Thunderstorm Wind — Terrell, Georgia

2019-04-14 · near Bronwood, Terrell, Georgia

Event narrative

Trees were blown down in Bronwood.

Wider weather episode

This event was characterized by a mid-level shortwave trough becoming negatively tilted as it entered the Tennessee Valley, initiating cyclogenesis in the Arklatex, with the resultant 992 hPa low pressure moving northeastward into the Ohio Valley. This setup a strong, meridional flow ahead of this feature. The 925 hPa low level jet of 44 kts was around 4 Standard Deviations above normal, and record for the date per the 12Z/14 TAE sounding. A pre-frontal trough pooled a narrow axis of moisture out ahead of the cold front, and served as a forcing mechanism for convection. Given Bulk Shear (0-6 km) around 60 knots and Surface Based CAPE around 1.2k J/kg, this was more than sufficient for organized, severe thunderstorms. The air mass just ahead of the pre-frontal trough was much drier and capped, initially limiting the development of more discrete cells ahead of the line. In fact, the 12Z/14 TAE sounding sampled a cap of over 5C just below 700 hPa! However as solar insolation and large scale ascent increased, this cap was broken around 15Z, and the QLCS intensified. The strong wind field and steep low-level lapse rates created an environment favorable for damaging wind gusts, particularly northwest of a line from the Apalachicola River to Tifton GA, where steeper mid-level lapse rates overlayed, leading to greater buoyancy. The tornado threat along the QLCS was dependent on storms becoming more favorably aligned with the Shear Vector (0-3 km), with otherwise sufficient CAPE (0-3 km) and low LCLs. Ahead of the QLCS, the low-level wind field was sheared in the 0-1 km layer, as evidenced on VAD Wind Profiles. As a result, the tornado threat increased with the more discrete cells after the cap broke. The aforementioned strong wind field and steep low-level lapse rates, combined with the isallobaric component of wind, lead to wind gusts around 40 mph well ahead of the QLCS. A total of 27 warnings were issued, including 15 SVRs, 6 TORs, and 6 SMWs.

View location on OpenStreetMap → (31.8300, -84.3600)

Source: NOAA Storm Events Database, event_id 814171. Narrative written by the NWS forecast office that issued the report.