Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA

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FXUS66 KMTR 250535

Area Forecast Discussion
National Weather Service San Francisco Bay Area
1035 PM PDT Tue Apr 24 2018

.SYNOPSIS...A cooling trend is forecast to persist through late
week and into the upcoming weekend as an upper level trough
approaches from the Pacific. This system may produce a few showers
over the North Bay late Friday into Saturday as it pushes inland
north of our region, yet widespread rainfall is unlikely.

&& of 8:38 PM PDT Tuesday...Visible satellite
imagery just before sunset revealed extensive stratus coverage
over the coastal waters. Onshore flow with a pressure gradient of
over 2 mb from San Francisco to Sacramento combined with a marine
layer of around 1,200 to 1,500 ft will allow for widespread
overcast conditions to return to much of the area overnight. In
fact, the stratus has already returned to Monterey with overcast
conditions reported shortly before 8 pm PDT.

Today`s onshore flow aided in bringing cooler temperatures to the
area, most notably to inland locations. For example, the high
temperature at the Sonoma County Airport KSTS was 82 degrees on
Monday and only 67 degrees today. Expect this cooling trend to
continue into the second half of the work week before the next
weak system approaches from the west. No major updates planned to
the forecast this evening with the short-term on track. For
additional details, please refer to the previous discussion


.PREV of 01:48 PM PDT Tuesday...The mid/upper level
ridge axis continues to shift further inland away from the West
Coast today in advance of a broad trough well offshore. This has
allowed for cooling region-wide today (currently 16 deg F cooler
at Santa Rosa compared to 24 hours ago) with a marine layer
between 1,200-1,500 feet in depth. With this, onshore flow persist
along with coastal stratus.

The upper level trough and an associated low pressure system will
slowly approach the California coast through late week. As a result,
look for continued cooling, even inland, with coastal stratus
penetrating inland each night before retreating back to the coast
during the mid/late morning hours. Daytime temperatures will
generally range from the upper 50s to middle 60s at the coast to
middle/upper 70s inland through Thursday.

The center of the upper level low is then forecast to push into
northern California Friday into Saturday and bring a slight chance
of rain showers to the far northern portion of the North Bay.
However, not expecting much in the way of widespread rainfall as the
core of this system stays well to our north. Elsewhere, temperatures
cool to below seasonal averages with ongoing dry weather conditions
likely into the upcoming weekend.


.AVIATION...As of 10:35 PM PDT Tuesday...For 06z tafs. Stratus
visible along the Central Coast and beginning to make its way
inland. VFR conditions north of the Monterey Bay expected to hold
for another couple of hours before MVFR/IFR cigs develop.
Widespread stratus is expected to affect all terminals before
morning. Generally light winds overnight.

Vicinity of KSFO...VFR with low clouds beginning to move in. MVFR
cigs to return at around 10z.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...Stratus has moved into the Monterey Bay
area with IFR/MVFR cigs at KMRY. IFR/MVFR conditions expected to
arrive at KSNS over the next few hours. Once cigs move in,
expecting them to remain in place through the early morning.
Generally light winds through the period.

&& of 08:17 PM PDT Tuesday...Light to moderate west to
northwest winds will continue through the week. Locally gusty
conditions possible near coastal gaps or prominent points such as
the Golden Gate and Point Sur. Light to moderate seas will also
persist through the forecast period with a mixed south and
northwest swell developing late in the week.





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