22/225 PM.
A shallower marine layer is expected over the next few days and a significant warming trend will continue through the next couple days, peaking on Wednesday, with well above normal afternoon temperatures. A push of moisture Tuesday and Wednesday will bring at least a low chance for rain or an isolated storm from Ventura County eastward and then drier conditions return. Temperatures are then expected to cool heading into the end of the week and the weekend.
(tdy-Thu), 22/222 PM.
One of the main points of emphasis in the short term forecast continues to be the building hear the next few days. A strong and broad high pressure over northern MX and the Desert Southwest is slowly expanding into the area, and 500mb heights continue to increase. Guidance continues to show heights will peak around 592-593dam by midday Tuesday. This will lead to continued surface warming that looks like it will peak Tuesday and Wednesday before gradually cooling back down, as the high pressure flattens with increasing troffing across the West heading into late week.
Everything remains on track with a continuation of the Heat Advisory for Tuesday through Thursday for portions of LA County (interior coastal plain, valleys and mountains). Afternoon high temperatures are forecast to be mostly around 3-8 degrees above normal, with coastal areas forecast to reach the upper 70s to upper 80s and low to middle 90s for inland valleys. These temperatures will lead to widespread Minor HeatRisk and areas of Moderate HeatRisk. Admittedly under normal conditions, these temperatures would be marginal for any heat products. However given the current influx of visitors and numerous outdoor events across the county, there is a higher risk and vulnerability. There will also be a small increase in surface moisture heading into Tuesday that may add to the discomfort from the heat. The forecast temperatures for Thursday continue to slowly trend down model run to model run, with a quicker intrusion of troffing from the northwest. So, will continue to monitor trends for whether the advisory will be continue through Thursday.
Forecast with the mid-level moisture push Tuesday into Wednesday remains on track. The bulk of the moisture is still expected to stay just east and south of the area, but with PWATs still pushing up to 125-175% of normal in portions of LA County. This moisture flux is enough to still support at least low-end PoPs (5-15%) Tuesday afternoon into Wednesday across LA and Ventura counties. There will be a weak perturbation wave rolling through the area, which will help steepen mid-level lapse rates. Otherwise, there will not be much in the way of forcing with this setup. Latest HREF/REFS runs all point to some spotty high-based convection developing and staying east of LA County late Tuesday into Wednesday morning. Main concern with any convection will be gusty outflow winds and dry lightning. The layer below 700mb will remain very dry, so a lot of the precipitation will likely evaporate before reaching the ground.
Other than temperatures and shower chances, no significant issues are expected through Thursday. The marine layer will remain, impacting the coastal plain and lower coastal valleys. However the areal extent each night should be a little bit less than the night before. The layer will also be more shallow, which may lead to more morning fog impacts. As for winds, there will continue to be the gusty southwesterly winds across interior sections, but any advisory level winds will remain localized in the desert foothills.
(Fri-Mon), 22/222 PM.
For the extended period, models continue to exhibit good synoptic agreement. At upper levels, trough will sag across the state with cyclonic flow over the area through the weekend. At the surface, moderate onshore flow will continue with some enhancement of northerly offshore gradients next weekend.
Forecast-wise, no dramatic changes to current forecast thinking. Friday through Sunday, the cyclonic flow aloft will usher in a cooling trend for all areas with lowering thicknesses and increased areal coverage of marine layer stratus. Typical onshore winds will continue across interior sections each afternoon and evening. However, with the increase in northerly offshore gradients, there will be an increase in northerly winds across the Santa Ynez Range and the I-5 Corridor. Winds across the western half of the Santa Ynez Range could approach advisory levels next weekend.
22/1722z.
At 1610Z at KLAX, the marine layer was 2000 feet deep. The top of the inversion was 3400 feet with a temperature of 17 C.
High confidence in VFR TAFs for desert airfields (KPMD & KWJF).
For all other sites, low to moderate confidence in 18Z TAFs. Timing of CIG/VSBY restrictions may be off +/- 2 hours and flight minimums by one category.
There is a 50% chance of LIFR CIGs at KPRB from 23/10-15Z.
KLAX, Moderate confidence in TAF. Timing of flight category changes could be +/- 2 hours of current forecasts. No significant east wind component is expected.
KBUR, Moderate confidence in TAF. VFR conditions expected. However, there is a 10% chance of CIG/VSBY restrictions from 23/08-15Z.
22/818 AM.
High confidence in winds and seas remaining below Small Craft Advisory (SCA) levels through Wednesday. Local gusts could reach 21 kts near Point Conception in the evening. Moderate chances for SCA conditions return to the Outer Waters Thursday afternoon/evening persisting into the weekend. These conditions could reach into the nearshore waters along the Central Coast and the Santa Barbara Channel at times. Main concern is wind although seas could approach SCA levels later into the weekend.
Ca, Heat Advisory remains in effect from 8 AM Tuesday to 9 PM PDT Thursday for zones 88-368-372-373-379-380-548. (See LAXNPWLOX). PZ, NONE.
