textproduct: San Diego

SYNOPSIS

Periods of rain, wind, and mountain snow are expected through the week. There is a slight chance of thunderstorms this evening through early Tuesday morning. Areas of light showers will continue into Tuesday with strengthening west winds along the mountain crests and desert slopes, which peak Tuesday evening into Wednesday morning. A second round of rain and lower elevation mountain snow is expected late Tuesday into Wednesday. Cool with decreasing chances for showers for Thursday and Friday. Chances of precipitation increase again into early next week.

DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE

SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES...

Key Points: *A winter storm will bring widespread heavy snow to the mountains above 5500 ft creating hazardous travel conditions through Thursday. Snow levels as low as 3500 to 4000 ft Wednesday into Thursday may result in light accumulations through the Cajon Pass and along I-8.

*Gusty south to west winds will continue this afternoon from the coast to the deserts. Stronger and potentially damaging west winds along the mountain crests and adjacent desert slopes Tuesday afternoon through Wednesday. *Moderate to locally heavy rain is expected below the snow level through this evening. Ponding of water on roads and minor street flooding in urban areas possible. Increased flows on rivers, especially the San Diego, Santa Margarita, and Whitewater Rivers.

The first round of rain, wind, and mountain snow is currently moving across Southern California. Peak wind gust and rainfall summaries are headlined on our weather.gov/sandiego homepage. Moderate to locally heavy rain is expected to continue through early this evening. Scattered showers will continue into Tuesday morning, with light to moderate rain expected. Snow levels at 1 PM were 6000-6500 ft. Snow levels are expected to drop through tonight falling to as low as 4500-5000 ft by Tuesday morning. More details on expected rain and snow can be found in the Hydrology section below.

The next shortwave is still on track to bring additional rounds of widespread rain, winds, and continued mountain snow Tuesday afternoon into Wednesday morning. Winds are expected to be stronger with this round shortwave for the mountain ridges and desert mountains slopes with gusts to 60 to 70 mph, potentially higher in wind prone locations. For the coast and valleys, peak gusts of 30 to 45 mph are expected and in the deserts gusts of 50 to 60 mph.

There will be lower chances for mostly lighter showers for Thursday into Friday. Chances for precipitation for next weekend are 10 to 15 percent, increasing to 20 percent for Sunday. High temperatures will warm slightly for Thursday and Friday, then gradually warm for Saturday through Monday with Monday high temperatures a few to around 5 degrees above average. High temperatures for next Monday will range from the mid to upper 60s near the coast to the lower to mid 70s for the valleys with the lower deserts around 80.

MARINE

A storm system is generating strong winds with high and choppy seas, but will weaken a bit on Tuesday before increasing again on Wednesday. Seas expected to be around 8-12 feet with wind gusts 25-35 knots, with briefly higher to 40 knots. A Gale Warning is in effect through tonight with another Gale Warning in effect for Wednesday. There is also a slight chance of thunderstorms over the waters today/tonight.

BEACHES

Strong westerly swell (9-11 feet with an average period of about 10- 12 seconds) will produce large breaking waves up to 8-12 feet on most beaches across Orange and San Diego Counties today through Friday night. Widespread, strong rip currents are also likely with these waves and dangerous swimming conditions expected. A High Surf Advisory is in effect and contains more information.

HYDROLOGY

Widespread rain and snow is expected to continue through this evening. Peak rainfall rates of 0.30-0.60" per hour are expected through the afternoon, with rates up to 0.30" per hour expected in showers overnight and into Tuesday morning. Snow levels are expected to drop to 4500-5000 ft by Tuesday morning and high resolution models are showing persistent showers in the mountains into Tuesday morning. Isolated showers will continue into Tuesday afternoon, with the highest chances of precipitation in the mountains.

Another round of rain and mountain snow is expected Tuesday night into Wednesday. Hourly rainfall rates are expected to be 0.20-0.30" per hour. Forecast rainfall totals for Tuesday into Wednesday are 0.25-0.60" for the coast and valleys, 0.20-0.30" for the High Desert, and 0.10-0.25" for the low deserts. 1-2" of rain are expected below the snow level Tuesday night into Wednesday. For Tuesday into Wednesday snow forecast has an additional 4-10" 5000- 6000 ft, 10-20" 6000-7000 ft, and up to 2 ft above 7000 ft. The San Diego County mountains may see some accumulating snow, with totals of 1-3", locally higher at the highest peaks.

The San Diego River at Fashion Valley and the Santa Margarita river are expected to reach monitor stage. The San Diego River is expected to reach monitor stage by 11 PM. The Santa Margarita River is expected to start responding tonight/early Tuesday morning, but is not expected to reach monitor stage until Wednesday. Interested parties should continue to closely monitor the river forecast and observed river levels this week. Current forecast indicates minor flood impacts to Avenida del Rio may occur. Please see the latest River Statement or CNRFC website for more information. There may be impacts to Whitewater River although with significant snow forecast to impact the higher elevations of the mountains, flood impacts may be limited.

Scattered light rain and snow showers are possible through Wednesday into Thursday as a third shortwave moves north of the area. Snow levels for Wednesday and Thursday are expected to be 3500-4000 ft so if any snow showers develop accumulating snow could impact the Cajon Pass and along higher portions of I-8.

There remains slight chances of precipitation Friday through the weekend ahead of the next trough set developing over the Gulf of Alaska. There remains considerable uncertainty in the details of the forecast but periods of unsettled weather looks possible next week.

SGX WATCHES/WARNINGS/ADVISORIES

CA...Wind Advisory until 8 PM PST this evening for Orange County Coastal Areas-Orange County Inland Areas-San Bernardino and Riverside County Valleys-The Inland Empire-San Diego County Coastal Areas-San Diego County Valleys-Santa Ana Mountains and Foothills.

Wind Advisory from 8 PM Tuesday to 8 AM PST Wednesday for Orange County Coastal Areas-Orange County Inland Areas-San Bernardino and Riverside County Valleys-The Inland Empire- San Diego County Coastal Areas-San Diego County Valleys- Santa Ana Mountains and Foothills.

High Surf Advisory until 10 PM PST Friday for Orange County Coastal Areas-San Diego County Coastal Areas.

Winter Storm Warning until noon PST Wednesday for Riverside County Mountains-San Bernardino County Mountains.

Wind Advisory until 1 AM PST Tuesday for San Diego County Deserts-San Diego County Mountains-San Gorgonio Pass near Banning.

Wind Advisory from 10 AM Tuesday to 4 PM PST Wednesday for Apple and Lucerne Valleys-San Diego County Deserts-San Diego County Mountains-San Gorgonio Pass near Banning.

Wind Advisory until 10 PM PST this evening for Apple and Lucerne Valleys.

PZ...Gale Warning until 7 AM PST Tuesday for Coastal Waters from San Mateo Point to the Mexican Border and out to 10 nm-Waters from San Mateo Point to the Mexican Border Extending 10 to 60 nm out including San Clemente Island.

Gale Warning from 8 PM Tuesday to 1 PM PST Wednesday for Coastal Waters from San Mateo Point to the Mexican Border and out to 10 nm-Waters from San Mateo Point to the Mexican Border Extending 10 to 60 nm out including San Clemente Island.