Using KDP Cores as a Downburst Precursor Signature

Abstract

Decades of research has investigated processes that contribute to downburst development, as well as identified precursor radar signatures that can accompany these events. These advancements have increased downburst predictability, but downbursts still pose a significant forecast challenge, especially in low-shear environments that produce short-lived single and multicell thunderstorms. Additional information provided by dual-polarization radar data may prove useful in anticipating downburst development. One such radar signature is the KDP core, which can indicate processes such as melting and precipitation loading that increase negative buoyancy and can result in downburst development. Therefore, KDP cores associated with 81 different downbursts across 10 states are examined to explore if this signature could provide forecasters with a reliable and useable downburst precursor signature. KDP core characteristics near the environmental melting layer, vertical gradients of KDP, and environmental conditions were quantified to identify any differences between downbursts of varying intensities. The analysis shows that 1) KDP cores near the environmental melting layer are a reliable signal that a downburst will develop, 2) while using KDP cores to anticipate an impending downburst’s intensity is challenging, larger KDP near the melting layer and larger vertical gradients of KDP are more commonly associated with strong downbursts than weak ones, 3) downbursts occurring in environments with less favorable conditions for downbursts are associated with higher magnitude KDP cores, and 4) KDP cores evolve relatively slowly (typically longer than 15 min), which makes them easily observable with the 5-min volumetric updates currently provided by operational radars.

Strange Storms: Rainfall Extremes From the Remnants of Hurricane Ida (2021) in the Northeastern US

“…For the near‐saturated conditions in Ida, melting of mixed phase hydrometeors is likely an important source of negative buoyancy. Descending K DP columns provide a potentially useful polarimetric signature of downdraft‐driven rainfall extremes (Kuster et al., 2021; see also Kumjian et al., 2010; Romine et al., 2008; Trapp et al., 2017). The tropical aspect of the storm environment contributed to a deep layer of humidity, a typical setting for extreme rainfall from warm rain processes.…”