09/12/2023, 12:48 pm EDT

Season 1-3 Ahead U.S.: Changeable winter, cool West/warm Northeast spring, and another hot Central/East summer of 2024.

Highlight: Changeable winter, averaging seasonably cold (except mild Northeast), cool West/warm Northeast spring, and another hot Central/East summer of 2024. Executive Summary: The North America season 1-3 ahead forecast is updated and valid for meteorological winter 2023-24 through summer 2024. The forecast is based on a constructed analog using primarily regional SSTA and historical correlation of upper air patterns to generate the sensible forecast. Winter 2023-24 is an El Nino winter. However, El Nino is (cautiously) forecast to weaken by Q2/2024. Forecast highlights include a seasonably cold winter except milder than normal across the Northeast. An energetic El Nino inspired storm track brings heavy precipitation for the Southeast/East U.S. and eventually snow for the northern fringe. Springtime is chilly in California while Northeast is warm and South-central U.S. the beneficiary of the spring storm track. Summer 2024 is hot once again for the Central and East U.S. with enhanced heat in drought areas which is likely to still include Texas. Climate discussion: The Climate Impact Company season 1-3 ahead outlook valid for DEC/JAN/FEB 2023-24 through JUN/JUL/AUG 2024 is updated. The forecast is based on a constructed analog. The analog is generated by correlating historical upper air patterns with regional SSTA. Snow cover projection is added to the forecast just-prior to the cold season. Soil moisture is added just prior to next summer’s forecast. Traditionally, El Nino southern oscillation (ENSO) is the primary contributor to climate forecasts. However, during the past decade, mid-latitude oceanic warming (and cooling in a few locations) has become increasing and almost equal contributors. Consequently, an optimum climate normal (OCN) is developed and added to the forecast process. OCN usage indicates the forecast is biased toward similar SSTA conditions and their correlated upper air pattern of the past 10 years. The nature of the OCN is generally warmer but more chaotic climate patterns. The selected regional SSTA on the U.S. winter outlook, in order of importance is described and projected for the 2023-24 winter season. ENSO: A vigorous El Nino has formed in the eastern equatorial East Pacific as identified by a traditional measuring index of ENSO phase, the Nino34 SSTA. HOWEVER, the response of the atmosphere to equatorial warming is weak. Multivariate ENSO index (MEI), a measure of the atmosphere’s reaction to equatorial SSTA patterns, indicates neutral ENSO for JUL/AUG 2023 (Fig. 1). The atmospheric response to the equatorial SSTA pattern is the one that counts. Consequently, the season 1-3 ahead forecast is based on a MEI analog (Fig. 2). The reason for the lack of atmospheric response, based on MEI, is not well-understood. The preliminary explanation (by Climate Impact Company) is the traditional consolidation of anomalous warmth in the tropical East Pacific is not happening in 2023 as many other sectors of the global oceans are warmer than normal plus the usual cooling in the equatorial West Pacific during El Nino is weak. In fact, the subsurface equatorial Pacific remains warmer than normal which is not typical of vigorous El Nino episodes. The Nino34 SSTA analog forecast indicates oceanic El Nino is vigorous (Fig. 3). However, El Nino 2023-24 will feature a moderate El Nino climate likely to fade back toward La Nina one year from now. Fig. 1: Comparing Nino34 SSTA and multivariate ENSO index since January 2020 reveals MEI has consistently lagged Nino34. Fig. 2: ENSO analog forecast projecting atmospheric ENSO using MEI. The warmer solution is based on a consensus between the MEI analog and warmer Nino34 forecast. Fig. 3: ENSO analog forecast based on conventional Nino34 SSTA. OCN: During the past 10 years, mid-latitude oceans have demonstrated generation of large regions of anomalous warm SSTA (marine heat waves) and areas of cooler than normal SSTA particularly south of Greenland commonly referred to as the North Atlantic warm hole (NAWH). The effects of the warming/cooling are evident in the mid-troposphere (where sensible weather is created) with prevailing upper ridge patterns near and downwind MHW patterns and upper troughs across or downwind cool SSTA zones (Fig. 4). The pattern is remarkably consistent and consequently applied to the operational climate forecast. Fig. 4: The prevailing upper air pattern as related to regional SSTA in the middle latitudes of the past 10years. AMO/PDO: The North Atlantic basin has witnessed the warmest SSTA pattern on record. The monthly Atlantic multi-decadal oscillation (AMO) and tropical North Atlantic (TNA) index were record warm. In the Northeast Pacific, a long-standing cool phase of the Pacific decadal oscillation (-PDO) continues. The +AMO/-PDO was certainly a significant contributor to emerging drought areas in Texas and the Midwest States of the past warm season in the U.S. (Fig. 5). The +AMO/-PDO regime is likely to continue well into 2024 according to most global SSTA forecast models. Normally, +PDO emerges when El Nino is present. While persistent +AMO is a confident project well into 2024, the -PDO forecast is made with below average forecast confidence. During El Nino the Midwest is typically drier than normal and a persistent -PDO/+AMO regime may inspire drought in that region to continue well into 2024 despite the La Nina to El Nino transition of 2023-24 (Fig. 6). Fig. 5-6: Prevailing U.S. drought risk based on the combination of the PDO/AMO regimes and cold season El Nino precipitation climate across the U.S. Northern oceans: The tendency for a much warmer than normal ocean surface in-between the constricted polar ice cap and northern land masses during late autumn can lead to quickly gathering above normal snows in the northern continents. Cold winds across open water create an “ocean effect” advection snow that can cause early season deep snows across northern Canada and Russia. Occasionally, snow cover spreads south quickly and can produce an early season cold air mass source region surrounded by a warmer than normal climate. This phenomenon is most common in Central Russia but can also occur in Western Canada (Fig. 7). The El Nino climate is likely to prevent this scenario from occurring this winter season. Fig. 7: “Ocean effect” snows forming early in the winter season are common in recent years due to the tendency of open ocean north of continents in late autumn. Solar activity: The sunspot number for August dropped considerably from July (163 to 114). The negative drop is uncharacteristic of the over-achieving strength of solar cycle 25 of the past couple years. Consequently, the onset of solar maxima projected by NASA to peak in 2025 may be delayed until after winter 2023-24. During the northern hemisphere winter when the sun is unusually active, solar flares can cause large disturbances in the ionosphere which warm the stratosphere sometimes rapidly. When the stratosphere warms rapidly, the troposphere below contracts and cools and arctic air is generated. The risk of sudden stratospheric warming (SSW) events is slightly above normal for the winter 2023-24 season. Climate influences summary: A moderate-to-strong oceanic El Nino is forecast for the remainder of 2023 into early 2024. The atmospheric response to the El Nino warming is weaker than normal so far, and therefore not expected to be as strong as the ocean signature for Q4/2023 and Q1/2024. El Nino 2023-24 is forecast to weaken by Q2/2024. Other statistical/dynamic model forecasts are mixed on the ENSO trajectory for 2024. Forecast confidence on El Nino for winter 2023-24 is excellent but diminishes rapidly for Q2/Q3 of 2024. The OCN pattern will weigh heavily on each seasonal forecast. The -PDO forecast is uncharacteristic of El Nino and could negative some of El Nino’s historical influence on U.S. winter climate. The +AMO influence could enhance El Nino-inspired South and East U.S. wet climate. The early cold season tendency for open oceans north of North America and Eurasia leads to above normal snowfall over central/northeast Russia and northwestern North America. However, El Nino warming is expected to weaken this tendency during winter 2023-24 lowering the risk of early season gathering cold air source regions. Finally, SSW episodes caused by solar activity have not occurred since the early 1990’s. The risk of SSW events for upcoming winter is lowered from moderately above normal to slightly greater than normal. DEC/JAN/FEB 2023-24: On average, much of the U.S. observes a seasonably cold winter season. Exceptions are in the Northeast States where the seasonal average is milder than normal. However, the near normal look to the winter outlook is likely the average of a very changeable pattern featuring mild El Nino climate, El Nino storm generated regional cold, and potential for 1 or 2 cold outbreaks possibly featuring arctic air. The winter storm track is intense from the Southeast U.S. to the Atlantic Seaboard. During mid-to-late winter, the northern fringe of the storm track features possible significant snow. Included in the snow risk area is the Ohio Valley, central and northern Appalachian States. Outside of the Southeast/East U.S. storm track a drier climate is indicated especially for California and Texas. The dry forecast in California and Texas is generated with below average confidence as both regions have a wet tendency during EL Nino winter. However, the implications are that torrid drought in Louisiana/Texas may not benefit as much as hoped for wintertime El Nino rainfall. The overall forecast trend since the initial forecast is less cold and less stormy in Texas. Fig. 8-9: The Climate Impact Company constructed analog forecast for temperature and precipitation anomalies during DEC/JAN/FEB 2023-24.  MAR/APR/MAY 2024: An El Nino climate lingers during spring 2024 although oceanic El Nino is weakening. The forecast theme is mild across Canada while the previously chilly U.S. forecast is less widespread. During next spring the West U.S. is cooler than normal while the Upper Midwest to Mid-Atlantic States is warmer than normal. The storm track is evident most prominently across the southern half of the Great Plains. The southwest quadrant of the U.S. could also be wetter than normal (and snowy in mountain areas). The Coastal Northwest U.S. is drier than normal. The northeast quadrant of the U.S. is drier than normal including the Ohio Valley and Northeast Corridor. Fig. 10-11: The Climate Impact Company constructed analog forecast for temperature and precipitation anomalies during MAR/APR/MAY 2024.  JUN/JUL/AUG 2024: The preliminary summer 2024 outlook for the U.S. features another hotter than normal summer for the Central and East U.S. while California is not as hot as normal. Drought conditions will add considerable intensity to the anomalous heat. These potential drought zones are Texas/Louisiana where winter/spring rains are not as buoyant as needed to erase drought. The Midwest U.S. may enter the summer season with lingering drought while beneficial rains are forecast in this region during summer. Fig. 12-13: The Climate Impact Company constructed analog forecast for temperature and precipitation anomalies during JUN/JUL/AUG 2024.