A friend who hangs around only as long as you can provide what he or she cannot (or would rather not) provide for him or herself. This is the friend who is always lamenting their lack of money and makes you feel a certain level of pressure when the time comes to pay for lunch or other entertainment you've shared. This feeling can go as far as a feeling of guilt for being well-off (or not so necessitated) yourself and you may end up offering this person money to help them out. However, the welfareweather friend never pays back and their situation never seems to improve.
friend: "Should we invite Carmen to lunch with us?"
you: "I'd rather not have to pay for her today."
friend: "Yeah, that's true. And we'd have to pay for her kids' lunch too, for sure"
you: "Whenever I tell her I can't invite, she says no to everything. She's a welfareweather friend."