textproduct: Los Angeles

SYNOPSIS

13/1138 PM.

It will be cooler today with onshore flow and some high clouds. A significant heat wave will kick off Sunday, peak next Tuesday and Wednesday and then continue through Friday. MODERATE to HIGH heat impacts will occur each day Monday through Friday.

LONG TERM (WED-SAT)

14/1251 PM.

Overall, 12Z models remain in good synoptic agreement through the period. At upper levels, the high will slowly meander to the southeast through the period. Near the surface, models continue the trend of previous runs, the GFS forecasts weak diurnal gradients while the ECMWF has weak offshore gradients through the entire period.

Forecast-wise, nothing in the latest model guidance deviates from the expectation of a historic, long-duration, heat event for the area. The only uncertainty remains around the surface pressure gradients. If the ECMWF is correct with the persistent weak offshore flow, then temperatures will even be warmer than the currently forecast temperatures (which have many areas breaking daily and even monthly records). Essentially, just how extreme will the extreme heat be is the major question. For the forecast, have continued toeing the line between the NBMEXP and the 75th percentile NBM numbers both for the maximum and minimum temperatures. So with the afternoon forecast, will keep EXTREME HEAT WATCHES in effect through Friday for all coastal and coastal valley zones as well as the mountains. Most likely, these will be upgraded tomorrow.

Given the unprecedented length and magnitude of this extreme heat wave, heat stress will be a real threat each day, especially in areas that aren't used to the heat, like the coastal areas, where people may not have methods to cool off their homes. Try to complete outdoor activities early in the day or in the evening, and don't leave people or pets in cars.

As for any rain chances, latest deterministic and ensembles have changed tunes slightly, indicating some low chances of light showers after the 25th. However, models do not indicate any significant storms.

AVIATION

14/1949Z.

At 1922Z at KLAX, there was no marine layer or inversion.

There will be chances for IFR-LIFR cigs at KCMA (20%), KOXR (30%), and KSBA (10%) between 07Z-17Z Sun. For KSMO, KLAX, and KLGB, cigs may arrive as early as 03Z Sun, with a 20% chance of 1/2SM FG VV002 conds from 13Z-16Z Sun. Otherwise high confidence in wind forecasts and all other sites.

KLAX...Moderate confidence in TAF, with a 20% chance of 1/2SM FG VV002 conds 13Z-16Z Sun, and a 10% chance of mostly VFR conds through the period. Any east wind component will be below 7 kts.

KBUR...High confidence TAF.

MARINE

14/1250 PM.

Small Craft Advisory (SCA) level NW-N winds of 20-30 kt are likely across the Outer Waters through Sunday night. Gusts will reach GALE FORCE (35 kt) at times especially beyond 30 NM from Shore. Short-period seas will also peak near 10 ft across these waters through tonight. Conditions are likely to improve early next week, with relatively small seas expected.

SCA level NW winds will affect the Inner Waters along the Central Coast especially during the afternoon and evening hours today, with localized SCA wind gusts lingering into Sunday.

Inside the Southern California Bight, conditions are expected to remain below SCA levels for the foreseeable future, except for marginal SCA winds this afternoon and evening focused across the western portion of the Santa Barbara Channel.

LOX WATCHES/WARNINGS/ADVISORIES

CA...Heat Advisory in effect from 10 AM to 8 PM PDT Monday for zones 87-88-340>342-345>358-366>376-378>380-548. (See LAXNPWLOX). Extreme Heat Watch in effect from Monday evening through Friday evening for zones 87-88-340>342-345>358-362-366>376-378>380-548>550. (See LAXNPWLOX). PZ...Small Craft Advisory in effect until 3 AM PDT Sunday for zone 645. (See LAXMWWLOX). Small Craft Advisory in effect until 10 PM PDT this evening for zone 650. (See LAXMWWLOX). Gale Warning in effect until 3 AM PDT Sunday for zones 670-673-676. (See LAXMWWLOX).