textproduct: Los Angeles

SYNOPSIS

12/1139 PM.

A heat wave is expected to continue to affect the region through Sunday, aside from minor cooling on Saturday. For next week, significant additional warming is likely, with potential for MODERATE to HIGH heat impacts as a very strong ridge of high pressure builds over the area. Heat stress will be a threat each day.

LONG TERM (TUE-FRI)

13/152 PM.

For the extended, 12Z models still on track with the synoptic pattern. At upper levels, impressive high will develop over the area Tuesday/Wednesday then slowly drift to the southeast on Thursday/Friday. Near the surface, models still exhibit the same differences as previous runs...with the GFS indicating weak diurnal flow while the ECMWF indicates weak offshore flow.

With this pattern, the entire area is still on track for a historic March heat event next week. 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

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.

With little change in the overall forecast, confidence remains very high with a near 100% chance of HEAT ADVISORIES for most areas in the Tuesday through Friday time frame. 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. Over the weekend, the WATCHES may be expanded into interior sections.

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

13/2130Z.

At 21Z at KLAX, there was a surface based inversion to 900 ft and 26 C temp.

High confidence in TAFs, except for KLAX, KLGB and KSMX where there is a 30 percent chance of LIFR or lower cigs/vsbys 08-16Z.

KLAX...Moderate confidence in TAF with a 30 percent chance of VLIFR cigs/vsbys between 08Z-16Z. Any east wind component will be below 6 kts.

KBUR...High confidence TAF.

MARINE

13/253 PM.

Small Craft Advisory (SCA) level NW-N winds of 20-30 kt are likely across the Outer Waters through Sunday night. Seas will peak near 10 ft (especially beyond 40 NM from shore) during this period. Gales with wind gusts to 30-40 kt are likely from this evening through late Saturday night. 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 during the afternoon and evening hours today and Saturday, with a 30% chance SCA winds linger into Sunday.

Inside the Southern California Bight, conditions are expected to remain below SCA levels for the foreseeable future, except for a moderate chance winds reach SCA levels Saturday afternoon and evening 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). Heat Advisory remains in effect until 8 PM PDT this evening for zones 88-340>342-346>352-354>358-362-366>375-548. (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 to 9 PM PDT Saturday for zone 650. (See LAXMWWLOX). Small Craft Advisory in effect until 9 PM PDT this evening for zones 670-673. (See LAXMWWLOX). Gale Warning in effect from 9 PM this evening to 3 AM PDT Sunday for zones 670-673. (See LAXMWWLOX). Small Craft Advisory in effect until 3 AM PDT Saturday for zone 676. (See LAXMWWLOX). Gale Warning in effect from 3 AM Saturday to 3 AM PDT Sunday for zone 676. (See LAXMWWLOX).