Abstract
Abstract. This paper explored the potential of a global climate model for sub-seasonal forecasting of precipitation and 2 m air temperature. The categorical forecast skill of 10 precipitation and temperature indices was investigated using the 28-year sub-seasonal hindcasts from the Climate Forecast System version 2 (CFSv2) over the contiguous United States (CONUS). The forecast skill for mean precipitation and temperature as well as for the frequency and duration of extremes was highly dependent on the forecasting indices, regions, seasons, and leads. Forecasts for 7- and 14-day temperature indices showed skill even at weeks 3 and 4, and generally were more skillful than precipitation indices. Overall, temperature indices showed higher skill than precipitation indices over the entire CONUS region at sub-seasonal scale. While the forecast skill related to mean precipitations was low in summer over the CONUS, the number of rainy days, number of consecutive rainy days, and number of consecutive dry days showed considerably high skill for the western coastal region. The presence of active Madden–Julian Oscillation (MJO) events improved CFSv2 weekly mean precipitation forecast skill over most parts of the CONUS, but it did not necessarily improve the weekly mean temperature forecasts. The 30-day forecasts of precipitation and temperature indices calculated from the downscaled monthly CFSv2 forecasts were less skillful than those calculated directly from CFSv2 daily forecasts, suggesting the usefulness of CFSv2 for sub-seasonal hydrological forecasting.
Highlights
IntroductionSub-seasonal (or intra-seasonal) timescale forecasts are typically between medium-range weather forecasts (1 or 2 weeks) and seasonal climate predictions (1 to 12 months)
Sub-seasonal timescale forecasts are typically between medium-range weather forecasts (1 or 2 weeks) and seasonal climate predictions (1 to 12 months)
The medium-range weather forecast is strongly influenced by atmospheric initial conditions (Vitart et al, 2008), while the seasonal climate forecast depends on slowly evolving components of the climate system (Troccoli, 2010)
Summary
Sub-seasonal (or intra-seasonal) timescale forecasts are typically between medium-range weather forecasts (1 or 2 weeks) and seasonal climate predictions (1 to 12 months). The medium-range weather forecast is strongly influenced by atmospheric initial conditions (Vitart et al, 2008), while the seasonal climate forecast depends on slowly evolving components of the climate system (e.g., sea surface temperature and soil moisture) (Troccoli, 2010). Since the subseasonal timescale is usually too long to be favored by the atmospheric initial conditions (Vitart, 2004) and too short to be strongly influenced by the variability of the ocean, making skillful sub-seasonal forecasts is difficult and far has less progress than the medium-range weather forecasts and seasonal climate forecasts. Sub-seasonal forecast information can be useful for developing strategies for proactive natural disaster mitigation (Brunet et al, 2010; Vitart et al, 2012). Previous studies have evaluated the potential of sub-seasonal to seasonal forecasts for heat wave forecasting (e.g., Hudson et al, 2011a; White et al, 2014), hydrological forecasting (e.g., Orth and Seneviratne, 2013; Yuan et al, 2014), water resources management (e.g., Sankarasubramanian et al, 2009), hydropower production management (e.g., Garcia-Morales and Dubus, 2007), and crop yield predic-
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