13/505 AM.
A warming trend early this week will give way to dangerous heat by mid week. A few showers and thunderstorms could impact interior areas during the afternoon hours of Monday and Tuesday. Gusty northwest to north winds will impact southern Santa Barbara County to the Interstate 5 Corridor during the afternoon through overnight hours Tuesday and especially Wednesday.
(tdy-Wed), 13/506 AM.
The upper pattern over the western CONUS remains especially favorable for deep, southerly moisture transport to facilitate the influx of copious monsoonal moisture -- aided by convective debris from Arizona and northwest Mexico circulating into the area. Precipitable water values over the local area have increased by a quarter to half inch over the past 24 hours, owing to southerly flow between an expansive upper ridge centered over the central CONUS and upper troughing off the Pacific Coast. Amplification of the upper trough and eventually its cutting off from steering currents will correspond to downstream ridge amplification and height rises over Southern California through mid-week. Temperatures will become increasingly warm to hot from day-to-day, with the most widespread and dangerous heat on Friday once the marine layer becomes more shallow. Heat headlines continue. By Wednesday, high temperatures will range from 90 to 105 degrees in most areas away from the beaches. And with the monsoonal moisture boosting humidity, widespread Major HeatRisk is expected Wednesday. Overnight low temperatures Tuesday night and Wednesday night will only be in the lower 70s in many areas south of Pt. Conception, further increasing potential heat impacts.
Precipitation chances will be highest today owing to the continued influx of mesoscale perturbations from previous, diurnally enhanced convection well east of the local area coupled with peak precipitable water values. Convective chances today will be focused over interior areas of Los Angeles and Ventura Counties, where diurnally enhanced convection is forecast to develop in the Noon-3PM PDT time period this afternoon. The greatest chances for this activity will be where convergence is enhanced in northeast L.A. County by multi-directional flow channeling from surrounding gaps in high terrain. Strong evaporative cooling in downdrafts amid deep inverted-V thermodynamic profiles will support the risk for local gusts to reach 45-60 mph, especially as 15-25 kt of effective shear would be sufficient for multicellular convective modes. Also of note, lightning strikes peripheral to rain cores could ignite new fires, and the gusty and erratic outflow winds could enhance fire spread, including for ongoing fires. An outside chance for localized flooding cannot be ruled out where convection repeatedly moves over the same locations. This activity will dissipate this evening, and thereafter warming midlevel thermodynamic profiles from the intensifying upper ridge will tend to lower convective chances going forward starting Tuesday. However, a few showers and an isolated thunderstorm will remain possible over the high terrain of L.A. and Ventura Counties Tuesday afternoon.
Additionally, expanding surface high pressure behind the aforementioned upper troughing off the Pacific Coast will result in northwest to north winds strengthening over areas north of Pt. Conception Tuesday into Wednesday. The overall pattern, characterized by Santa Barbara-Santa Maria pressure gradients trending to offshore at 2-4 mb, will favor the potential for a strong Sundowner wind event -- aided by both thermodynamic forcing and the development of a coastal jet off Pt. Conception especially Wednesday night. There is a 30-50% chance for wind headlines to become necessary for southern Santa Barbara County to the Interstate-5 Corridor, especially for Wednesday later afternoon to overnight.
(Thu-Sun), 13/506 AM.
Very gradual lowering of midlevel heights later this week into the weekend, combined with the eventual influx of deep moisture from distant, low-latitude East Pacific storms bringing increasing cloudiness, along with reinforcing onshore flow, will all contribute to temperatures slowly cooling to near-normal readings by next weekend. Hot conditions will still be present on Thursday when heat headlines remain in effect. While a few diurnally enhanced showers cannot be ruled out over the high terrain late this week and into the weekend owing to the increasing moisture, confidence in the development of this activity is too minimal for mention in the forecast at this time. Otherwise, the onshore flow will bring an increase in night through morning patchy low clouds and fog across coastal areas by next weekend.
13/1206z.
At 1130Z at KLAX, the marine layer depth was 800 ft. The top of the inversion was at 3600 ft with a max temperature of 23 C.
Moderate confidence in the TAFs. Patchy low clouds during the night through morning result in uncertainty in CIGS for coastal and coastal valley sites. There is a 20-30% for thunderstorms in or near KPMD/KWJF this afternoon, capable of strong and variable winds and heavy rain.
KLAX, Moderate confidence in the 12Z TAF. There is a 30% chance for CIGS to be off by at least one category during the night through morning hours. High confidence that any east wind component will be below 6 kt.
KBUR, Moderate confidence in the 12Z TAF. There is a 30% chance for CIGS to be off by at least one category during the night through morning hours.
13/506 AM.
The primary marine impacts will come with strengthening NW to N winds to SCA levels (at least 80% chance) Tuesday and continuing through Thursday night over PZZ670, PZZ673, and PZZ676. There will be a 20% chance for gales over PZZ673 and PZZ676 later Wednesday into Wednesday night. Seas are forecast to build over 10 feet in conjunction with these winds. The elevated winds and seas will extend into the western Santa Barbara Channel Wednesday into Wednesday night. While a few showers may drift across the local waters through early parts of this week, thunderstorms are unlikely.
13/506 AM.
Dangerous rip currents and breaking waves with elevated surf are expected for coastal areas and the beaches of Los Angeles, Ventura, Santa Barbara, and San Luis Obispo Counties, as enhanced southerly swell continues. A Beach Hazards Statement remains in effect through Wednesday evening for these areas. Minor coastal flooding will be possible during the evenings, given abnormally high tides of 7.0 to 7.5 feet. An isolated lightning strike will be possible at the beaches today, however higher chances will be over areas farther inland. Later this week and into the weekend, distant storms over the East Pacific waters well south of the area could produce increasing southerly swell resulting in even more significant beach hazards by the weekend.
Ca, Heat Advisory remains in effect until 10 AM PDT Tuesday for zones 38-88-343>345-353-368-372-373-375>380-548. (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). Beach Hazards Statement in effect through Wednesday evening for zones 340-346-349-350-354-362-366. (See LAXCFWLOX). PZ, NONE.
