Cooldown expected this weekend with chances of thunder, lightning

SAN DIEGO (FOX 5/KUSI) -- This weekend, the San Diego region is trading the excessive heat for slightly cooler temperatures and an influx of monsoonal moisture, which means muggy conditions and a chance for thunderstorms.

The area of high pressure that blocked flow and brought record-breaking temperatures this week has now shifted east, opening the door for an influx of moisture from the southeast.

Altocumulus clouds have been streaming through the region Friday afternoon, which signals unstable weather and increased moisture.

It's going to feel cooler but a bit muggier this weekend, especially in mountains and inland valleys. Watch out for booms of thunder and flashes of lightning as thunderstorms are possible Friday evening and mainly in the late afternoons Saturday and Sunday.

Saturday daytime highs will reach the mid 70s for the coast, mid 80s for valleys, low 90s for mountains and around 108 degrees for deserts.