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The JUN/JUL/AUG 2018 probabilistic rainfall forecast issued by NOAA/CPC may be the wettest summer outlook issued in the 23-year history of the (NOAA) long-lead forecast product.

Discussion: NOAA/CPC began issuing probabilistic long-lead climate forecasts in 1995. During the 23-year period of long-lead climate forecasts the outlook issued for meteorological summer 2018 is the wettest (for summer) in the East. The highest probability of wet weather for upcoming summer is in the central Appalachian Mountains northward to Ohio to New York (Fig. 1). The Climate Impact constructed analog forecast confines the wet risk to the East Coast (Fig. 2). Forecast confidence is above average that the East Coast will observe a humid and frequently rainy summer season.

Fig. 1: The NOAA/CPC JUN/JUL/AUG 2018 probabilistic rainfall outlook.

Fig. 2: The Climate Impact JUN/JUL/AUG 2018 analog precipitation outlook.

Implications: The wet forecast has many implications on this high population zone of the eastern U.S. First, the wet pattern recently evolved in the eastern states is likely to produce wet soils activing as a feedback mechanism to the atmosphere to inspire more rainfall. As summer arrives much of the rain becomes more convective, i.e. thunderstorms. An unusual amount of thunderstorm activity and attendant risk (heavy rain, microbursts and cloud to ground lightning) occurs in high population centers. Potentially implied is wet risk from tropical events for later this summer as they move inland off the Gulf of Mexico or Atlantic Seaboard. Be aware of the wet risk when planning a summer vacation.