The month picked up where August left off, with an active monsoon pattern bringing periods of showers and thunderstorms to the mountains and deserts. The storms were confined to the deserts where intense isolated strong/severe thunderstorms on the 7th, 8th and 9th produced damage and impacts.
Every event with a place to put it. 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.
The month picked up where August left off, with an active monsoon pattern bringing periods of showers and thunderstorms to the mountains and deserts. The storms were confined to the deserts where intense isolated strong/severe thunderstorms on the 7th, 8th and 9th produced damage and impacts. Flash flooding was especially intense in Palm Springs and Cathedral City on the 9th, where structures throughout the city were flooded and roads were covered in debris. At Palm Springs High School 31 classrooms were inundated. Major flood damage also occurred at the Safari Mobile Home Park. Palm Springs set a daily record with 1.19 inches of rainfall. Many trees were toppled on September 8th when 62 mph winds occurred at Thermal Airport.
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 7, 3:20 PM PST, 30 minutes earlier.
Area Forecast Discussion
National Weather Service San Diego CA
420 PM PDT Thu Sep 7 2017
.QUICK UPDATE...
Just sent a quick update to extend thunderstorms into the lower
deserts this evening. A cluster of showers and storms will bring
patchy rainfall to the Coachella Valley over the next could of
hours. No other changes attm.
&&
.SYNOPSIS...
Decreasing moisture and instability today will result in lower
chances for mountain and desert thunderstorms. Cooler through
Saturday with a cut-off low forming off the West Coast. The low
will bring increasing moisture Friday through Sunday, with better
chances for afternoon and early evening thunderstorms in the
mountains and deserts. Widespread shower and thunderstorm activity
is possible on Sunday, from the deserts all the way to the coast
and coastal waters. Warmer Monday with just a slight chance for
afternoon thunderstorms for the northern mountain and desert
areas. Cooling will likely occur Tuesday through Wednesday with a
trough of low pressure moving into Central California. Expect
night and morning marine layer clouds in the coast and portions of
the valleys.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
Afternoon visible satellite imagery shows scattered mid level
clouds moving up from the south and towering cumulus/cumulonimbus
clouds over the mountains and high deserts. Radar has shown a
couple isolated thunderstorms developing over the San Diego county
mountains this afternoon. Expect this convective activity to
continue through early evening, with the focus being the San
Diego county mountains and deserts. The 12Z Miramar sounding
indicates a 7 deg C marine layer inversion at around 1000 ft msl,
a precipitable water of 1.1 inches (down from 1.45 inches
yesterday) and 385 J/KG of MUCAPE (down from 662 J/KG yesterday).
With the weak inversion and patchy, thin nature of the stratus,
the stratus clouds from earlier today were able to clear
relatively quickly.
On water vapor satellite imagery, a broad trough is noted off the
coast of the Pacific Northwest while a ridge is over the Great
Basin area. The trough will deepen a little along the West coast
today, and with the lower heights aloft we are seeing temperatures
which are mostly a few degrees lower than 24 hours ago. The
trough will continue to deepen on Friday and then split-off into
a cut-off low Saturday just southwest of Point Conception,
meander there on Sunday before slowly lifting north late Sunday
Tuesday. For Friday through Saturday, the low will lift plentiful
amounts of moisture (up to 1.8+ inches precipitable water) up from
the south over eastern Imperial and Riverside counties and
western Mexico, while the models still show only marginal amounts
of precipitable water (up to around 1 inch) moving into extreme
eastern portions of our forecast area. Even with this unimpressive
moisture content, the hi-res models do show afternoon/early
evening shower/thunderstorms occurring over the eastern San
Bernardino/Riverside/San Diego county mountains and deserts on
both those days. The nearby low will also bring cooling for Friday
and Saturday, with highs widespread 5-10 degrees below normal.
The lower heights aloft may also bring some subtle deepening of
the marine layer. Flow aloft turns to the southeast over our
region late Saturday night/early Sunday morning, with the GFS and
NAM showing mid-level moisture and some elevated instability
moving in over the entire forecast area, creating the potential
for scattered elevated showers/thunderstorms from the deserts all
the way to the coast/coastal waters. Precipitable water increases
to 1.4-1.5 inches Sunday afternoon, which in combination with high
amounts of instability (near or above 1000 J/KG of SBCAPE) could
lead to an active afternoon of thunderstorms over the mountains,
deserts, valleys and there's even a chance that the coast could
get some as well. With the southeast to east flow, some warming
could occur on Sunday, but this will depend on how much cloud
cover there is across the area.
Although drying occurs Monday, there may be enough residual
moisture for a few afternoon/early evening thunderstorms in the
San Bernardino county mountains and high deserts. Drying looks to
continue Tuesday through Wednesday as the low develops into an
open trough and moves inland into Nevada. Expect night and marine
layer stratus in the coast and portions of the valleys.
&&
.AVIATION...
072000...Coast/Valleys...VFR conditions through this evening. Patchy
stratus, with bases around 1200 ft MSL and tops near 1500 ft MSL,
will redevelop along the coast and around 15 SM inland by Friday
morning. Low VIS of 1-3 SM BR is expected over areas of higher
terrain where stratus develops. Low clouds will clear towards the
coast by mid-Friday morning.
Mountains/Deserts...FEW/SCT mid-level clouds today, with isolated
TSRA possible this afternoon over the desert mountain slopes of San
Diego/Riverside Counties. Storm bases will be about 9000 ft MSL with
tops up to 30 Kft MSL. Strong up/down drafts are possible near
storms, with gusty surface winds.
&&
.MARINE...
A Small Craft Advisory remains in for the outer waters for West-
Northwest wind gusts of 20-25 kt through this evening. Otherwise, no
hazardous marine weather is anticipated through Monday.
&&
.SKYWARN...
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
&&
.SGX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory until 9 PM PDT this evening for Waters from
San Mateo point to the Mexican Border Extending 30 to 60 nm
out including San Clemente Island.
&&
PUBLIC...Harrison/JMB
AVIATION/MARINE...JJTThe San Diego radar (KNKX), 113 km away, was scanning. The volume nearest the first event began at 23:48 UTC.
6 flash flood, 4 thunderstorm wind, 2 lightning. Local standard time, as filed.
Downburst winds from a thunderstorm toppled several trees at the Children's Discovery Museum in Rancho Mirage, CA, the irrigation system was also damaged.
A lightning strike struck a palm tree, catching the tree and a residence on fire.
A state park ranger reported water up to 6 feet deep and 100 yards wide near the intersection of Salt Wash and Cutacross Trail. An additional photo from twitter showed minor road damage at Highway 78 and Fault Wash near Ocotillo Wells.
Flash flooding washed out the shoulder of the S22 (Borrego Salton Seaway) near Borrego Springs.
The ASOS at Jacqueline Cochran Regional Airport in Palm Springs reported a 62 mph wind gust between 1740 and 1746 PST. Multiple large trees and a fence were also toppled near the airport. Radar indicated the potential for additional severe gusts between 1730 and 1800 PST.
A state park ranger reported strong outflow winds from a thunderstorm with estimate peak gusts of 60 mph.
A lightning strike knocked out power to 1000 customers in Palm Springs.
A mix of water and debris flowing through the normally dry Coyote Wash was reported around 1500 PST, by 1515 PST several inches of water and debris were flowing near Canyon Entrance dirt road and the Citrus Groves.
Strong downburst winds from a thunderstorm produced a 55 mph wind gust at Palm Springs International Airport. Winds may have been stronger elsewhere in the city. Southern California Edison reported 1000 power outages.
A 1-3 ft wall of water and debris surged through the Safari Mobile Home Park in Palm Springs. Multiple homes were damaged, Santa Monica Street was filled with debris and several residents were stranded in their homes.
Palm Springs High School suffered major flood damage for the second time in a month. A total of 31 classrooms were flooded.
The second intense thunderstorm of the day rolled over Palm Canyon and Palm Springs producing a daily rainfall record. Intense runoff through Palm Canyon Creek and the Whitewater River resulted in a closure of Cathedral Canyon Road and a swiftwater rescue and closure at Golf Club Drive. South Araby Drive was also closed. Other sections of the city were inundated with standing water and street flooding. Numerous homes suffered flood damage, cars were water logged and streets covered in debris.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2017Every state in 2017This day in weather historyWarnings in California, September 2017
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: 723123, 723124, 722820, 722845, 722821, 722819, 722824, 722822, 722860, 722857, 722859, 722825.