Monsoon moisture could make for a humid Labor Day in Southern California

Monsoon moisture will spread across the region Sunday and Monday, increasing the possibility of mountain and desert thunderstorms, according to the National Weather Service. The mid-level moisture will inhibit formation of the marine layer in some locations and the added humidity will make the above-normal temperatures more uncomfortable.

Upper-level high pressure over the Four Corners is expected to weaken and shift to the east, beginning Sunday night. As a result, the flow aloft will switch to the southeast, pulling up monsoonal moisture from Mexico.

There is a slight chance of thunderstorms in the eastern San Gabriels on Monday afternoon, and the air is likely to feel a bit more sticky during Labor Day picnics, cookouts and other outdoor holiday activities.