Seasonally predicted precipitation at a resolution of 2.5° was statistically downscaled to a fine spatial scale of ~20 km
over the southeastern United States. The downscaling was conducted for spring and summer, when the fine-scale prediction of
precipitation is typically very challenging in this region. We obtained the global model precipitation for downscaling from
the National Center for Environmental Prediction/Climate Forecast System (NCEP/CFS) retrospective forecasts. Ten member integration
data with time-lagged initial conditions centered on mid- or late February each year were used for downscaling, covering the
period from 1987 to 2005. The primary techniques involved in downscaling are Cyclostationary Empirical Orthogonal Function
(CSEOF) analysis, multiple regression, and stochastic time series generation. Trained with observations and CFS data, CSEOF
and multiple regression facilitated the identification of the statistical relationship between coarse-scale and fine-scale
climate variability, leading to improved prediction of climate at a fine resolution. Downscaled precipitation produced seasonal
and annual patterns that closely resemble the fine resolution observations. Prediction of long-term variation within two decades
was improved by the downscaling in terms of variance, root mean square error, and correlation. Relative to the coarsely resolved
unskillful CFS forecasts, the proposed downscaling drove a significant reduction in wet biases, and correlation increased
by 0.1–0.5. Categorical predictability of seasonal precipitation and extremes (frequency of heavy rainfall days), measured
with the Heidke skill score (HSS), was also improved by the downscaling. For instance, domain averaged HSS for two category
predictability by the downscaling are at least 0.20, while the scores by the CFS are near zero and never exceed 0.1. On the
other hand, prediction of the frequency of subseasonal dry spells showed limited improvement over half of the Georgia and
Alabama region.
Keywords Downscaling - Precipitation - Regional climate - Prediction - Extremes