Los Angeles, CA 90020 Weather

UPDATED AVIATION SECTION

Synopsis

28/225 AM.

Gradual cooling will continue through the week as will coastal flooding issues due to very high tides. The next storm system is expected to arrive late Friday or Saturday with rain chances continuing into Sunday.

Short term (tdy-fri)

28/704 AM.

***UPDATE***

Latest satellite and surface observations indicate partly cloudy skies across the area with a mix of low clouds and high clouds. Current sounding data indicates marine inversion ranging in depth between 2500 and 3000 feet. No significant winds of note are currently observed.

For the immediate short term, forecast is very benign. Mostly sunny skies can be expected today after any patchy stratus dissipates. Overall, it should be a slightly cooler day across most areas with an uptick in onshore pressure gradients and a slightly cooler boundary layer (per TEMP STUDY database).

Overall, current forecast has good handle on the immediate short term. For the afternoon forecast, attention will be on the rain chances for Halloween weekend. Models still are all over the place with potential timing and amounts. So, hopefully the 12Z runs will come into better agreement.

***From Previous Discussion***

Very benign conditions will occur today and Thursday. The upper level flow will turn more and more to the SW and on Thursday will become more cyclonic. All of this in response to a cold upper low spinning out of British Columbia. There is not much of any inversion and there will only be patchy low clouds this morning. Skies, otherwise, will be partly cloudy as high clouds embedded in the upper flow drift overhead. The increase in cyclonic turning combined with lowering hgts will bring a more robust marine layer stratus field to the csts and some vlys Thursday morning. An increase in the mid and high clouds will make the day a mostly cloudy one. 1 or 2 degrees of cooling each day will keep most max temps across the csts/vlys in the 70s or 3 to 6 locally 8 degrees blo normal.

Friday will look a lot like Thursday with a broad mix of low, mid and high clouds creating overcast skies. A few more degrees of cooling will bring max temps down to the upper 60s and lower 70s. The only real difference will be an ~20 percent chc of a little light rain with rainfall amounts, if any, under .05 of an inch.

Long term (sat-tue)

28/214 AM.

The weekend storm forecast still remains a the tricky side. This system is more of a slug of moisture moving into and over the area rather an organized front or low pressure system. And since all of the moisture is over the data sparse eastern Pacific there is a good chance that the initial conditions for the forecast mdls are less than perfect. Right now the best moisture assoc with the plume is forecast to move in south of LA county. There is still quite a bit of disagreement on how wet the plume will be. One thing is becoming more clear - the best dynamics will occur Saturday evening as a trof assoc with the upper low moving through the PACNW will move through Srn CA. NVA follow close on the heels of this trof and the chc of rain will diminish quickly from w to e later Sunday morning. The most likely rainfall totals for this system south of Pt Conception are about a third to a half inch with double those amounts across some south facing slopes. Less than quarter inch is forecast for areas north of Pt Conception. There is only moderate confidence in these numbers as some solutions show quite a bit more rainfall and some even less. Shorter range hier rez mdls will begin to forecast this storm later today and this may provide more clarity.

Due to the SW origin of the moisture plume snow will not be an issue and will only fall above 9000 ft. Max temps will only be in the 60s on Saturday with some warming into the upper 60s and lower 70s Sunday as there will likely be some sunshine in the afternoon.

As is so often the case with trof passages upper level ridging and offshore flow will develop. It does not look like there will be advisory level winds but skies will be mostly clear and max temps will rise 4 to 5 degrees on Monday and maybe a degree or 2 on Tuesday. Longer range mdls are showing the chc of a weak system arriving next Wednesday.

Aviation

28/1703Z.

At 1600Z at KLAX, the marine layer was 3600 ft deep. The top of the inversion was at 5700 ft with a temperature of 14 C.

High confidence in VFR TAFs for desert airfields (KPMD & KWJF).

Moderate confidence in remaining TAFs. SCT-OVC250 with chc for VFR CIGs 030-50. MVFR CIGs 025-030 possible especially earlier in fcst.

KLAX: Moderate confidence in TAF. SCT/BKN035-055 likely after 29/06Z. Any east wind component is expected to remain under 8 kt.

KBUR: Moderate confidence in TAF. SCT/BKN 030 possible after 29/06Z. No wind issues expected.

Marine

28/802 AM.

Conditions are expected to remain below Small Craft Advisory (SCA) levels through Friday. Southwest flow aloft will produce chances for drizzle and isolated light rain showers Thursday and Friday.

A storm system is expected to impact the coastal waters this weekend. There is a wide range of outcomes, but there is at least a low threat of a 12-24 hour period of strong winds and steep seas. Worst conditions look to be focused south of Pt Conception.

Watches, warnings and advisories

CA: Coastal Flood Advisory in effect until 1 PM PDT Thursday for zones 87-340-346-349-350-354-362-366. (See LAXCFWLOX). PZ: NONE.