21/825 PM.
A shallower marine layer is expected over the next few days and a significant warming trend will start Monday, peaking around Wednesday with well above normal afternoon temperatures. A push of moisture midweek will bring at least a low chance for rain and then drier conditions return. Temperatures are expected to cool heading into the end of the week and the weekend.
(tdy-Wed), 22/801 AM.
***UPDATE***
Morning satellite imagery shows a similar picture to the previous couple of days, with marine layer clouds filled in across coastal and inland valley areas north of Point Conception and more broken in coverage south of Point Conception. There is also evidence of small eddies along the coast of Ventura and LA Counties. The one change is the marine layer has continued to lower, with aircraft- reported cloud tops around 2000 ft north of the point and closer to 1500 ft to the south. With this lowering there were a few sensor reports of visibility under 1 mile in fog.
For the rest of the day the forecast remains on track for a degrees of warming from yesterday, under sunny skies, with coastal areas mostly in the 70s and some of the warmest inland valleys in the 80s this afternoon, while desert valleys reach the 90s.
***From Previous Discussion***
Overall, 00Z models in good synoptic agreement through the short term period. At upper levels, ridge will nose in from the southeast through the period, peaking in strength on Tuesday. At the surface, moderate to strong onshore gradients will persist to the east with some weak northerly offshore gradients.
Forecast-wise, main issue in the short term will be the building heat. As the ridge builds overhead, warming boundary layer and more limited marine influence, temperatures will be on the upswing for all areas through Wednesday. In fact, by Tuesday/Wednesday, areas away from the immediate coastal plain will generally be 4-8 degrees above seasonal normals. Additionally on Wednesday, an influx of some mid-level moisture across LA and Ventura counties may exacerbate the heat a little bit more. At this time, Heat Risk guidance indicates some areas of moderate heat risk across LA county on Tuesday/Wednesday, especially across the interior coastal plain and valleys. Admittedly under normal conditions, these conditions would be marginal for any heat products. However given the current influx of visitors and numerous outdoor events across the county, will continue with the HEAT ADVISORY for Los Angeles county (interior coastal plain, valleys and mountains) from Tuesday through Wednesday.
Secondary issue for the short term will be an influx of some mid-level moisture on Wednesday. Deterministic models and their respective ensembles still indicate PWATs increasing to 125-175% of normal during the day on Wednesday, mainly across Ventura and LA counties. Still a question whether or not any sort of weak shortwave will move across the area on Wednesday. However, given the situation will continue with the 5-15% POPs across Ventura and LA counties with the highest POPs over the higher terrain. If any showers do develop, they will be high-based and likely to produce minimal rainfall at the surface. As for the potential for any thunderstorms, chances still look rather limited (around 5%), but this will need to be monitored closely. If any thunderstorms would happen to develop on Wednesday, dry lightning and gusty outflow winds would be the main concerns.
Other than temperatures and shower chances, no significant issues are expected through Wednesday. 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. 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.
(Thu-Sun), 22/148 AM.
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. On Thursday, the heat will have one last hurrah across the area, although it will be a couple degrees cooler than Wednesday. So, HEAT ADVISORIES for LA county will remain in effect through Thursday evening.
For 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.
