A Pacific storm will continue to impact the region through the weekend. Heavier and more widespread precipitation will develop this morning, including a chance of thunderstorms. The weather pattern will remain active with another winter storm expected to impact the region for Monday into Tuesday with another system expected to impact the region later next week.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Scattered mostly light showers continue to lift north across the region this morning with rainfall rates generally 0.10 inch per hour or less. However, that will change drastically later this morning as the upper level closed low currently around 300 mi west of San Diego drifts eastward and a vort max lifts north over So Cal. This forcing combined with forecast Integrated Vapor Transport (IVT) of over 500 kg/m/s and PW near 1.5" will produce widespread moderate to heavy precipitation today, mainly between 6 AM and 4 PM. Rainfall rates for urban areas are forecast to peak around 0.30-0.50"/hr, and as high as 0.80"/hr on the south facing mountain slopes. There is a 15-30% chance of thunderstorms today as well, which could produce locally higher rainfall rates/amounts. Rainfall rates of this intensity will likely produce roadway flooding, especially in poor drainage areas, and bring a threat of mud and debris flows in and below the recent burn scars. A Flood Watch remains in effect from 4 AM through 10 PM today.
Additional total rainfall through Sunday evening will be around 1.50-2.25" for the coasts and valleys, 2-4" for the mountains, and 0.50-0.80" for the deserts. Snow levels will remain above 7500 ft through the day, lowering to 6500-7000 ft tonight into Sunday morning, then rising to around 7500-8000 ft during the day Sunday, with snowfall totals of 1-4" above 7500 ft.
Rain turns to scattered showers this evening, some of which could be heavy as thunderstorm chances continue, then weaken and become more isolated Sunday morning. Isolated light showers will persist through the day Sunday into Monday morning. We may get a brief break late Monday morning before the next round of precipitation moves in sometime during afternoon, heaviest and most widespread late Monday into Tuesday morning. This second system will be another slow mover with precipitation lingering into Wednesday. A weak Atmospheric River is forecast to accompany this system, but there is still a lot of spread in total rainfall amounts. For the coasts and valleys, NBM 25th to 75th percentile precipitation range anywhere from 0.10-0.20" on the dry end to around 1-1.5" on the wet end. The chance of 48 hr rainfall totals exceeding 0.50" is around 45-65%, and chance of exceeding 1" is 25-50%, lowest in the Inland Empire. Snow levels with this storm will be lower, falling to 5500-6000 ft Monday night, then rising to 6000-6500 ft for Tuesday afternoon into Wednesday. Drier weather will then follow for Wednesday afternoon through Thursday morning.
For the next potential storm later in the week, huge uncertainty remains. Ensembles are split about 50/50 on the low tracking south just off the coast (wetter) versus a more inside track (drier), and a few ensemble members are completely dry. The timing is also questionable, with precipitation onset as early as Thursday afternoon and as late as Friday morning or afternoon.
Aside from precipitation, high temperatures will range from around 10 to 20 degrees below normal through much of the week with periods of breezy southwest to west winds as each storm system moves through.
151000z, Scattered -SHRA moving south to north over the region this morning with BKN-OVC deck 3000-5000 ft MSL and a few SCT lower decks 1000-3000 ft MSL. Main frontal band to reach the coast around 13Z, bringing widespread moderate to heavy rain from west to east. At least two waves of precip likely 13-21Z, bringing bases as low as 500-1000 ft MSL and VIS 1-3 SM in intermittent +RA, with brief breaks of improved conditions likely. 10-20% chance TSRA, highest for the coast and in inland valleys 13-22Z then higher chances migrate inland after about 20Z. Coverage of TSRA and RA (along with associated CIG/VIS restrictions) begins to decrease from south to north after 21Z, with scattered -SHRA continuing through the period.
Frontal band to bring south to southeast winds gusting 20-30 kts west of the mountains, highest along coast, 13Z to about 20Z. Winds turn southwesterly after about 20Z and diminish along the coast, while WSW gusts 25-40 kts pick up over mtns and desert slopes through the late evening.
Another round of heavier SHRA along the coasts and valleys along with breezy southeast winds possible after 08Z Sun, bringing lowered bases and reduced VIS, with high res guidance indicating highest chances in SD County for impacts.
South winds increase to 15-25 kts early this morning, with gusts 25- 35 kts possible through the afternoon, strongest in the late morning and early afternoon. This will bring steep, mixed seas 5-8 feet throughout the coastal waters. See the Small Craft Advisory for more. Winds become west-southwesterly mid-afternoon and then weaken to 10-15 kts tonight with periods of stronger winds still possible through Sunday with outflow under showers.
Additionally, heavy rain will lead to reduced visibility and thunderstorms embedded within the rain resulting in gusty, erratic winds, lightning, and possible waterspouts. A Marine Weather Statement in effect through late today contains more details.
Winds strengthen again Monday afternoon ahead of the next storm system. There is still some uncertainty in exact intensity of winds, but gusts in excess of 20 knots are possible along with another round of precipitation.
West swell 4-5 feet will combine with a south wind swell to create elevated surf 4-7 feet with local sets to 8 feet through the late afternoon today. Additionally, there is a chance (20-30%) for thunderstorms through late this afternoon. See the Beach Hazard Statement for more.
Ca, Beach Hazards Statement through this afternoon for Orange County Coastal Areas-San Diego County Coastal Areas.
Flood Watch through this evening for Apple and Lucerne Valleys- Coachella Valley-Orange County Coastal Areas-Orange County Inland Areas-Riverside County Mountains-San Bernardino County Mountains-San Bernardino and Riverside County Valleys-The Inland Empire-San Diego County Coastal Areas- San Diego County Deserts-San Diego County Mountains-San Diego County Valleys-San Gorgonio Pass near Banning-Santa Ana Mountains and Foothills.
PZ, Small Craft Advisory until 4 PM PST this afternoon 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.
