Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
1055 am PDT Tuesday Jul 26 2016
Synopsis...a warming trend remains on track for the inland areas
beginning today and persisting through late week as high pressure
builds in from the Desert Southwest. However, typical cool Summer
conditions will prevail along coast. A cooling trend is
anticipated for the upcoming weekend as an upper level trough
develops off of the Pacific northwest coast.
Discussion...as of 08:55 am PDT Tuesday...low cloud remained
confined mostly to the coast this morning and only spread locally
inland, especially around the Monterey Bay region where patchy
dense fog was observed as well. This is a result of a much more
compressed marine layer that is now around 1000 feet in depth this
morning. As temperatures aloft warm in response to the building
mid/upper level high pressure, expecting a robust warming trend to
take place today. Most inland areas will be 6-10 degrees warmer
compared to yesterday while continued onshore flow will result in
little change along the coast. Very warm and dry conditions will
also persist in this hills/mountains as well as the inland valley
locations where a few spots will exceed the 100 degree mark this
afternoon. As a result of light and variable winds off the
surface, smoke from the soberanes fire will continue to impact
much of the region today. Thus, have increased coverage of smoke
and haze in the official forecast across much of the San Francisco
Bay area and Monterey Bay region. The ongoing forecast remains on
track and no major changes are needed at this time.
Previous discussion...as of 3:09 am PDT Tuesday...building high
pressure is compressing the marine layer this morning as indicated
by The Fort Ord profiler which is showing a marine layer depth of
just under 1000 feet. The compressed marine layer is resulting in
low clouds, ceilings around 200 feet, along the coast and patchy
dense fog in the Monterey area. The current infrared satellite fog
product continues to Show Low clouds over the coastal waters,
stretching into the Salinas valley. The heat signature associated
with the soberanes fire is also evident on the fog product.
The 0000z European model (ecmwf) and gfs20 have initialized well with the current
synoptic weather pattern and remain in good agreement through
roughly Saturday, building The Four Corners high to 594dm. As the
high pressure builds 850mb temperatures heat up. In fact 850mb
temperatures are forecast to reach 25 to 26c today and 26 to 27c
Wednesday and Thursday. This translates to hot inland temperatures
reaching into the mid to upper 90s. The hottest areas will be in
interior Monterey and San Benito counties where low 100s will be
common. Pinnacles National Monument is expected to reach a high of
107 today and tomorrow before cooling to 106 on Thursday. In
addition to the heat the 0000z gfs20 is also indicating that some
monsoon moisture will begin to move into southern Monterey
Wednesday. At this point the atmosphere does not look unstable
enough to support convection, but we will continue to monitor this
moisture as it moves into the area. A cooling trend remains on
track for the weekend as a trough of low pressure begins to swing
into the Pacific northwest.
Aviation...as of 10:50 am PDT Tuesday... the compressed marine
layer has mixed out and retreated primarily offshore as of 1045am
this morning. The more significant flight nuisance today will be
smoke lofted into the atmosphere by the soberanes fire just south
of kmry. Smoke will impact kmry ksns and kwvi most today with some
additional haze due to fu at ksjc and potentially klvk and koak.
Additional cloud condensation nuclei will generate more clouds
than forecast across the entire region today and likely the next
several days. Forecasts are generally based on webcams,
persistence, and smoke models more so than typical forecast
models. Expect to see a very compressed marine layer again tonight
bringing low cigs to kmry and ksns (though the smoke will already
do bring low cigs).
Vicinity of ksfo...VFR with fu in at or below 10-20k feet above ground level. Potentially
some mild haze issues due to fu. Onshore winds around 16 kts.
Compressed marine layer tonight means it will be tough to get low
clouds, but not impossible.
Sfo bridge approach...similar to ksfo.
Monterey Bay terminals...poor visibility through the forecast
period with vlifr to IFR cigs and visbys due to fu/hz. Winds
should generally be light onshore but not strong enough to clear
the air over kmry. Fog will mix with fu overnight to create very
poor (ie 1/4sm) visibilities overnight. Airport sensor reporting
sct002 at this time, however given manual observation it appears
broken-ovc002 due to smoke.
Fire weather...as of 3:09 am PDT Tuesday...the marine layer has
compressed to around 900 feet this morning. Although relative
humidity recoveries have been good below a 1000 feet tonight, Max
relative humidity above 1000 feet remains poor. Surface winds over
the waters along the Big Sur coast are anticipated to be around 10
mph and out of the north. Generally light and variable winds, 4
to 8 mph, are anticipated over Santa Lucia mountain and Los Padres
National Forest. This will result in another day of smokey
conditions for the Monterey area.
Marine...as of 10:43 am PDT Tuesday...light to moderate northerly
winds will continue over the coastal waters as a sfc ridge lingers
offshore of the pacnw and high pressure remains aloft of the
region. The strongest winds will be over the northern outer
waters and in localized areas of the northern San Francisco Bay.
Hazardous conditions from squared seas will also be possible in
the northern outer waters. Winds will taper off through the week
as a mixed swell moves through the coastal waters.
... Arena to Pigeon pt 10-60 nm
Small Craft Advisory...sf Bay from 11 am
Public forecast: rgass
fire weather: Larry
Visit US at www.Weather.Gov/sanfrancisco
Follow US on facebook and twitter at: