S255 Continental Divide: A Comparison of the Vertical Structure in Northern Pacific and Continental Atmospheric Rivers Associated with Winter Extratropical Cyclones during February 2019

Sunday, 12 January 2020
Ketzel Levens, Univ. of Wisconsin–Madison, Madison, WI

Atmospheric rivers (ARs) are corridors of high water vapor that are transported from the tropics. On the West Coast of the United States, the AR feature found in extratropical cyclones in the northern Pacific plays a huge role in producing winter-time precipitation and dictating California’s water budget. Such features, identified by a stream at least 1500 km long of integrated vapor transport (IVT) above 250 km m-1 s-1, a length twice as long as it’s width, and low-level integrated water vapor (IWV) that is above 20mm for the entire AR, are also involved in the development of continental extratropical cyclones impacting the central and eastern parts of the United States. The present analysis diagnoses differences in the vertical characteristics of west coast and continental ARs via examination of two storms from February 2019. Using radiosonde and dropsonde data from National Weather Service Forecast Offices (NWSFOs) and the Center for Western Weather and Water Extremes (CW3E) 2019 AR-Reconnaissance field campaign, one gains a spatial and temporal understanding of the AR-specific features in each event. Despite the existence of some difference between them, the ARs in both events share a number of similarities including saturation depth, low-level (below 700 hPa) water vapor anomalies, the presence of a low-level jet (LLJ), warm air advection due to veering winds with height, and the timing of a cold frontal passage with maximum water vapor values. While AR features in the continental storm are sometimes not as well defined as those in the west coast case, it is presumed these are likely due to the complexities that arise in the AR traveling farther over land and being subject to more mesoscale processes.
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