The Recurrence of Heavy Rainfalls in December 2015 and March 2016: Long Range Forecasting Implications

In late December 2015 and Mach 2016, heavy rain caused economic losses throughout the mid-to-lower Mississippi River Valley (former) and the lower part of that region (latter). In some places up to ten inches of rain fell causing flooding that rivalled the summer 1993 flooding. Previous work has shown that there is some predictability at the two to four week time-scale, and this may be due to long-period Rossby Wave propagation in the Pacific North American Region. Using the National Centers for Environmental Prediction / National Center for Atmospheric Research reanalyses and teleconnecition indexes from the National Climatic Data Center, it will be demonstrated that there is some indication that there may be predictability at the two to three month time-scale and the two events above may be related. This can be shown using autocorrelation in teleconnection index time-series and Fourier decompostion of these indexes as well as the 500 hPa height field. The reult is that it may be possible to make long-term forecasts intraseasonally to as much as one season ahead with more certainty than is currently available.