08/450 PM.
Above-normal temperatures will persist into Monday, before a weak storm system crosses the region Tuesday through Wednesday. Light to moderate rain is expected, mainly Tuesday evening through early Wednesday, with gusty southerly winds over the higher terrain, especially Tuesday night. Temperatures will cool during the middle of this week, followed by a gradual warming trend for late week into the weekend. For the following week, multiple rounds of precipitation and much cooler conditions are appearing increasingly likely.
(Sun-Wed), 08/829 PM.
***UPDATE***
A fairly expansive sheet of low clouds and fog off the Central Coast is working its way towards the south. High clouds are making it hard to see at night, but it is there. Normally, after several days of offshore flow, it is almost a guarantee that the first day of low clouds would also bring dense fog with low visibilities. Observations to the north however, at KMRY and KSNS show unlimited visibility and cloud bases above 1000 feet. Added some dense fog to the forecast, but if those observations are any indication, maybe fog will not be much of a concern. Otherwise, the forecast is in good shape for the next 24 hours.
***From Previous Discussion***
Warm conditions persist beneath upper ridging, with temperatures this Sunday afternoon having risen into the lower to middle 80s in many coastal valleys and the LA Basin. Large diurnal temperature fluctuations will continue in the dry air mass, with lows tonight in the 40s and 50s across most of the area under mostly clear skies.
High clouds will begin increasing from the north and northwest before dawn on Monday, but not before sufficient radiational cooling and ground moisture potentially bring patchy fog along the coast north of Pt. Conception and across the southern Salinas Valley, along with coastal locations near and south of Santa Monica Bay. Also, modestly boosted northerly pressure gradients (LAX-Bakersfield around 4-5 mb) will bring 30-40 mph gusts to the I-5 Corridor area tonight and early Monday morning. Isolated gusts to 45 mph will be possible through favored passes and canyons, though the coverage and intensity of these winds do not currently appear sufficient to warrant a Wind Advisory without a stronger pressure gradient and/or stronger upper support. Nevertheless, there will be a 20% chance for a shorter-fuse Wind Advisory to become necessary tonight.
Any fog will quickly dissipate after sunrise Monday, with Monday high temperatures generally just a couple degrees cooler than those of Sunday as high clouds thicken across the region through the day. More significant cooling is anticipated in San Luis Obispo County in conjunction with the leading edge of height falls overspreading the Central Coast. The clouds overspreading the area on Monday will be associated with a stream of mid and upper moisture preceding a compact midlevel vort max spreading toward central/northern California during the early/mid-week timeframe. However, it will remain mostly dry through Monday and into early Tuesday.
The southern periphery of the lobe of ascent accompanying the upper vort center will track across the region later Tuesday through Tuesday night and into early Wednesday, exiting the region by late Wednesday. In addition to much cooler temperatures (highs Tuesday and Wednesday 10-20 degrees below those of Sunday and Monday), a relatively quick-moving shield of light to moderate rain will overspread the area from north to south, primarily from 6PM Tuesday to 6AM Wednesday. Preceding the window of most consistent rainfall, warm-advection showers will likely be on the increase through the day Tuesday along the coastal ranges, and scattered showers may linger through the day Wednesday beneath the midlevel cold core. Precipitation is expected to have mostly exited the area or have dissipated by sunset Wednesday. All areas are expected to receive at least some rain by late Wednesday, with total amounts generally one-quarter to one-half inch, except one- half to one inch in the mountains and foothills especially coast- facing slopes, with total rainfall below one-quarter inch for the Antelope Valley. Neither these total rainfall amounts, nor the 0.10-0.25 inch per hour rainfall rates anticipated, are expected to support any flooding concerns.
Aside from rainfall with the passage of the compact vort max, related low-level mass fluxes will be boosted with its passage over the area. With a 50-kt 700-mb jet intercepting the high terrain in the southeast quadrant of the vort max, southerly wind gusts of 45-55 mph will be common over much of the high terrain of the Transverse Ranges for Tuesday evening and night. There is at least an 80% chance for wind headlines to become necessary during that time frame.
(Thu-Sun), 08/230 PM.
A reinforcing and diffuse cyclonic-flow perturbation behind the departing vort max will anchor mid/upper troughing over the local area on Thursday, keeping seasonably cool conditions in place. However, stronger ascent should be well east of the area by Thursday while mostly dry conditions prevail. Thereafter, a midlevel ridge is forecast to quickly build over the local area, with high temperatures rebounding into the upper 60s and lower 70s over the coastal valleys and L.A. Basin by Friday and Saturday under mostly sunny skies.
Thereafter by late next weekend and into the extended outlook beyond next weekend, medium-range model guidance is continuing to suggest increasing probabilities for a much cooler pattern featuring multiple rounds of precipitation. This would be in conjunction with a longwave, high-amplitude trough developing offshore and along the Pacific Coast vicinity. Uncertainty inherent to the forecast regarding weather conditions and related impacts is significant. However, in general, numerical models are offering above-average consensus regarding the longwave pattern over the local area for this distant of a time range. While the details are highly uncertain, there is growing concern for precipitation and cool-temperature impacts in the extended outlook starting next Sunday and continuing through the following week. Interests across the local area are encouraged to monitor the latest information from the National Weather Service in Los Angeles/Oxnard, California, as forecast details become refined over the coming days.
09/0048z.
At 2354Z at KLAX, there was no marine layer. There was a surface based inversion up to around 900 feet deep with a temperature of 23 degrees C.
High confidence in the 00Z TAFs. There is a 15% chance of brief IFR-MVFR conds at KLGB between 12Z-17Z Mon, and a 10% chance for KLAX. There is a 25% chance of LIFR-IFR conds developing at KPRB sometime between 12Z-18Z Mon. KLAX, High confidence in the 00Z TAF, except for a 10% chance of IFR to MVFR conds developing briefly between 12Z-17Z. Any northeast wind component is expected to be less than 6 knots.
KBUR, High confidence in the 00Z TAF.
08/751 PM.
Across the Outer Waters and nearshore waters along the Central Coast, hazardous ocean conditions will be common much of the time through Wednesday, and again late Thursday through the weekend. SCA winds are expected to continue into Monday afternoon, and then Gale Force southwesterly winds are likely mid- morning Tuesday into Tuesday night, especially for the waters north of Point Conception. Small Craft Advisory (SCA) seas will be likely Tuesday through Wednesay, followed by periods of SCA winds and seas late Thursday into the weekend.
For the Santa Barbara Channel and southern inner waters, hazardous conditions are likely Tuesday afternoon through Wednesay night, with SCA level winds (especially in the channel) and choppy steep seas. SCA conditions will be possible across the Santa Barbara Channel Thursday night through Friday night.
08/743 PM.
Elevated surf will likely continue through this coming week. High surf will affect the Ventura County beaches through Wednesday. The swell will primarily be out of the west, but will briefly become more southwest late Tuesday through Wednesday. During this time period, typically more sheltered south to southwest-facing beaches and harbors will see elevated-to-high surf conditions. Friday into the weekend, another large northwest-to-west swell will bring even higher surf conditions to at least the Central Coast with the potential to extend south. Please see SRFLOX and the CFWLOX for additional details.
Ca, High Surf Advisory in effect until 9 PM PST Wednesday for zone 354. (See LAXCFWLOX). PZ, Small Craft Advisory in effect until 9 PM PST Monday for zones 645-670-673-676. (See LAXMWWLOX).
