11/214 PM.
Temperatures will increase each day into mid-week, resulting in widespread Moderate to Major HeatRisk Tuesday-Thursday. Monsoonal moisture moving into the area will add to the discomfort, additionally bring shower and thunderstorm potential each day, highest in the mountains.
(Sat-Tue), 11/743 PM.
***UPDATE***
Plenty of mid and hi level clouds were moving off the SAN County coast and over the srn CA coastal waters early this evening. Latest Doppler RADAR was showing showers over the coastal waters moving rather quickly NW and should move into some coastal areas tonight. However, as these showers moved over coastal SAN County earlier this evening, they produced brief very light rain with no measurable rainfall (just trace amounts), so it was mostly virga as the air mass below the mid-level clouds is still very dry. Likewise, any showers that do affect the area tonight should produce mainly sprinkles. However, there is still about a 10%-20% chance of a heavier shower or thunderstorm which may produce light measurable amounts of rain mainly over portions of SLO/SBA Counties overnight. The main concern is the potential for dry lightning.
Otherwise, low clouds over the coastal waters should move inland overnight and affect many coast and vlys. There is a possibility the mid and hi clouds could disrupt the low cloud coverage to some degree, however. So confidence in the low cloud forecast tonight into Sun morning is moderate at best.
***From Previous Discussion***
Today has been a mixed bag in the way of temperatures trends, but in general most locations are experiencing highs fairly similar to yesterday. Today is expected to by the "coolest" through the remainder of the forecast period and Sunday will kick off a general warming trend in most places, with moisture streaming in from the south raising humidities and making tomorrow feel a bit muggier than today. 500 mb heights will experience little changes, but onshore flow will become much weaker, with some model guidance even shower weak offshore by Tuesday. This shutoff of nature's air conditioning will help temperatures increase each day through Tuesday, with Tuesday certainly being the warmest day in the short term. We're looking at widespread Moderate to Major HeatRisk, posing the threat of heat related illnesses to much of the population, not just those most vulnerable. All headlines (Advisories and Watches) remain in effect with the timings untouched, with Advisories continuing into Tuesday morning, then the Extreme Heat Watches are in place Tuesday morning through Thursday evening.
The upper level pattern shows the ridge over the four corners progressing to the east over the next few days. However, southeast flow aloft continues and will help pull in tropical mositure from the Gulf of California. The increasing monsoonal moisture (around 1.5 inch PWATs) from the south will not just lead to muggy days, it also brings a chance of thunderstorms and showers each day in the short term, including a 15-20 percent chance on the Central Coast tonight into early Sunday. Elsewhere tonight a 5 percent chance exists due to the uncertain nature of this type of setup. Sunday through Tuesday will feature a 10-20 percent chance of thunderstorms and showers over the LA, Ventura, and far interior Santa Barbara County mountains into Tuesday, while a 5-10 percent chance exists elsewhere (including lower elevations). Moisture will be somewhat limited tonight, so rainfall accumulations are expected to be light with any, which leads to more of a concern for dry lightning impacts regarding fire weather. Storms are expected to be wetter Sunday, and especially Monday and Tuesday.
Due to the influx of mid to upper level moisture, expect partly to mostly cloudy skies each day. Marine layer clouds may develop again overnight into Sunday morning, but confidence is quite low in if and where marine layer clouds would develop.
As mentioned previously, decreasing onshore winds will be common each day. There aren't any strong signals for gusty winds, except for Tuesday night where there is a signal for moderate Sundowner winds in southwest Santa Barbara County, and increasing northwest winds across interior areas.
(Wed-Sat), 11/211 PM.
The synoptic pattern is favored to bring more of a southwest upper level flow to the region Wednesday as the ridge marches more towards the middle of the United States, somewhat limiting shower and thunderstorm chances Wednesday and most likely Thursday to just the eastern LA County mountains. However, greater chances for slightly more widespread thunderstorm potential return Friday into the weekend as the ridge moves back towards the Four Corners, with southeast flow aloft favored in both the EC and GFS. The thunderstorm forecast this week is a complex and fairly low confidence one, as storm development will be highly dependent on mesoscale features and even potential outflows form storms well outside of our forecast area. With that being said, a 10-20% chance of thunderstorms exists each day next week, highest in the mountains in Ventura and LA Counties Friday through the weekend.
The other and potentially more impactful concern next week is the continual and increasing heat. Wednesday and Thursday are on track to be the warmest days in the forecast, with widespread moderate to major HeatRisk across the region, including at the coasts (focused south of Point Conception). Extreme Heat Watches are currently in effect for most of the region save for the immediate Central Coast. The most likely outcome is for some locations to be converted to Heat Advisories, while others will become Extreme Heat Warnings. While temperatures will trend down Friday into the weekend, there is a fairly large range of outcomes as to how much. The most likely scenario would bring temperatures back down to near normal for mid-July by the weekend. However, the humidity is poised to stay through the extended period (and beyond), and this would still present Minor to Moderate HeatRisk across much of the region, especially away from the coasts. Ensembles suggest PWATs hover around 1.5 inches during the period and even into the next week, so muggy days are in the near and long term future here is Southwest California.
The biggest concern wind-wise remains the potential for moderate Sundowner winds and northwest winds over the interior Wednesday night and potentially Thursday night, although weaker Thursday. Otherwise winds will trend slightly more onshore Thursday into the weekend.
12/0300z.
At 0019Z at KLAX, the marine layer depth was was 1000 ft. The top of the inversion was at 4200 ft with a max temperature of 25 C.
High confidence in TAFs for KPMD, KWJF and KPRB.
Low to moderate confidence in the remaining TAFs. IFR conds expected from the Ventura sites and northward, with MVFR conds for the LA sites. The timing of low clouds and IFR/MVFR conds may be off +/- 2 hours. The arrival of mid to upper level clouds may disrupt the marine layer cloud formation, hence the reduced confidence for the coastal sites.
KLAX, Moderate confidence in the 00Z TAF. Arrival time of low clouds this evening could be off +/- 2 hours. Clearing of the low clouds on Sun morning could be off by the same amount. High confidence that any east wind component will be below 6kt.
KBUR, Moderate confidence in the 00Z TAF due to uncertainty in marine layer clouds and clearing times if cigs reach BUR tonight. There is a 40% chance of no CIGs.
11/826 PM.
For the outer waters, winds and seas are largely expected to be below Small Craft Advisory (SCA) levels through Tuesday, then there is a 50%-60% chance of SCA winds and seas developing Tuesday night through Thursday night.
For the nearshore waters along the Central Coast, mainly light winds are expected through Tuesday, but winds will begin to increase on Tuesday, Likely reaching SCA levels Wednesday afternoon through Thursday night. Short period seas may also reach SCA levels.
For the inner waters south of Point Conception, conds are expected to remain below SCA levels through the forecast period, except for a 50% chance of SCA wind gusts over the western portions of the Santa Barbara Channel Wednesday and Wednesday night.
11/150 PM.
A south to southwest swell will continue to affect the coastal waters through next week. With this longer period swell, the potential for larger surf and a greater risk for rip currents will continue.
Evening high tides are expected to increase this weekend going into next week with Monday expected to be the highest tide of 7.1 to 7.7 ft above MLLW. There is the potential for some minor coastal flooding next week with the evening high tides and south swell. One thing that will need to be watched late next week into the weekend will be the potential of a greater south to southwest swell from potential tropical cyclone over the eastern Pacific.
Thunderstorms will be possible along the beaches starting Sunday and going through next week (10-20% chance). For more information, please refer to the Beach Hazard Statement.
Ca, Heat Advisory remains in effect until 10 AM PDT Tuesday for zones 38-343>345-353-376>380. (See LAXNPWLOX). Extreme Heat Watch in effect from Tuesday morning through Thursday evening for zones 38-88-341>345-347>358-362-366>376-378>383-548. (See LAXNPWLOX). Heat Advisory remains in effect from 10 AM Sunday to 10 AM PDT Tuesday for zones 88-368-372-373-375-548. (See LAXNPWLOX). Beach Hazards Statement in effect from Sunday morning through Wednesday evening for zones 340-346-349-350-354-362-366. (See LAXCFWLOX). PZ, NONE.
