Add spaces: OnFridayitwillbemainlycloudy,butmostlydryforawhile.Theafternoonwillbringisolatedshowersorthunderstorms.Intheeveningvariablecloudswithrainshowerswillprevail.
On Friday it will be mainly cloudy, but mostly dry for a while. The afternoon will bring isolated showers or thunderstorms. In the evening variable clouds with rain showers will prevail.