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fxus66 kmtr 212128 
afdmtr

Area forecast discussion
National Weather Service San Francisco Bay area
228 PM PDT Sat Sep 21 2019

Synopsis...most areas will experience some cooling tomorrow and
Monday as an upper low slides down inland California and into the
Desert Southwest. High pressure will then build over the eastern
Pacific early to mid next week. This combination will bring
continued warming temperatures, dry offshore flow and increased
fire weather concerns. A trough of low pressure will move through
the region late next week resulting in significantly cooler
temperatures and possible precipitation.

&&

Discussion...as of 02:28 PM PDT Saturday...temperatures across
the region this afternoon are around 5 degrees warmer than
yesterday as an upper ridge is stretched over California and
northward into the Pacific northwest. Most locations are currently
in the upper 70s to mid 80s with isolated areas in the low 90s.
Expect a few degrees of additional warming today with temperatures
peaking in the low 70s to low 80s along the coast to mid 80s and
90s inland. The upper ridge will quickly shift eastward into
tomorrow and be replaced by an upper trough. The upper trough will
split into a cut off low on Monday that will move southward
across interior California and Nevada before settling into the
Desert Southwest Monday night. This will stall warming across the
area and bring some minor cooling to some locations for tomorrow
and Monday.

The combination of low pressure to our southeast and high pressure
over the eastern Pacific will create offshore flow across the
region from Monday night into Wednesday morning. This will bring
warm to hot temperatures across the region Tuesday and Wednesday
with offshore flow bringing these temperatures to coastal areas as
well. 850 mb temperatures look similar to the last brief heat
event at around 22-23 deg c. Models did a fairly poor job in the
extended of capturing the degree of warming expected, particularly
for coastal areas. Given that this event will likely bringing
stronger offshore flow, went ahead and bumped up temperatures for
Tuesday. For now, expecting coastal areas in the 80s with low 90s
possible around the northern Monterey Bay and along the San
Francisco Bay shoreline. Interior locations are currently forecast
in the 90s to low 100s. Uncertainty remains fairly high as
temperatures will depend on the strength of the offshore flow. As
we get closer to Tuesday, will look into whether or not heat
products are necessary. Wednesday looks to be warm as well but a
few degrees cooler as onshore flow returns. The other concern with
this pattern will be for fire weather (see discussion below).
Dry/gusty offshore winds and low humidities could bring critical
fire weather conditions to the north and East Bay hills Monday
night through early Wednesday morning. Therefore, a Fire Weather
Watch has been issued.

Temperatures will then cool down quickly late this week as a deep
mid/upper trough forms over the West Coast and then digs into
California. This will bring high temperatures down around 10 to 15
degrees inland from Wednesday to Thursday and leave highs across
the region well below normal by Friday. There are still differences
between the models as to the positioning and timing of this
system at the end of the week, but the central coast and Bay area
could see some precipitation into the start of next weekend. Lots
of weather changes for the area this week. Stay tuned to the
forecast.

&&

Aviation...as of 10:20 am PDT Saturday...for 18z
tafs...widespread VFR with clear skies. Light winds becoming
locally breezy onshore by the afternoon, especially near the
coast. For tonight, short term models indicate enough moistening
in lower levels (ie +3-5f dew points) to finally allow for return
of some low coastal clouds overnight Saturday into Sunday. As
such, latest taf reintroduces low clouds at predominately
coastally dominated locations briefly overnight into Sunday. Any
clouds that do form will likely be compressed below 1000 ft and
remain near the shoreline or just inland. These clouds will not
be robust enough to persist beyond mid morning Sunday.

Vicinity of ksfo...VFR.

Sfo bridge approach...similar to ksfo.

Monterey Bay terminals...VFR.

&&

Fire weather...as of 2:28 PM PDT Saturday...as of yesterday, the
energy release component (erc) and 100 hour fuel values are right
around normal for the region. An inside slider is still expected
to bring an offshore flow event Monday night and through early
Wednesday morning. A Fire Weather Watch has been issued from 9 PM
Monday to 5 am Wednesday for the North Bay mountains and East Bay
hills & Diablo Range. Offshore flow will develop on Monday with
winds peaking Monday night into Tuesday morning. The strongest
winds thus far are expected in the North Bay mountains where the
local WRF model shows gusts up to 45 mph possible overnight
Monday. Generally expect north to northeast winds 10 to 25 mph
with gusts 30 to 35 mph. Winds will ease some Tuesday morning, but
will increase and become gusty again in the afternoon and
overnight. Daytime humidity values are forecast in the teens to
low 20s with poor overnight humidity recoveries both Monday and
Tuesday night of 30 to 50 percent. Additionally, very warm to hot
conditions are forecast for Tuesday with highs in the low to mid
90s and isolated areas reaching triple digits. This along with low
humidities will contribute to further drying of fuels.

&&

Marine...as of 08:10 am PDT Saturday...light to locally breezy
northwest winds across the waters through this weekend. Strongest
winds will in the outer waters north of Point Reyes where
hazardous squared seas are also possible. Winds will increase
again by Monday as another low pressure trough drops into the
Great Basin. A 9 to 10 second northwest swell will be mixed with a
long-period southerly swell.

&&

Mtr watches/warnings/advisories...
... Arena to Pigeon pt 10-60 nm
Small Craft Advisory...pt Arena to pt Reyes 0-10 nm from 3 am

&&

$$

Public forecast: as
aviation: Sims
marine: Sims

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