Do they still even use weather balloons?
Apparently so.
From Ballooning and Meteorology in the Twentieth Century:
Balloons are ideal for gathering meteorological information and have been used for that purpose throughout their history. Meteorological measurements of wind and air pressure have gone hand in hand with the earliest balloon launches and continue today. Balloons can climb through the denser air close to the Earth to the thinner air in the upper atmosphere and collect data about wind, the different layers of the atmosphere, and weather conditions as they travel.
From the bit of research I did scientists also use balloons all the time to study the atmosphere and near space.