Swell Matrix

Area Forecast Discussion

National Weather Service Los Angeles/Oxnard Ca

810 pm PST Wed Jan 17 2018

Synopsis

An incoming weak storm system will bring cooling temperatures, gusty winds, and light rain and mountain snow showers to the region by Friday. Snow showers will linger into Saturday morning for the northern slopes. Conditions return to warm and dry next week.

Short Term

(tonight-Sat)

Weak offshore flow and increased sunshine brought some warming to the region today. Satellite imagery showing some high clouds returning to the region tonight, with some low clouds filling in across the Central Coast. Still on track for good cooling trend on Thursday for the Central Coast, and a few degrees of cooling for areas south of Point Conception. Latest 00z NAM model showing cold upper level low pressure system continuing to bring a chance of showers to the region from Thursday night into Friday night, with some snow showers potentially lingering on the north facing mountain slopes on Saturday morning. For the Montecito area, still estimating less than 0.10 inches with this system.

The big story with this event will be the low snow levels and strong winds behind the front Friday afternoon into Saturday morning. Snow levels could fall to between 2500 and 3500 feet Friday night into Saturday morning, with the lowest snow levels on the north facing slopes. Many mountain areas could see between 1 and 3 inches of snow accumulation with this event, with higher elevation north slopes seeing potentially 3 to 6 inches. Interstate 5 near the Grapevine could see significant travel impacts from Friday afternoon through Saturday morning, with potentially 1 to 3 inches of snow accumulation and strong winds gusting up to 50 mph. Given the ongoing closures of Highways 101 and 33 forcing additional vehicle traffic through the Grapevine this could have significant impacts to drivers trying to go north and south. As we draw closer to the event, winter weather advisories will likely need to be posted for this event. Also of note, will likely need several wind advisories for the region Friday afternoon into Saturday morning. Much cooler temperatures Friday with highs mostly in the 50s and lower 60s.

*** From previous discussion ***

A cool but mostly dry and breezy day on Saturday with highs again in the 50s to low 60s at lower elevations and 30s and 40s in the mountains. Advisory level northwest winds possible along the Central Coast, srn SB County, and the I5 corridor.

Overnight lows will be quite cold, likely dropping to near or below freezing in many wind protected locations away from the immediate coast. Frost advisories and/or freeze warnings may be needed.

Long Term

(Sun-Wed)

Temps will continue to slowly rebound Sunday/Monday but still remain cooler than what we've been used to this winter so far but actually very close to seasonal norms. The tail end of a weak system will brush northern SLO County Monday and there could be some very light precip there, otherwise just some increasing mid and high clouds. Dry conditions and slowly warming Tue/Wed as weak offshore flow develops. Forecast highs were trimmed a few degrees as there doesn't appear to be enough offshore gradient and ridging aloft to justify temps much warmer than the lower 70s.

Next chance of rain looks to be next Thursday, but again a glancing blow at best and likely nothing south of Pt Conception.

Aviation

17/2345z,

At 2309Z, there was an inversion around 300 ft deep at KLAX. The top of the inversion was near 1100 ft with a temperature of 23 deg C.

Generally hi confidence in the 00Z TAFs. Low clouds and LIFR cigs/vsbys are likely for KSBP and KSMX starting early this evening and persisting thru Thu morning, with MVFR cigs expected to continue thru Thu afternoon. For KPRB, there is a 70 percent chance LIFR cigs/vsbys will develop at the airfield by 12Z and persist thru about 19Z Thu, altho the timing of the onset of the LIFR conditions may be up to 2 hours too late. MVFR vsbys will prevail at KLAX and KLGB at times later tonight into Thu as well. Otherwise, VFR conditions can be expected at the airfields thru Thu afternoon.

KLAX, Generally hi confidence in the 00Z TAF. MVFR vsbys can be expected late tonight into Thu morning, and a 60 percent chance MVFR cigs will move into the airfield starting around 04Z Thu evening. Otherwise, VFR conditions will prevail at the airfield during the period.

KBUR, Generally hi confidence in the 00Z TAF with VFR conditions expected through Thu afternoon.

Marine

17/800 PM,

For the Outer Waters, moderate to high confidence in current forecast. High confidence in Small Craft Advisory (SCA) level conditions due to hazardous seas. Large westerly swell will gradually diminish this evening into Thursday morning, but an even larger westerly swell will move into the waters Thursday afternoon, peaking Thursday night/Friday morning (with swell heights 13-19 feet). SCA level seas will continue through Monday. As for winds, northwest winds are expected to increase to SCA levels on Thursday and remain at SCA levels through Monday. There is a 50% chance of Gale force winds developing Friday afternoon through Saturday evening across the southern two zones (PZZ673 and PZZ676).

For the Inner Waters, moderate to high confidence in current forecast. For the waters north of Point Sal, high confidence in Small Craft Advisory (SCA) level conditions due to hazardous seas. Large westerly swell will gradually diminish this evening into Thursday morning, but an even larger westerly swell will move into the waters Thursday afternoon, peaking Thursday night/Friday morning (with swell heights 14-17 feet). SCA level seas will continue through Monday. As for winds, northwest winds are expected to increase to SCA levels Friday and Saturday. For the Inner Waters south of Point Conception, winds are expected to increase to SCA levels Friday and Saturday with a 50% chance of Gale force winds developing.

Beaches

17/100 PM..,

An extended period of large surf is expected along west and northwest-facing beaches through Saturday as westerly swells move through the coastal waters. The first pulse of large westerly swell will slowly diminish this evening and Thursday morning. However, a second, much larger westerly swell will develop Thursday afternoon and continue through Saturday.

For west and northwest-facing beaches along the Central Coast, surf heights of 10-16 feet with local sets to 18 feet will continue through Thursday morning and a HIGH SURF ADVISORY will remain in effect. By Thursday afternoon, the surf will increase to 15-20 feet with local sets to 25 feet through Saturday afternoon. Therefore, a HIGH SURF WARNING remains in effect from Thursday afternoon through 800 PM Saturday evening.

For the west and northwest-facing beaches south of Point Conception, surf heights of 7-10 feet with local sets to 12 feet will slowly diminish late tonight and Thursday morning. However, surf heights are expected to increase to 8-12 feet with local sets to 15 feet by Thursday evening and continue into Saturday evening. A HIGH SURF ADVISORY remains in effect through 800 PM Saturday.

Watches, Warnings, Advisories

Ca, High Surf Advisory in effect until noon PST Thursday for zones 34-35. (See LAXCFWLOX). High Surf Warning in effect from noon Thursday to 8 PM PST Saturday for zones 34-35. (See LAXCFWLOX). High Surf Advisory in effect until 8 PM PST Saturday for zones 40-41-87. (See LAXCFWLOX). PZ, Small Craft Advisory for hazardous seas in effect until 3 PM PST Thursday for zones 645-670. (See LAXMWWLOX). Gale Watch in effect from Friday afternoon through Saturday evening for zones 650-655-673-676. (See LAXMWWLOX). Small Craft Advisory in effect until 1 PM PST Friday for zones 673-676. (See LAXMWWLOX).

Share this forecast!