Early summer convection in central Argentina and Uruguay
18 December 2020 21:00 UTC-19 December 23:00 UTC
Severe convection in central Argentina in December 2020, viewed by GOES-16.
26 January 2021
11 January 2021
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 90 km/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).
These cold areas coincide with the darker red (to black) areas in the Dust RGB (Figure 10). Darker red shades are connected to negative brightness temperature difference between IR window channels (BTD12-10), which generally indicate thin cirrus clouds (e.g. edges of the main storm anvil, or AACP in this case), or even a higher moisture content (e.g. cloud-free area to north of the system) as seen in Figure 9.
AACPs are colder than warm lee troughs, which are the warm 'pole' of aforementioned temperature dipoles, but seem to be warmer than wider updraft area, best seen from the 'sandwich loop' in Figure 11. Note that wind in the level of storm anvil was westerly.
This event was covered by one of the MESO scan sectors of GOES-16 between 19 and 20 December 2020. The Argentinian weather service, Servicio Meteorológico Nacional (SMN), and NOAA have coordinated frequent scans in the past for the Remote sensing of Electrification, Lightning, And Mesoscale/microscale Processes with Adaptive Ground Observations (RELAMPAGO) project. This future the SMN plans to request operational MESO scans to cover hazardous situations like the one presented in this case.
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