An upper level system with a strong cold front moved through the Bay Area at the turn of the month with precipitation beginning late the evening of the 28th. This system brought widespread rainfall causing localized roadway flooding, strong winds, lightning, and small hail.
Every event with a place to put it; 7 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 MTR wrote it up.
An upper level system with a strong cold front moved through the Bay Area at the turn of the month with precipitation beginning late the evening of the 28th. This system brought widespread rainfall causing localized roadway flooding, strong winds, lightning, and small hail. Gusts in the mountains reached 60 mph and hail was seen up to 1/2 an inch. The bulk of the precipitation and subsequent impacts were seen in early March.
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 Francisco Bay Area, CA wrote its last area forecast discussion before the first event at Mar 1, 12:04 AM PST, 2 hours 22 minutes earlier.
Area Forecast Discussion
National Weather Service San Francisco Bay Area
1204 AM PST Thu Mar 1 2018
.SYNOPSIS...A potent frontal system remains on track to push
through the region on Thursday bringing widespread rainfall and
strong, gusty winds. Lingering showers will persist through
Saturday along with lowering snow levels. A drying trend is then
expected late in the upcoming weekend and into early next week.
&&
.DISCUSSION...as of 9:30 PM PST Wednesday...Rain associated with
a warm front began in the North Bay shortly after 00Z and has just
started along the San Francisco Bay Area coast. Thus far gages in
the North Bay have measured up to one-half inch. Rain will spread
over the SFO Bay Area tonight reaching the MRY Bay Area after
10Z. This will be followed by the cold front which will move into
the North Bay around sunrise and the SFO Bay Area during the
morning commute hours. Rain will become locally moderate to heavy
as the front passes especially over the mountains.
As the front moves over the Santa Cruz and Santa Lucia Mountains
Thursday afternoon it will slow down as the upper low starts to
dig south along the west coast. As a result the largest rainfall
amounts will be in these areas where there will be a slightly more
prolonged rain event. Southerly winds will increase overnight
with the strongest winds in the higher elevations as well as
coastal areas from early Thursday morning through Thursday night.
Winds of 15 to 30 MPH will be possible in these areas with gusts
potentially exceeding 45 MPH. Some of the highest peaks across the
region may see gusts upwards of 60 MPH. Inland valley locations
such as the Santa Clara and Santa Cruz Valleys will also see
breezy conditions with gusts to 30 MPH possible.
Rain will turn to showers behind the front as the upper low
continues to spin off the Pacific Northwest coast and send
moisture into our district. Models indicate another organized
line of precip moving through late Thursday night and Friday
morning with additional showers continuing through Friday night.
There is a slight chance of thunderstorms for Thursday and Friday
afternoon and early evening in the cold unstable air behind the
front. While lightning wont be a huge concern... small hail and
locally heavy showers could accompany the stronger convection that
does develop. Snow levels will start out around 4000 feet on
Thursday then lower to 2500-3000 feet Friday into Saturday.
The upper low moves inland on Saturday and showers will decrease.
There is still a chance of residual showers Saturday. Saturday
night and Sunday will be dry.
Rainfall amounts with this storm will range from 0.5 to 1.5 inches
in the urban areas with the greatest in the North Bay with lesser
amounts in the inland valleys. Up to 2 to 4 inches are possible in
the North Bay Hills and the Santa Cruz Mountains...and 4 to 6
inches in the Santa Lucias. And of course there could be up to a
few inches of snow in the highest peaks.
Fro previous discussion...Drying conditions will develop late
Saturday into Sunday as the main mid/upper level trough shifts
inland. However, colder overnight temperatures will be likely late
in the weekend into early next week as skies clear and a colder
air mass remains in place. Daytime temperatures will warm slightly
and dry conditions will persist into early next week as a weak
short-wave ridge builds over the region. Forecast confidence
greatly drops off by the middle part of next week as the models
have diverged from one another. The GFS continues to bring another
chance of precipitation as early as Tuesday while the ECMWF has
dry conditions through Thursday of next week. Will continue to
focus our attention on the short-term and monitor the models in
the coming days with respect to weather conditions next week.
&&
.AVIATION...as of 12:04 AM PST Thursday...Cigs and visibilities
will lower to MVFR with areas IFR into this morning. Rain moderate
to locally heavy at times into this morning mostly focusing on the
windward slopes while there'll be some rain shadowing in the valleys
in the lee of the mountains.
Stronger and gusty SW winds aloft will precede cold frontal passage
this morning. Recently amended tafs to include low level wind shear
(LLWS) for KSTS, KOAK, KSFO, KSJC and KLVK tafs. Conditions are
favorable for strong directional and speed shear from the surface
through 2 thousand feet. The WRF model forecasts a band of 50-60
knot winds at 925 mb level from early to mid morning. This band will
continue to spread south toward the north Central Coast today, thus
expect gusty SW winds to develop there as well. S to SW wind gusts
to 20 to 30 knots are possible vicinity KSNS per recent NAM MOS
guidance. Midnight shift may want to consider adding LLWS in for
12z KMRY and KSNS tafs for late this morning through the afternoon.
Winds will be lower everywhere by late today.
Vicinity of KSFO...Cigs lowering to MVFR in rain into this morning,
and SE wind 10-15 knots becoming increasingly gusty to 20-25 knots
Thursday morning. Strong low level wind shear forecast 12z-19z
today. Cold front forecast to pass near 18z today resulting in
gusty westerly winds to 30 knots possibly higher at times. Gusty
winds through this afternoon and evening, diminishing late in the
day.
SFO Bridge Approach...Similar to KSFO.
Monterey Bay Terminals...Cigs lowering to MVFR in rain into this
morning. Pre-frontal winds strengthen especially during the day,
low level winds near 925 mb level reaching 50-60 knots based on
recent WRF model output. Less wind by later this evening.
&&
.MARINE...as of 10:39 PM PST Wednesday...A rapidly moving cold
front over the eastern Pacific will gradually decrease in forward
speed prior to moving southeastward across the coastal waters and
bays Thursday. Gusty winds will accompany frontal passage with
steep fresh swell expected through Thursday morning. Winds will
veer and weaken slightly in the wake of the front. Rain tonight
into Thursday will then turn to unseasonably chilly and showery
weather conditions by later Thursday into the weekend.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
.Tngt...Wind Advisory...CAZ006-505>510
SCA...SF Bay
SCA...Mry Bay
SCA...Pt Arena to Pt Reyes 0-10 nm
SCA...Pt Reyes to Pigeon Pt 0-10 nm
SCA...Pigeon Pt to Pt Pinos 0-10 nm
SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm
SCA...Pt Arena to Pigeon Pt 10-60 nm
SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm
&&
PUBLIC FORECAST: W Pi
AVIATION/MARINE: Canepa
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www.youtube.com/nwsbayareaThe Sacramento radar (KDAX), 96 km away, was scanning. The volume nearest the first event began at 10:26 UTC.
16 hail, 15 flood, 11 strong wind, 1 high wind, 1 lightning, 1 heavy rain, 1 debris flow. Local standard time, as filed.
Roadway flooding reported at US 101N and Lucky Drive off ramp.
Sustained winds around 30 mph gusting to between 45 and 49 mph were observed during this time period at Atlas Peak RAWS.
Measured wind gusts of at least 50 mph and peaking at 61 mph at Los Gatos RAWS.
Roadway flooding at 2020 Junction Ave.
Measured wind gusts between 45 and 53 mph observed during this time frame at Las Trampas RAWS.
Wind gusts of 46 mph observed at Woodacre RAWS.
Roadway flooding reported at SR 121 and Sears Point Dr.
News report states roughly 1200 customers around the Bay Area are without power.
Measured wind gust of 45 mph at the Calavares Road RAWS.
Roadway flooding reported at 250 BonAir Road.
Roadway flooding at I80 E and Pomona Street on ramp.
Measured wind gusts over 45 mph observed at Spring Valley RAWS.
Roadway flooding reported at I 280N and Cesar Chavez Street off ramp.
Roadway flooding reported at I 280N and Stevens Creek Blvd on ramp.
Roadway flooding reported at I 280N and SR 1.
Roadway flooding reported at Pacheco Blvd and Arthur Road.
Sustained southerly winds of 35 mph gusting to 50 mph was observed at the Los Vaqueros RAWS.
Roadway flooding reported at US 101S and Oyster Point east off ramp.
Roadway flooding reported at I 280S and Hickey Blvd off ramp.
Roadway flooding at I 680N and Scott Creek Road off ramp.
Downed tree reported at Montecito Drive and English. Exact timing unknown.
Roadway flooding reported at S Davis Road and Foster Road.
Spotter reported 47 mph wind gusts at the docks.
Tree down on Crest Ave.
Roadway flooding reported at 455 8th Street.
Several reports of pea-sized hail in Oakland via social media.
Pea-sized hail reported in north Berkeley via social media.
Small hail reprted on I-87 in San Jose.
Small hail reported in Felton.
Lightning detected over the San Francisco Bay.
Pea-sized hail reported in Scotts Valley.
Social media reports of another round of hail this morning in Berkeley.
Accumulating hail reported in Kensington.
Roadway flooding reported at Almonte Blvd and SR 1.
Small hail reported.
Heavy rain triggered a domino effect of falling trees. A redwood came down onto smaller trees and one hit a house.
Highway 1 closed due to mudslide at Limekiln State Park.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2018Every state in 2018This day in weather historyWarnings in California, March 2018
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: 737483, 738615, 738587, 737484, 738586, 738616, 737485, 738491, 738584, 738492, 737486, 737487, 738617, 737489, 737490, 737491, 737492, 738614, 737493, 737494, 737496, 738494, 737498, 738495, 738496, 738485, 738498, 738500, 738501, 738502, 738503, 738504, 738506, 738507, 738508, 738486, 738509, 738510, 738511, 738512, and more.