.SHORT TERM (THU-SUN)...19/811 PM.

***UPDATE***

The upper low moving across the region is currently centered near Point Conception, and will continue to shift southeastward along the coast through late Friday morning. An area of strong thunderstorms developed over the interior of Santa Barbara and San Luis Obispo Counties this afternoon into the early evening hours.
The strongest storms produced heavy downpours and small hail, with rain rates of 1 to 2 inches per hour. Rainfall observations in the area were mostly light, up to 0.10 inch, but the stronger storms produced between 0.45 to 0.78 inches of rain. Roadway flooding and landslides were reported from Highway 166 in an area that received persistent, heavy rainfall.

Radar images as of 800 PM show the activity has diminished significantly, however localized flooding or landslides may be possible in areas that had the heavier rain. As the low moves along the coastline overnight, the threat of showers and thunderstorms will shift to Ventura and L.A. Counties. Shower activity will likely be isolated to scattered, and many areas may not see any rain. However, there is potential that heavy rain will affect some locations through around noon Friday. Models indicate that the steering flow aloft will be stronger, so that storms will not be stationary, helping to decrease the likelihood of flooding issues.

Friday afternoon will see showers decreasing and with partial clearing and warming. Highs will bump up on average 4 to 8 degrees compared to today's high temperatures.

***From Previous Discussion***

An unseasonably cold upper low is located just west of the Central Coast this afternoon. Earlier this morning there were some thunderstorms that developed across the northern interior of SLO County. Hi res models were accurate depicting a lull in the activity through the rest of the morning and early afternoon. But now with the afternoon heating and cooler air aloft we're starting to see some building cumulus clouds that should develop into showers and thunderstorms over the next couple hours and into the evening across Santa Barbara and SLO Counties, especially over the elevated terrain. HRRR models continue to focus in on the area around the interior SLO/SBA County border as the most likely location for stronger storms and heavier rainfall, but certainly can't rule out strong storms in other parts of those counties as well as northern Ventura County. Not all areas will get rain, but in the most favorable areas rainfall rates up to an inch per hour are possible with hail and gusty winds as well. Hi res models are also indicating some rotation potential with these storms so there is a non-zero threat of a funnel cloud or small tornado. A flood watch was issued earlier for the Hurricane and Apache burn scars, however, as the system has shown a slightly farther west trajectory it was decided to include the Lake burn scar near the Santa Ynez Valley, and extend the time through 5am Friday morning.

The upper low is expected to turn east as it rounds Pt Conception tonight and follow the coastline into Orange County Friday morning. As this happens, the threat for active weather, showers and thunderstorms will increase south of Pt Conception. Again, not everywhere will get rain, but where it does rain there is a potential for high rain rates. Steering flow increases as the low starts to move east which would limit rain amounts in any one area so for now there are no flood watches south of Pt Conception except for the northern Ventura County mountains tonight. By Friday afternoon most if not all the shower/storm activity should be east of Ventura County, and east of LA County by around 6pm Friday.

Saturday and Sunday will be dry and clear with significant warming by Sunday, especially inland. Valley highs expected to be back in the 90s Sunday while inland coastal areas are in the low to mid 80s. Minimal if any marine layer expected following the storm.

.LONG TERM (MON-THU)...19/201 PM.

Warm weather to peak Monday and Tuesday with some cooling back to normal levels expected mid to late week. There is a larger spread of possible solutions later next week as some of the ensemble runs are indicating the ridge more or less continuing while others show a weak trough coming in Thu/Fri that would bring additional cooling. Neither solution is extreme in any way so impacts would be minimal and certainly dry weather expected. Longer rain projections show little or no chance of any additional precipitation beyond Friday through the early part of Oct.

AVIATION
20/0022Z.

At 1653Z at KLAX, there was a deep moist layer up to 4300 feet.
The top of the inversion was at 6200 feet with a temperature near 10 degrees Celsius.

Moderate to high confidence in TAFs for KPMD and KWJF, with the reduced confidence due to a slight chance of thunderstorms in the vicinity between 10Z to 21Z.

Low confidence in remaining TAFs. Cig heights will vary frequently due to an upper level low moving over the region. Timing of flight cat and VCSH/VCTS changes could be off by +/- 4 hours.

For KPRB, TSTM (30% chc) and SHRA chances diminish after 06Z.

For KSMX, KSBP, and KSBA, low confidence in cig height and timing.
Thru 12Z, there is a 20-40% chance of -DZ or -SHRA, with highest chances thru 06Z. There is also a 20-40% chance of thunderstorms thru 12Z, with best chances at KSMX and KSBP before 06Z. LIFR conds possible (20% chance) at KSBP and VLIFR conds possible (20-30% chance) at KSMX from 10Z thru 17Z.

For Ventura and Los Angeles County TAFs, there is a 20-30% chance of -DZ or -SHRA at all sites from 00Z thru the remainder of the period, and a 20% chance of thunderstorms between 06Z-18Z.

Thunderstorms may produce brief +RA and gusty, erratic winds.

KLAX...Low confidence in the 00Z TAF. Cigs may vary between BKN015-035 frequently from 04Z thru at least 18Z, and there is a 30 percent chance of -SHRA and a 20% chance of thunderstorms during this period. No significant east wind component expected.

KBUR...Low confidence in the 00Z TAF. Cigs may vary between BKN015-035 frequently from 04Z thru at least 18Z. There is a 30% chance of thunderstorms from 04Z to 18Z.

MARINE
19/713 PM.

For the Outer Waters (Central coast south to San Nicolas Islands), moderate to high confidence in the forecast. High confidence in winds and seas remaining below Small Craft Advisory (SCA) level thru early next week in the northern zone (off the Central Coast) except for a 20-30% chance for SCA level winds in the afternoon thru evening hours Friday. For the southern zones (Pt Sal to San Nicolas Island) there is a 50-60% chance of SCA level winds through late tonight. There is a 60% chance of more widespread SCA winds tomorrow afternoon thru late night over the waters near Point Conception. From Sat thru Tues, moderate to high confidence in winds and seas remaining below SCA level in the southern outer waters.

For the inner waters along the Central coast, high confidence in winds remaining sub advisory level thru early next week.

For the Santa Barbara Channel, moderate confidence in the forecast. There is a 50-60% chance of SCA level wind gusts, mostly in the western portion of the channel tomorrow afternoon thru late tomorrow night. Then, moderate confidence in conditions remaining below SCA level Sat thru Tues.

For the inner waters off the coast from LA and Orange County, high confidence in conditions remaining sub advisory level thru early next week. Low end SCA level gusts are possible (20-30 percent) in the afternoon thru evening hours tomorrow, isolated to the San Pedro Channel.

Isolated to scattered thunderstorms will be possible across all of the coastal waters through tomorrow morning, as an upper level low pressure system moves from off the Central Coast thru Southwestern California. The trough will move southeastward across the southern California bight tonight and onshore over southern California through Friday. The northern waters have a greater chance to be impacted thru late tonight, while the southern zones have a better chance from late tonight thru tomorrow morning. A Marine Weather Statement is in effect to communicate the hazards from thunderstorms to the marine community.

LOX WATCHES/WARNINGS/ADVISORIES
CA...Flood Watch in effect until 5 AM PDT Friday for zones 38-344-345-348-353-377. (See LAXFFALOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Friday for zones 650-673-676. (See LAXMWWLOX).