A low pressure system off the coast of northern California brought a cold front through the Bay Area in early April. This system produced heavy rainfall creating minor roadway flooding as well as gusty winds and scattered thunderstorms with small hail.
Every event with a place to put it; 8 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.
A low pressure system off the coast of northern California brought a cold front through the Bay Area in early April. This system produced heavy rainfall creating minor roadway flooding as well as gusty winds and scattered thunderstorms with small hail. Wind gusts across the higher elevations were observed between 35 and 65 mph. Breezy surface winds also downed several trees and limbs across the area.
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 Apr 5, 3:34 AM PST, 2 hours 47 minutes earlier.
Area Forecast Discussion
National Weather Service San Francisco Bay Area
434 AM PDT Sun Apr 5 2020
.SYNOPSIS...Light to locally moderate showers will continue
today as a cold front moves south through the region. Widespread
rain is forecast for today as a stronger system drops down the
coast. Locally heavy rain, possible thunderstorms, and gusty winds
can be expected with this system. Rain will turn to showers
tonight into Monday as an upper low moves south offshore. Showers
may linger across the Central Coast into Tuesday, and possibly
Wednesday, as the upper low slowly exits the region. A warming and
drying trend is forecast for the second half of the week.
&&
.DISCUSSION...As of 3:10 AM PDT Sunday...The first of two frontal
boundaries that are anticipated to move across the region today
is presently stretched across the Monterey Bay/Central Coast
region. Rain rates associated with this weak front have been
light to locally moderate with gages reporting anywhere from
0.04" to 0.08" an hour across most locations to 0.10" to 0.20" an
hour locally over elevated terrain. Accumulations over the last 6
hours have shifted southward from the North Bay and area currently
concentrated over the Bay Area with mostly light accumulation of
0.10" or less across lower elevations to upward of 0.30" to 0.60"
across the East Bay hill. The Santa Cruz mountains reported the
greatest accumulation over the past 6 hours with values of 1" to
1.26" at Loma Prieta, Uvas Canyon County Park, Ormsby Rd and Mount
Umunhum. While the Ben Lomond RAWS didn't quite reach the 1" mark
over the last 6 hours is holds the lead with the most precip over
the last 24 hours across the forecast area with a storm total of
2.67" so far.
The front will continue a slide south and east at approximately 5
to 10 kt and is forecast to be overrun by the next boundary
pushing in from the northwest. This next system will bring
widespread rain to the region today with periods of heavy rain
expected as this significantly stronger cold front moves through.
Latest model runs remain consistent with the timing of the front
and have this next front moving into the North Bay this morning
then sliding south into the Bay Areas in through the afternoon and
through the Monterey Bay Area late in the afternoon and early
evening. WPC's (Weather Prediction Center) latest guidance put
the Central California Coast at a slight risk (10-20%) of
Excessive Rainfall for today, meaning there is a slight chance
that rainfall will exceed flash flood guidance. The slight risk
category is generally confined to the Santa Lucia mountains while
the Monterey peninsula and portion of the Santa Cruz mountains
remains in a marginal (5-10% risk). See go.usa.gov/cu3Dw for more
information.
SPC (Storm Prediction Center) Day 1 Convective Outlook continues
to show thunderstorm chances across the forecast area. The 06z NAM
continues to show significant instability over the district for
the next 12 to 16 hours therefore the slight chance of isolated
thunderstorms across the area remains in place for this morning
through 00z this afternoon.
From previous discussion...Additional rainfall through late
Sunday is expected to range from 0.50-1.50" in most areas, with
locally lower amounts in rain- shadowed valleys such as the Santa
Clara Valley. Up to 2-3 inches of additional rainfall is possible
in the coastal ranges. The latest HRRR focuses the heaviest rain
in the Santa Lucia Mountains above Big Sur, with accumulations of
up to 7 inches by Sunday evening. Most other models forecast less
than half that in the Santa Lucias.
Gusty southerly winds will develop ahead of the incoming front on
Sunday. Strongest winds are expected along the coast where local
gusts up to 40 mph are possible. The latest local WRF model
continues to focus the strongest winds on coastal Monterey County
from Pebble Beach south through Carmel and along the Big Sur
Coast. A Wind Advisory is in effect for coastal Monterey County
from 5 AM to 5 PM Sunday. The WRF model has recently trended
lighter on winds, but will maintain the Wind Advisory for now as
subsequent models may reverse course. Winds are forecast to
diminish quickly behind the cold front by late Sunday.
Rain will change to showers on Sunday night and showers will
continue through Monday as an upper low moves slowly south
offshore. Snow levels are forecast to quickly drop behind the cold
front on Sunday night, down to 3000 feet or even lower in the
North Bay by Monday morning. However, most precipitation will end
by the time the coldest airmass arrives and so snow accumulation
in the hills above 3000 feet should be light.
Both the NAM and GFS are moving the upper low off to our south
more quickly than previous model runs. If this faster movement
verifies, then showers will be confined to only the far southern
portion of our area on Tuesday, with dry weather returning to all
areas by Wednesday. The 12Z ECMWF forecasts a slower southward
movement and thus continued shower potential across our southern
areas through Wednesday. But the overall model trend is for a
quicker return to dry weather next week. The upshot is that the
northern portion of our area will likely start to dry out as
early as Tuesday, with all areas possibly returning to dry
weather by Wednesday, or Thursday at the latest. Dry weather is
then expected to prevail for the remainder of next week and into
next weekend as an upper ridge develops off the West Coast.
Temperatures are expected to be below normal for the first half of
the week, but then climb back to near seasonal averages during
the second half.
&&
.AVIATION...as of 4:34 AM PDT Sunday...MVFR developing with IFR
also developing in heavy rain showers. An isolated thunderstorm is
possible today as well. Instability steadily ramping up as a cold
core low pressure system arrives from the Gulf of Alaska today
into Monday.
Vicinity of KSFO...South to southeast surface wind shifting to
southwest later this morning, MVFR in occasionally moderate to
heavy showers and strong and gusty winds per statistical guidance.
Could be close to needing an airport weather warning for winds
nearing 35 knots later on this morning.
SFO Bridge Approach...Similar to KSFO.
Monterey Bay Terminals...South surface winds except locally southeast
in the Salinas Valley until frontal passage this morning, locally
strong and gusty winds per statistical guidance. Winds shifting
to the southwest later this morning. MVFR in occasionally moderate
to heavy showers, IFR at times in heavy showers.
&&
.MARINE...as of 4:18 AM PDT Sunday...A cold upper level low from
the Gulf of Alaska will result in moderate to heavy showers
through early week along with a slight chance of thunderstorms
today. The low will move by to our south late Monday night into
Tuesday morning. A high pressure system will result in dry weather
from mid to late week. A prevailing moderate northwesterly swell
will persist through much of the forecast period.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
.Tday...Wind Advisory...CAZ530
SCA...Mry Bay from 7 AM
SCA...Pigeon Pt to Pt Pinos 0-10 nm from 7 AM
SCA...Pt Arena to Pigeon Pt 10-60 nm until 9 AM
SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm from 9 AM
SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm until 3 PM
SCA...Pt Arena to Pt Reyes 0-10 nm until 1 PM
SCA...Pt Reyes to Pigeon Pt 0-10 nm until 1 PM
SCA...SF Bay from 7 AM until 1 PM
&&
PUBLIC FORECAST: CW
AVIATION/MARINE: Canepa
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www.youtube.com/nwsbayareaThe San Francisco radar (KMUX), 14 km away, was scanning. The volume nearest the first event began at 18:34 UTC.
9 strong wind, 2 flood, 2 hail. Local standard time, as filed.
Tree down on Hopkins Gulch Road.
Large tree limb down blocking westbound lane at Portola and Sandhill Rd.
Tree down on road near Saw Mill Rd and SR 9.
Tree down blocking lanes at Mt Hermon and Graham Hill Rd near Felton.
Tree down blocking roadway.
Tree down blocking eastbound lanes at SR-152 and Mt Madonna.
Tree down at Rodeo Gulch Rd and Soquel Dr.
Large tree blocking both lanes at Sir Francis Drake Blvd and Taylor Park Rd.
Flooding reported on the street at 21020 Redwood Road.
Tree down at SR-9 and Sylvan Ave.
Heavy flooding in the area, roadway washed out. Information on exact location unknown.
Spotter reporting pea-sized hail near San Ramon.
MPING report shows dime sized hail near San Jose.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2020Every state in 2020This day in weather historyWarnings in California, April 2020
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: 879749, 879753, 879754, 879755, 879756, 879757, 879758, 879759, 879744, 879760, 879746, 879748, 879747.