A Comparison of Two Lake Breeze Severe Events with a Threat Chart Application

The effects of lake breezes are very important, with many urban populaces located near the eastern Great Lakes. Lake breeze initiated thunderstorms are very common across west-central New York and northern Ohio. Occasionally, lake breeze boundaries migrate eastward from Lakes Ontario and Erie into eastern New York and western New England. Severe thunderstorms producing damaging winds in excess of 25 ms-1, large hail greater than 1.9 centimeters in diameter, or even tornadoes may occur with lake breeze boundaries.

Two distinct lake breeze severe weather events occurred on 9 August 2001 across upstate New York and western New England, and 19 April 2002 over northern and central Ohio. On 9 August 2001, a strong lake breeze boundary moved east of Lake Ontario during the mid to late afternoon into the National Weather Service at Albany county warning area. A cluster of severe thunderstorms developed in a hot and humid air mass where surface temperatures exceeded 35°C, dewpoints were greater than 20°C, and surface based convective available potential energy values exceeded 2500 J kg-1. Deep layer shear (0-6 km) values were 15 ms-1 or less. The severe convection that developed downstream of Lake Ontario and north of the Mohawk River Valley knocked several trees and power poles down and produced two large-hail reports in excess of 5.0 cm. On 19 April 2002, a lake breeze boundary, interacting with a southward-moving strong cold front entering an anomalously warm mid-April air mass, spawned a supercell in northwest Ohio. This storm resulted in numerous hail reports, one of which was about 5 cm in diameter, and an F0 tornado.

This poster presentation will compare the synoptic, mesoscale, and storm-scale environments of these two events utilizing a wide array of observational datasets including surface, sea-surface temperature, upper-air, satellite, and radar. The performance of initialized model guidance including: the 40-km RUC, 80-km ETA and the experimental 1km WRF will be briefly reviewed in the lake breeze cases. Finally, these two cases are included in an 11-case dataset over the past eight years, where a lake breeze flow chart has been developed from CSTAR research. The flow chart and subsequent threat charts classify cases based on thresholds of meteorological parameters that include: 1000-500 hPa thickness values, thermal difference between the water and near shore temperatures in the late morning, precipitable water values, boundary layer conditions and stability parameters. Threat chart checklists have been developed for potential lake or sea breeze severe weather. There are ten criteria threat elements. A point is scored for each severe threat chart element that verifies. The threat or risk of severe weather with the lake or sea breeze boundary is high, when the tally is close to ten. It will be shown that these two cases scored high on the threat chart. The flow and threat assessment charts are intended for future application in forecasting lake or sea breeze convection by the operational forecast community.