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 (MON-THU)

13/254 AM.

Next week will see the development a large long lasting and dangerous heat wave. Quite possibly one of the top heat wave events for the month of March - Ever.

On Monday an east Pacific high will approach Srn CA from the west and hgts will rise to 588 dam. On Tuesday the upper high will be atop of Srn CA with 590-592 dam hgts - this will put Srn CA under the area of maximum subsidence (compressional warming) from the high. The upper high will remain over the southern third of the state on Wednesday with hgts 592 to 593 dam. The upper high moves to the SE on Thursday but hgts will remain near 592 dam, but there will be less subsidence over the area. At the sfc there will be offshore flow from the north. The fcst for the E/W gradient is more uncertain with the GFS showing onshore flow (and thus a little less hot), while the EC shows offshore flow (thus adding further warming to the already near record to record temps.

On Monday look for max temps in the 80s across the csts and lower to mid 90s across the vlys. Tuesday looks to be the warmest day with cstl high in the mid 80s to lower 90s and the vlys reaching 95 to 102 degrees. Slightly cooler temps are forecast for Wed and Thu but max temps will remain dangerously high. Current min temps are forecast to remain in the 60s and these might be low and could come in warmer and this would add to the heat danger.

Details that make this heat event very impressive:

1. 500 MB heights are forecast to range between 591 and 595 DM which would be the highest March H5 heights since records began in 1948. The record is 591 dam which occured on March 7

2. 1000-500 MB thickness are forecast to peak in the 580 to 584 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.

At this time, there is a near 100 percent chc of HEAT ADVISORIES for most areas next Tuesday through Thursday, and possibly as early as Monday for some areas. Additionally, there is a 40-50% chance that EXCESSIVE HEAT WARNINGs may be needed for some areas Tuesday through Thursday.

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

13/1150Z.

At 0850Z at KLAX, there was no marine layer. There was a sfc based inversion with a top at 1100 ft and a temperature of 28 C.

High confidence in TAFs, except for KLAX, KLGB and KSMX where LIFR conds are possible as early as 14/09Z, but also a 30 percent chc of no flight restrictions.

KLAX...High confidence VFR TAF through 09Z then lower confidence. 1/2SM VV002 conds could arrive as early as 09Z. There is also a 30 percent chc of no cig/vis restrictions. No significant east wind component expected.

KBUR...High confidence TAF.

MARINE

13/1232 AM.

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. Have upgraded to a GALE Warning for PZZ670, Wind gusts to 35 kt are likely from Friday evening through late Saturday night. Confidence is lower for PZZ673/676, so will hold off and pass to next shift for further consideration. 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/eve hours Friday 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/eve across the western portion of the Santa Barbara Channel.

LOX WATCHES/WARNINGS/ADVISORIES

CA...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 from 3 PM this afternoon to 3 AM PDT Saturday for zone 645. (See LAXMWWLOX). Small Craft Advisory in effect until 9 PM PDT this evening for zones 670-673. (See LAXMWWLOX). Gale Watch in effect from this evening through late Saturday night for zones 670-673. (See LAXMWWLOX). Small Craft Advisory in effect until 3 AM PDT Saturday for zone 676. (See LAXMWWLOX). Gale Watch in effect from late tonight through late Saturday night for zone 676. (See LAXMWWLOX).