weather.com suggests about a 40% chance of scattered scattered thunderstorms Friday and Saturday. Is this enough for you to stay home? Are you a vendor or a buyer?
Honestly, by Friday/Saturday most vendors have already left anyways. Most arrive Tuesday or Wednesday and setup immediately to sell to the early guys. I've been arriving Tuesday for the last 3yrs and I'm hardly the first to setup on my row. Things are pretty heated selling-wise all day Tues-Thurs, super quiet on Friday, and then a minor uptick on Saturday because of general public coming out (weather permitting). As for the forecast, looks like storms rolling in overnight on Thursday PM, and then spotty chance for the next few days, so definitely might make an impact on Good-Guys and they're crowd, but I feel folks will be disappointed by the number of remaining vendors by then in the swap meet.
From when I went to Pate when it was on the Museum grounds in the 70's it was either rain or so damned hot for April that the best sale item was water or beer. I used to have to take a load of stuff to sell to have any money to spend and always managed to do both there.