December 20, 2022

Freezing Rain Guide

Hello, Pacific Northwesterners! 

Thank you for reading The UW Dawgcast’s freezing rain guide. 

While some people in this region are accustomed to this precipitation type, Seattle and many other areas of Western Washington rarely receive freezing rain, and many don’t even know what it is! 

To help you understand, we have made a guide about freezing rain and its hazards. 

Freezing rain (FZRA/ZR) is the most hazardous precipitation type. The National Weather Service defines freezing rain as, “rain that falls as a liquid but freezes into glaze upon contact with the ground.” This occurs when liquid precipitation (falling through an above-freezing layer of the atmosphere) contacts a sub-freezing surface and instantly freezes. 

Thanks to David Lee (@WoodinvilleWx) for the photo of freezing rain on a branch. 

Here is a graphic from the National Weather Service about different precipitation types, including freezing rain. 

Freezing rain is dangerous because it looks like regular rainfall when it starts but creates a sheet of ice on roadways and other surfaces, making it extremely difficult to control a vehicle. 

In addition, freezing rain can easily take down trees and power lines. Unlike snow, wind doesn’t easily blow freezing rain off trees and power lines, making them extremely heavy with any wind. If any snowfall is present underneath the freezing rain, this just exacerbates the problem. 

When the temperature finally rises above the freezing mark, urban flooding is often an issue as all the frozen precipitation can melt quite rapidly. 

Thank you to Randy Small (@RandySmall) for the image of freezing rain damage in Whatcom County. This was from a half-inch of freezing rain, enough to bring down power lines. 

Some areas of Western Washington are prone to more frequent freezing rain events, such as the foothills of the Cascade gaps and Whatcom County, which are sometimes exposed to shallow cold east and northeast winds. 

Although these regions and some suburbs of the Seattle metro area have received freezing rain in the past few years, the last major freezing rain event for the city of Seattle was in January 2012, when a quarter-inch or so of freezing rain shut down Seattle-Tacoma Airport for the entire day. KUOW reported that 2,300 accidents occurred in a 24-hour period, quadrupling the typical number. 

If freezing rain is in the forecast, do whatever possible to avoid travel, and prepare for widespread power outages.