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Hazardous Heat Across the Western U.S.; Heavy Rain and Flooding in the Southwest and Western Gulf Coast

Dangerous heat will persist over portions of interior California, the Great Basin, and the northern Rockies through Thursday. Heat will gradually spread into the northern Plains today. Across the western Gulf Coast, heavy to excessive rainfall will persist through mid-week. Additionally, the Southwest Monsoon will continue to bring a flash flooding threat to the Four Corners Region this week. Read More >

Overview

Thunderstorms initiated along a surface trough to our west and northwest during the early-mid afternoon on 6/16. Coupled with northwest flow aloft and steep mid-level lapse rates, the environment was characterized by a decent amount of deep layer shear, fairly steep mid-level lapse rates, and moderate-strong instability. Storms moved into Louisa County from the northwest just before 6 PM. By this time, there was some degree of backing in the surface flow, and lower LCLs than usual during a northwest flow event. In fact, the 21z/5 PM observations at Charlottesville (KCHO) and Louisa were 91/78 and 85/77, respectively (w/ light SSE winds). At 6 PM, KLKU reported 81/76 and an ESE wind around 10 mph. It is also important to note that dew points were ~5F higher from CHO-LYH (near the surface trough) than in areas along the I-95 corridor. Note that the mesoanalysis maps may have underestimated the SRH (due to the localized backing in the wind field) and overestimated the LCLs (the dew points in the analysis were as much as 5°F too low across the Piedmont).

The storms that entered Louisa County eventually spawned three tornadoes across the northwest portion of our area. Radar imagery showed that these were indeed supercells with deep, persistent circulations. Two of the tornadoes were EF-0s and one was an EF-1. All three tornadoes were warned for. Fortunately, no injuries or fatalities were reported.

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