Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
1134 am PDT Monday Jul 28 2014
Synopsis...subtropical moisture from the south will bring a
slight chance of showers and thunderstorms to our area today and
Tuesday. Temperatures are forecast to remain near normal or
slightly above normal through the week.
Discussion...as of 09:18 am PDT Monday...stratus slowly burning-
off this morning across the region with a 1500 feet marine layer in
place. Meanwhile...increased middle-level moisture continues to
advect northward out of Southern California. With this...continue
to see returns on the kmux radar this morning across southern
Monterey and San Benito continues...yet no reports of measurable
rainfall at this time. Given the lack of a decent lifting
mechanism...not expecting much convection this afternoon.
However...will keep slight chances between 10 to 15 percent given
the elevated moisture values and some instability.
Otherwise...the previous forecast package remains on track.
Updates have been sent out.
Previous discussion...as of 3:00 am PDT Monday...at this hour kmux
radar is indicating echos advancing from the south into Monterey
County. Radar values are very small -- generally less than 15 dbz
so probably no rain is falling in our County Warning Area yet. However, coverage
over slo County is picking up, so decided to add a slight chance
for showers over the southern quarter of the County Warning Area this morning.
More instability is in the cards for later today into Tuesday as
an additional piece of subtropical moisture moves in from the
south. Model guidance has changed some from yesterday although
overall thinking is still the same that moist unstable air will
advance to the north bringing a slight chance for showers and
thunderstorms today and tomorrow. Convective parameters have
backed off a bit from Sunday although modified total totals are
still in the 29-31c range (down from 32-36c). MUCAPE has also
diminished from yesterday with peak values just around 100.
Showers will end late on Tuesday or early Wednesday as a more
stable SW flow returns to our region. Temperatures will remain at or a
bit above normal as the ridge of high pressure tries to build
back toward the coast while 850 mb temperatures remain in the 23-26c
range. Look for 60s and 70s at the coast with 80s and 90s inland.
Aviation...as of 11:30 am PDT Monday...morning low clouds continue
to roll back to the coastline. Elsewhere kmux radar is picking up
on some light shower activity associated with middle level sub-tropical
moisture right on the southeastern Monterey County line as well as
over easternmost San Benito County. We've not seen any ground
truth yet with these showers although they're not very close to
any one or more remote rain gauges. Suspect at most a few convective
rain drops are reaching the ground as is usually the case with
these patterns...the rest is probably evaporating before reaching
the ground. Middle level winds are on the light side so these showers
are very slow moving.
Additionally the marine layer inversion is holding together fairly
well per recent Fort Ord and Bodega Bay profilers and the San Carlos
sodar. The inversion level (at approx 1600 feet) is fairly uniform
in depth over the Bay area and north central coast. Afternoon and
evening onshore breezes today and again Tuesday will bring a similar
stratus pattern inland each night and early morning.
Vicinity of ksfo...low clouds cleared just a little ahead of
forecast. VFR will prevail through the afternoon and early
Ksfo bridge approach...similar to ksfo.
Monterey Bay area terminals...similarly to the Bay area low clouds
have cleared back to the immediate coast. Forecast is close to
persistence with expected return of stratus between 02z-03z this evening.
Marine...as of 04:27 am PDT Monday...moisture streaming in from the
south will continue to produce showers and possibly a thunderstorm
along the central coast today. Otherwise...northerly flow will
continue over the coastal waters. Seas will remain rather small
for much of the upcoming week.
... Bay north of the Bay Bridge from 1 PM
Small Craft Advisory...sf Bay south of the Bay Bridge from 1 PM
Public forecast: rgass
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