Thunderstorm Wind — Grayson, Kentucky

2023-06-25 · near Spring Lick, Grayson, Kentucky

Event narrative

The National Weather Service in Louisville conducted a storm survey for the macroburst damage extending from western Grayson County, through Edmonson County, before ending in northeastern Warren County. The first area of concentrated damage was observed along US Highway 62 around Caneyville, which consisted mostly of softwood and hardwood tree damage, including numerous uprooted trees and large snapped branches. One double wide trailer suffered considerable roof damage in along Highway 62, though structural damage was otherwise rare in this area. Estimated winds across western Grayson County were generally between 80 and 90 mph. Sporadic tree damage was also observed along Kentucky Route 259 between Leitchfield and the Edmonson County line.

All tree and structural damage was blown to the southeast along the path. This damage pattern is consistent with downburst winds, with the large scale of damage suggesting a macroburst event.

Wider weather episode

An anomalously strong mid- and upper-level trough for late June moved across the Great Lakes and Ohio Valley from the afternoon hours on June 25th through the morning hours on June 26th. A 60-70 kt 500 mb jet bisected the mid-Mississippi Valley, placing central Kentucky and southern Indiana in the left exit region, contributing to broad rising motion over the area. Near the surface, a well-defined cold front crossed the Mississippi River during the mid-to-late afternoon hours on June 25th, with temperatures in the upper 80s and lower 90s and dewpoints in the upper 60s and lower 70s in the warm sector ahead of the front. In the warm sector, mixed-layer CAPE of 2500-3500 J/kg provided plenty of fuel for convective development aside from the aforementioned favorable jet forcing. With 25-35 knots of flow at 850 mb, there was also ample vertical wind shear across the region, with effective bulk shear values generally above 45 kt, leading to the development of supercellular structures. The parameter space was favorable for all severe hazards. 0-1 km storm-relative helicity was over 200 m2/s2 and significant tornado parameter values were frequently greater than 1, suggesting the potential for rotating mesocyclones and tornadoes. Downdraft CAPE was over 1200 J/kg along and west of Interstate 65, suggesting the potential for strong winds from any formidable downdrafts. Finally, sufficient mid-level lapse rates and significant hail parameter values warranted concerns for severe hail. As would be expected given the parameter space, all severe hazards were observed, with a couple tornadoes and numerous straight-line wind and hail reports across southern Indiana and central Kentucky. Straight-line winds of up to 100 mph and multiple reports of golf ball or larger size hail serve as evidence of the highly unusual setup across the Ohio and Tennessee valleys June 25th and 26th.

View location on OpenStreetMap → (37.4270, -86.5730)

Source: NOAA Storm Events Database, event_id 1119116. Narrative written by the NWS forecast office that issued the report.