Rialto, CA Weather

Synopsis

Cooler conditions with periods of rain through early Friday morning. There are chances of thunderstorms late Wednesday into Thursday morning. Warmer and drier for the weekend with offshore flow on Saturday. The offshore flow weakens for Sunday into early next week. Tides increase over the weekend, remaining elevated through much of next week.

Discussion

FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES...

At 12 PM the main rainfall band was west of Los Angeles County. Rain is expected to continue to move south and east, reaching Orange County late this afternoon and San Diego County early this evening. Two main bands of precipitation are expected with the first one at the onset of precipitation and the next early Thursday morning. Instability will increase overnight as colder air aloft moves across record warm coastal waters for this time in October, around 7 degrees warmer than the long-term average. While coverage of precipitation may be less overnight, there is greater potential for brief higher-intensity rainfall from isolated thunderstorms and stronger showers.

Additional showers will continue on Thursday along with a slight chance of thunderstorms during the afternoon. The greater coverage is expected for Orange and southwestern San Bernardino Counties from the coast to the mountains. The upper level flow will turn northwesterly Thursday evening, with scattered showers continuing for San Diego County into Friday morning, with drier conditions further north.

Through Thursday night for Orange and southwestern San Bernardino Counties, rainfall is expected to range from 0.50-0.75 inch near the coast to 1 to 1.5 inches for the San Bernardino County mountains. For San Diego County, rainfall will decrease from north to south with 0.75 to locally 1 inch over northwestern San Diego County to 0.25 to 0.50 inch across far southern San Diego County. For the most part, rainfall rates will peak at 0.20-30 inches per hour, with the potential for rates 0.45-0.70 inches where thunderstorms develop.

High temperatures will run 5 degrees below average along the coast Thursday and 10 to 20 degrees below average inland. Temperatures will gradually warm Friday onward. For next Monday, high temperatures for coastal areas will be 5 to locally 10 degrees above average with the mountains and deserts a few to around 5 degrees below average. Additionally, the flow will turn offshore on Saturday. Gusty northeast to east winds will develop in and below mountain passes and canyons as well as the Inland Empire corridor between the Cajon Pass and the Santa Ana Mountains. The offshore flow weakens for Sunday into early next week.

Aviation

211900Z...SCT-BKN cumulus cloud layers around 1-8 kft feet are covering most of the region. The first band of +SHRA/RA with a few embedded TSRA are expected to reach northern Orange County around 20- 21z, reaching SD County by 00z, and passing through the region from west to east into the mountains through around 08z. Cigs will drop to 2500-3500 feet MSL and vis 3-6SM during this band's passage. A few embedded +SHRA/TSRA could produce brief and local IFR conditions and locally gusty winds. Winds shift from south to southwest and cigs lift to about 3000 feet MSL. SCT +SHRA/SHRA/TSRA are expected to continue through the coastal basin through the TAF period, bringing intermittent MVFR/IFR conditions and briefly gusty winds.

Marine

A storm system is moving through the outer waters, bringing widespread light to moderate rain. Southerly winds this afternoon will shift to southwest tonight, then westerly Thursday, with occasional wind gusts exceeding 20 knots. A few rumbles of thunder are possible within the first round of rain Thereafter, more rounds of showers with a 10-20% chance for a few thunderstorms at times through Friday. No hazardous marine conditions are expected Friday night through Sunday.