The Evolution of Lake-Effect Convection during Landfall and Orographic Uplift as Observed by Profiling Radars

Abstract

A pronounced snowfall maximum occurs about 30 km downwind of Lake Ontario over the 600-m-high Tug Hill Plateau (hereafter Tug Hill), a region where lake-effect convection is affected by mesoscale forcing associated with landfall and orographic uplift. Profiling radar data from the Ontario Winter Lake-effect Systems field campaign are used to characterize the inland evolution of lake-effect convection that produces the Tug Hill snowfall maximum. Four K-band profiling Micro Rain Radars (MRRs) were aligned in a transect from the Ontario coast onto Tug Hill. Additional observations were provided by an X-band profiling radar (XPR). Analysis is presented of a major lake-effect storm that produced 6.4-cm liquid precipitation equivalent (LPE) snowfall over Tug Hill. This event exhibited strong inland enhancement, with LPE increasing by a factor of 1.9 over 15-km horizontal distance. MRR profiles reveal that this enhancement was not due to increases in the depth or intensity of lake-effect convection. With increasing inland distance, echoes transitioned from a convective toward a stratiform morphology, becoming less intense, more uniform, more frequent, and less turbulent. An inland increase in echo frequency (possibly orographically forced) contributes somewhat to snowfall enhancement. The XPR observations reproduce the basic vertical structure seen by the MRRs while also revealing a suppression of snowfall below 600 m AGL upwind of Tug Hill, possibly associated with subcloud sublimation or hydrometeor advection. Statistics from 29 events demonstrate that the above-described inland evolution of convection is common for lake-effect storms east of Lake Ontario.

Understanding Heavy Lake-Effect Snowfall: The Vertical Structure of Radar Reflectivity in a Deep Snowband over and downwind of Lake Ontario

“…This distribution is noted particularly near Lake Ontario (Jiusto and Kaplan 1972;Wilson 1977;Minder et al 2015;Veals and Steenburgh 2015), as was the case for an LLAP event on 11 December 2013. The present study focuses on this particular event, observed intensively as part of the Ontario Winter Lake-effect Systems (OWLeS) project (Kristovich et al 2016).…”

“…This study aims to present evidence corroborating (or refuting) each of these processes in one LLAP event observed during OWLeS. It builds on Minder et al (2015), who use K-band radar reflectivity profiles collected from four sites between the shore and the Tug to show that with increasing inland distance, echoes transition from a convective toward a stratiform morphology, becoming less intense and more uniform, in IOP2 and in other LeS events during OWLeS. The next section will describe the instruments and analysis methods used in the study.…”

“…The range resolution of the MRRs is 200 m in OWLeS. Reflectivity calibration and data processing of the MRR array in OWLeS is discussed by Minder et al (2015) and Maahn and Kollias (2012).…”

“…The IOP2b event was one of the more intense, deep, and long-lived LLAP events encountered in OWLeS (Minder et al 2015;Frame et al 2015;Campbell et al 2016). A precipitation maximum [27 mm of snow water equivalent (SWE) in 12 h] occurred on the Tug, about 40 km downwind of the shore of Lake Ontario on 11 December 2013, according to National Centers for Environmental Prediction (NCEP) stage-IV data (Fig.…”

Forecasting the Inland Extent of Lake Effect Snow Bands Downwind of Lake Ontario

“…Typical capping inversion heights for most LES bands were found to be in the range of 1-2 km, whereas more intense LES bands had inversion heights of >3 km (Niziol 1987). Minder et al (2015) found that the inland enhancement of snowfall totals was not due to orographic invigoration of convection, which is a potential crucial finding with regards to determining what parameters may or may not modulate IE. Niziol et al (1995) classified different types of LES bands.…”