A rare winter time offshore wind event affected the Greater Bay Area in mid to late January. It was unusual given the long duration and wide areal coverage as well as the time of year.
Every event with a place to put it; 58 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 rare winter time offshore wind event affected the Greater Bay Area in mid to late January. It was unusual given the long duration and wide areal coverage as well as the time of year. An upper level disturbance passed over the region the 17th-18th leading to a tightening offshore pressure gradient before a second and stronger disturbance the 18th-19th tightened it further. This lead to two bursts of strong offshore winds. Higher elevations across the region reported gusts between 60 and 80 mph with two sites reaching 90. Lower elevations also were notably in excess of 40 mph. These winds resulted in tree damage, downed trees, and downed powerlines causing power outages. This all led to a rare January Red Flag Warning for Monterey and San Benito counties where fuels remained dry from lack of rainfall. Roughly a dozen small fires broke out in the Santa Cruz Mountains, with two becoming relatively large for January. Full storm summary https://www.weather.gov/mtr/Wind_1_17-19_2021.
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 Jan 18, 4:07 AM PST, 3 hours 1 minute earlier.
Area Forecast Discussion
National Weather Service San Francisco Bay Area
407 AM PST Mon Jan 18 2021
.SYNOPSIS...Warm, dry weather will continue through Monday, along
with gusty offshore winds in the hills of the San Francisco Bay
Area. A strong, and much more widespread, offshore wind event is
forecast from this evening through Tuesday morning. During this
time, damaging winds are possible in the hills and locally in the
valleys and near the coast. Winds will gradually diminish on
Tuesday afternoon. A cooling trend is forecast from Wednesday
through Friday and slight rain chances develop by the end of the
week.
&&
.DISCUSSION...as of 02:45 AM PST Monday...A dry mid/upper level
short-wave trough is currently dropping southward across the
region with surface high pressure developing to the north and
northeast. While there is an increase in high level clouds,
surface conditions are beginning to dry out as offshore flow
develops and strengthens in response to a tightening pressure
gradient. Wind gusts of 40 to 60 mph are being reported in the
higher elevations of the Bay Area with Mount Diablo seeing gusts
in excess of 70 mph. Winds are forecast to increase region-wide
today and become more widespread tonight into Tuesday resulting in
strong, damaging winds in the region's higher elevations. While
the the stronger winds look to be mostly confined to the higher
elevations through the day today, stronger wind gusts may
occasionally mix down to the lower elevations. This threat greatly
increases late tonight into Tuesday morning as wind gusts
increase to 60 to 80 mph in the peaks and ridges potentially mix
down locally to the valleys and near the coast. All this said, a
Wind Advisory is in effect for much of the Bay Area today and then
expands to the Central Coast tonight. A High Wind Warning will go
into effect this afternoon through Tuesday morning for the
region's higher elevations. For additional details, please see
NPWMTR for the latest wind products.
While conditions aloft begin to cool slightly in response to the
mid/upper level trough, dry offshore flow will allow for
unseasonably warm temperatures again this afternoon. Additionally,
moderate to high fire weather concerns are expected over portions
of our region through Tuesday in response to the strong offshore
winds and low relative humidity. While precipitation totals so far
this winter season remain well below normal, there has been enough
rainfall across the San Francisco Bay Area, particularly in the
North Bay, to moisten fuels and limit the threat critical fire
weather concerns. That said, fuels remain drier over the Central
Coast, enough so to warrant a Fire Weather Watch for elevations
above 1,000 feet across Monterey and San Benito Counties. To allow
for the coordination with our fire partners later this morning, will
hold off on upgrading this watch to a Red Flag Warning at this time.
For additional details, please see the Fire Weather Discussion
below.
Winds will begin to diminish region-wide during the day on Tuesday,
yet remain locally strong and gusty into Tuesday night across the
North and East Bay. Temperatures will also cool both during the
daytime and overnight through the remainder of the week as a
mid/upper level ridging noses into the Pacific Northwest and a cut-
off low spins off of the southern California coast. Medium to longer
range ensembles indicate the Pacific ridge will retrograde to the
west late this week and into the upcoming weekend. This will allow
for a series of mid/upper level trough to drop southward along the
West Coast providing cooler and potentially unsettled weather
conditions. Confidence in the details remain low at this time and
will be fine tuned in the coming days, especially once short-term
wind and fire weather concerns pass.
Safety remainders from a previous discussion...The offshore wind
event continues to look strong and now is the time to act. In case
of power outages: make sure cell phones/devices are fully charged,
gather up flashlights and extra batteries, and have a supply of non-
perishable food/water. If there are widespread power outages,
remember that it may take crews longer to get the power back on so
make sure you have what you need in case you have to go a day or two
without power. Other things to remember: secure loose outdoor
objects, trim dead tree branches on your property, be cautious when
driving as occasionally strong gusts may suddenly hit your vehicle,
making it difficult to control.
&&
.AVIATION...as of 4:05 AM PST Monday...For the 12Z TAFs.
Widespread VFR as potent dry trough shifts SSE across Bay Area and
Central Coast early Monday morning. A bank of broken to scattered
clouds AOA 18000-20000 feet will accompany this trough with very
dry, very wind N/NNE winds on the lee of the trough. Low level
wind shear of 30-40kt can be expected overnight at Bay Area
terminals, with these winds mixing down to the surface later
today, bringing rather gusty surface winds. Offshore winds expand
and become stronger, even at the surface, late today through
tonight and into Tuesday. Low level wind shear of 35-50kt can be
expected at most terminals Monday night into early Tuesday, with
wind gusts at these terminals reaching similar ranges Tuesday
morning, including at KSFO. Strongest winds will be around
1500-2000 feet AGL this morning, with them lowering to 1000-1500
feet tonight, even as winds may become weak at ground level - thus
the elevated low level wind shear concerns through the current TAF
package. Otherwise -- rather strong winds of 65-85mph over
mountain peaks/ridges and upper lee slopes through Tuesday.
Vicinity of KSFO...VFR with sct high clouds and light winds.
Increasing NNE winds aloft overnight will generate LLWS concerns
from through the morning and possibly into early afternoon.
Surface winds may become gusty tomorrow afternoon with even
stronger offshore winds expected tomorrow night. Surface wind
gusts up to or in excess of 50mph are possible early Tuesday
morning.
SFO Bridge Approach...Similar to KSFO.
Monterey Bay Terminals...VFR with few high clouds and calm winds.
VFR should prevail through the TAF period. Breezy northerly winds
expected in the afternoon, becoming gusty near the end of the TAF
period. Some localized low level wind shear concerns are possible
at KMRY/KWVI late Monday night into early Tuesday morning as the
offshore wind event strengthens and expands southward to encompass
portions of the Central Coast.
&&
.BEACHES...as of 09:45 PM PST Sunday...A large, very long period
northwest swell has arrived at the coast creating hazardous
conditions through Monday afternoon. Large swell heights will
lead to breaking waves of 18 to 22 feet, locally higher at
favored breakpoints, along west to northwest facing beaches. As a
result, a High Surf Advisory is in effect through Monday afternoon
for west and northwest facing beaches while a Beach Hazard
Statement has been issued for the northern Monterey Bay including
Santa Cruz. With unseasonably warm temperatures this holiday
weekend, it will likely attract more people to the coast.
Individuals should be reminded that our coastline and the cold
Pacific waters remain dangerous as these larger than normal waves
impact the coast. Extreme caution is advised when visiting area
beaches. Never turn your back to the ocean.
&&
.CLIMATE...Record Type: Highs (Old Record Temp/Year)
Jan 18th
Santa Rosa 74/1976
Kentfield 70/2014
Napa 76/1920
Richmond 71/2018
Livermore 74/1919
San Francisco 70/1920
SFO 68/1948
Redwood City 74/2009
Half Moon Bay 72/2009
Oakland Downtown 73/2014
San Jose 74/1920
Gilroy 80/2014*
Santa Cruz 83/1920
Salinas Airport 81/1994
King City 83/2009
*Monthly Records
&&
.FIRE WEATHER...as of 02:45 AM PST Monday...While the Fire Season
had officially been declared over and the calendar does say
January, the active weather pattern is more typical of autumn and
will bring moderate to high fire weather concerns to the region
through Tuesday. Meteorologically it looks like a slam dunk, gusty
offshore flow and low to moderate humidity. However, the wildcard
are the fuels. The Bay Area has received below normal precip thus
far this wet season. That being said, some early season rains did
bring some moisture and allowed fuels moistures to increase. A
"green up" is also being reported in most areas as well. That
being said, Monterey and San Benito counties have received much
less rainfall than areas to the north. Therefore, the drier
conditions along the Central Coast increase the fire weather
threat. After coordination with agency partners and other forecast
offices decided to issue a Fire Weather Watch Monday evening
through Tuesday afternoon. Conditions will be most severe Monday
night through early sunrise Tuesday. Local models may be a tad
aggressive but show RH values potentially dipping into the upper
single digits to lower teens with winds 20 to 30 mph with gusts to
around 45 mph over Monterey and San Benito. Coordination with
agency partners will continue with the potential need to upgrade
the current Fire Weather Watch into a Red Flag Warning later
today. Stay tuned...
&&
.MARINE...as of 02:45 AM PST Monday...Breezy north winds will
prevail over the waters through Monday. The strongest winds are
expected over the northern outer waters where occasional low end
gale- force gusts will be possible. Locally breezy conditions will
also be present along the Big Sur coast south of Point Sur. These
winds will persist into tomorrow before a burst of offshore winds
over land spills over into the waters starting late this evening
through tonight. This will bring gale force conditions across the
entire coastal waters and through portions of the San Francisco
Bay into Tuesday resulting in widespread hazardous conditions. A
large, very long period northwest swell will impact the waters
through late tomorrow bringing additional hazards. The next long
period northwest swell arrives mid-week.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
.Tday...Wind Advisory...CAZ518-528-530
High Surf Advisory...CAZ006-505-509-530
High Wind Warning...CAZ507-511-512-517
Wind Advisory...CAZ507-511-512
Wind Advisory...CAZ006-505-506-508>510-513-529
SCA...Pt Arena to Pt Reyes 0-10 nm
SCA...Pigeon Pt to Pt Pinos 0-10 nm
SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm
SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm
SCA...Pt Arena to Pigeon Pt 10-60 nm
SCA...SF Bay until 3 PM
SCA...Pt Reyes to Pigeon Pt 0-10 nm until 3 PM
GLW...SF Bay from 3 PM
GLW...Pt Reyes to Pigeon Pt 0-10 nm from 3 PM
SCA...Mry Bay from 9 AM
&&
PUBLIC FORECAST: RGass
AVIATION: DRP
MARINE: DRP
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www.youtube.com/nwsbayareaThe national radar mosaic for the moment the first event began.
57 strong wind, 7 high wind, 1 wildfire. Local standard time, as filed.
Tree down blocking Eastbound 128 near Fort Bennett Lane.
Large redwood tree down at Airport Blvd and Old Redwood Highway in Larkfield.
Tree down blocking both lanes on Bear Creek Rd at Greenview Dr.
Mesonet station (PG&E) at Diablo-Blackhawk reported gusts between 45 and 60 mph.
Mesonet station (PG&E) at Diablo-Blackhawk measured sustained winds around 40 mph and gusts between 60 and 70 mph.
Mesonet station (PG&E) reported sustained winds at or just above 40 mph.
Mesonet station (PG&E) reported wind gusts between 45 and 65 mph with a peak gust of 70 mph.
Mesonet station (PG&E) at East Bay MUD reported gusts between 45 and 55 mph with a peak gust of 64 mph.
Mesonet station (PG&E) at Wolf Back Ridge reported gusts between 50 and 60 mph.
Mesonet station (PG&E) at Dimeo Lane.
Spring Valley RAWS station reported gusts between 45 and 50 mph with a peak gust of 54 mph.
Mesonet (PG&E) station at Healdsburg Hills North reported wind gusts between 50 and 60 mph with a peak gust of 65 mph.
Station at Moss Landing reported gusts between 45 and 50 mph.
Mesonet station (PG&E) measured gusts between 45 and 55 mph with a peak gust of 62 mph.
Mesonet station (PG&E) on Old Coast Tower measured sustained winds of 43 mph and gusts to 71 mph.
Santa Rosa RAWS station reported gusts.
Mesonet station (PG&E) at Diablo-Blackhawk measured sustained winds of 40 mph and gusts between 55 and 65 mph.
Public reported winds of 60 mph.
Mesonet (PG&E) station at Wolf Back Ridge reported gusts between 45 and 59 mph.
Station reported a wind gust in the mountains of Sonoma County at 97 mph.
Tree uprooted near Berkeley.
San Francisco Airport ASOS reported wind gusts between 45 and 50 mph with a peak gust of 54 mph. Sustained winds were also generally between 30 and 40 mph.
Station (CWOP) in San Francisco measured wind gusts between 50 and 57 mph.
Oakland RAWS station reported gusts between 45 and 49 mph.
Tree limb damaged.
Tree uprooted and damaged at least the roof of a parked car.
Mesonet station in San Jose reported wind gust of 50 mph.
Little Hollywood neighborhood lost power for about 30 minutes. Trees down across lanes of traffic.
Mesonet station (PG&E) on Old Stage Road measured wind gusts between 45 and 65 mph with a peak gust of 67 mph.
Wind gusts setting off car alarms in the Missions.
Redwood tree down blocking lanes on SB-13 and Lincoln Ave off ramp.
Mesonet station (PG&E) on Old Coast Tower measured gusts between 45 and 55 mph.
Mesonet station (PG&E) at Moss Landing Road.
Power lines down blocking all lanes at SR-35 and Swett Rd.
Tree down blocking roadway at Wildcat Canyon Rd and San Pablo Dam Rd.
Wires, telephone pole, and multiple trees down blocking road at 235 Orchard Rd near Felton.
Three 50 ft long 1 ft wide trees blocking road at I-680 S and SR-237 E.
Large tree down blocking on ramp at SR-92 E and Edgewater Blvd.
Tree down on Empire Grade Rd at Heller Dr.
Power pole down in roadway at 2nd St and Panitz St.
Smaller trees down around park, and limbs of larger trees down.
Blown transformer, power lines down across road at Bolduc Ct and Bonita Rd.
Wires down starting a fire on Day Valley Rd.
Tree down blocking both lanes on Old Stage Rd and Herbert Rd.
Tree fallen over wires and cables blocking roadway at Call of the Wild Rd and Old Santa Cruz Hwy.
Live wires down across roadway on Whalebone Gulch Rd and Bear Creek Rd.
Large tree down at Toll House Gulch Rd and Upper Scenic Dr.
Mesonet station (PG&E) at Dimeo Lane.
Mesonet station (PG&E) at Diablo-Blackhawk measured gusts between 45 and 60 mph.
Large tree blocking lanes at SR-17 N and Alma Bridge off ramp.
Large pine tree snapped at fork and fell on a fence at Berkeley View Reservoir.
Tree down across roadway at Mountain Charlie Rd and Old Santa Cruz Hwy.
Downed tree on top of parked car in SF Heights near Alta Plaza.
Large tree down in the middle of the road at Santa Ana Valley Rd and John Smith Rd.
Tree down on San Miguel Canyon Rd.
Tree down on Tustin Rd.
Tree fell on telephone pole knocking it into Farmer St.
Large tree blocking lane at SB-680 and Washington Blvd.
Tree down blocking roadway at Stage Rd and SR-84.
Large tree and power lines down in the road on Granite Ridge Dr.
Down tree blocking lane on Parker Ave at 7th St.
Down evergreen tree blocking off ramp on I-680 S and Jacklin Rd.
Scaffolding was blown off a building.
Dry conditions and strong offshore winds allowed several small wildfires to break out in the Santa Cruz Mountains. The largest of the two were the Freedom and Panther Ridge Fires https://www.fire.ca.gov/incidents/2021/ https://www.ksbw.com/article/cal-fire-will-try-to-contain-the-still-burning-fires-in-santa-cruz-county-on-wednesday/35269289#.
Mesonet station O'Neill Sea Odyssey.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2021Every state in 2021This day in weather historyWarnings in California, January 2021
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: 931872, 931873, 931874, 932274, 932275, 932225, 932268, 932247, 932216, 932303, 932266, 932226, 932307, 932305, 932291, 932219, 932276, 931875, 932217, 931876, 931877, 932229, 932215, 932236, 931878, 931879, 932288, 931880, 932293, 931881, 931882, 932292, 932302, 931883, 931884, 931885, 931886, 931887, 931888, 931889, and more.