Periods of rain, wind, and mountain snow are expected through late Thursday. The final two rounds of widespread rain, snow, and gusty winds will be tonight into Wednesday morning and Thursday afternoon and evening. Strong southwesterly winds and heavy mountain snow tonight into Wednesday. There is a slight chance of isolated thunderstorms overnight. Periods of dry conditions expected Wednesday mid-morning into Thursday morning. Chances for showers decrease into Friday, with dry conditions through the weekend. Chances of precipitation increase again into early next week.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
*A winter storm will bring widespread heavy snow to the mountains above 5000 ft creating hazardous travel conditions through Thursday evening. Snow levels as low as 3500 to 4000 ft Wednesday night and again on Thursday may result in light accumulations through the Cajon Pass.
*Gusty and potentially damaging southwest to west winds along the mountain crests and adjacent desert slopes through Wednesday afternoon. Gusty westerly winds for the coast and valleys will peaking early Wednesday morning.
*Light to moderate rain is expected below the snow level at times through Thursday night. Ponding of water on roads and minor street flooding in urban areas possible. Increased flows on rivers, especially the San Diego and Santa Margarita which are both forecast to reach Monitor Stage Wednesday morning.
Evening update, Light showers continue this evening with the greatest coverage across the San Bernardino Mountains. Satellite water vapor imagery shows the center of the upper level low moving east into the Bay Area with a trough axis extending south off of Point Conception. An area of light to moderate showers is currently moving through Ventura County, with the main cold front and heavier showers and thunderstorms back in Santa Barbara and San Luis Obispo Counties. This front will progress eastward overnight, reaching Orange and San Bernardino Counties around 2-4 AM, then quickly spreading south and east through the morning, tapering off after 8 AM. Snow levels currently around 5000-5500 ft this evening will rise slightly to around 5500-6000 ft in the southwesterly warm air advection ahead of the front, then fall to around 4000-5000 ft with the cold front, and as low as 3500-4500 ft as precipitation tapers off Wednesday morning. Moderate to heavy snow and blowing snow could reduce visibility to near zero in the mountains at times. Isolated light showers will continue at times through the day Wednesday into Thursday morning, mainly across San Diego County. The next short wave moves through late Thursday morning through Thursday afternoon, bringing another round of more widespread precipitation and mountain snow.
In addition to the precipitation, southwest to west winds will continue to strengthen tonight, peaking late tonight into Wednesday morning across all areas. Gusts near the northern foothills of the San Bernardino Mountains have already exceeded 70 mph, with one gust of 91 mph along Highway 18 at the base of the mountains earlier this afternoon. In general, expect peak gusts of 60-70 mph on the remote desert mountain slopes with isolated gusts in excess of 75 mph, gusts of 45-60 mph for remaining mountains and deserts, and gusts of 30-40 mph west of the mountains. Winds will weaken across the coastal areas and valleys pretty rapidly behind the front Wednesday morning, but persist in the mountains and deserts into Wednesday afternoon.
Previous discussion, There will be decreasing chances for showers into Friday morning. Much of Friday through Sunday is trending drier than previous forecasts. High temperatures will warm each day for Friday through Monday with high temperatures on Monday around 5 degrees above average, ranging from the mid to upper 60s near the coast to the lower to mid 70s for the valleys with the lower deserts around 80. Shower chances begin to increase again early next week, with NBM showing chances of precipitation as early as Monday. The NBM is a bit of an outlier with individual ensemble members of the GEFS and ECMWF beginning to cluster around the middle of the week for the onset of the next round of precipitation.
Isolated light showers will slowly increase in coverage and intensity the remainder of this evening. The next round of more widespread showers with heavier precipitation is expected late tonight into Wednesday morning. An additional round of more widespread showers is expected late Thursday morning through Thursday afternoon, though with lesser totals than for previous rounds this week. Additional rainfall this evening will generally be less than 0.10" for most areas, with isolated amounts up to 0.25" on the coastal slopes of the mountains.
For late tonight through Wednesday afternoon, precipitation totals will range from 0.25 to 0.40 inch for coastal areas to 1 to 1.5 inches in the mountains, locally to around 2 inches. For the deserts, 0.15 to 0.50 inches is expected for the Apple and Lucerne Valleys, highest near the foothills of the San Bernardino Mountains, with 0.05 to 0.30 inch for the lower deserts. For late tonight into Wednesday morning, peak hourly rainfall rates of 0.30 to 0.50 inch are expected, with isolated rates to 0.70 inch per hour in heavier showers and thunderstorms.
For Thursday night into Friday, additional rainfall and liquid- equivalent above the snow level will range from 0.25 to 0.35 inch near the coast to 0.75 to 1 inch for the mountains, locally exceeding 1.25 inch.
The snow level will remain around 5000 to 5500 feet this evening, rising slightly to 5500-6000 ft tonight, then fall to around 3500 to 4500 feet by Wednesday morning. Snow levels rise to 4000-4500 ft late Thursday morning, then fall back to 3500-4500 ft early Friday morning as precipitation tapers off. Additional snow accumulations tonight into Wednesday of 1-2 ft above 6000 ft, and around 3-6 inches at the 5000 ft level. Another 3-6 inches is possible Thursday into Friday, with the potential for light accumulations through the Cajon Pass and near Pine Valley and Crestwood Summit on I-8.
The San Diego River at Fashion Valley is forecast to reach Monitor Stage again by 7 AM Wednesday. Crests above monitor stage are sufficient to begin flooding of low-water crossings in Mission Valley. The Santa Margarita River at Ysidora is forecast to reach Action Stage by 11 AM Wednesday. See the Hydrologic Statement (RVSSGX) for more details on the river forecasts.
180500z, Coast/Valleys, SCT/BKN low clouds based 3000-5000 ft MSL currently through the coastal basin will fill in and lower to 2000- 3000 ft MSL through the early morning as precip moves in from the northwest. Strengthening south to southwest winds will gust 25-35 kts through the basin (isolated gusts over 40 kts at the coastline) after 06Z ahead of a main band of moderate to heavy precipitation. This band is expected to sweep through from northwest to southeast from 09-16Z bringing widespread MVFR cigs/vis with intermittent IFR conditions expected in heavier showers. Slight chance (10-20%) for TSRA within the main band. Winds turn west and slowly weaken, thereafter, with generally VFR conditions expected. ISO-SCT -SHRA may briefly create MVFR cigs/vis through the day, especially in San Diego County.
Mountains/Deserts, RA is currently spreading into San Bernardino County ahead of the next storm system. Precip will continue to increase in coverage and intensity overnight as another line of moderate to heavy precip sweeps northeast to southwest across the area. Mountains shrouded in FG through Wednesday morning. Intermittent MVFR vis due to RA in the High Desert 09-13Z. Additionally, strong south to southwest winds will continue to strengthen this evening with widespread gusts up to 35-45 kts after 06Z. Gusts to 60 kts along desert slopes of the mtns with isolated gusts exceeding 65 kts along the slopes in San Diego County. Areas BLDU (vis 3-5SM) and moderate to strong up/downdrafts in the lee of mtns. Precip will slowly come to an end from north to south from 12- 18Z (except for persistent -SHRA/SHSN along coastal slopes) with winds turning westerly, but remaining elevated (strong along eastern facing slopes) through 00Z Thu.
Winds continue strengthening tonight with winds frequently gusting to 35 kts after midnight. Hazardous boating conditions expected with steep seas building to 11-13 feet. Check the Gale Warning for more details. Winds slowly weaken through late Wednesday morning. After another lull, strong winds will redevelop Thursday, likely producing hazardous conditions once again. Conditions will improve by Friday.
High surf of 4 to 9 feet is expected, with sets as high as 11 feet, highest in San Diego County on Wednesday. Dangerous swimming and surfing conditions and localized beach erosion can be expected. A High Surf Advisory is in effect through Friday and contains more details.
Ca, High Surf Advisory until 10 PM PST Friday for Orange County Coastal Areas-San Diego County Coastal Areas.
Wind Advisory until 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.
Winter Storm Warning until 10 PM PST Thursday for Riverside County Mountains-San Bernardino County Mountains.
Winter Weather Advisory until 10 PM PST Thursday for San Diego County Mountains.
Wind Advisory until 4 PM PST Wednesday for Apple and Lucerne Valleys-San Diego County Deserts-San Gorgonio Pass near Banning.
Wind Advisory until 4 PM PST Wednesday for Coachella Valley.
PZ, Gale Warning until 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.
