Early summer convection in Argentina & Uruguay

By José Prieto and Jochen Kerkmann (EUMETSAT), Ivan Smiljanic (CGI), Hans-Peter Roesli (Switzerland), Gabriela Ishikame (Servicio Meteorológico Nacional (SMN))

Intensive thunderstorm activity connected to a trough and a cold front affected central Argentina in mid-December 2020. Later it progressed towards Uruguay and southern Brazil.

Cold fronts can sometimes occur in central Argentina in December, quickly weakening as they move north. Around 15 December a trough which formed over the Pacific Ocean started to move across the Andes. Numerical models had predicted the development of a low pressure system in central Argentina. An upper level wave on 18 December in the same area generated intense convection in La Pampa, San Luis and south of Córdoba.

The GOES-16 Night Microphysics RGB (Figure 1) describes the synoptic situation and the Airmass RGB animation (Figure 2) shows the evolution on 19 December, as recorded by the GOES-16 ABI instrument.

The night convection RGB animation (Figure 3) shows the main features of this evolution for around six hours starting on 18 December at 21:00 UTC.

A haboob developed on the eastern side of Andes in the afternoon of 18 December. It reinforced and gained speed northwards as the cold air from Andes capped it, see the GOES-16 satellite imagery (Figure 4) and on-ground video (Figure 5)

Later the wave progressed towards Uruguay and southern Brazil (Figure 6) at a ground rate of 90km/h, see Figure 1, and radar image in Figure 7.

Anvil-level storm dynamics

Anvil-level temperature dipoles are made of a cold updraft and a warm trough on its lee. They can be noticed around the most persistent or intense updrafts (see right loop in Figure 3 (above) and Figure 8).

Next to a 'warm pole', there seemed to be another temperature minimum for the Above-Anvil Cirrus Plume (AACP) in the wake of the strongest updrafts (Figure 9).