09/100 AM.
A warming and drying trend will continue into Monday as a ridge of high pressure continues to build aloft and the offshore flow at the surface continues. Temperatures above seasonal levels are likely through Monday, with highs in the 80s and 90s across most coastal and valley locations. A storm system will likely move over the region during the latter half of next week and could bring moderate to heavy rainfall.
(tdy-Tue), 09/334 AM.
High pressure aloft will continue to build over SW CA through Monday before weakening and shifting eastward on Tuesday. As the high pressure builds, the offshore gradients will continue to strengthen a little bit through Monday morning.
Currently, marine layer clouds are stretching all across the coasts of the four counties, with some some clouds sneaking into the San Gabriel Valley, a small patch in the eastern San Fernando Valley (right over Burbank airport), and into the Ventura County inland Coast (and up to the top of the Conejo Grade). While a Dense Fog Advisory is in place until 9 AM for the Malibu Coast as well as the Ventura Coast and Inland Coast, the rest of the coastal and inland coastal areas may see areas of patchy dense fog down to a quarter mile visibility or less. As for tonight, marine layer clouds may make a return to the coasts if the offshore flow remains weak enough, and patchy dense fog will be possible again into Monday morning anywhere these clouds may form. Otherwise, skies are expected to clear through Monday. By Tuesday morning, there will be the chance of some stratus/fog returning to coastal areas. Please slow down and leave a larger gap for the vehicle in front if dense fog is encountered while driving.
As for temperatures, a warm up across the region is still expected these next two days thanks to the ridge of high pressure aloft and the offshore flow. High temperatures are expected to reach into the 80s to 90s by Monday, with a little bit cooler temperatures at the immediate coasts. These temperatures will be around 10-15 degrees above normal for this time of year. Some locations will approach record highs, but do not anticipate any record breaking readings. One caveat, however, is if the offshore gradients end up being weaker than the models are forecasting, which would result in cooler temperatures, especially across the LA Basin. Overnight lows will also be warm, especially across the foothills and valleys.
As for winds, the offshore flow is on the weaker side this morning (around -2 mb for both offshore LAX gradients), with the pressure gradients forecast to reach around -4.0 and -2.6 mb (LAX-DAG and LAX-BFL, respectively) Monday morning. The offshore flow, with weak upper level support and lack of cold air advection, will result in a weak (maybe barely moderate) Santa Ana event, with gusty winds across the typical Santa Ana Corridor of Ventura and Los Angeles Counties as well the Santa Lucias this morning and tonight into Monday morning. Expecting winds to remain below advisory levels, with a isolated mountain locations reaching around 45 mph.
(Wed-Sat), 09/334 AM.
Overall for the extended period, models continue to be on the same synoptic page with a wet and unsettled period of weather. Unfortunately, there still are still differences in the details (timing, amounts, etc.), so not much change in the forecast at all for the extended.
On Wednesday, increasing clouds and cooler temperatures can be expected as storm system approaches the West Coast. Some light warm frontal precipitation will be possible Wednesday evening, ahead of the storm.
For Thursday and Friday, both the deterministic GFS/ECMWF and their respective ensembles indicate a storm will roll across the area and will bring significant measurable rainfall to the area. However, the ECWMF and its ensembles (as well as the ECWMF-AIFS) are slower with the progression of the system and generate more significant rainfall than the GFS and its respective ensemble members. With these differences, confidence in the forecast details remains on the low to moderate side. Current best forecast estimate is for a widespread 1-2 inch rain event across coasts and valleys, and 2-4 inches across mountains and foothills. As mentioned before, there is quite a wide range across model outcomes, so there remains a 30% chance of a lesser event, or a heavier event including some convective potential. As for rain rates and specific burn scar concerns, it really depends on the tilt of the trough, direction of flow, and the convective potential, so it is still too early to come up with reasonable rain rates. Additionally, based on thicknesses, snow level look like they could drop to around 6000 feet and the resorts could see some decent snow accumulations. However, much like with rain totals, confidence in the exact snow levels remain on the low to moderate side. By late Monday or Tuesday, the window for the higher resolution models opens up, so hoping by Tuesday, there will be more model agreement and details can be fine tuned.
09/1201z.
At 0753Z at KLAX, the marine layer was 800 feet deep. The top of the inversion was 2300 feet with a temperature of 25 C.
High confidence in TAFs for desert airfields (KPMD & KWJF).
Overall, low to moderate confidence in 12Z TAF Package. In general, expecting V/LIFR to low IFR conditions for coastal sites roughly through 18Z Sunday. Timing of CIG/VSBY restrictions may be off +/- 2 hours and flight cats could be off one or two when CIGs are present.
KLAX, Moderate to low confidence in TAF. LIFR to IFR conditions expected through around 19Z Sunday (+/- 2 hours). There is a 10% chc of no clearing through 12Z Monday. If clearing does occur, there is low confidence if LIFR CIGs OVC002-004 return around 03Z Monday. Good confidence in MVFR or VFR conditions after 12Z Mon. There is a 15% chance that east wind component reaches 7-8 kts after 12Z Monday.
KBUR, Moderate confidence in TAF. MVFR VSBYs with BR through 15Z Sunday (+/- 2 hours). Then, VFR conditions expected.
09/402 AM.
Seas are below Small Craft Advisory (SCA) levels across all the outer waters. 10-15 knot E to NE winds will be common early Sunday morning through Monday afternoon nearshore from Ventura to Point Dume. Local wind gusts could reach 21 kts near Pt. Mugu during the early morning hours on Sunday & Monday (30% chance). Otherwise, relatively mild conditions will continue into at least Tuesday.
Moderate to high confidence that a storm system will approach the Coastal Waters as early as Wednesday night, bringing rain and at least Small Craft Advisory level winds and large steep and choppy seas to the region, including nearshore. There is a potential for Gale Force Winds. Confidence is low in timing and magnitude of impacts.
Ca, Dense Fog Advisory in effect until 9 AM PST this morning for zones 354-355-362. (See LAXNPWLOX). PZ, NONE.
