Modulation of ENSO-Based Long-Lead Outlooks of Southwestern U.S. Winter Precipitation by the Pacific Decadal Oscillation

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Abstract
Seasonal predictability of winter precipitation anomalies across the U.S. Southwest derived from knowledge of antecedent, late-summer Pacific Ocean surface temperatures is examined empirically. Previous studies have shown that equatorial Pacific SST anomalies associated with the El Niño–Southern Oscillation (ENSO) cycle, which are persistent from late summer through winter, exhibit a strong relationship with winter precipitation in Arizona and New Mexico. Here the degree to which seasonal predictability in this region is modulated by longer-term oceanic fluctuations associated with the Pacific decadal oscillation (PDO) is assessed. When all years from 1950 through 1997 are considered as a single dataset, inclusion of the PDO signal adds only slightly to the ENSO-based statistical predictability of Southwest winter precipitation anomalies. However, when the dataset is split into two subperiods delineated by a major shift in the PDO (before and after 1977), the ENSO-based predictability and, to a l... Abstract Seasonal predictability of winter precipitation anomalies across the U.S. Southwest derived from knowledge of antecedent, late-summer Pacific Ocean surface temperatures is examined empirically. Previous studies have shown that equatorial Pacific SST anomalies associated with the El Niño–Southern Oscillation (ENSO) cycle, which are persistent from late summer through winter, exhibit a strong relationship with winter precipitation in Arizona and New Mexico. Here the degree to which seasonal predictability in this region is modulated by longer-term oceanic fluctuations associated with the Pacific decadal oscillation (PDO) is assessed. When all years from 1950 through 1997 are considered as a single dataset, inclusion of the PDO signal adds only slightly to the ENSO-based statistical predictability of Southwest winter precipitation anomalies. However, when the dataset is split into two subperiods delineated by a major shift in the PDO (before and after 1977), the ENSO-based predictability and, to a l...