Seasonal Skillful Prediction of Western North America Atmospheric Rivers

Abstract:

Atmospheric rivers (ARs) - narrow filaments of concentrated moisture transport that bring heavy precipitation and flooding - exert significant socioeconomic impacts along the West Coast of North America. About 30% of the annual precipitation over coastal California and Washington/Oregon is determined by ARs that occur in less than 15% of winter time, indicating both the benefits to water supply and the hazard from extreme precipitation when an AR makes landfall. While most prevailing research has focused on the subseasonal prediction ( ≤ 5 weeks) of ARs, only limited efforts have been made for AR prediction on seasonal to multiseasonal timescales (3 months to 1 year) that are crucial for water resource management and disaster preparedness.

Through the analysis of observational data and retrospective predictions from a new seasonal to decadal prediction system, GFDL SPEAR (Seamless System for Prediction and Earth System Research), this research shows the existing potential of seasonal AR forecasts over western North America with predictive skills 9 months in advance. Additional analysis of leading AR variability indicates the Pacific Decadal oscillation (PDO) and Central Pacific type El Niño are potential predictability sources for AR seasonal prediction. The challenge of seasonal AR prediction over certain locations of the western North America is also elucidated in this research.