16/428 PM.
Scattered to isolated showers will persist through late tonight across the area. A cooler storm system will spread rain from northwest to southeast across the area late tonight through Monday night, with decreasing showers continuing into Tuesday. Wednesday will offer a brief respite from the rain with warmer temperatures. Another storms is slated to arrive next Thursday and linger into Friday.
(Sun-Wed), 16/916 PM.
***UPDATE***
We are in the anticipated lull between storms right now with spotty drizzle or showers continuing under varying cloud cover. A weak impulse offshore may enhance shower activity overnight for LA County in particular - although any showers would be light. The upcoming cold front and associated showers look at track with it sweeping through most of Southwest California between 4 am to 4 pm Tuesday. See below for storm details.
***From Previous Discussion***
The next projected storm is still on track to impact the region late tonight through Tuesday. A progressive cold front is expected to bring steady moderate rain to the region starting late tonight in San Luis Obispo County pushing through the remainder of the forecast area on Monday. Within the cold front, there will likely be embedded areas of brief heavier rainfall, especially across south and southwest facing foothills and coastal slopes, with the highest risk for the Santa Ynez mountains and western Ventura mountains. There is a 20 percent chance of thunderstorms within the cold front as latest NAM model indicting modest instability (with CAPE values peaking at 400-600 J/jg). Behind the cold front, a cold and unstable air mass associated with a cold upper level low pressure system will bring scattered showers and a 10-20 percent chance of thunderstorms by Monday afternoon across the Central Coast and by late Monday evening across LA county. A smaller threat of scattered showers and isolated thunderstorms will continue into Tuesday, however rain intensities are expected to be less as the system takes a more inland track.
The most likely outcome for storm total rainfall from late tonight into Tuesday would be most areas receiving another 1 to 2 inches of rain, except locally up to 3 inches across the Santa Ynez range. Peak rain rates of 0.25-0.50 inches per hour will be common, with isolated rates up to 0,80 inches per hour likely near thunderstorms and S-SW facing foothills/coastal slopes(especially in the Santa Ynez mountains and western Ventura mountains). Due to the abundant rainfall during the past 48 hours, additional expected rainfall will bring threats of minor roadway/small stream flooding, additional rockslides/mudslides, and minor/shallow debris flows in recent burn scars. There is a 20-30 percent chance of reaching debris flow thresholds (15, 30, 60 minute durations) in the recent burn scars. The wet grounds will also bring an increased risk of downed trees during any convective bursts. There is also the potential for isolated waterspouts.
Snow levels are expected to be above 7000 feet during the onset of this next storm, but are expected to lower to between 5000 and 6000 feet by Monday night, and around 4500 feet on Tuesday. Snow accumulations of 1-3 inches will be possible for elevations above 6000 feet, with higher amounts above resort levels (above 8000 feet) likely. On Tuesday, there is a small chance of snow showers reaching down to the Grapevine along I-5, but any accumulations would likely be minimal. A winter weather advisory may need to be considered for the higher mountains as we draw closer to the event. Dry and mild conditions are then expected on Wednesday.
(Thu-Sun), 16/233 PM.
Another system is expected to affect the state on Thursday and/or Friday. There is still considerable disagreement on track and speed of this system. While there is still considerable uncertainty in the rain amounts, timing, and intensities, the official forecast calls for 40 to 50 percent chance of rain on Thursday and a 20 to 30 percent chance on Friday with additional rainfall amounts most likely between a quarter inch and one inch. This system is quite a few days away and is embedded in a fast moving storm track, so it is very likely that the forecast will change as the day draws nearer.
While the model forecasts have different synoptic patterns next Saturday, almost all of the solutions are dry. Max temps should warm, but will likely still remain a few degrees below normal
17/0607z.
At 06Z at KLAX, there was no marine layer. There was a deep moist layer up to around 7000 feet.
Overall low to moderate confidence in the 06Z TAFs due to reduced confidence in CIGs preceding an approaching cold front, and in CIGs/VSBY during and after the frontal passage. The timing of rain and flight category changes may be off by 3 hours.
KLAX, Low to moderate confidence in the 06Z TAF. Light showers possible throughout the forecast period, but most likely from 20Z Mon to 04Z Tue. 40-70% chance RA from 20Z to 00Z, with a 30% chance of IFR or lower conds during this time. There is a 40 percent chance of east wind component reaching 10 to 12 kts sometime 15Z to 21Z.
KBUR, Low to moderate confidence in the 00Z TAF. Light showers possible throughout the forecast period, but most likely from 20Z Mon to 00Z Tue. 40-70% chance RA from 20Z to 00Z along with a 30% chance of IFR or lower conds during this time.
16/810 PM.
For the waters from southwest through northwest of the Channel outside the southern California bight and the nearshore waters along the Central Coast, winds are expected to increase (70-90 percent chance) to SCA levels between 900 PM and midnight, with seas increasing to SCA levels on Monday. These conditions will persist through late Tuesday night. Winds and seas will likely fall below SCA levels for Wednesday and Thursday, then there is a moderate to high (30-50 percent) chance of SCA conditions developing on Friday.
Inside the southern California bight, winds and seas will likely remain below Small Craft Advisory levels through early Monday morning, then there is a moderate-to-high (30-50 percent) chance of SCA winds developing Monday afternoon and evening through late Monday night. Short period seas will grow to near-SCA levels (4-5 feet at 5-6 seconds) Monday night. Conditions will likely fall below SCA levels for Wednesday and Thursday, then there is a moderate- to- high (30-50 percent) chance of SCA conditions developing on Friday.
There is a 10-20 percent chance of thunderstorms across the coastal waters Monday and Monday night. Any thunderstorms that develop will be capable of producing brief heavy rain, small hail, dangerous cloud to surface lightning, gusty and erratic winds, locally rough seas, and possible waterspouts.
Ca, NONE. PZ, Small Craft Advisory in effect until 9 PM PST Tuesday for zone 645. (See LAXMWWLOX). Small Craft Advisory in effect until 3 AM PST Wednesday for zones 670-673. (See LAXMWWLOX). Small Craft Advisory in effect from 3 AM Monday to 3 AM PST Wednesday for zone 676. (See LAXMWWLOX).
