python - Write to CSV on first empty line

I'm developing an application to write lines to a CSV. However, when I run the application a second time, the line that was already written is overwritten with the new line. How can I make it so that the writer writes to the next blank line, not one that already has data in it? I haven't found anything on how to do this. Here's my code below:

listsof = [1, 2, 3, 4]
with open('C:/Users/Family3/Downloads/weather.csv', 'w', newline='') as csvfile:
    writer = csv.writer(csvfile, delimiter=',',
                            quotechar='|', quoting=csv.QUOTE_MINIMAL)
    writer.writerow(listsof)