As Snowpack is under an open source licence, you are warmly welcomed to contribute to it. Even if you are not a developer, you can contribute by proof reading or expanding the documentation, reporting issues, advertising for Snowpack around you...
If you want to start contributing code, you can look into the open issues, register to the system (please also send an email to Mathias Bavay in order to request the validation of your registration) and attribute the issue to yourself. You can also consider validating that old issues are still relevant and can still be reproduced with the latest version of the model.
Here is a list of issues that could be a good starting point or suitable for an internship project: