Case study: 24 January 2018

Several severe storms occurred in central São Paulo state on 24 January 2018. The cities of Araraquara (https://g1.globo.com/sp/sao-carlos-regiao/noticia/chuva-forte-em-araraquara-sp-derruba-arvores-e-destelha-casas-veja-video.ghtml) and Bragança Paulista (https://g1.globo.com/sp/vale-do-paraiba-regiao/noticia/telhado-de-universidade-cai-durante-temporal-em-braganca-paulista-veja.ghtml) were the most affected.

The environment was characterized by relatively high geopotential heights in the mid and upper troposphere (Fig. 1), with anticyclonic circulation in the flow. This prevented strong convective overturning and guaranteed a low number of storms in the region, some of which were severe. São Paulo sounding was not launched in this day, unfortunately, but GFS estimative of CAPE ranged between 2000 and 2500 J/kg at 18Z.

Fig. 1: Wind speed (m/s, shaded), wind barbs (kt) and geopotential height (dam, black contours) at 18Z 24 January 2018.

Among the most impressive characteristics of the storms that affected Araraquara and Bragança Paulista was the very high value of vertically integrated liquid (VIL). Figs. 2 and 3 shows VIL values over 50 mm in both storms, which was likely associated with high amounts of hidrometeors (mainly hail) in the troposphere.

 Fig. 2: VIL derived from São Roque S-band radar at 18:20Z 24 January 2018.

 Fig. 3: VIL derived from São Roque S-band radar at 18:50Z 24 January 2018.