Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA
FXUS66 KMTR 280545
Area Forecast Discussion
National Weather Service San Francisco Bay Area
1045 PM PDT SAT AUG 27 2016
.SYNOPSIS...Temperatures will remain near to slightly below
seasonal averages through early next week before further cooling
by midweek as an upper level trough pushes inland to our north.
This pattern will change little through late next week with
continue below average temperatures and widespread night/morning
.DISCUSSION...As of 9:00 PM PDT Saturday...For the second
consecutive day, inland temperatures today were as much as ten
degrees cooler than normal. The marine layer remained deep at
about 3000 feet and light southerly flow continued to transport
cool marine air well inland. The marine layer was deep enough for
low clouds to mix out along the coast from Santa Cruz County
southward this afternoon. Expect low clouds to redevelop in all
coastal areas overnight as the boundary layer cools.
A shortwave ridge is beginning to build over California this
evening and models forecast this ridge to strengthen over central
and southern California through Sunday and into Monday. This
should bring about a decrease in the depth of the marine layer
over the next couple of days which would result in inland
warming. In addition, low level winds are forecast to gradually
turn from light southerly to west and then eventually northwest,
something that will also contribute to inland warming, especially
in the North and East Bay Valleys. But the amount of warming is
expected to be modest with high temperatures forecast only to
warm back to near normal.
The most important item that will require careful monitoring over
the next few days is the potential for showers or isolated
thunderstorms in the North Bay late Monday night and into early
Tuesday. Moisture from Tropical Storm Madeline...currently
centered near 15N/140W....is forecast to flow to the ENE out
ahead of an approaching trough early next week. The models
forecast precipitable water values up near one inch approaching
the northern California Coast by late Monday night. Combine this
moisture with instability associated with the incoming shortwave
trough and we may see convective precip moving into northern
California...and as far south as the North Bay...late Monday
night and into Tuesday morning. The 18Z NAM was quite bullish with
both moisture and instability in the North Bay, but the 00Z run
has backed off a bit. Will wait for the full compliment of 00Z
model data before making a decision on whether to add
shower/thunderstorm chances to the North Bay next Monday Night and
The shortwave arriving on Tuesday will result in cooling across
our region once again that day, with cooler than normal conditions
then expected to persist through the end of next week and into
the following weekend as a longwave trough positions itself near
the West Coast.
.AVIATION...as of 10:45 PM PDT Saturday...A sub-tropical ridge
over the eastern Pacific tilts eastward across CA/NV through early
next week. There`s been little change in marine layer depth this
evening, but lower level warming is forecast through late Sunday
night likely causing the marine layer depth to steadily compress.
Satellite and obs show stratus and fog has been slow to return to
the coast from Santa Cruz county southward, and very slowly moving
inland over the Bay Area. 06z terminals are based on continued
mainly light onshore wind flow and the marine inversion becoming
shallower with time. MVFR cigs with areas IFR developing tonight,
IFR lifting by late Sunday morning.
Vicinity of KSFO...VFR persists this evening. Light westerly winds
with MVFR cig forecast 08z-18z Sunday. VFR forecast for late Sunday
morning and afternoon. Westerly wind gusts to near 20-25 knots resuming
late Sunday afternoon and evening.
SFO Bridge Approach...Similar to KSFO.
Monterey Bay Terminals...Stratus and fog are very slow to fill back
in over the coastal areas. MVFR cigs with areas IFR cigs forecast for
tonight/Sunday morning. Clearing likely returning late Sunday morning.
.MARINE...as of 9:10 PM PDT Saturday...Light wind and seas will
continue over the coastal waters through this weekend except gusty
onshore winds are expected from the San Francisco Bay to the Delta
Sunday afternoon and evening. Over the coastal waters northwest
winds increase early into next week. Mixed short period northwest
swell and a smaller long period southerly swell will continue to
move through the coastal waters.
PUBLIC FORECAST: Dykema
Visit us at www.weather.gov/sanfrancisco
Follow us on Facebook and twitter at: