Skillful Subseasonal Prediction of U.S. Extreme Warm Days and Standardized Precipitation Index in Boreal Summer

• Published in: Journal of climate 2021-07, Vol.34 (14), p.5887-5898
• Main Authors: Miller, Douglas E., Wang, Zhuo, Li, Bo, Harnos, Daniel S., Ford, Trent
• Format: Article
• Language: English
• Subjects: Agriculture; Anomalies; Anticyclones; Blocking anticyclones; Clear sky; Climate models; Climate system; Enthalpy; Extreme heat; Extreme high temperatures; Extreme values; Extreme weather; Heat; Heat flux; Heat transfer; Irrigation scheduling; Latent heat; Latent heat flux; Mathematical models; Mitigation; Moisture effects; Precipitation; Public health; Reservoir operation; Sea surface; Sea surface temperature; Sea surface temperature anomalies; Sensible heat; Sensible heat flux; Sensible heat transfer; Soil; Soil conditions; Soil moisture; Soil temperature; Standardized precipitation index; Statistical models; Summer; Surface temperature; Temperature extremes; Water management; Wave trains; Weekly
• ISSN: 0894-8755; 1520-0442
• DOI: 10.1175/JCLI-D-20-0878.1

Skillful subseasonal prediction of extreme heat and precipitation greatly benefits multiple sectors, including water management, public health, and agriculture, in mitigating the impact of extreme events. A statistical model is developed to predict the weekly frequency of extreme warm days and 14-day standardized precipitation index (SPI) during boreal summer in the United States. We use a leading principal component of U.S. soil moisture and an index based on the North Pacific sea surface temperature (SST) as predictors. The model outperforms the NCEP Climate Forecast System, version 2 (CFSv2), at weeks 3–4 in the eastern United States. It is found that the North Pacific SST anomalies persist for several weeks and are associated with a persistent wave train pattern, which leads to increased occurrences of blocking and extreme temperature over the eastern United States. Extreme dry soil moisture conditions persist into week 4 and are associated with an increase in sensible heat flux and a decrease in latent heat flux, which may help to maintain the overlying anticyclone. The clear-sky conditions associated with blocking anticyclones further decrease soil moisture and increase the frequency of extreme warm days. This skillful statistical model has the potential to aid in irrigation scheduling, crop planning, and reservoir operation and to provide mitigation of impacts from extreme heat events.