Scientific Forecaster Discussion
fxus66 kmtr 140559
Area forecast discussion
National Weather Service San Francisco Bay area
959 PM PST Wed Nov 13 2019
Synopsis...cloudy conditions today ahead of an incoming dry
upper trough that will bring a cooling trend into Thursday. By
Friday temperatures start to rebound leading to another warming
and drying trend this weekend with some light offshore winds
possible. Dry pattern continues through the middle of next week.
Discussion...as of 8:56 PM PST Wednesday...high clouds continue
to increase out in front of an approaching upper level trough.
The increased clouds cover significantly affected temperature this
afternoon with most locations cooling 5 to 9 degrees, while many
coastal and coastal valley locations cooled upwards of 10 to 15
degrees. The cooling trend will continue into Thursday as the
above mentioned upper trough moves into the area bringing with it
a cooler airmass and a deeper marine layer. The affects on the
marine layer are already apparent from looking at The Fort Ord
profiler which shows the rapidly deepening marine layer around
2000 feet at this hour.
While difficult to see because of the high clouds blocking The
View of the surface, low clouds have returned to the coast.
Observations indicate higher ceilings then 24 hours ago with Half
Moon Bay and Monterey reporting ceiling heights of 1400 ft and
1300 ft, respectively. For tonight anticipate low clouds to once
again move inland through coastal gaps and valleys. Patchy drizzle
remains possible for late tonight into early Thursday morning as
is typical with a deepening marine layer.
Another day of significant cooling is anticipated Thursday with
temperatures forecast to cool another 5 to 10 degrees across the
forecast area. Coastal temperatures will see minimal cooling if
any while inland locations will see the biggest change.
Temperatures are expected see warm a degree or two Friday if
anything as the upper trough exits the region and high pressure
begins to rebuild over the district. Warmer and drier weather is
forecast over the weekend as high pressure takes hold.
From previous discussion...one area of concern this weekend will
be heightened fire weather concerns. Medium range models continue
to show high pressure building into the Great Basin with lower
pressure along the California coast by Saturday. Flow at 2500 feet becomes
north to northeast. This set up will allow for some drying and
breezy/gusty winds over the north and East Bay higher terrain. Not worthy
of a red flag warning, but something to monitor.
The ridge begins to flatten by early next week as the epac begins
to become more active. The longwave pattern shows a tight low
pressure system moving into the pac northwest with a secondary pulse
moving through almost as an inside slider Monday/Tuesday.
Interesting to note the European model (ecmwf) brings some rain into norcal Monday
night, but other models remain dry including some ensembles. As
the trough progresses eastward models are trending that the trough
deepens enough and becomes a cut-off low over socal by mid- week
with precip. For the Bay area, this pattern could mean continued
dry weather and possibly another push of offshore/northerly winds.
Aviation...as of 09:59 PM PST Wednesday...for 06z tafs.
Continuous high clouds are moving in from over the ocean to the
Bay area out ahead of the next system. Conditions remain VFR but
cigs are beginning to lower. As a weak trough moves east through
California a chance for light drizzle is mainly for the North Bay
as low to mid level moisture increases into Thursday morning,
dropping cigs to MVFR to locally IFR. Winds are also expected to
shift to the west-southwest with the frontal passage and increase
in the afternoon with locally gusty conditions. Cigs will only
increase marginally in the afternoon.
Vicinity of ksfo...high clouds remain, but cigs are slowly
lowering and are expected to lower to IFR conditions into
Thursday morning. The low clouds will lift to mid levels by
Thursday afternoon with impacts to visuals possibly through
midday Thursday. Winds are currently out of the northwest, but
will shift to become more southerly early Thursday morning. As a
cold front passes over the Bay area, winds will increase with
locally gusts, that will eventually subside after the front
Sfo bridge approach...similar to ksfo.
Monterey Bay terminals...northwesterly movement of clouds continue
over the peninsula, but conditions remain VFR. However, ceilings
have slowly stared to lower and are forecast to continue to do so
through the night where ceilings can be at there lowest by 12z.
Winds have calmed and are expected to shift to be more southerly
tomorrow associated with a cold frontal passage. Expect locally
gustier conditions, particularly closer to the Monterey peninsula,
though winds subside Post-frontal passage.
Marine...as of 09:43 PM PST Wednesday...winds remain light and
southerly across the coastal waters. However, as a part of a front
approaching the California coast, the winds begin to switch to the
northwest Thursday night into Friday morning with increasing
winds, particularly on Friday. Expect northwest wind shift to
appear in the northern waters first before the southern waters,
due to the angle of the front. The northwest dominant swell will
remain light and continue through Thursday morning. By Thursday
night, a larger, longer period northwest swell will arrive and
continue through Friday and Saturday.
Public forecast: CW
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