Scientific Forecaster Discussion
fxus66 kmtr 221116
Area forecast discussion
National Weather Service San Francisco Bay area
416 am PDT sun Apr 22 2018
Synopsis...high pressure over California will maintain dry
conditions, and warm temperatures inland, through Monday. Cooler
temperatures are expected by the middle of the week as a low
pressure system develops over the eastern Pacific. This low may
bring showers to the region next weekend.
Discussion...as of 3:00 am PDT Sunday...early morning satellite
imagery indicates patchy low clouds have developed in coastal
areas overnight. Expect low clouds and fog to become somewhat
more widespread along the coast and into the Salinas valley by
daybreak. Low clouds are expected to clear by late morning,
leaving mostly sunny skies for the balance of the day. A shortwave
trough currently moving into the Pacific northwest and far
northern California is not expected to have a significant impact
on our weather today. However, the shortwave will weaken the
ridge over California and likely result in slightly cooler
temperatures today compared to Saturday. In any case, temperatures
today are expected to be 5 to 10 degrees warmer than normal.
By Monday, the upper ridge is forecast to rebuild over California
and offshore flow at 925 mb is expected to develop and bring
drier air into the boundary layer. These developments indicate the
potential for at least slight warming on Monday.
An upper trough currently in the Gulf of Alaska is forecast to dig
south over the next few days and form a cutoff low west of
California along 135w by Tuesday. The models agree that this low
will then move very slowly eastward towards the California coast
through the remainder of the week. The result will be a cooling
trend starting on Tuesday, with temperatures expected to cool
back down to near normal, or slightly below normal, by midweek.
The models agree that precipitation associated with the upper low
will remain offshore through at least Friday. But the models
diverge by next weekend. The European model (ecmwf) forecasts the low to track
inland near the California/or border on Saturday and then continue to move
steadily to the east-northeast. Under the European model (ecmwf) solution, only the far
northern portion of our forecast area would have any potential for
rain. Initially, the GFS also tracks the low towards the California/or
border, but then forecasts the low to change direction and drop
southeast and into central California. The GFS solution would
result in widespread shower activity in our area on Friday night
and Saturday, with showers potentially continuing into next
Sunday. The Canadian is similar to the GFS. Have introduced shower
chances to the for forecast Friday night and Saturday. But this
portion of the extended forecast is low confidence, as one would
expect with a cutoff low scenario during the Spring months.
Aviation...as of 4:16 am PDT Sunday for 12z tafs. Infrared
satellite imagery shows some areas of low clouds near Half Moon
Bay as well as near Monterey. Overall, the stratus coverage is not
as extensive as it was at this time 24 hours ago. With this in
mind, do think VFR conditions are expected to prevail at most
terminals through the taf period. The terminals that will see some
issues through early/mid-morning include kmry and possibly ksns
with low clouds, and ksts with localized fog. Light winds in the
morning will become onshore again in the afternoon around 10 to 20
kt, with higher gusts possible.
Vicinity of ksfo...VFR conditions are expected to prevail through
the taf period. Light winds in the morning will increase through
the day to around 20 kt by the afternoon, with higher gusts possible.
Sfo bridge approach...similar to ksfo.
Monterey Bay terminals...kmry has been bouncing back and forth
between IFR-LIFR this early morning as low clouds have developed
practically on top of the terminal. Expect improvement sometime
around mid-morning. Ksns hasn't reported any ceilings at this
point in time, but there remains a chance the low clouds could
creep their way toward the Salinas valley around daybreak.
Expect VFR conditions at both terminals for the afternoon with
onshore winds around 8 to 14 kt.
Marine...as of 2:37 am PDT Sunday...moderate northwest winds
will continue into Sunday over the waters as high pressure resides
over the eastern Pacific. These winds will aid in producing fresh
swell and choppy seas. Winds will gradually subside overnight and
... Pt to pt pinos 0-10 nm from 3 PM
Small Craft Advisory...pt Arena to Pigeon pt 10-60 nm
Small Craft Advisory...pt Arena to pt Reyes 0-10 nm
Small Craft Advisory...Pigeon pt to pt Piedras Blancas 10-60 nm
Small Craft Advisory...pt pinos to pt Piedras Blancas 0-10 nm until 9 am
Public forecast: dykema
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