19/359 AM.
Some showers will linger today over the southern waters and interior mountains. The next storm will bring widespread light to moderate rain and mountains snow Thursday into Friday. Cool conditions will persist through Friday. Northeast winds and high pressure aloft will push temperatures back to normal this weekend continuing through next week.
(tdy-Fri), 19/358 AM.
With ample clear skies and a cold air mass over the area, the soggy ground will result in pockets of dense fog over the colder valleys this morning, but unsure how expansive that will be. Based on the minimal extent at this hour, any dense fog will likely be very localized.
The low pressure system that brought the rain on Sunday and Monday is now centered over San Diego County. A few showers formed between Catalina and Orange County closest to that core, but they should decrease and slide to the south over the next few hours. With the position of the low, the flow aloft will be northeasterly. While the majority of the area will be rain free today, there is moisture in that flow, which will bring chances of showers to the LA and Ventura County interior mountains and valleys today. Those showers could come in the form of showers from central San Bernardino county moving into our area, or the daytime afternoon heating playing with that moist flow to form a few cumulus showers. Cannot rule out a thunderstorm or two, but the chance is under 10%. Daytime temperatures will be in the mid 50s to mid 60s, which is about 10 degrees below normal.
In what seems to be a broken and skipping record, yet another storm system will quickly replace our most recent one. A long and narrow cold front is just off the Oregon Coast, and will sweep down the California coast tonight through Thursday. Widespread light to moderate rain will affect all four of our counties on Thursday. By Thursday afternoon, the center of the low pressure system driving this front will quickly drop south and over north- central California. This fairly unusual development will reverse the typical evolution of our cold fronts and actually enhance it as it moves from north-to-south. The higher totals and rates will be over LA County as a result, instead of San Luis Obispo County. As the low continues to dive southward into San Diego by Friday morning, LA and Ventura Counties will continue to be dealing with showers well after the front passes. With 500 millibar temperatures around 25C, there should be a few thunderstorms or thunderstorm- like cells - which could bring some very localized but strong and swirling wind gusts.
Rain totals and rates are a bit tricky. Fairly confident that San Luis Obispo and Santa Barbara Counties will have lighter totals (0.25 to 0.50 inches common, except 0.5 to 1.0 inches in some favored mountains) and rates (0.10 to 0.25 inches per hour). Impacts should be fairly minor. For Los Angeles and Ventura Counties, the most likely outcome is for moderate amounts (0.5 to 1.0 inches except 1 to 2 inches in favored mountains and hills) and rates (0.20 to 0.33 inches per hour). The convective and dynamic nature of the proximity of the low brings the potential of double those amounts, but moderate easterly flow which can evaporate some of the rain brings a potential for half those amounts. The best estimate is for those competing factors to generally cancel each other out, but that is far from certain. As a result, impacts will likely be minor to moderate, with a focus on road issues and enhanced mudslides and rockslides due to the soggy soils. If the higher end scenario pans out, still think the potential for major impacts is quite small, but some localized shallow debris flows and flooded road closures would likely materialize.
Snow levels will be above 6,000 feet for most of the precipitation, but will drop to as low at 5,000 feet on Friday. Snow amounts of 3 to 6 inches is the most likely outcome for elevations above 6000 or 6500 feet. Winter Weather Advisory will probably be issued for the San Gabriels and Mount Pinos areas, with some snowy and icy road impacts.
(Sat-Tue), 19/357 AM.
There is a possibility that the Thursday and Friday low pressure system, which does cut off from the prevailing jet stream, lingers in the region on Saturday. Cannot discount additional isolated showers during the day on Saturday, but the trends will certainly be going down. Eventually that low will move on its merry way to the east, and get replaced by a small but good-enough high pressure ridge. With weak offshore flow and pressure gradients, temperatures will climb back to around normal by Sunday and Monday, when highs in the mid 60s to mid 70s will be common. Little change expected through the Thanksgiving holiday. Not seeing any significant signals for rain through at least Black Friday.
19/1150z.
At 09Z at KLAX, there was no marine layer and no inversion.
There is a 10-20% chance of -SHRA on Wednesday for KWJF KPMD. 30% chance of -SHRA at KPRB, KSBP after 09Z Thursday.
LIFR to IFR conditions are expected to continue at KPRB through 16Z Wed (+/- 1 hour).
Chances for LIFR conditions through 16Z Wed: KOXR/KCMA (15%), KBUR/KVNY/KWJF (20%).
Otherwise, high confidence in VFR conditions with light winds.
KLAX, Moderate confidence in 12Z TAF. Good confidence in VFR conditions with east wind component remaining under 8 knots through 12Z Thursday. Then, 30% chance of reaching 8 knots thru end of forecast period. In addition, MVFR CIGs 020-030 with -DZ or even -SHRA possible during this timeframe.
KBUR, There is a 20% chance of LIFR FG through 16Z Wednesday. Otherwise, high confidence in VFR conditions and lighter than usual winds.
19/1257 AM.
Seas should continue to decrease and remain below Small Craft Advisory (SCA) levels through early Thursday morning. Then, another storm system will bring elevated seas up to 14 feet across the outer waters and up to 6 feet for the inner water south of Point Conception as early as Thursday afternoon. Seas will improve some but remain at or near Small Craft Advisory (SCA) levels through much of the weekend across the Outer Waters. Wind directions will vary considerably as the storm moves through the region, with 20-30 kt winds common as early as Thursday afternoon into the weekend.
Winds may locally reach 21 kts across the Santa Barbara Channel and near the Channel Islands this afternoon & evening. A few showers with a 5% chance of a thunderstorm is expected across PZZ655 through this morning. The strongest cells will be capable of producing brief heavy rain, gusty and erratic winds, locally rough seas, dangerous cloud to surface lightning, and even a remote chance for a waterspout.
19/1253 AM.
A 12-16 second 12-14 foot west-northwest swell will enter the region Thursday evening, increasing surf heights to 12-16 feet across northwest and west facing beach along the Central Coast through the weekend, peaking Friday. Peak surf will flirt with the 7ft threshold for west-facing beaches across the Ventura coastline on Friday, and possibly through the weekend.
High Surf Advisories are in effect from Thursday evening through Sunday evening along the Central Coast. Beach erosion with isolated, minor coastal flooding is possible for west-northwest facing beaches, especially from 8 AM to 1 PM from Friday through Sunday.
Will let future shifts decide if a Surf Advisory is necessary for the Ventura Coastline (40% chance).
Ca, High Surf Advisory in effect from 9 PM Thursday to 9 PM PST Sunday for zones 340-346. (See LAXCFWLOX). PZ, NONE.
