An infusion of monsoonal moisture from Arizona and Baja California threatens to trigger showers and slow-moving thunderstorms in the Southland Friday, forecasters said.
If today's "moist and unstable conditions'' produce thunderstorms, it will occur this afternoon and this evening, according to a National Weather Service advisory.
Because the winds in the upper atmosphere are light, thunderstorms will be slow-moving, "increasing the potential for heavy rainfall and associated flash flooding,'' it said.
"The greatest probability of flash flooding in our forecast area will be the eastern San Gabriel mountains, the washes and arroyos across the Antelope Valley, as well as the Lockwood Valley area in the Ventura County mountains.''
Temperatures will remain a few degrees above normal today but short of the heat wave-levels recorded between Aug. 5 and Wednesday, NWS forecasters said.
The Western San Fernando Valley is likely to experience temperatures 8-10 degrees higher than they should be, said NWS meteorologist Curt Kaplan. The NWS forecast highs today under partly cloudy skies of 102 in Woodland Hills.
Saturday's highs will be up to five degrees lower in some areas and go down some more over succeeding days, according to an NWS forecast.