FXUS66 KMTR 250040
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
540 PM PDT Fri Sep 24 2021

.SYNOPSIS...A cooling trend will occur through the weekend as 
onshore flow and marine influences spread inland. Even cooler, 
unsettled conditions are likely early next week with the potential
for light rain to return to the North Bay. 

&&

.DISCUSSION...as of 01:46 PM PDT Friday...We're seeing another 
warm day across the interior with temperatures in the upper 80s to
lower 90s as high pressure aloft lingers over the region. 
Meanwhile, the marine layer has been deepening through the day and
is now around 1,000 feet in depth over the North Bay and 1,500 
feet based off of the Fort Ord Profiler. With this, temperatures 
are holding in the upper 50s to middle 60s for most coastal areas 
where low clouds also linger. As the aforementioned ridge aloft 
weakens through the weekend and more of a zonal flow develops, 
look for marine influences to spread further inland. This will 
result in a region-wide cooling trend with night/morning low 
clouds likely to become more widespread across the coastal 
adjacent valleys. 

A larger pattern shift is forecast for early next week as a 
mid/upper level trough develops and pushes inland over the Pacific 
Northwest. This will drive a frontal boundary into northern 
California from Monday into Tuesday resulting in widespread 
precipitation over the northern portion of the state. Both 
deterministic and ensemble guidance suggest precipitation along the 
cold front will dissipate as it advances toward the San Francisco 
Bay Area. With the best mid/upper level support north of the region, 
the North Bay would be the most likely region to see some light 
rainfall with this system with chances greatly tapering off south of 
the Golden Gate. Slight warming is expected mid/late next week as 
the aforementioned trough shifts inland and ridging builds back over 
the region. 

&&

.AVIATION...as of 5:40 PM PDT Friday...For the 00z TAFs. Wildfire
smoke reducing slant range visibilities, also surface visibilities
reduced locally to MVFR. SCT-BKN layer of smoke aloft 8,000 to 12,000
feet tonight and Saturday due to generally southerly winds advecting
smoke from SoCal/Southern Sierra Nevada. 

The marine layer depth is 1,200 feet. Satellite shows widespread 
coastal stratus and fog, onshore winds will usher stratus and fog 
/VLIFR-IFR/ inland tonight and Saturday morning. Light patchy coastal
drizzle tonight and Saturday morning. MVFR-VFR late Saturday morning
and afternoon. Stratus and fog moving back inland Saturday night
and Sunday morning.

Vicinity of KSFO...VFR, west to northwest wind 15 to 20 knots until
mid evening then decreasing to 5 to 10 knots. MVFR ceiling due to
stratus developing 08z continuing to 1730z Saturday. A smoke layer
from 10,000 to 12,000 feet through the period. West to northwest wind
resuming to 15 to 20 knots Saturday afternoon and evening. 

KSFO Bridge Approach...Slant range visibility reduced through the
period. Otherwise similar to KSFO.

Monterey Bay...VFR except VLIFR-IFR in stratus, fog, light coastal
drizzle tonight and Saturday morning. Slant range visibilities reduced
due to wildfire smoke, mainly aloft, otherwise a smoke layer near
10,000 feet through the period. Conditions lifting to MVFR-VFR by
late Saturday morning and afternoon. 

&&

.MARINE...as of 4:57 PM PDT Friday...Light to moderate southwest 
to northwest winds over the coastal waters through the weekend. 
Locally breezy afternoon and evening winds expected near the 
Golden Gate. Northwest winds will begin to increase across the 
waters early next week. Mixed seas continue with a moderate 
northwest swell and a longer period southerly swell. A new longer 
period northwest swell will arrive on Sunday associated with a 
developing low over the Gulf of Alaska. Seas will quickly build 
into Tuesday.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...SCA...SF Bay until 9 PM

&&

$$

PUBLIC FORECAST: RGass
AVIATION: Canepa
MARINE: AS

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