20/812 PM.
A weak upper level trough will move over the area tonight into Monday, cooling temperatures slightly and increasing marine layer stratus. A warming trend will begin Tuesday and peak on Thursday, with highs 5 to 10 degrees above normal.
(Sun-Wed), 20/810 PM.
***UPDATE***
The marine inversion was around 1400 ft deep and VBG and near 1800 ft deep at LAX early this evening and is expected to deepen some overnight in response to an approaching upper level low pressure system. Low clouds were along portions of the Central Coast and SBA S coast this evening, with patchy low clouds starting to form along the VTU/L.A. County coast. These low clouds are likely to expand this evening and push inland quickly overnight. Would not be surprised to see some drizzle develop later tonight as well especially S of Point Conception. Current forecast is on track and do not anticipate any zone updates this evening. ***From Previous Discussion***
An upper low is just west of the Central Coast this afternoon. The low is spreading lots of high clouds across the area today but the lack of moisture below 15000 feet is preventing any precip from developing. Can't completely rule out a stray drop or two at higher elevations but otherwise dry conditions are expected through at least tonight. With the high clouds decreasing through the night and less trapped heat overnight lows will likely be a little cooler.
As the low moves overheat tonight, models have been consistent indicating a rapidly developing marine layer, possibly deepening to 4000 feet or higher by Monday morning. Given the rapid increase there's good chance that some drizzle will develop, especially in the south facing foothills of LA County. Some light measurable rain is possible in the most favored areas, namely from the eastern San Fernando Valley into the San Gabriel Valley and adjacent foothills.
Significant cooling will accompany the deepening marine layer Monday with the warmest valleys barely reaching 80 and desert areas only in the low 80s, roughly 10 degrees below normal. Skies are expected to clear eventually Monday but it may be a reverse clearing day where coastal areas clear before the valleys.
A warming trend will begin Tuesday and continue through at least Wednesday, by which time most areas will be 4-8 degrees above normal. Downtown LA still has about a 40-50 percent chance of reaching 90 Wednesday while the warmer valleys have a similar chance of reaching 100. Chances for heat advisories in those areas remains around 30%
(Thu-Sun), 20/229 PM.
Uncertainty remains with regard to the length of the next heat wave but there are still at least 30% of the solutions showing little to no change in high temperatures through at least Saturday. However, more of the guidance products suggest a slow cooling trend after Wednesday due to a slowly deepening trough along the West coast.
21/0023z.
At 2358Z at KLAX, the marine layer was 1400 ft deep. The top of the inversion was at 3500 ft with a temperature of 20 C.
High confidence in VFR conds for KPMD & KWJF.
Moderate confidence in the remaining sites. The timing of CIG and any VSBY restrictions may be off 3 hrs and flight minimums by one category. High clouds may disturb the marine layer and sites with cigs may bounce between categories at times. There is a 5-10 percent chance of -DZ/-SHRA focused through 18Z.
KLAX, Low to moderate confidence in TAF. Flight cat changes may be off by 3 hours. Any east wind component is expected remain less than 6kt.
KBUR, Low to moderate confidence confidence in TAF. Flight cat changes may be off by 3 hrs.
20/817 PM.
For the outer waters, moderate confidence in the current forecast. Small Craft Advisory (SCA) level winds are likely (60-80 percent chance) for the waters northwest of Point Conception through tonight and for the waters around Point Conception through Monday night. There is a 40-50% chance of SCA wind gusts west and south of Point Conception Tuesday afternoon and night as well, otherwise conds will be below SCA levels through Thursday night. Expect steep, choppy seas with the SCA conditions.
For the inner waters N of Point Sal, moderate confidence in the current forecast. SCA wind gusts are possible (30-40 percent chance) during the afternoon and evening on Monday and again Tuesday. Conds are otherwise expected to be below SCA levels through Thursday.
For the inner waters S of Point Conception, moderate to high confidence in the current forecast. Conds are expected to be below SCA levels for the most part through Thursday night. However, for the western Santa Barbara Channel, there is a 30-40% chance Monday afternoon/evening and Tuesday afternoon/evening.
Ca, NONE. PZ, Small Craft Advisory in effect until 3 AM PDT Monday for zone 670. (See LAXMWWLOX). Small Craft Advisory in effect until 5 AM PDT Tuesday for zone 673. (See LAXMWWLOX).
