Upper level high pressure centered over the Four Corners ushered in moisture from the southeast into SoCal starting on Labor Day. Monsoon thunderstorms impacted the mountains and deserts September 2 through 5th.
Every event with a place to put it; 4 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS SGX wrote it up.
Upper level high pressure centered over the Four Corners ushered in moisture from the southeast into SoCal starting on Labor Day. Monsoon thunderstorms impacted the mountains and deserts September 2 through 5th. The event started with a nocturnal MCS over the Coachella Valley early in the morning on September 2nd, dumping 1-1.5 inches over a couple of hours. Even more thunderstorms formed Monday afternoon, especially in the mountains. Hail was reported on I-8 Monday afternoon. Storms continued each afternoon and evening in the mountains through September 5th. Some thunderstorms even reached the San Diego County coast on September 4th. Widespread outflow wind gusts of 30-45 mph were reported on the coast and in the valleys on September 4th.|At the end of September, 24-26, tropical moisture was wrapped into southern California from a closed upper low. This initially brought Santa Ana winds and very warm temperatures to the coast and on 25-26 brought scattered thunderstorms to the San Diego mountains. The flooding rains were confined to the Mojave Desert and Imperial Valley.
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 San Diego, CA wrote its last area forecast discussion before the first event at Sep 2, 1:42 AM PST, 18 minutes earlier.
Area Forecast Discussion
National Weather Service San Diego CA
242 AM PDT Mon Sep 2 2019
.SYNOPSIS...
Monsoon moisture will bring scattered showers and thunderstorms
to the region today, except near the coast. The chance of
thunderstorms will continue Tuesday through Thursday, but mainly
in the mountains and deserts during the afternoons. Hot late
summer weather will continue this week. High pressure weakens and
the monsoon moisture decreases Friday through the weekend,
bringing dry and slightly cooler weather.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
It's Labor Day, but Mother Nature thinks it's the fourth of July
with all the fireworks she's shooting off in the desert. A massive
thunderstorm complex in Arizona crossed the Colorado River west
and spread showers and thunderstorms and strong gusty winds across
the desert and into the mountains. Some of those winds and showers
even made it into the Inland Empire. A gust of 78 mph was observed
in an isolated spot in the Mojave Desert west of Needles last
evening as the gust front whipped through. Dust warnings and
advisories were issued for those eastern deserts. Some of that
mess reached the Coachella Valley and into the San Jacinto
Mountains, where some wind gusts reached 45 mph briefly, and
enough heavy thunderstorms with heavy radar estimates prompted a
flash flood warning. Palm Springs recorded 0.58 inch and Mt. San
Jacinto 0.84 inch. We expect this current crazy wave of
thunderstorms to settle down before sunrise. The moisture content
in the air will continue to saturate today. With all that moisture
and a favorable convective environment, a flash flood watch has
been issued for mountains and deserts. It will be a warm and muggy
day across the entire region, but the filtered sunshine should
dampen the heat. Feeling left out apparently, the coast has its
own weather, patchy dense fog. No boring Labor Day weather today!
The monsoon moisture will continue to flow into the region Tuesday
and Wednesday, with some decrease Thursday. Each day there is a
chance of thunderstorms in the mountains and deserts mainly during
afternoons and early evenings. The coast will continue to have
patchy fog nights and mornings, emphasis on patchy. By Friday it
looks like no more chances of thunderstorms. Models show a low
pressure trough trying to press down through the massive ridge
over the four corners region. That would bring a cooling trend and
a return of more marine layer presence and coastal clouds.
Confidence is low but growing as models are not in the best
agreement yet. Ensembles are somewhat non-committal. Let's get
through today first.
&&
.AVIATION...
020900Z...Coast...Patchy stratus and fog along the immediate coast
will likely reach KSAN at times 10-16Z. Vis below 1SM is possible.
Low confidence in any CIGS or FG at KCRQ or KSNA. Clouds and fog
clearing 15-17Z. Fog will be even patchier along the coast tonight
into Tuesday morning, with only small chances of impacts at the
coastal airports.
Valleys...Isolated -SHRA and -TSRA this morning, mainly in Riverside
County, dissipating by 13Z. Local east winds with sfc gusts 25-35 kt
likely near the foothills and below the San Gorgonio Pass through
13Z as well. No significant weather 13-20Z. After 20Z, -SHRA and
-TSRA may drift off the mountains and into foothills, with isolated
stronger convection across central portions of the Inland Empire.
Storms will diminish by sunset.
Mountains/Deserts...Areas of SHRA and TSRA continuing across the
Coachella Valley and Riverside County mountains this morning with
isolated outflow winds to 30-45 kt and vis 3 SM or less in BLDU and
TSRA. Storms will gradually drift northwest and weaken, dissipating
by about 13Z. TSRA redeveloping this afternoon, mainly over the
mountain crests and high desert. Gusty outflow winds and local heavy
rain are likely with these storms. Storms diminishing by sunset.
&&
.MARINE...
Patchy dense fog with visibility below 1 NM will continue through
about 9 AM Monday. Fog may redevelop again late tonight through
Tuesday morning. No hazardous marine weather is expected Tuesday
afternoon through Friday.
&&
.SKYWARN...
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
&&
.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Flash Flood Watch from 10 AM PDT this morning through this
evening for Apple and Lucerne Valleys-Coachella Valley-
Riverside County Mountains-San Bernardino County Mountains-
San Diego County Deserts-San Diego County Mountains-San
Gorgonio Pass Near Banning.
PZ...NONE.
&&
PUBLIC...MM
AVIATION/MARINE...SSThe Santa Ana Mts radar (KSOX), 104 km away, was scanning. The volume nearest the first event began at 10:00 UTC.
4 heavy rain, 2 flash flood, 2 strong wind, 1 wildfire, 1 high wind, 1 debris flow, 1 hail. Local standard time, as filed.
Palm Springs Airport ASOS recorded 0.98 inches of precipitation between 0200 and 0600 PST on September 2nd. The heaviest rain was between 0300 and 0400 PST.
Flash flooding along Date Palm Drive at Los Gatos Road from heavy rain from 0400 through mid-morning on 9/2. At one point, there was roughly 12 inches of water on the road.
North Indian Canyon Drive was closed on the morning of 9/2 due to water over the roadway. Media reports that the road was still closed monday evening.
Over 1 inch of rain fell in Anza between 1400 and 1500 PST on 9/2.
An electrical cable was dislodged and was draped across the road. A wind gust of 40 mph was reported about 5 miles to the northwest of this location.
The Tenaja Fire started on September 4th in the town of La Cresta in Riverside County and quickly grew to over 1,900 acres over the course of two days. 1,200 people were evacuated, and many schools closed due to the poor air quality. Two structures were damaged and three firefighters suffered minor injuries. The cause of the fire is still under investigation, but lightning may be the cause. The fire was contained on September 14th.
Wind gust of 53 knots reported in Pine Valley near I-8. A tree was down on the roadway near Pine Blvd. and Cedar Lane. USBP station on I-8 in Pine Valley reported hail and near zero visibility. Spotter John Grisafi reported wind damage at his home.
Around 1 inch of precipitation fell in Pine Cove near the Cranston Burn Scar in 1 hour on 9/5.
CHP reported several basketball-sized boulders blocking lanes on highway 78 near Banner.
Spotter reports branches down, dead tree down near Warner Springs. Estimated gusts to 35 mph at the time.
Spotter reports penny sized hail near Warner Springs.
Heavy rain for 20 minutes ending at 1515 PST with accumulations around 3/4 of an inch. Road flooding in Chihuahua Valley.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2019Every state in 2019This day in weather historyWarnings in California, September 2019
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: 858094, 858095, 858096, 858097, 858098, 858107, 858099, 858105, 858100, 858102, 858103, 858104.