08/14/2022, 12:03 pm EDT

U.S. Month 1-3 Outlook Valid for Meteorological Autumn 2022

Highlight: A warm autumn; Wet in the East. East-central dryness. Western heat. Executive Summary: The Climate Impact Company month 1-3 ahead climate forecast for meteorological autumn is updated. Primary climate catalysts are restrengthening La Nina and very warm mid-latitude SSTA in both the North Pacific and North Atlantic. Climate forecast highlights include potential excessive rainfall Louisiana to the Northeast U.S. in September, strengthening dryness in the Mid-south States and each month of autumn is mostly quite warm. The La Nina climate supports above normal tropical cyclone risk for SEP/OCT/NOV 2022 and an eventual shift of drought risk into the Southeast U.S. During autumn, expanding drought remains an issue for the Northwest to western Midwest U.S. Fig. 1-2: Climate Impact Company autumn 2022 outlook.  Climate discussion: Calendar summer has produced very hot weather across much of the U.S. especially Texas and the southern Great Plains plus the Interior Northwest and New England States (Fig. 3). The lack of rainfall has enhanced the hottest anomalies from Texas to the Midwest U.S. (Fig. 4). The upper air pattern has featured a vigorous upper trough over Hudson Bay during this time with broad high-pressure ridge extending across the U.S. (Fig. 5). The broad ridge triggered the anomalous heat. A dynamic jet stream has separated the upper trough and ridge pattern and occasionally caused renegade extreme rainfall events most profound in St. Louis, MO to eastern Kentucky. All models indicate a pattern change for the second half of August. The Hudson Bay trough will weaken, and the western North America ridge amplifies and is compensated for by a downstream trough over the Interior East U.S. (Fig. 6). The upper air pattern change pushes the excessive heat risk to the Northwest U.S. and Canada where drought concerns are amplified while in the East and South U.S. a cooler/wetter regime develops although the Northeast can still be quite warm. Will this pattern change carry through late summer? Fig. 3-6: Calendar summer 2022 temperature and precipitation anomalies plus the prevailing upper air pattern so far and the pattern change forecast for late August. The IMME global SSTA forecast for September 2022 (Fig. 7) projects La Nina continuing somewhat enhanced by the presence of a robust negative phase Indian Ocean dipole (-IOD). Of more influence on U.S. climate than La Nina is a robust warm SSTA across the mid-latitudes of both the North Pacific and North Atlantic basins while the tropics/subtropics of the North Atlantic are marginally warm. Fig. 7: IMME global SSTA forecast for September 2022. September 2022: The prevailing projected upper air pattern for early meteorological is an upper trough over Western Canada which would require a complete pattern change from late August and a sprawling upper ridge from the Southwest U.S. to Southeast Canada. The result is a cooler pattern change for the Northwest States after the excessive heat of late meteorological summer. Anomalous heat is dominant in the Southwest States. Anomalous warmth featuring late season hot weather is forecast for the Northeast States extending to the Mid-Atlantic. The very warm temperature forecast for the Northeast/Mid-Atlantic States occurs with an excessive rainfall risk which is a rare combination. Implied is the wet weather is subtropical/tropical in nature raising the risk of tropical cyclone presence. Louisiana is also wet likely related to tropical cyclone risk. The Central/East-central U.S. forecast is not as dry as the previous outlook. Fig. 8-9: The Climate Impact Company temperature/precipitation anomaly forecast for September 2022.  October 2022: During mid-autumn, a polar vortex returns in northern Canada and to the south of this feature sweeping mild westerlies dominate the U.S. The Southwest U.S. gains a late season surge of monsoon moisture. The forecast implies October tropical cyclone activity stays away from the U.S. Coast (except southern Florida). Much-needed wet weather remains in the forecast for Texas and the southern Great Plains while important dryness increases in the nearby Mid-south States plus parts of the North-central to Interior Northwest U.S. Fig. 10-11: The Climate Impact Company temperature/precipitation anomaly forecast for October 2022. November 2022: The early cold season brings risk of chilly air to the East, most anomalous with southern latitude. The forecast is not as chilly as the previous outlook. In the West/North-central U.S. the forecast flips from cool to warm due to the warm North Pacific. The ending of an active late season tropical cyclone season should lead to some high-latitude high-pressure blocking which opens the door for some periods of chilly weather in the East separated by mild periods. Fig. 12-13: The Climate Impact Company temperature/precipitation anomaly forecast for November 2022. The previous forecast is below.