textproduct: Los Angeles

SYNOPSIS

20/229 PM.

Below normal temperatures will continue through the weekend, with a deep marine layer, as well as gusty winds over the interior. A significant warming trend will start Monday and peak around Wednesday. A push of moisture midweek will bring at least a low chance for rain.

LONG TERM (THU-SUN)

21/105 AM.

Through the extended period, models continue to exhibit good synoptic agreement. At upper levels, ridge slowly weakens Wednesday and Thursday with broad cyclonic flow developing on Friday and Saturday. At the surface, moderate to strong onshore flow will continue with some increase in northerly offshore flow later in the period.

Forecast-wise, main issue in the extended period will be temperatures. On Wednesday, there will be some slight warming in most areas. These warm temperatures on Wednesday may be exacerbated a bit due to some increase in mid-level moisture across the area. On Thursday, there will be some slight cooling, but conditions, overall, will remain quite warm. So, the EXCESSIVE HEAT WATCH will remain in effect for parts of LA county through Thursday with a good chance that it will be upgraded to an advisory by later shifts. For Friday and Saturday, there will be several degrees of area-wide cooling each day as the ridge retreats to the east.

Secondary concern for the extended will be increasing mid-level moisture across the area on Wednesday. Current deterministic models indicate increasing PWATs across Ventura and LA counties with values anywhere from 100-150% (GFS) and 125-200% (ECMWF) of normal for late June. The respective ensemble solutions indicate the same PWAT trend. There really does not seem to be any noticeable "trigger" in the atmosphere to kick off any convective activity. However, given the time of year, will indicate 5-15% chance POPs across Ventura and LA counties Wednesday afternoon and evening with the highest POPs over the higher terrain. If anything does develop, it will be high-based, resulting in limited rainfall. If any thunderstorms were to develop, dry lightning and gusty outflow winds would be the main concerns. This will need to be watched closely over the coming days.

AVIATION

21/1817Z.

At 1540Z at KLAX, the marine layer was around 800 feet deep. The top of the inversion was 4300 feet with a temperature of 19 degrees Celsius.

For the 18Z TAF package, moderate to high confidence in KSBA, KBUR, KVNY, KPMD and KWJF.

For all other sites, moderate confidence in the 18Z TAF. Timing of flight category changes could be +/- 3 hours of current forecasts. For KSMO, KLAX and KLGB, there is a 40-60% chance of MVFR CIGs Monday morning.

KLAX...Moderate confidence in 18Z TAF. For tonight, moderate confidence in return of CIG restrictions, but low confidence in timing (+/- 3 hours of current forecast). No significant easterly wind component is expected.

KBUR...High confidence in CAVU conditions through the day and into the evening. Moderate confidence in overnight conditions with a 40-50% chance of MVFR/IFR CIGs after 10Z.

MARINE

21/105 AM.

For the Outer Waters, moderate to high confidence in current forecast. Today through Wednesday, high confidence in winds and seas remaining below Small Craft Advisory (SCA) levels. On Thursday, there is a 30-50% chance of SCA level winds, beginning in the late afternoon hours across PZZ670/673.

For the Inner Waters north of Point Sal and south of Point Conception, high confidence in current forecast. Today through Thursday, winds and seas are expected to remain below SCA levels.

LOX WATCHES/WARNINGS/ADVISORIES

CA...Extreme Heat Watch in effect from Tuesday morning through Thursday evening for zones 88-368-372-373-379-380-548. (See LAXNPWLOX). PZ...NONE.