Case study: 05 March 2018

Some cities in the Paraiba river valley experienced strong winds in the afternoon of 05 March 2018. In São José dos Campos, the wind gusts peaked at 75 km/h, and nearly 100 trees fell, causing trouble to the traffic (https://g1.globo.com/sp/vale-do-paraiba-regiao/noticia/temporal-com-ventos-de-mais-de-75-kmh-derruba-cerca-de-100-arvores-e-deixa-bairros-sem-energia-em-sao-jose.ghtml).

The lower and middle troposphere had very weak winds on te 05/03 afternoon, with low-level winds from the southwest at no more than 10 m/s. The precipitable water ranged from 40 to 45 mm, which is typical at this time of the year. This very moist environment helped in the high precipitation caused by some storms in the region. The 925 hPa winds and specific humidity in the lowest 100 hPa (figure below) show the very moist air mass over the area and weak 925-hPa winds. However, the sea breeze at this time caused inland-directed winds, and enhanced low-level convergence over the Paraiba river valley at this time.

Specific humidity in the lowest 100 hPa and 925-hPa winds at 1800 UTC 05/03/2018.

The reflectivity core that passed over São José dos Campos is shown below. The highest reflectivity was nearly 55 dBZ at 1.0° elevation, which characterizes high amounts of hydrometeors. The most affected area was the south of the city, exactly where the convective core is located at 1920 UTC.

Refletividade (dBZ) no PPI de 1.0° às 1920 UTC do dia 05/03/2018.

O VIL mostra valores altíssimos (>50mm) sobre a região. Esses valores sõ condizentes com alta quantidade de hidrometeoros na tempestade. Devido aos fracos ventos na troposfera, pode-se concluir que a descida da precipitação nas correntes ascendentes foi o que mais contribuiu para causar ventos fortes em superfície.

 

Vertically Integrated Liquid (VIL; mm) no CAPPI de 3km às 1920 UTC do dia 05/03/2018.

Abaixo está o Echo-top de 35 dBZ, que mostra que refletividades de 35 dBZ foram observadas pelo radar em mais de 12 km de altura, ou seja, tratava-se de grande quantidade de gelo na alta troposfera. Essa é uma assinatura de severidade da tempestade.

 

 Echo-top de 35 dBZ (km) às 1920 UTC do dia 05/03/2018.