Strong thunderstorms generated strong outflow winds across sections of Southern California. Wind gusts up to 78 MPH were reported by observation sites within the local mesonet.
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The episode as NWS LOX wrote it up.
Strong thunderstorms generated strong outflow winds across sections of Southern California. Wind gusts up to 78 MPH were reported by observation sites within the local mesonet. No significant damage was observed.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Los Angeles, CA wrote its last area forecast discussion before the first event at Oct 4, 4:26 PM PST, 1 hour 58 minutes earlier.
Area Forecast Discussion...UPDATED National Weather Service Los Angeles/Oxnard CA 526 PM PDT Mon Oct 4 2021 updated aviation discussion .SYNOPSIS...04/204 PM. An upper level low pressure system will bring a chance of showers and a slight chance of thunderstorms, mainly to Los Angeles and Ventura Counties through late tonight. A cooling trend is expected today through Thursday, with an increase in night through morning low clouds. A frontal system may bring rain to the entire area by Thursday night and Friday, Dry weather is expected for the weekend. && .SHORT TERM (TDY-THU)...04/145 PM. An upper low to our southwest continues to send moisture up into southern California. So far convection has been minimal and confined to areas near the MX border but this should change later this afternoon and evening as the upper low moves closer and instability increases with better diffluence aloft and higher precipitable waters. Hi res models continue to indicate minimal activity through around around 7pm this evening. Then showers and thunderstorms becoming more active mid to late evening in LA County, with the steering flow taking that activity towards the northwest as far as extreme southern San Luis Obispo County around midnight when LI's drop to around -2 there. Increased pops slightly across LA County as that area has the best chance due to it's proximity to the upper low and CAPE values from 1000-1500 j/kg. Southeast flow around the upper low will steer the showers towards the northwest and most shouldn't linger too long over any one area. However, in this scenario it's possible there could be some training of storms that could allow showers to persist, so isolated but mostly minor flooding is possible. And while the system does have a fair amount of moisture to work with there is always a small chance of isolated dry lightning outside of the primary rain cores, especially early in the event. Shower/storm chances expected to continue through the overnight hours, especially LA County before the low moves inland Tuesday morning and northwest flow develops and shifts the moisture and unstable air to the east. Still a small chance of a shower in LA County early Tuesday but otherwise it should be a dry day and cooler with stronger onshore flow. Quiet day overall Wednesday with cooler onshore flow and likely a widespread return of marine layer clouds to coast and valley areas. Not much different Thursday, though an upper level trough will be approaching from the west with increasing mid and high clouds through the day. Could see some morning drizzle for coast and valleys Thursday with a deepening marine layer. .LONG TERM (FRI-MON)...04/201 PM. Models in decent agreement with the approach of the next trough through Thursday evening, but then go their separate ways Friday with the ECMWF by far the leader in terms of strength and precip chances. A vast majority of the EC ensembles show at least some rain late Thursday into Friday , though most of them are under a quarter inch and many are under a tenth. Meanwhile, the GFS is much drier but does show some decent PVA with the trough passage Friday morning much like the EC. In any case, this is not looking like a significant rain maker by any means but could be the first widespread rain event in quite some time, albeit light rain. Broad northwest flow will dominate the weekend with warmer and dry conditions but breezy at times, especially southern Santa Barbara County. Another trough will move into the eastern Pacific early next week bringing more cooling. This one appears to be taking more of an inside track so it's mostly dry but should bring some gusty northerly winds and cooler temperatures. && .AVIATION...05/0023Z. At 2357Z at KLAX, there was no marine layer. There was a surface- based inversion with a top near 1100 feet at a temperature of 24 C. Moderate confidence that there will be no marine layer low clouds tonight with higher confidence south of Point Conception. There is a 30% chance of IFR or lower cigs at KSMX and KSBP after 03Z. Otherwise there will mainly be high VFR ceilings associated with an upper-level low moving through. There is a 30% chance of showers and thunderstorms across Los Angeles and Ventura County coastal and valley sites. Brief IFR cigs are possible under any shower or storm, as well as gusty erratic winds. There is a 20% chance of showers at KSBA, then a lower chance farther north. Fairly good confidence in a chance of showers through 12Z, then will taper off through the morning. KLAX...Moderate confidence in TAF. There is a 30% chance of a shower or thunderstorm. Locally gusty winds are possible with any isolated thunderstorm. There is a 30% chance of an east wind component of around 5 kt. KBUR...Moderate confidence in TAF. There is a 30% chance of a shower or thunderstorm. Locally gusty winds are possible with any isolated thunderstorm. && .MARINE...04/100 PM. High confidence in the current forecast. Winds and seas are expected to remain below Small Craft Advisory (SCA) levels for all of the coastal waters through at least Wednesday. There is a moderate chance of SCA level winds for the outer waters Thursday and Friday. An upper low pressure system about 375 NM southwest of Los Angeles will bring a slight chance of showers and thunderstorms to the coastal waters this afternoon and tonight, mainly over the waters south of Point Conception. Gusty and erratic winds and cloud-to-ocean lightning are possible. Patchy dense fog with visibility one nautical mile or less is expected this morning across the coastal waters. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...NONE. PZ...NONE. && .HAZARD POTENTIAL OUTLOOK (THU-MON). No significant hazards expected. && PUBLIC...MW AVIATION...Stewart MARINE...Sweet SYNOPSIS...MW/DB weather.gov/losangeles
The Los Angeles radar (KVTX), 14 km away, was scanning. The volume nearest the first event began at 02:23 UTC.
5 thunderstorm wind. Local standard time, as filed.
Gusty thunderstorm outflow winds impacted the mountains of Ventura county. The RAWS sensor at Rose Valley reported a gust of 77 MPH.
Gusty thunderstorm outflow winds impacted the South Coast of Santa Barbara county. The RAWS sensor at Montecito reported a gust of 78 MPH.
Gusty thunderstorm outflow winds impacted the mountains of Los Angeles county. An automated sensor at Mount Lukens Truck Trail reported a gust of 60 MPH.
Gusty thunderstorm outflow winds impacted the Santa Monica Mountains. An automated sensor at Corral Canyon Park reported a gust of 59 MPH.
Gusty thunderstorm outflow winds impacted the valleys of Ventura county. An automated sensor at Crimea Fire Station reported a gust of 63 MPH.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2021Every state in 2021This day in weather historyWarnings in California, October 2021
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 990998, 990997, 990999, 991000, 991002.