.SHORT TERM (TDY-MON)...05/213 PM.

The long lasting and extreme heat wave continues, peaking through Saturday. This is a dangerous situation with all the ingredients for a high risk of heat-illness and fast growing fires. PLEASE avoid hiking in the mountains and the hills through this weekend, make plans on how you will stay cool in the afternoon and evening hours, and stay away from anything that could spark a fire.

A 595-98 decameter upper level high pressure system will dominant the west coast through most of next week. The high is currently centered over northwest California, which is in a position favorable for causing the near neutral onshore pressure gradients that we saw today, and the shift to northerly for the north-to- south gradients. Any of those three ingredients alone would heat things up, but when they all happen together we are in extreme territory. Many valley and mountain areas are already near to or exceeding 100 degrees, with the Santa Clarita Valley hovering around 115 (no official records available for that location). The extreme heat is also causing a deep mixing/boundary layer which has allowed for some fair weather cumulus clouds over the mountains but will not be a convection threat. Near the coast, a shallow but persistent marine layer remains, and does not look to be going anywhere. As a result, the immediate coastal areas will be closer to mild than hot, but the temperatures will ramp up quickly for every mile inland of the beach. With the shallow marine layer, dense fog will remain a concern especially with the lingering smoke particles in the air from all the firework activity.

The high will gradually slide into southeast California through Monday. As a result, the northerly shift in the flow from today will transition to more onshore Saturday afternoon through Sunday or Monday. On the COASTAL side of the mountain ranges, this shift will bring a much earlier than usual daytime peak in temperatures (closer to 10am than the afternoon) as a less hot air mass over the ocean pushes in. While it will still be hot Saturday and Sunday, will not be as hot as today and the trends should be going down. The marine layer should also expand a little as well. As a result, decided to pull the end time of the Heat Warnings and Advisories back a day to Saturday or Sunday (depending on your location)...and they back need to all be pulled back to Saturday.
Over the INTERIOR mountains and valleys/deserts, this shift will do very little. In fact, with the shift of the core of the high moving closer, Saturday very well could be the hottest day of the event for the furthest interior areas, with Sunday still hot but down a few degrees with the peak of the onshore flow. As such, did not touch the Heat Warnings for those locations.

Many calendar day records are expected to be broken today. All-time records (for any calendar day) could break on Saturday at Palmdale, Lancaster and Paso Robles.

.LONG TERM (TUE-FRI)...05/213 PM.

The upper level high, centered over southeast California on Monday, is poised to meander northwest into Nevada Tuesday through at least Thursday. This will cause the strength of high pressure over southwest California to drop a bit, resulting in a few degrees drop in the temperatures over the mountains and interior (still very hot). This will also cause the onshore flow to weaken once again (similar to today but likely not to this magnitude). As a result, coastal and valley areas will likely trend hotter again.
While there is a range in the ensemble projections, most push temperatures inland of the beaches back up to about 5 degree below today and tomorrows temperatures. On top of that, northwest winds will increase, especially over southwest Santa Barbara County, which will further warm it up. So the morale of the story is that this heat wave may not be done with us just quite yet.

AVIATION
05/1800Z.

At 17Z at KLAX, the marine layer was 700 feet deep. The top of the inversion was at 3300 feet with a temperature of 34 deg C.

Moderate to hi confidence in the 18Z TAFs. Most airfields will be VFR thru the fcst period. Low clouds should move back into coastal airfields from KOXR southward at some time tonight and persist into Sat morning, with IFR/MVFR conds. There is also a 30% chance of LIFR conds at KSMX late tonight and early Sat. Timing of the onset and any dissipation of the low clouds may be off +/- an hour or two. There will also be some MVFR to even local IFR vsbys early in the TAF period for the coast and vly airfields of L.A. County due to haze. Some more haze is possible (50% chance)
late tonight into Sat morning for KBUR and KVNY with MVFR vsbys.

KLAX...Moderate confidence in the 18Z TAF. MVFR vsbys due to haze should end around 20Z. Tonight, there is a 40% chance that IFR cigs will arrive as early as 04Z. Cigs are expected to improve to MVFR around 14Z. Timing of onset and dissipation of the low clouds may be off +/- an hour or two. There is a 20% chance of an east wind component of 7-8 kt from 10Z-17Z Sat.

KBUR...Moderate to high confidence in the 18Z TAF. VFR conds should prevail for most of the fcst period. However, MVFR vsbys in haze is expected until about 20Z and again tonight from about 09Z-15Z.

MARINE
05/113 PM.

In the Outer Waters, Small Craft Advisory (SCA) level winds will continue in the southern zones (PZZ673/PZZ676) thru Sat morning.
In the northern zone (PZZ670), SCA conds are likely (70% chance)
this afternoon thru tonight. For the most part, expect winds to remain below SCA levels Sat afternoon thru Wed night except for a 50% chance of SCA level wind gusts at times Sunday night. There is also a 30% chance of SCA level NW winds in the far outer waters and from near Pt. Conception to NW of San Nicolas Island, especially during the late afternoon thru late evening hours.

For the Inner Waters N of Pt. Sal, SCA conds are likely (70% chance) this afternoon/eve. There is a 30% chance of SCA level winds Sat afternoon/eve, otherwise SCA conds are not expected Sat night thru Wed night.

For the Inner Waters south of Pt. Conception, there is a 30% chance of SCA conds late this afternoon and evening and Tuesday evening in western portions of the Santa Barbara Channel, mainly from Santa Cruz Island to the SBA County south coast from Pt.
Conception to Gaviota to Refugio State Beach. Otherwise, conds will be below SCA levels for the southern inner waters thru Wed night.

Areas of dense fog will affect portions of the coastal waters tonight into Sat morning. Please reference the Marine Weather Statement for additional information.

BEACHES
05/115 PM.

A moderate southerly swell will affect the Southern California coastal waters through Sunday, with a 15-17-second period this weekend. While surf is not expected to be particularly high, surf heights of up to 4 to 6 feet are anticipated at beaches exposed to southerly swell, especially the LA and Ventura County beaches.

The significant wave energy with the long-period swell will combine with the elevated surf to create dangerous conditions at area beaches, with powerful and dangerous rip currents expected.
This is especially the case for the south-facing beaches of LA and Ventura Counties. A Beach Hazards Statement is in effect through the weekend to address these concerns.

LOX WATCHES/WARNINGS/ADVISORIES
CA...Excessive Heat Warning now in effect until 9 PM PDT Wednesday for zones 38-343>345-353-376>379-381>383. (See LAXNPWLOX).
Excessive Heat Warning now in effect until 9 PM PDT Sunday for zones 88-342-348-351-352-356>358-369>375-380. (See LAXNPWLOX).
Heat Advisory now in effect until 9 PM PDT Saturday for zones 341-347-355-367-368. (See LAXNPWLOX).
Excessive Heat Warning now in effect until 9 PM PDT Saturday for zones 349-350. (See LAXNPWLOX).
Wind Advisory remains in effect from 6 PM this evening to 3 AM PDT Saturday for zones 349-351. (See LAXNPWLOX).
Beach Hazards Statement in effect through Sunday evening for zones 354-362-366. (See LAXCFWLOX).
Heat Advisory now in effect until 9 PM PDT Sunday for zone 548. (See LAXNPWLOX).
Red Flag Warning in effect until 6 AM PDT Saturday for zones 342>345-349-351>353-376>378-381. (See LAXRFWLOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Saturday for zones 645-670. (See LAXMWWLOX).
Small Craft Advisory in effect until 9 AM PDT Saturday for zones 673-676. (See LAXMWWLOX).