Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
1104 am PDT Friday may 22 2015
Synopsis...a low pressure trough over the West Coast will keep cooler
than normal weather for the area along with the possibility for light
showers through Friday. Slight warming can be expected over the
weekend as the low moves out of the area.
Discussion...as of 08:38 am PDT Friday...the overall weather
picture this morning is very similar to yesterday...a mix of sun
and clouds with scattered showers. The longwave pattern shows
ridging over epac with an upper trough swinging through socal into
S Nevada. The upper low is the likely cause for this morning/S
light shower activity as wrap-around moisture streams over the Bay
area. Kmux imagery keep most shower activity confined from roughly
Sunnyvale southward. Rainfall amounts over the past 12 hours have
mostly been a few hundredths with the higher amounts over the
Santa Cruz Mountains.
For the rest of today...scattered showers will be possible for
much of the region...but the highest probability for showers will
be south of sf Bay. An additional few hundredths will be
Precipitation chances taper off overnight with drier and slightly warmer
weather expected over the Holiday weekend.
Aviation...as of 11:00 am PDT Friday... a sluggish low pressure
system over socal/Vegas region will lead to increased cloudiness
through the day today. Cloud bases have been up and down today as
airmasses interact with a general trend of rising over the last
few hours. Mixed bag of dirty VFR ceilings or MVFR expected today at
most coastal influenced sites... with early return of MVFR
expected at or above 02-04z. IFR ceilings possible late tonight into early
tomorrow morning at coastal influenced sites in wake of upper low.
Predminately onshore flow at most sites through the period.
Vicinity of ksfo...intermittant VFR/high based MVFR today with
early return of MVFR ceilings this evening. Onshore flow 10 to 15 knots.
Confidence is moderate.
Ksfo bridge approach...similar to ksfo.
Monterey Bay area terminals... dirty VFR with broken-overcast clouds
4000ft and above through the day. MVFR ceilings return 02-04z with IFR
posbl after 10z.
Confidence is moderate.
Marine...as of 10:53 am PDT Friday...northwest winds will
increase later today as the pressure gradient tightens. Seas will
also build over the next 24 hours leading to generally
deteriorating conditions over the coastal wters into the weekend.
Unfavorable winds and seas persist through the weekend before
beginning to taper off early next week.
... Arena to pt Reyes 10-60 nm from 5 PM
Small Craft Advisory...pt Arena to pt Reyes 0-10 nm from 7 PM
Small Craft Advisory...sf Bay north of the Bay Bridge from 2 PM
Public forecast: mm
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