Modification of long-axis lake-effect snow bands associated with landfall and orographic uplift: Results from a profiling radar network deployed during OWLeS

Intense east-west oriented bands of well-organized lake-effect convection often cross the eastern shore of Lake Ontario and are lifted over the 600 meter high Tug Hill plateau. Heavy snows from these bands produce a pronounced local maximum in climatological snowfall about 40-50 km downwind of the Ontario shoreline over the Tug Hill (one of the snowiest locations in eastern North America). The specific dynamical and microphysical mechanisms that produce this maximum are poorly characterized, in part due to a paucity of observations.

An east-west transect of four vertically profiling radars was deployed downwind of Lake Ontario and over the Tug Hill to better characterize the evolution of lake-effect convection and gain insights into the mechanisms of local snowfall enhancement. This effort was part of the Ontario Winter Lake-effect Systems (OWLeS) field campaign. The instruments were MRR2 profiling 24 GHz FM-CW-Doppler radars. All four MRR2's were deployed in October 2013 and taken down in early 2014 (2 in late-January, 2 in March). The resulting observations offer a detailed view of how the vertical and temporal structure of lake-effect convection and snowfall are modified by landfall and orographic uplift.

Comparing MRR2 data across the transect reveals that with increasing downwind distance from the shoreline, echo depths stay roughly constant and convective updraft intensity decreases. This suggests that snowfall enhancement is not a result of invigorated convection. While peak MRR2 reflectivity is often highest near the Ontario shoreline, the frequency of echo occurrence is often higher over the Tug Hill, suggesting a downwind transition to “more-stratiform” conditions. Contoured frequency by altitude diagrams of MRR2 reflectivity reveal that snowfall enhancement over the Tug Hill often occurs at very low levels (< 1.5km AGL), possibly limiting the effectiveness of quantitative precipitation estimation from the local NEXRAD radar.

Comparing the downwind evolution of lake-effect convection seen by the MRR2 transect with surface observations reveals the relationship between observed echo structures and surface snowfall rates and crystal habits. This helps to constrain the microphysical mechanisms of snowfall enhancement.