If the certificate is unable to be verfied, you can open set strict-ssl to false. You should be able to configure this by runnning
yarn config set "strict-ssl" false -g
But the command is currently not working, see issue 980.
As an alternative you can navigate to C:\Users\\ and open .yarnrc and manually update it as follows:
# THIS IS AN AUTOGENERATED FILE. DO NOT EDIT THIS FILE DIRECTLY.
# yarn lockfile v1
strict-ssl false