Dominant factors influencing the seasonal predictability of United States precipitation and surface air temperature

Dominant Factors Influencing the Seasonal Predictability of

United States Precipitation and Surface Air Temperature

by

R. W. Higgins, A. Leetmaa, Y. Xue, and A. Barnston

Climate Prediction Center, NOAA/NWS/NCEP

Washington, D.C.

Wayne.Higgins @ncep.noaa.gov

Ph: 301-763-8000 (x7547)

Fax: 301-763-8395

Abstract

The relative influences of El Niño Southern Oscillation (ENSO), long-term tropical Pacific variations and the Arctic Oscillation (AO) on the potential seasonal predictability of United States precipitation and surface air temperature are investigated. The time variability of monthly precipitation in the tropical Pacific basin is separated into highpass- and lowpass-filtered components. The leading EOFs of the highpass-and lowpass-filtered data capture ENSO cycle-related interannual variability and ENSO-like interdecadal variability, respectively. The dominant mode of variability in the extratropics is the AO, which has been implicated in some of the secular variability of climate in the NH extratropics.

ENSO produces large, reasonably reproducible spatial and temporal shifts in tropical rainfall. The tropical interdecadal variability produces more subtle, but still significant shifts in tropical precipitation that contribute significantly to potential predictability and to trends in the North Pacific sector, over the United States and extending into the North Atlantic sector. Consistent with previous studies, the largest and most significant AO-related contributions are during the cold season (October-March), particularly over the eastern half of the United States, the North Atlantic sector, Eurasia and the polar cap.

The results indicate that a significant portion of the skill of climate forecast models will likely arise from an ability to forecast the temporal and spatial variability of the interdecadal shifts in tropical precipitation as well as the associated teleconnection patterns into midlatitudes. Because the Atlantic sector manifestation of the AO is the North Atlantic Oscillation (NAO), it appears that additional increases in skill are linked to the ability to forecast the NAO.