Observations of a squall line and its near environment using high-frequency rawinsonde launches during VORTEX2

Nine soundings were released within 3 h, allowing for unprecedented analysis of the squall line's internal structure and nearby environment. Four soundings were released in the prestorm environment and they document the following features: low-level cooling associated with the reduction of solar isolation by a cirrus anvil; abrupt warming (1.5 K in 30 min) above the boundary layer, which is probably attributable to a gravity wave; increases in both low-level and deep-layer vertical wind shear within 100 km of the squall line; and evidence of ascent extending at least 75 km ahead of the squall line.

The next sounding was released ~5 km ahead of the squall line's gust front; it documented a moist absolutely unstable layer within a 2-km-deep layer of ascent, with vertical air velocity of approximately 6 m s⁻¹. Another sounding was released after the gust front passed but before precipitation began; this sounding showed the cold pool to be ~4 km deep, with a cold pool intensity C ≈ 35 m s⁻¹, even though this sounding was located only 8 km behind the surface gust front.