SAN DIEGO (FOX 5/KUSI) -- Beautiful and warm weather is on tap this weekend, but it'll be toasty in the deserts as temperatures soar close to 110 degrees. There will be a low pressure system in the southwest and an area of high pressure over Arizona, but it looks like warmer weather is winning the battle here in San Diego. An Excessive Heat Warning is in effect for county deserts Friday and Saturday.  Patchy fog is expected to develop Saturday morning along the coast and a few miles inland, so watch out for lower visibility on the roadways. The marine layer should clear a bit faster for coastal areas, but days will end and start with overcast conditions. Daytime highs for beaches on Saturday will be in the mid-70s, upper 80s for inland valleys, mid-80s for mountains and close to 110 degrees for deserts.  A slight cooling will happen regionwide for Sunday before warmer temperatures bounce back again early next week.  An irregular warm and dry pattern is expected to set up the first half of October for nearly the entire western half of the U.S.