Intense thunderstorms in Argentina and Uruguay, with hail and rain, helped extinguish fires in February 2018.
Néstor Santayana (INUMET), Jochen Kerkmann and Jose Prieto (EUMETSAT)
From 15–19 February, a strong anticyclone centred on northern Argentina and Uruguay keeping the fronts restricted to the southern tip of the continent. The jet stream was at high latitudes too.
The low level jet (LLJ) pushed the air mass to the south and brought instability and convection over those five days. The convection was triggered by thermal, orographic and pre-frontal mechanisms in the beginning, then more frontal mechanisms towards the end.
The thunderstorms brought hail and rain to the region and relieved the drought associated with the La Niña period. The areas of expected rain and heat on the week 15-21 February are depicted on this forecast graphic.
On 16 February at 18:30 UTC there were several storms in the Andes foothills. The storm nearest the fires developed with very bright NIR2.3 colours close to a moisture boundary, perhaps because the ash from the fires delayed the generation of the ice phase.
The GOES-16 Natural Color RGB (Figure 2) shows the storm which developed close to the humidity boundary and to the fires.
It is not clear which of the two influences causes the special colouring, compared with other storms nearby. Also, that cloud seems to start its development as a mesoscale convective system (MCS) before and faster than the other MCSs north and south of it.
Figure 3: ABI Near-Infrared 2.25µm, 16 Feb 11:00–23:15 UTC. Download animation (MP4, 2 MB)
Figure 3 is the animation of the ABI Near-Infrared imagery, showing the daily cycle with the evolution of size particle inside the MCS. This channel shows a deeper layer under the cloud top than 1.6µm or 0.6µm, old friends of Meteosat users.
Figure 4: ABI Cloud Type RGB, 16 Feb 11:00–23:15 UTC. Download animation (MP4, 3 MB)
Figure 4 is the animation of the ABI Cloud Type RGB (1.38µm, 0.64µm, 1.61µm), which illustrates the growth of a few storms, south of the fires in the centre of the image. They start as cyan lines, at low level, then they turn into yellow when the small droplets and crystals reach higher levels. Finally, they turn red while losing severity and dissolving.