Dual Polar Radar ZDR Arch as a Precursor to Surface Impacts from Bow Echoes

Severe weather impacts to utilities are increasing at an alarming rate, with thunderstorm gusts being a primary driver of increasing SAIDI and outage duration. Following the impact from the New Castle, DE microburst event in July of 2019, an analysis of multiple bow-echo events is presented in order to determine whether or not the "ZDR Arch" feature is a reliable signature to use operationally to help determine whether or not severe wind gusts are reaching the ground and causing damage. This idea is examined by looking at multiple events and comparing when the arch develops to local storm reports and observations in its vicinity.

It was hypothesized by Taylor Trogdon in the June 2015 Storm of the Month Webinar that this feature is collocated with the developing updrafts atop the surface cold pool, just behind the surface gust front. As storm-relative inflow enters into the system, the associated hydrometeors get size sorted since there is likely an introduction of some water coated ice given the features proximity to the freezing level. As the front-to-rear flow becomes more horizontal and parallel to the ground, these suspended hydrometeors eventually fall out of the clouds through the descending rear-inflow jet. As a result, this helps transfer this higher momentum flow down to the surface. Therefore, the rearward base of the arch maybe the interface of the rear inflow jet with the surface.