A round of more widespread moderate to locally heavy showers are expected this evening into the overnight hours, moving from northwest to southeast across the area. Shower activity is expected to become isolated and light for later Monday morning into Tuesday. Dry weather may return as early as Wednesday, with greater chances for dry conditions by Thursday or Friday. By the weekend, dry conditions are expected with warmer temperatures and the potential for Santa Ana winds.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
.Evening Update,
Light showers continue across areas along and west of the mountains, the heaviest of which have remained across LA County through the early evening today. Showers are seen off the coast this evening, which will move inland through the overnight hours. Rain rates across the mountains have generally been under one half inch, where localized flooding may be possible. Showers off the coast that are moving toward Orange and San Diego Counties look to be fairly light, but some showers may become more intense as the evening progresses. Agree with my colleague below that storm threat continues to decrease as our latest sounding only shows minor instability and lightning has not been observed in the area so far.
Models continue to show a drier scenario by Monday as the trough begins to deepen over California. Isolated showers will be primarily focused in San Diego County on Monday with other areas being mostly dry by the afternoon hours. As the system along the West Coast that is currently impacting us becomes a closed low by Tuesday and Wednesday, it will be interesting to see where exactly this low goes. Model guidance is still not aligned on this thinking, which will be key to see if we see more rain before we dry out by the latter half of the week.
.Previous Discussion (107 PM Sunday),
For this evening into the overnight hours, another round of widespread moderate to locally heavy precipitation is expected to move from northwest to southeast across the area. Much of the rain will fall in and west of the mountains, with minimal accumulation expected in the deserts. Peak hourly rainfall rates for the evening and overnight period are expected to be 0.30-0.60"/hour. Confidence in thunderstorm potential has decreased given that the best factor that may contribute to convective initiation is an area of MUCAPE between 250-500 J/kg in the mid-layers, which current model guidance is showing mainly south of San Diego county. After the passage of the main band of precipitation overnight, shower coverage and intensity will become more isolated and light for much of Monday.
Snow levels are expected to remain above 7000 ft through this evening, eventually dropping to 6000 ft by Monday morning. Elevations 6000-7000 ft are forecast to pick up an inch or two of snow, with the most accumulation of snowfall occurring at 7500 ft and above.
The passing shortwave that is bringing us precipitation will also increase onshore flow. That will bring periods of gusty south to southwest winds over the mountains and into the deserts. As the main front passes tonight, elevated south winds can be expected along the immediate coast. Overall peak wind gusts of 40 to 50 mph, locally up to 55 mph are expected for the mountains; gusts 30 to 40 mph are expected in the deserts; and gusts of 20 mph to locally near 30 mph along the coast. Winds will quickly decrease along the coast after the front passes with a more gradual decrease in winds for the mountains and deserts into Monday night.
For Tuesday and Wednesday a closed low is expected to begin to dig south out over the Pacific ocean. Overall, model solutions are taking the track of the low south of the border but there remains some uncertainty in how far off the coast of California it will be and how far south it will dig. A more easterly track will maintain chances of precipitation for Southern California, especially for the coast and valleys. A more westerly track would keep us dry. How far south the low digs will also have an impact on our precipitation forecast with the potential for wrap around moisture into the Riverside and San Diego county mountains and adjacent desert areas. Current forecast has a 15-25% chance of precipitation for Tuesday into Wednesday morning with dry conditions for much of Wednesday into Thrusday. The speed of the eastward progression of the low will certainly play a role in how the forecast develops in the coming days. About 30% of ensemble solutions are trending slower, which would maintain chances of precipitation into Thursday.
By Saturday, all ensemble solutions are showing ridging over the US West Coast or the Western US, which will bring warmer conditions to the area. A robust surface high is currently forecast to develop over the Great Basin on Saturday which would turn the pressure gradient offshore bringing periods of Santa Ana winds. Current ensemble guidance is showing a 30-40% chance of moderate Santa Ana winds developing by Saturday, with a 60-80% chance of weak to moderate Santa Ana winds.
The San Diego River at Fashion Valley is expected to exceed Action/Monitor stage early Monday morning, peaking at 8.1 ft by 8 AM Monday. River levels will slowly fall through Monday afternoon, eventually falling below Action/Monitor stage by mid-afternoon. Based on forecast water level, main impacts are expected to be confined to Avenida del Rio. Stay informed on the latest river forecasts and conditions. Do not drive through flooded areas or around barricades.
050400z, Several bands of -SHRA/SHRA are moving northwest to southeast across the region, bringing cigs 1500-2500 ft MSL and vis 2-5 SM as they pass. Elsewhere, multiple layers of clouds 3000-6000 ft MSL are covering most of the region. Conditions will continue to vary from low end VFR to MVFR tonight, with occasional IFR in locally heavier showers, as these bands pass through overnight. Showers become more isolated and cigs trend higher 5000-7000 ft MSL 15-18Z Mon, but -SHRA continue in San Diego Co and over mtns through the afternoon.
Low desert regions likely remain dry through the period, with a low (20%) chance for -SHRA late tonight. Otherwise, SCT to locally BKN 3000-5000 ft MSL through early Mon.
No hazardous marine conditions expected through Thursday.
Highest daily tides fall below 6.5 feet by Monday morning, and will continue to gradually decrease through the week.
The elevated westerly swell decreases tonight and Monday, but breaking waves of 4 to 6 feet will continue through Monday morning. This will lead to hazardous swimming conditions and contribute to potential coastal flooding.
A Beach Hazards Statement remains in effect for these hazards and contains more details.
Ca, Beach Hazards Statement through Monday morning for San Diego County Coastal Areas.
PZ, None.
