Building surface high pressure over the Great Basin generated dry and gusty offshore winds across the region increasing fire weather concerns. Wind gusts over the mountains were observed between 40 and 50 mph while the highest peaks across the North and East Bay saw gusts in excess of 60 mph.
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.
Building surface high pressure over the Great Basin generated dry and gusty offshore winds across the region increasing fire weather concerns. Wind gusts over the mountains were observed between 40 and 50 mph while the highest peaks across the North and East Bay saw gusts in excess of 60 mph. This also brought temperatures well above normal in mid October with 23 daily high temperature records broken or tied between the 14th and the 17th. Downtown San Francisco reached the low to mid 90s towards the end of that week.
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 Oct 14, 9:52 PM PST, 58 minutes earlier.
Area Forecast Discussion
National Weather Service San Francisco Bay Area
1052 PM PDT Wed Oct 14 2020
.SYNOPSIS...The warming trend will continue through Friday as
high pressure builds inland and flow turns increasingly offshore.
Locally strong and gusty north to northeast winds are expected at
higher elevations today through Friday morning, especially in the
North and East Bay Hills. Strongest winds are forecast from this
evening through Thursday morning. As these winds will occur in
conjunction with a warm and very dry air mass, critical fire
weather conditions will result.
&&
.DISCUSSION...as of 09:05 PM PDT Wednesday...Temperatures were up
by about 5 deg F for most of the region this afternoon with
widespread 70s to mid 80s near the coast and mid/upper 80s to mid
90s across the interior. This resulted in Kentfield setting a
daily record of 93 - previously 92 set back in 2015 and Napa tied
their daily record of 97 last set back in 1961. This is as high
pressure continues to build aloft and offshore flow increases
across the interior and in the region's higher elevations. As a
result, relative humidity values continue to fall region-wide and
are 10 to 25 percent drier compared to 24 hours ago in many
locations, especially in the North and East Bay Hills/Mountains.
Winds are forecast to ramp up through the overnight in the
aforementioned locations as well as the higher elevations of the
Santa Cruz Mountains where a Red Flag Warning remains in effect.
Even warmer temperatures are likely region-wide Thursday into
Friday with a Heat Advisory going into effect at 11 AM Thursday.
With this said, only minor adjustments were made to the ongoing
forecast this evening. For complete details, please see the
forecast discussions below.
&&
.PREV DISCUSSION...as of 01:30 PM PDT Wednesday...The afternoon
forecast package will focus around three main weather impacts to
the Bay Area and Central Coast through Friday: Heat Risk, Wind,
and Critical Fire Weather Conditions.
Synoptically speaking surface high pressure continues to build
across Oregon and into the Great Basin. The SFO-WMC gradient is
beginning to gradually increase and becoming more offshore. The
offshore gradient is enhancing the warming trend and increasing
winds over the hills. The latest 24 hour trend shows many places
running several degrees warmer than yesterday. Gusts of 25 to 30
mph are being observed in the hills as of now. Much drier air is
lurking to the north as well. Several mesonet stations are
dropping into the lower teens RH wise this afternoon.
For tonight - the offshore gradient will continue to increase with
models putting the gradient near 15-16 mb, which would be a
moderate offshore flow setup. Peak winds will be late tonight and
early tomorrow with gusts 35-45 mph over the higher terrain and
possibly up to 60 mph over the highest peaks of the North Bay.
Additionally, the drier air to the north is forecast to march
southward this evening and overnight. Needless to say, the
combination of gusty N to NE and dropping RH will create critical
fire weather conditions. The breezy to gusty N to NE and low RH
will continue through Friday. Therefore Red Flag Warning remains
in effect through early Friday. For more details about Fire
Weather see below. Given the potential for gusty winds up to 45
mph decided to issue a Wind Advisory for the North Bay Mts/Valleys
tonight into early Thursday. Winds will be strongest above 1,000
feet. Not super confident on winds surfacing to the valley floor,
but enough of the foothills 500-1,000 feet (higher slopes above
Santa Rosa) to warrant the advisory. Winds will breezy to gusty
for the East Bay Hills and Santa Cruz Mts, but don't think it will
be as long as the North Bay. Winds will ease through the day on
Thursday, but remain offshore. Would not be surprised to see some
strong winds through gaps and passes as well. Winds at Pacifica
and Half Moon Bay could be rather breezy to gusty late tonight.
One other potential impact from the wind will be fire weakened
trees that now have a greater likelihood of coming down.
Last but not least well above normal temperatures Thursday/Friday.
The downsloping flow over the region will only enhance any
potential warm up. This particular setup will yield temperatures
15-25 degrees above normal with a handful of climate sites
flirting near record territory. The offshore flow will also bring
the warmth to the coast. Current forecast highs will be in the
80s/90s at the coast and 90s to lower 100s inland Thursday and
Friday. Not a lot of relief expected at night with 50s/60s valleys
and 60s/80s in the hills. Heat Risk values are in the moderate to
high category so decided to issue a Heat Advisory for the entire
area. Temperatures finally cool and return closer to average over
the weekend and early next week.
Longer range forecast still show no precip over the next seven
days and potentially through the end of the month. One thing to
keep an eye on for next week will be another offshore flow setup
per the ECMWF.
&&
.AVIATION...As of 10:52 PM PDT Wednesday...For the 06Z TAFs. Strong
surface pressures over northern CA to the Great Basin is resulting
in offshore winds. The ACV-SFO pressure gradient is 10.2 mb, UKI-STS
2.8 mb and WMC-SFO 9.7 mb. High confidence VFR for the 06z taf cycle.
Surface winds decoupling from winds aloft enhancing low level wind
shear tonight and Thursday morning.
Vicinity of KSFO...VFR. West to northwest wind 5 to 10 knots. Low
level wind shear with NE winds aloft from 05z to 19z Thursday.
SFO Bridge Approach...Similar to KSFO.
Monterey Bay Terminals...VFR. Winds light southeast by late evening.
SE wind increasing in the Salinas Valley to near 10 knots by Thursday
morning. Variable winds 10 knots in the late afternoon and evening
on Thursday.
&&
.FIRE WEATHER...As of 03:15 PM PDT Wednesday...Critical fire
weather conditions will continue to develop through this evening
and into the overnight hours, especially in the North Bay
Mountains and East Bay Hills, but also at the higher elevations of
the Santa Cruz Mountains. This is where the north to northeast
winds will increase and become strong and gusty from this evening
through Thursday morning where gusts of 45 to 55 mph will be
likely in the peaks and 35 to 45 mph in elevations down to around
1000 feet. Additionally, locally gusty conditions may mix into the
valleys and foothills of the North and East Bay Valleys with
gusts to 30 mph. While winds diminish slightly during the day on
Thursday, critically dry conditions will prevail region-wide with
daytime humidity dropping into the upper single digits to teens.
An uptick in wind speeds is likely again on Thursday night, but
winds then are not expected to be as strong or as widespread as
those Wednesday night. However, the critically dry conditions will
persist with very poor overnight humidity recoveries.
As a result, critical fire weather conditions continue to be
expected at elevations above 1000 feet in the North Bay
Mountains, East Bay Hills, and Santa Cruz Mountains today through
Friday morning and a Red Flag Warning remains in effect. A Red
Flag Warning also remains in effect for the North and East Bay
Valleys, as extremely dry conditions will develop there too, with
some locally gusty winds possible as well.
Winds are forecast to subside in all areas by Friday afternoon
with a gradual cooling trend beginning on Saturday.
&&
.MARINE...as of 9:05 PM PDT Wednesday...Northwest winds strongest
over the northern outer waters tonight and Thursday morning. Winds
will subside Thursday and become more offshore. Seas remain mixed
with a moderate northwest swell and a longer period southerly
swell.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
.Tngt...Red Flag Warning...CAZ506-507-510>512
Wind Advisory...CAZ506-507
SCA...Pt Arena to Pt Reyes 0-10 nm until 3 AM
SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm until 3 AM
GLW...Pt Arena to Pigeon Pt 10-60 nm
&&
PUBLIC FORECAST: RGass/MM
AVIATION/MARINE: Canepa
FIRE WEATHER: RGass/Blier
Visit us at www.weather.gov/sanfrancisco
Follow us on Facebook, Twitter, and YouTube at:
www.facebook.com/nwsbayarea
www.twitter.com/nwsbayarea
www.youtube.com/nwsbayarea3 strong wind. Local standard time, as filed.
Healdsburg Hills North mesonet (PG&E) station reported wind gusts between 40 and 50 mph with a peak gust of 52 mph.
Highland Peak Road mesonet (PG&E) station recorded wind gusts in excess of 45 mph with a peak gust of 54 mph.
Marciel Road mesonet (PG&E) station reported gusts of 45 to 50 mph with a peak gust of 57 mph.
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, October 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: 921023, 921026, 921027.