Scientific Forecaster Discussion
fxus66 kmtr 172055
Area forecast discussion
National Weather Service San Francisco Bay area
1255 PM PST sun Nov 17 2019
Synopsis...seasonably warm conditions will persist to start the
workweek with a slight increase in onshore flow heading into
Tuesday. Cooler conditions develop Tuesday into Wednesday as a
weather system moves through the region. Gusty north to northeast
winds are likely to develop in the north and East Bay
hills/mountains from late Tuesday night through early Thursday
morning resulting in increased fire weather concerns. Dry
conditions, along with seasonable temperatures, are forecast from
Thursday through next weekend.
Discussion...as of 12:54 PM PST Sunday...temperatures region-
wide are warmer compared to this time yesterday as conditions in
the boundary layer dried out preventing any low clouds/fog this
morning. At this hour, kapc (napa County airport) is running 17
degrees warmer while other locations are a few to about 10 degrees
warmer. High pressure will remain in place through a good part of
the day on Monday and result in similar conditions heading into
the start of the work week. Look for a cool start to the morning
with overnight lows in the 40s to lower 50s and afternoon
temperatures warming into the 70s and even lower 80s.
The ridge will then weaken in advance of an approaching mid/upper
level trough late Monday into Tuesday. This will allow for an
increase in onshore flow ahead of an approaching frontal boundary
that will move from north to south across the region on Tuesday.
The core of the trough will shift to our south and is forecast to
develop into a closed low over Southern California by Wednesday.
Overall, mainly dry conditions are likely as this system will be
moisture starved until it taps into deeper moisture well to our
south. However, we cannot rule out an isolated shower or two over
the southern portion of the central coast from late Tuesday into
The primary impact from this system will be cooler temperatures
and the development of offshore flow. Expecting daytime
temperatures to drop back into the 60s region-wide by Tuesday
afternoon with locally breezy northerly winds. By late Tuesday
night, north to northeast winds are forecast to increase over the
north and East Bay hills/mountains. Gusty winds combined with
lowering humidity in these areas will result in an increase in
fire weather concerns. As a result, a Fire Weather Watch will be
issued for the aforementioned locations shortly (for early
Wednesday morning into Thursday morning). Be sure to stay up to
date with the latest information as timing/location(s) may need to
be adjusted in the coming days.
Wind speeds are forecast to diminish by Thursday as the upper
level low over Southern California shifts to the east.
Temperatures will remain near seasonal averages for the remainder
of the week and even into the upcoming weekend. However, dry
conditions will prevail with generally light winds.
Aviation...as of 09:55 am PST Sunday...for 18z tafs. Increased
subsidence has resulted in shallowing and drying of the boundary
layer air mass with the result of mostly clear skies districtwide.
VFR conditions prevail at all terminals and high confidence will
continue through the day and evening hours. Light winds this
morning turning onshore for coastal sites this afternoon at around
10-15 kt, with light offshore winds inland.
Vicinity of ksfo...VFR with light north-northeast winds becoming onshore less
than 15 kt during the afternoon. High confidence.
Sfo bridge approach...similar to ksfo.
Monterey Bay terminals...VFR. Winds turning onshore to around 10
kt as the day progresses, except in the Salinas valley where will
remain offshore 10-15 kt through early afternoon. High
Marine...as of 09:19 am PST Sunday...light to moderate northwest
winds will persist across the coastal waters through the rest of
the weekend and into Monday, strongest over the northern outer
waters. Northerly winds will then increase across the waters on
Tuesday and remain moderately strong and gusty through mid- week.
Northwest seas and swells will continue to subside tomorrow before
re-building in strengthening winds beginning Tuesday resulting in
hazardous seas conditions.
... Arena to Pigeon pt 10-60 nm until 9 PM
Public forecast: rgass
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