Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
446 PM PDT Wednesday Jul 27 2016
Synopsis...very warm conditions will persist inland through the
remainder of the week as high pressure remains over the west.
Meanwhile, cooler temperatures will continue near the coast as a
result of weak onshore flow. Slight cooling is expected over the
weekend as an upper level trough develops off of the Pacific
Discussion...as of 2:00 PM PDT Wednesday...satellite imagery
shows a dry clockwise circulation over the Great Basin associated
with a 597dm high pressure system. Water vapor imagery shows some
moisture rotating around the southern flank of this system and
pushing into southern and central California from the south.
This monsoonal moisture will primarily impact the Sierra Nevada by
spawning high base showers and thunderstorms over the Sierra
Nevada well to our east. Closer to home... visible imagery depicts
marine stratus banked offshore and just along our coastlines. The
marine layer is extremely compressed as a result of subsidence
aloft from the aforementioned ridge and will struggle to push
inland until the ridge influences weakens. Additionally... smoke
from the soberanes is evident at varying concentrations across a
swath of the broader region, from the Bay area to western Nevada
and south towards los angles. Todays smoke plume has primarily
spread another round of smoke towards the northeast of the fire...
but latest winds are now veering towards more of an easterly
direction. Transport winds above the fire are anticipated to veer
further towards the southeast into the late afternoon/evening.
The soberanes wildfire smoke has continued to fill in a layer
between 3000 and 6000 feet above the surface. This smoke layer is
mitigating the extent of insolation and has a minor cooling
influence on the area versus theoretically maximum temperatures.
That said, triple digit temperatures will continue to be possible
today, especially in the extreme North/East/South Bay and the
extreme southern Salinas valley. The potentially hottest air
temperatures (104-108f) are forecast across the Big Sur ridgetops
where the soberanes fire is currently burning approximately 23500
acres of wild land. Additionally, the interaction of the hot, dry
stagnant air mass of the ridge with the soberanes smoke is leading
to poor to unhealthy air quality for a large number of communities
in and around California today. Be sure to visit
http://www.Airnow.Gov for additional air quality readings for
your local zip code. The marine layer will continue to be
suppressed by the ridge into tonight and will not provide much
support to firefighting efforts.
The high pressure ridge is expected to weaken and dissipate late
in the week allowing increased onshore flow and a gradual cooling
trend for the region. The pattern will shift to become more of a
mean quasizonal flow by the weekend and into early next week
heralding a return towards near normal conditions. A weak
disturbance passing to the north after the weekend should help to
deepen the marine layer and promote additional cooling. No
precipitation is expected locally through the next several days,
however, for those travelling to the Sierra Nevada, there could be
some isolated high base thunderstorms as monsoonal moisture
rotates around the ridge Thursday into the weekend.
Aviation...as of 4:46 PM PDT Wednesday...IFR ceilings and visibilities
due to stratus and fog along the immediate coast will move locally
inland tonight into Thursday morning. Fresh onshore breezes are
helping to keep visibilities good in the vicinity of San Francisco
Bay, but generally increasingly hazy and smokey conditions exist
from the inland valleys southward to the north central coast.
Vicinity of ksfo...VFR. Northwest-west winds under 20 knots this evening.
Sfo bridge approach...similar to ksfo.
Monterey Bay terminals...VFR followed by IFR cigs/vsbys developing
in the 01z-05z time-frame. IFR tonight into Thursday morning, partial
clearing returning by late Thursday morning.
Fire weather...as of 3:35 am PDT Wednesday...warm and dry
conditions will continue today, especially at elevations above
1500 feet as high pressure remains over the region. While weak
onshore flow continues near the coast, light and variable to light
southerly winds remain over the Santa Lucia mountains and Los
Padres National Forest. In addition, southerly flow aloft has
caused smokey conditions to persist over much of the Monterey Bay
region and as far north as the South Bay. While surface winds are
forecast to remain light, west to northwest winds are expected to
increase slightly through late week which should help push the
smoke associated with the soberanes fire inland and south in the
coming days. Regardless, warm and dry conditions will continue to
impact firefighting efforts through late week.
Marine...as of 10:40 am PDT Wednesday...moderate to locally
gusty winds will persist over the coastal waters as high pressure
remains over the eastern Pacific. The strongest winds will be
across the northern outer waters and north of the Bay Bridge.
Winds will then diminish later this week while a mixed swell
moves into the coastal waters. A long period southwest well
arrives later in the week.
... Arena to Pigeon pt 10-60 nm
Small Craft Advisory...sf Bay until 3 am
Public forecast: drp
fire weather: Sims
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