Since at least 1971.
28 Apr 2017 – With the mercury plunging to -5.2ºC, São Joaquim registered the strongest freeze in the month of April in the last 46 years.
On the grass, the thermometers reached an impressive -11.4 ° C (Climaterra station, -4.1 ° C shelter, also a record). (Not exactly sure what they mean by “on the grass.”)
The vast majority of cities in the state of Santa Catarina (southern Brazil) recorded the lowest April temperature in many decades, in some cases the coldest April temperature on record.
Thanks to Lucas Pimenta for this link