A Climatology of Atmospheric Rivers over the Northeast United States

Atmospheric Rivers (ARs) are characterized by long, narrow corridors of enhanced integrated water vapor (IWV) and integrated vapor transport (IVT) located in the warm sector of midlatitude extratropical cyclones. ARs are well-known contributors to high-impact precipitation and precipitation-related events (e.g., floods, landslides, avalanches, etc) and water resources across Western U.S. Recent research has also demonstrated that ~40% of Southeast U.S. heavy precipitation events in the winter and the transition seasons occur in association with ARs, AR-like, or AR-related features (e.g., Moore et al. 2012; Pfahl et al. 2014; Moore et al. 2015; Mahoney et al. 2016).

The goal of this research was to develop a complementary climatology of ARs over the Northeast U.S. NEUS for 38–48N and 80–66W every six hour for 1988–2017 and apply those results to different occurrences of high-impact weather. While many objective algorithms have recently been developed to automatically identify corridors of IWV and IVT resembling ARs (e.g., the Atmospheric River Tracking Method Intercomparison Project; Shields et al. 2018), herein we seek to subjectively identify ARs using objective criteria (e.g., an IVT magnitude >250 kg m^–1s^–1that is >2000 km in length and <1000 km wide or an aspect ratio of ~2:1, and linked to an extratropical cyclone). The subjective identification method ensured that corridors of IWV and IVT not associated with ARs, that an automated routine might identify as an AR (e.g., enhanced IWV and IVT during the summer to the west of the Bermuda High), would be excluded from the climatology.

This presentation will review the results of the climatology summarizing the >3000 ARs identified (~101 per year) over the NEUS. The ARs are approximately evenly distributed throughout the year, with an average duration over the domain of 43 hours, average direction of southwest, and an average maximum IVT magnitude of 737 kg m^–1s^–1. Additional results include ~750 ARs, primarily during the warm season, that occurred in “chain” or in sequence overlapping in time with another AR over the NEUS domain. This presentation will also summarize the results of four research projects that used this climatology to identify associations among NEUS ARs and (1) annual precipitation, (2) snowfall, (3) flood-related watches, warnings, and advisories issued by the National Weather Service, and (4) water quality.