendency of warm SSTA off each coast increases the risk of high-pressure ridging forcing a cold trough in-between across the West-central U.S. justifying the colder forecast for winter in that region. OCN: The evolution of warming mid-latitude oceans as demonstrated by the emergence of MHW’s has caused winter climate to average warmer than normal during the past decade. Consequently, the warm bias of the recent climate commonly referred to as optimum climate normal (OCN) is added to the forecast. Northern oceans: Snow cover will govern anomalous cold weather presence during winter 2023-24. The constricting polar ice cap leaves open ocean water on the north coast of North America and Eurasia during OCT/NOV/DEC and as the atmosphere cools due to lack of sunlight, cold wind across the open water leads to ocean effect snow which can bury the northern continent in early season snow setting up the potential for regions of cold air to gather and persist. This early winter tendency is not a sign of mid-winter cold risk. However, early season cold outbreaks can occur. Regardless of ENSO, the early season cold risk is present and close monitoring for northern continent snow is necessary. Solar activity: During winter 2002-03, 1993-94, and 1982-83 sudden stratospheric warming (SSW) episodes formed causing the troposphere (where weather occurs) to contract and cool leading to arctic air generation. Arctic outbreaks into the U.S. were observed. The SSW events are linked to solar flares which when strong enough cause ionosphere disruption leading the warming of the stratosphere below. Solar activity triggering SSW events is more likely during an active period of the sun which has developed during the past 1-2 years. SSW events causing arctic outbreaks occur regardless of ENSO. Forecast methodology: The outlook covers the cold season (November 2023 to March 2024). The forecast is based on a constructed analog which considers all climate factors previously listed. Highest emphasis is given to ENSO followed closely by the SSTA regimes as defined by PDO, AMO, and MHW’s. The influence of solar activity has the lowest influence. As confidence is gained with the arrival of winter, snow cover presence and trend are added to the forecast. November 2023: The late autumn forecast trend is warmer across the Southwest, West-central U.S., and into the Great Plains. The previously indicated chilly pattern for November is cut back with a cool anomaly over the Ohio/Tennessee Valley(s) only. The storm track eases as the East-central States shift drier and wet weather is confined to Florida to the Carolinas for late autumn. The West U.S. trend is warmer, and the Northwest remains mostly dry. Fig. 3-4: The Climate Impact Company temperature/precipitation anomaly climate forecast for November 2023. December 2023: El Nino climate influence on early meteorological winter is traditionally warmer than normal. This year, December is mild for the Great Plains eastward to the Atlantic Seaboard. However, the mild weather is accompanied by a lot of rain, especially in the Southeast States. Mixed precipitation has tendency to shift toward mostly snow in the Midwest by late month. The northwest quadrant of the U.S. is colder than normal due to above normal snow cover in Western Canada likely to extend into this region of the U.S. Fig. 5-6: The Climate Impact Company temperature/precipitation anomaly climate forecast for December 2023. January 2024: Mid-winter continues to look mild. Pacific westerlies are dominant and arctic air outbreaks are not indicated. The mid-winter forecast is adjusted wetter in the Southeast U.S. and the northern fringe of the stormy weather is likely snow and ice. Areas effected are Arkansas/Missouri eastward to the Interior Mid-Atlantic States. Given the lack of cold air delivery, snow on the ground is likely short-lived in the southern locations. Given the mild climate across northern areas, below normal snowfall/snow cover is expected. The California forecast is adjusted less wet and the Northwest trend is drier for mid-winter. Fig. 7-8: The Climate Impact Company temperature/precipitation anomaly climate forecast for January 2024. February 2024: Gathering cold just-after mid-winter in Canada is expected and the release of that chill into the Central U.S. is likely. Arctic air is possible, but the risk is average to slightly below average. The East is likely to stay milder than normal at the end of the winter season. In February, the Central cold/mild East clash will generate a potent storm track featuring heavy rains for the Southeast to Coastal Mid-Atlantic States and increasing risk of significant snow from the Mid-south States and across the Ohio Valley to the Northeast States. Fig. 9-10: The Climate Impact Company temperature/precipitation anomaly climate forecast for February 2024. March 2024: The cold season ends with additional mild climate in the East which is unchanged from the previous outlook. However, the West stays cold likely due to above normal late season snow cover although the Northwest States are quite dry. Storminess shifts from the Southeast during winter to the East-central States and features some snowfall on the west/north section. The East Coast finishes the cold season with a dry climate. Fig. 11-12: The Climate Impact Company temperature/precipitation anomaly climate forecast for March 2024. DEC/JAN/FEB 2023-24 HDD forecast: The high population areas of the East U.S. can expect below normal heating demand for meteorological winter 2023-24. However, the West and Central U.S. are likely to observe normal heating demand for the upcoming winter season. Fig. 13: The Climate Impact Company constructed analog HDD anomalies for DEC/JAN/FEB 2023-24.