Swell Matrix

Area Forecast Discussion

National Weather Service Los Angeles/Oxnard Ca

911 am PDT Wed Jun 19 2024

Synopsis

19/857 AM.

Onshore flow will maintain near-normal temperatures across the region through Thursday with overnight low clouds and fog along the coastal and valley areas. Expect warm on Friday with above normal temperatures across the valleys, mountains, and desert into early next week. Dangerously hot weather is possible across the interior over the weekend.

Short Term

(tdy-Fri), 19/910 AM.

***UPDATE***

Temperatures are 3-5 degrees cooler along the coast with stronger onshore flow along the south coast and widespread marine clouds. In the Antelope Valley, temperatures are up 3-5 degrees with westerly winds. The central coast was a bit cloudier than expected this morning, but there are no impactful changes from the previous discussion.

***From Previous Discussion***

Strong winds in the outer waters coupled with a near shore S to N sfc pressure gradient has created a decent eddy. The marine layer is 1500-2000 ft deep and the eddy has pushed low clouds into the coasts from SBA southward as well as the LA Vlys. By dawn low clouds should also cover most of the VTA vlys. Additionally some low clouds have formed from ground cooling across western SBA county. Onshore flow will increase to 7 or 8 mb to the west in the afternoon and this may keep some beaches cloudy in the afternoon. Elsewhere clearing should be complete by noon as the marine inversion is not that strong. Otherwise hgts will lower slightly and this along with the more extensive marine layer will bring 2 to 3 degrees of cooling to most of the area.

Strong NW winds coming off the waters of the Central Coast will filter through the Western Santa Ynez range and produce low end advisory level gusts across the western half of the SBA south coast.

Two competing forces will be at work on the marine layer cloud pattern on Thursday as increasing troffing aloft combines with the eddy to promote cloud development. On the other hand sfc gradients will be weaker than they are this morning. Short range ensemble guidance shows that the eddy will likely be weaker and this should tip the scales to a clearer forecast. The best chance for low clouds will be over the southern portion of LA county and the Central Coast. The offshore trends will delay and weaken the seabreeze and this will bring 2 to 3 degrees of warming to the area with the exception of the Central Coast which will cool due to a more robust marine layer presence. The Summer Solstice will occur at 151 PM PDT.

Friday will kick off a fairly dramatic warm up as a large and hot upper high over the middle of the county expands westward. The eddy looks a little stronger so probably a little more morning low clouds across the coasts and into some of the lower vlys. By noon the whole area will be clear. Hgts will climb to 588 dam and max temps will warm 5 to 10 degrees across the interior and 2 to 4 degrees across the vlys. The coasts will still be under the marine influence and max temps will not change much. Antelope Vly residents will see max temps range from 100 to 103 degrees or about 8 degrees over normal.

Long Term

(Sat-Tue), 19/324 AM.

All eyes on the weekend as a significant warm up will likely occur. A very large and warm upper high will move over AZ/NM and Srn CA will be covered by the upper high's western half. Hgts will be near 592 dam. There is no offshore flow and in fact there will be fairly strong onshore flow (esp to the east) This will result in a very different temperature forecast for the interior vs. the coasts. The high hgts will really snmoosh the marine layer down and create a very strong inversion. Such strong inversions are hard to break down and this could keep clouds at the beach all day long. The marine layer will be under 1000 ft and this will keep it out of most if not all of the vlys. The very steep inversion will also keep min temps much warmer than normal right at the top of the inversion so locations near 1000 ft in elevation will see these very warm overnight lows. Look for 3 to 6 degrees of warming on Saturday away from the beaches. Max temps across the interior will end up 6 to 12 degrees above normal while the vlys will be 2 to 4 degrees above normal. The beaches will be at or even below normals. Blended ensemble guidance shows some cooling on Sunday but think this may be optimistic as hgts and pressure gradients really do not change that much. If the current forecast temperatures are correct the only areas that might need heat advisories would be the mtns.

The high persists over the area both Monday and Tuesday. The temperature differences will continue with the coasts sitting near normal with a stubborn night through morning low cloud pattern in place and the interior seeing well above normal temps under cloud free skies.

Aviation

19/1138z.

At 1125Z at KLAX, the marine layer was 2600 feet deep. The top of the inversion was at 3900 ft with a temperature of 22 deg C.

High confidence in TAFs for KPRB, KSBP, KPMD and KWJF.

Moderate confidence in TAFs for other TAFs. Flight cat changes may be off by +/- 1 hour this morning and +/- 3 hours tonight. Cig hgts may be off by +/- 300 ft. There is a 30% chance of no cigs tonight at KSBA, KBUR and KVNY.

KLAX, Moderate confidence in TAF. There is a 30 percent chc of no clearing today, and 20% chance of BKN008 cigs from 06Z-15Z Thur. Any east wind component should be less than 6 knots.

KBUR, Moderate confidence in TAF. VFR transition could occur anytime between 17Z and 19Z. There is a 30% chance of no cigs tonight.

Marine

19/853 AM.

For the Outer Waters, high confidence in current forecast. Small Craft Advisory (SCA) winds are expected through Friday night. Brief lulls in the winds during the mornings hours are possible. Seas will be steep and choppy through Friday night. Conditions are then expected to be below SCA levels Saturday through Sunday night.

For the Inner Waters north of Point Sal, moderate to high confidence in current forecast. SCA winds and choppy seas will persist through tonight, and again Thursday afternoon and evening. For Friday through Sunday night, winds and seas should remain below SCA levels.

For the inner waters south of Point Conception, moderate to high confidence in current forecast. For the western Santa Barbara Channel, winds gusts will be at SCA levels each afternoon and evening today and Thursday. Elsewhere and otherwise over the southern inner waters, winds and seas should remain below SCA levels through Sunday night.

Watches, Warnings, Advisories

Ca, Wind Advisory in effect from 3 PM this afternoon to 3 AM PDT Thursday for zones 349-351. (See LAXNPWLOX). PZ, Small Craft Advisory in effect until 3 AM PDT Thursday for zone 645. (See LAXMWWLOX). Small Craft Advisory in effect from 3 PM this afternoon to 3 AM PDT Thursday for zone 650. (See LAXMWWLOX). Small Craft Advisory in effect until 3 AM PDT Saturday for zones 670-673-676. (See LAXMWWLOX).

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