An upper level strong trough of low pressure moved down the California coast on May 6th, becoming an unseasonably deep (552 DM at 500 mb) closed low over Southern California on the 7th. An associated surface low tracked from San Bernardino County south along the San Diego County coast.
Every event with a place to put it; 3 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.
An upper level strong trough of low pressure moved down the California coast on May 6th, becoming an unseasonably deep (552 DM at 500 mb) closed low over Southern California on the 7th. An associated surface low tracked from San Bernardino County south along the San Diego County coast. The two combined to produce favorable up-slope flow near Palomar Mt. and Birch Hill that resulted in nearly a foot of snow, setting records for May. Elsewhere snowfall was limited to 2 to 5 inches above 5000 ft. Showers and thunderstorms were widespread and persistent, but lower rain rates limited impacts. An isolated thunderstorm produced a weak landspout tornado near Victorville, and multiple locations including Cypress and Redlands reported accumulations of small hail. Peak rainfall totals occurred in San Diego County, where 0.50 to 2.5 inches fell west of the mountains. Winds were breezy in the deserts, especially as the system deepened on the 6th, but impacts were minimal.
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 May 6, 8:46 PM PST, 5 hours 14 minutes earlier.
Area Forecast Discussion
National Weather Service San Diego CA
946 PM PDT Sat May 6 2017
.SYNOPSIS...
A deep, cold upper low will will bring scattered showers and
isolated thunderstorms through Sunday night. Snow levels will hover
between 4000 to 5000 feet through Sunday evening with periodic snow
showers and some snow accumulation likely especially above 6000
feet. Scattered showers will continue Monday into Tuesday, mainly
over the mountains and inland valleys. Showers will decrease in
coverage Tuesday night. Dry and warmer Wednesday through Friday with
high pressure building in aloft.
&&
.EVENING UPDATE...
Cold upper low center is dropping across the Southern California
Bight this evening. This system will linger over SoCal and Northern
Baja Mexico through Sunday night bringing a multitude of weather
impacts to the region.
Snow levels have rapidly dropped this evening and we received a
report of sleet falling at Palomar Mountain a few hours ago. Snow
levels will persist through Sunday night between 4000 to 5000 feet.
Accumulations will be hit and miss at the lower elevations between
4000 to 6000 feet although even a quick inch of snow under a heavy
snow shower can cause havoc on the busy mountain passes of SoCal,
which is why the winter weather advisory will remain in effect
through Sunday evening. Above 5000 or 6000 feet, accumulations are
more likely, and we could see up to 6 inches or so at those higher
elevations through Sunday evening.
Showers will increase in intensity and coverage overnight as the low
center approaches the region. Gusty SSW winds will continue this
evening over the mountains and deserts and should diminish towards
early Sunday morning. Have extended the northern deserts wind
advisory through 2 am as winds continue to be gusty there and
hovering around advisory criteria with a few reports of blowing dust
and sand in the high deserts of San Bernardino County this evening.
No other significant changes were made to the forecast this evening.
&&
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...
(remainder of the earlier forecaster discussion, issued at 202 pm)
The rain and drizzle will transition to showers and isolated
thunderstorms tonight and Sunday. The leading edge of the cold core
aloft moves in tonight between 06Z-12Z, and the airmass destabilizes
quickly with CAPE increasing to 300-500 J/kg. Dynamic forcing from
embedded shortwaves, an increasingly unstable thermodynamic profile,
and increasing low level moisture will generate scattered showers
and thunderstorms tonight and Sunday. Small hail is likely with the
strongest cells.
Forecast rain amounts remain the same as earlier. The totals will
vary quite a bit due to the scattered nature of the precipitation,
but the current storm track favors the highest amounts over San
Diego County. Rain totals through Tuesday are for 0.50"-1.00 near
the coast to 1 to 2 inches in the mountains. Amounts in San Diego
County will range from 1 to 1.5 inches near the coast, and from 2
to 3 inches in the mountains. In the deserts...amounts will range
from one quarter to one half inch in the upper deserts with around
one quarter inch in the lower deserts.
A Winter Weather Advisory was issued for the mountains above 5000
feet for Sunday. Snow levels will fall quickly tonight as the low
occludes and cold air wraps around the upper low from the
southwest. Wet bulb 0 level falls to 5000 feet early Sunday, with
snow levels bottoming out between 4500-5000 feet. Pinpointing
snow amounts and locations is challenging with these systems, and
some areas may not see much snow, but 1-3 inches of snow is
possible in some mountain between 5000-7000 feet. Greater amounts
of 3-5 inches is possible above 7000 feet. Convective showers may
briefly lower the freezing level to 4000 feet. Graupel or small
hail is likely in the strongest convection.
Long Range Outlook: The upper low trundles southward off the
coast of Baja Sunday night, then moves east toward southern AZ
Monday and Tuesday. This is close enough for wrap-around showers
over the mountains and deserts, perhaps into the inland valley if
the moisture is deep enough. High pressure aloft Wednesday and
Thursday will bring dry, warmer weather.
&&
.AVIATION...
070430Z...Coast/valleys...showers will gradually increase overnight
with cloud bases lowering to mostly 1500-2000 ft MSL, locally below
1000 ft MSL, and areas of vis 3-5 mi developing, locally lower.
These conditions will improve little until probably Sunday evening.
Terrain will be obscured at times. Isolated lightning strikes will
occur, especially Sunday. Local wind gusts from the west around 30
knots will occur tonight, mainly near the immediate coast.
Mountains...widespread terrain obscurations in rain and snow showers
and fog will occur through Sunday, with conditions improving
somewhat Sunday evening, though some mountains will continue to be
obscured in fog and scattered light precipitation. Isolated
lightning strikes will occur, especially Sunday.
Tops of the clouds will be 15000 feet or higher at times. Areas of
southwest winds 20-30 knots with gusts 50-60 knots will occur mainly
tonight, with decreasing winds Sunday.
Deserts...isolated/scattered showers or thunderstorms with bases
around 5000 ft MSL will occur at times late tonight and Sunday.
Areas of west winds 20-30 knots with gusts 40-55 knots will occur
mainly tonight, with decreasing winds Sunday.
&&
.MARINE...
West-northwest winds associated with a late-season low pressure
system will have gusts 25-35 knots overnight and Sunday morning with
combined seas of 6 to 12 feet. Showers are likely mainly Sunday into
Monday, with a chance of thunderstorms especially Sunday. Wind and
seas will gradually lower late Sunday through Tuesday.
&&
.BEACHES...
Showers will continue at times through Sunday, decreasing somewhat
Sunday night and Monday. There is a slight chance of thunderstorms
mainly late tonight and Sunday. A Beach Hazards Statement is in
effect for Orange and San Diego Counties Sunday.
&&
.SKYWARN...
Skywarn activation may be requested Sunday due to thunderstorms,
heavy rain and snow.
&&
.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Winter Weather Advisory from midnight tonight to 9 PM PDT Sunday
for Riverside County Mountains-San Bernardino County
Mountains-San Diego County Mountains.
Wind Advisory until 2 AM PDT Sunday for Coachella Valley-
Riverside County Mountains-San Diego County Deserts-San
Diego County Mountains-San Gorgonio Pass Near Banning.
Wind Advisory until 2 AM PDT Sunday for Apple and Lucerne
Valleys-San Bernardino County Mountains.
PZ...Small Craft Advisory from 2 AM to 11 PM PDT Sunday for Coastal
Waters from San Mateo Point to the Mexican Border and out
to 30 nm-Waters from San Mateo point to the Mexican Border
Extending 30 to 60 nm out including San Clemente Island.
Gale Warning until 2 AM PDT Sunday for Waters from San Mateo
point to the Mexican Border Extending 30 to 60 nm out
including San Clemente Island.
Small Craft Advisory for winds until 2 AM PDT Sunday for Coastal
Waters from San Mateo Point to the Mexican Border and out
to 30 nm.
&&
PUBLIC...Moede/JMB
AVIATION/MARINE/BEACHES...MaxwellPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN DIEGO CA
1005 PM PDT SAT MAY 6 2017
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0316 PM NON-TSTM WND GST 2 WSW LUCERNE VALLEY 34.44N 116.98W
05/06/2017 M54 MPH SAN BERNARDINO CA MESONET
MESONET STATION F0119, LUCERNE VALLEY (1
SW).
&&PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN DIEGO CA
1006 PM PDT SAT MAY 6 2017
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0215 PM NON-TSTM WND GST 1 NW GEORGE AFB 34.60N 117.38W
05/06/2017 M46 MPH SAN BERNARDINO CA AWOS
AWOS STATION VCV, VICTORVILLE AIRPORT.
&&PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SAN DIEGO CA
1030 PM PDT SAT MAY 6 2017
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0938 PM NON-TSTM WND DMG LUCERNE VALLEY 34.44N 116.95W
05/06/2017 SAN BERNARDINO CA TRAINED SPOTTER
TRAINED SPOTTER REPORTED HIS NEIGHBOR'S 5TH
WHEEL (TRAILER) KNOCKED OVER BY STRONG
WINDS.
&&
JMBThe Edwards AFB radar (KEYX), 129 km away, was scanning. The volume nearest the first event began at 20:29 UTC.
2 winter weather, 1 heavy snow, 1 tornado, 1 flood. Local standard time, as filed.
Multiple spotters reported 2 to 5 inches of storm total snowfall. Lake Arrowhead received the most with 2 to 5 inches, Big Bear City reported 2 to 4 inches and 3 inches occurred in Twin Peaks.
A trained spotter reported a storm total snowfall of 10 inches at Birch Hill. The official coop site at Palomar Mountain reported 6 inches at 1500PST. Mount Laguna had a storm total snowfall of 4 inches.
A trained spotter in Idyllwild reported 2.5 inches of storm total snowfall.
A landspout tornado occured near Southern California Logistics Airport in Victorville.
A swift water rescue was conducted to rescue a man from a culvert. Urban and street flooding was reported in other portions of the San Diego metro.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2017Every state in 2017This day in weather historyThe tornado archive for California, 2017Warnings in California, May 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: 700409, 700408, 700410, 700418, 700440.