Scientific Forecaster Discussion
fxus66 kmtr 291143
Area forecast discussion
National Weather Service San Francisco Bay area
443 am PDT Thu Jun 29 2017
Synopsis...seasonable Summer pattern in place with a marine layer
along the coast leading to areas of night and morning low clouds
followed by sunny afternoons away from the coast. These conditions
are expected to continue through the 4th of July Holiday.
Discussion...as of 2:08 am PDT Thursday...satellite imagery
shows low clouds have spread into the Salinas valley as well as
across the San Francisco Bay to the East Bay hills, with less
coverage over the North Bay except for Marin County. The marine
layer depth has compressed somewhat and is now around 1100 feet
per The Fort Ord profiler, but low clouds and fog are still
expected to form even in the North Bay valleys by sunrise. Onshore
flow is still strong, with 3.3 mb between sfo and SAC last hour.
An upper level trough remains over the Great Basin with high
pressure aloft over the eastern Pacific. This ridge is forecast to
build in over California over the next couple of days resulting in
a slight warming trend, especially across inland areas where high
temperatures will once again approach 100 degrees in the warmest
locations. There will be a steep temperature gradient to the coast
where 60s to lower 70s will be the rule through the forecast
period, with continued marine influence.
An upper level trough is progged to approach the coast by the end
of the week which will deepen the marine layer and increase
onshore flow. Thus, cooler temperatures will filter inland as
By early next week, the upper level high will center over the
Desert Southwest. Differences in model output regarding the
position of this ridge mean either high temperatures warm once
again across our southern inland areas, or if the ridge remains
farther east, continued seasonable weather. The latest European model (ecmwf) still
keeps the ridge farther east with a deepening trough off the
coast. The current forecast trend is more in line with this
Aviation...as of 04:35 am PDT Thursday...for 12z tafs. Marine
layer compressed a little overnight and stratus coverage isn't as
much this morning. However, stratus is still slowly expanding.
Given the compressed nature will go with better burn off chance
this morning. VFR this afternoon. Onshore flow could be a tad
stronger today, especially at sfo.
Vicinity of ksfo...MVFR cigs. Tricky for sfo and Oak as satellite
shows edge of stratus deck is on the edge of both terminals and
moving north. Given the low conf will keep cigs through early this
am. May need to amend if the clearing line moves completely
through terminals. VFR this afternoon. Moderate west winds around
10 to 15 kt increasing to 20 kt with poss gust to 30 kt.
Sfo bridge approach...latest satellite and smb obs show clear over
approach. May see a few clouds creep in form the S and southeast.
Monterey Bay terminals...IFR cigs through 18z-19z Thursday
Marine...as of 04:34 am PDT Thursday...moderate to strong
northerly winds will continue over the coastal waters as high
pressure remains in place. Steep wind waves and fresh swell will
dominate the coastal waters as a result of the strong winds.
Persons operating small crafts should use extra caution along the
central California coast and bays through at least the
... Arena to pt Reyes 0-10 nm
Small Craft Advisory...pt Reyes to Pigeon pt 0-10 nm
Small Craft Advisory...Pigeon pt to pt pinos 0-10 nm
Small Craft Advisory...pt pinos to pt Piedras Blancas 0-10 nm
Small Craft Advisory...pt Arena to Pigeon pt 10-60 nm
Small Craft Advisory...Pigeon pt to pt Piedras Blancas 10-60 nm
Small Craft Advisory...mry Bay from 3 PM
Small Craft Advisory...sf Bay
Public forecast: Sims
Visit US at www.Weather.Gov/sanfrancisco