I need motivation to go the the gym..?

The weather has been pretty good where I live and I've been able to work out at home and outside for quite a long time. However, the weights I have at home aren't really heavy enough anymore and I can't afford to buy new ones now. It has also gotten very hot out here. About 105 degrees. And there are a lot of mosquitoes out which makes it hard to run outside. Plus I do have a gym membership that is not getting good use. And I feel like I get a better workout there, so I know I should go. For the past week I've been thinking about going to the gym, but I can't seem to motivate myself. How can motivate myself to go to the gym tomorrow?