Snow Level Characteristics and Impacts of a Spring Typhoon-Originating Atmospheric River in the Sierra Nevada, USA

Benjamin Hatchett

doi:10.3390/atmos9060233

Abstract

On 5–7 April 2018, a landfalling atmospheric river resulted in widespread heavy precipitation in the Sierra Nevada of California and Nevada. Observed snow levels during this event were among the highest snow levels recorded since observations began in 2002 and exceeded 2.75 km for 31 h in the northern Sierra Nevada and 3.75 km for 12 h in the southern Sierra Nevada. The anomalously high snow levels and over 80 mm of precipitation caused flooding, debris flows, and wet snow avalanches in the upper elevations of the Sierra Nevada. The origin of this atmospheric river was super typhoon Jelawat, whose moisture remnants were entrained and maintained by an extratropical cyclone in the northeast Pacific. This event was notable due to its April occurrence, as six other typhoon remnants that caused heavy precipitation with high snow levels (mean = 2.92 km) in the northern Sierra Nevada all occurred during October.

Highlights

The maritime midlatitude Sierra Nevada mountains provide key water resources, ecosystem services, and recreation opportunities for California and Nevada [1,2]
We focus on the period spanning from 25 March–7 April 2018, in other words, the period between when Jelawat was declared a super typhoon by the Japanese Meteorological Agency [17] and the most significant precipitation and impacts in the Sierra Nevada occurred
On 25 March 2018, super typhoon Jelawat can be identified as a region of negative outgoing longwave radiation (OLR) anomalies centered at 140◦ E, 8◦ N (Figure 2a) and as a region of precipitable water exceeding 65 mm and demonstrating radial inflow (Figure 3a)

Summary

Introduction

The maritime midlatitude Sierra Nevada mountains provide key water resources, ecosystem services, and recreation opportunities for California and Nevada [1,2]. The orientation of the northwest-southeast trending Sierra Nevada (Figure 1) perpendicular to the west-southwest flow during most cool season storms leads to orographic precipitation enhancement when ARs interact with the topography [9,10]. When snow levels are extremely high (>2.5 km), large catchment areas of watersheds throughout the range will receive rainfall and contribute runoff from both direct precipitation and heat transfer-driven snowmelt [11]. Because this precipitation is not being stored as snowpack, these warm storms create challenges for water and emergency managers who must handle the storm as a hazard rather than a resource [1,13,14]

Methods

Results

Discussion

Conclusion