09/521 PM.
Monday will again be very warm and dry, especially across the Los Angeles and Ventura County valleys. A cooling trend will start Tuesday, ahead of the incoming storm system. Rain may start as early as Wednesday night, however the heaviest rainfall and greatest impacts are likely to occur Thursday and Thursday night.
(Sun-Wed), 09/758 PM.
***UPDATE***
A very shallow marine inversion is creating areas of fog along much of the coast this evening, with some dense fog noted along portions of the Central Coast. A Dense Fog Advisory will likely be needed at some point during the overnight hours, if the dense fog becomes more widespread. Models, including the HREF, indicate that the shallow inversion could result in widespread fog, especially for the Central Coast and Santa Barbara South Coast.
High temperatures were noted across the valleys today with many readings in the mid 80s to lower 90s. As models indicate offshore gradients increasing some overnight, to -3.5 MB between LAX to Daggett, expect winds may be slightly stronger than today but still sub-Advisory level. While increasing offshore flow favors rising temperatures, the NAM12 indicated the 950 MB temps remaining similar in some areas, or decreasing slightly. Depending on how the marine inversion holds up, temperatures could warm at the coast.
***From Previous Discussion***
Upper level wind support wasn't strong enough with this Santa Ana event to push wind and hot temps to the coast today. Winds haven't been overly impressive with this event either with just a handful of sites over 25 mph. Models are still indicating a slight increase in offshore flow Monday but still with very minimal upper support so for the most part a very similar day as today except likely a few degrees warmer.
A significant cooling trend will begin Tuesday as high pressure weakens ahead of the next low pressure arrival. Gradients will quickly turn onshore and most areas will drop 5-10 degrees both Tuesday and again Wednesday. A deepening marine layer will push low clouds into the valleys by Wednesday morning with highs back down into the 70s.
(Thu-Sun), 09/1248 PM.
Starting to get some improved consensus in the models regarding the storm later in the week. Timing-wise models are zoning in on Thursday being the primary period for rain across the area, but with some early showers arriving Wednesday night along the Central Coast.
Models are also coming into better agreement on the amounts as well with a large percentage of the ensemble solutions showing a heavy, but relatively short period of rain as the main front moves through. Orographics will play a significant roll in the amounts with upslope areas getting twice to 3 times the amounts at sea level. Overall, sticking with the 1-2/2-4 inch range (coast and valleys/mountains), with much of that falling in 5-10 hour period, and hourly amounts between a quarter and half inch, and as much as 0.75 in the upslope areas.
Snow levels will likely remain at or above 8000' for most of the storm, then drop to around 6000 feet as the last of the precip is moving through later Thursday night into Friday morning. At this point it does not appear to be cold enough for snow on the Grapevine, but some light accumulations (2-4") are possible down to around 6000'.
Dry and cool weather expected next weekend with highs mostly in the upper 60s to low 70s.
10/0553z.
At 0537Z at KLAX, the marine layer was 600 feet deep. The top of the inversion was near 1800 feet with a temperature of 28 degrees Celsius.
High confidence in VFR TAFs for KPMD and KWJF.
Moderate confidence in VFR TAFs for KPRB, KBUR, and KWJF. There is a 10% chance for VLIFR-LIFR conds at each sight from 10Z-17Z.
Very low confidence in remaining coastal TAFs. Low clouds are pulling out of some coastal areas, but expecting them to push back in soon. Arrival times for sites without cigs may be any time this morning. Less than 1/2SM vsbys and cigs less than VV002 are possible (50% chance) at all coastal sites any time when cigs are present through at least 17Z. Timing of burn off may be off +/- 3 hours. Low confidence on any return of low clouds after 12/00Z.
KLAX, Low confidence in TAF. 50% chance for 1/2SM or lower vsbys with VV002 or lower cigs any time cigs are present through 17Z. Clearing time may be any time between 15Z and 20Z. 20% chance for OVC002-OVC006 cigs to return after 12/07Z. No significant east wind component expected.
KBUR, Moderate confidence in TAF. 10% chance for VV001-VV002 cigs and vsbys less than 1/2SM from 10Z-17Z.
09/732 PM.
For the Outer Waters and the Inner Waters north of Point SaL, moderate to high confidence in current forecast. Through Wednesday, high confidence in winds and seas remaining below Small Craft Advisory (SCA) levels. For Thursday and Friday, high confidence in a combination of SCA level winds and seas. Additionally, there is a 30% chance of Gale force Thursday night across PZZ676.
For the Inner Waters south of Point Conception, moderate to high confidence in current forecast. Through Wednesday, high confidence in winds and seas remaining below SCA levels. On Thursday and Friday, there is a 60-80% chance of SCA level winds with a 30-40% chance of Gale force winds.
Ca, NONE. PZ, NONE.
