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 (TUE-FRI)

14/242 AM.

The entire area remains on track for a historic March heat event. There is a near 100% chance of HEAT ADVISORIES for most areas in Tuesday through Friday. Additionally, the chances for extreme heat are growing, so EXTREME HEAT WATCHES have been issued from Tuesday through Friday for all coastal and coastal valley zones. The watches may need to be expanded into interior sections as well.

The upper high will reside over Srn CA Tuesday through Friday. Hgts will range from 592 to 594 dam. When the center of the upper high is overhead subsidence will bring synoptic scale compressional warming.

The biggest question mark for this event is the sfc gradients. There has been no change in the competing mdls with the GFS forecast period of onshore flow along with weaker offshore flow in the diurnal cycle. The EC is more offshore and in fact keeps the flow offshore in the afternoon when the onshore tendencies are the strongest. If the EC verifies the best both the highs and many of the lows will need an upward adjustment. Once again, here are the details that make this such an extreme event:

1. 500 MB heights are forecast to range between 590 and 594 DM which would be the highest March H5 heights since records began in 1948. The record is 591 dam which occurred on March 7 1997.

2. 1000-500 MB thickness are forecast to peak in the 580 to 583 DM range. Based on the 25+ year history of TEMP STUDY, the highest thicknesses recorded in March are 576 dam.

3. The Extreme Forecast Index (EFI) indicates values between 0.8 and 1.0 for both Maximum and Minimum temperatures, signifying a very usual or extreme event.

4. If the weak offshore flow, forecasted by the ECMWF, pans out then temperatures west of the mountains could be higher than currently forecast.

5. Based on current forecasts, both daily and monthly March temperatures records could fall for most climate sites.

6. Max temps during this period will be 20 to 30 degrees above normal.

7. For all 4 days (Tue-Fri) most cstl locations will see highs in the upper 80s and lower 90s. The vlys will see highs from 95 to 102. There will be plenty of 90s across the interior excluding the higher elevations.

With little change in the overall forecast,

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, deterministic and ensembles do not indicate any chances for significant rain through the 28th.

AVIATION

14/0945Z.

At 0439Z at KLAX, there was no marine layer. There was a sfc based inversion with a top at 1200 ft and a temperature of 26 C.

High confidence in TAFs except for KLAX & KLGB where there is a 20% chance of LIFR ocig/vis 14Z-16Z.

KLAX...Good confidence in TAF with only a 20% chance of 1/2SM FG VV002 conds 14Z-16Z. Any east wind component will be below 7 kts.

KBUR...High confidence TAF.

MARINE

13/1026 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. 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 through Saturday, 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 marginial SCA winds Saturday afternoon and evening focused across the western portion of the Santa Barbara Channel.

LOX WATCHES/WARNINGS/ADVISORIES

CA...Extreme Heat Watch in effect from Monday morning through Friday evening for zones 87-88-340>342-346>352-354>358-362-366>375-548>550. (See LAXNPWLOX). PZ...Small Craft Advisory in effect until 3 AM PDT Sunday for zone 645. (See LAXMWWLOX). Small Craft Advisory in effect from 2 PM this afternoon to 9 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). Small Craft Advisory in effect until 3 AM PDT early this morning for zone 676. (See LAXMWWLOX).