Synoptic–Dynamic and Airmass Characteristics Distinguishing Long- and Short-Duration Freezing Rain Events in the South-Central United States

Abstract

Though prolonged freezing rain events are rare, they can result in substantial damage when they occur. While freezing rain occurs less frequently in the south-central United States than in some regions of North America, a large number of extremely long-duration events lasting at least 18 hours have been observed there. We explore the key synoptic-dynamic conditions that lead to these extreme events through a comparison with less-severe short-duration events. We produce synoptic-dynamic composites and seven-day backward trajectories for parcels ending in the warm and cold layers for each event category. The extremely long-duration events are preferentially associated with a deeper and more stationary 500-hPa long-wave trough centered over the southwestern United States at event onset. This trough supports sustained flow of warm, moist air from within the planetary boundary layer over the Gulf of Mexico northward into the warm layer. The short-duration cases are instead characterized by a more transient upper-level trough axis centered over the south-central United States region at onset. Following event onset, rapid passage of the trough leads to quasigeostrophic forcing for descent and the advection of cold, dry air that erodes the warm layer and ends precipitation. While trajectories ending in the cold layer are very similar between the two categories, those ending in the warm layer have a longer history over the Gulf of Mexico in the extreme cases compared with the short-duration ones, resulting in warmer and moister onset warm layers.

A Multi‐Algorithm Analysis of Projected Changes to Freezing Rain Over North America in an Ensemble of Regional Climate Model Simulations

“…(2017) for western Canada, and McCray et al. (2021) for the south‐central United States. For example, Mittermeier et al.…”

Quantifying the compound hazard of freezing rain and wind gusts across CONUS

“…Structures at high-elevations most frequently experience rime icing due to cloud droplet deposition [15], while in most other areas it is glaze due to FZ associated with precipitation falling through an atmosphere with a lower tropospheric inversion and surface temperatures <0 • C [16]. Such conditions typically occur along frontal boundaries associated with midlatitude cyclones or cold air outbreaks [17][18][19]. The western USA can also experience FZ due to atmospheric rivers interacting with complex topography [20,21].…”