NWS Forecast Area Discussion - San Francisco Area

FXUS66 KMTR 181132

Area Forecast Discussion
National Weather Service San Francisco Bay Area
432 AM PDT Sun Apr 18 2021

.SYNOPSIS...Temperatures will be well above normal today as
ridging aloft continues. Slight cooling begins Monday, mainly in
coastal areas. More widespread cooling is forecast for Tuesday as
temperatures return to seasonal averages. Dry conditions persist
through Friday with slight chances of rain next weekend.

&& of 03:56 AM PDT Sunday...Goes-17 night imagery
reveals a stratus layer expanding along much of the CA coast and
spilling over onto a very narrow layer of land. A ridge of high
pressure off the west coast has helped to compress the marine
layer to just a few hundred feet, as observed on coastal
profilers. As a result, stratus has not pushed as far inland as in
previous nights. ASOS`s from Half Moon Bay down to Monterey are
reporting cloud bases 400 ft and lower, along with some patchy
fog. The very shallow marine layer will allow for a quick burnoff
of clouds by 9 a.m. for most areas.

Today will feature clear skies and the warmest temperatures of
the year for many locations, as the ridge expands over the state.
Max temp`s in the 80s will be felt in the north bay valleys, Santa
Clara Valley, southern Salinas Valley, San Benito County, and
inland East Bay. Spots around the SF Bay shoreline and elevated
areas of Santa Cruz County may also reach the low 80s. The Pacific
Coast will likely remain in the upper 50s to low to mid 70s, with
cooling onshore breezes dominating in the afternoon. Still, a
pleasant day for the coast, with warmer temp`s not seen in recent

This warm spell will be short-lived however, as the coastal ridge
begins to break down on Monday. Coastal areas will experience
significant cooling during the day, with a building marine layer
and more cloud cover. Further inland, it will be another warm day,
with marine air having less of an influence, and 850 mb temps
peaking, but still a few degrees of cooling can be expected. Thus
low to mid 80s will persist in inland valleys, with upper 60s and
70s around the SF Bay shoreline and upper 50s and 60s along the
Pacific coastline.

By Tuesday, the ridge moves well offshore, and an upper level
disturbance moves over the NE part of the state, reaching the
Great Basin early Wednesday. This will bring precip chances to the
Sierra but nothing to our area, except cooler temp`s, more clouds
and breezier winds. Though cooler, temp`s will be near normal.
Wednesday will be another seasonable day, with slight warming
forecast for the end of the week.

Things begin to get interesting towards Sunday when and upper low
from the Gulf of Alaska approaches the PAC NW. Latest
deterministic GFS run shows the low bringing light precip to
NorCal early sunday into Monday. Euro run shows a trough axis
pivoting over the west coast, bringing light to moderate rain to
much of central and southern CA monday into Tuesday. More than
half of the Euro ensemble members show QPF in this time frame,
while the GEFS is closer to 25 percent. Still far out, but
hopefully this isn`t just another tease.


.AVIATION...As of 04:32 AM PDT Sunday...For the 12Z TAFs. Stratus
has filled in along the coast, into the Monterey Bay, and down the
Salinas Valley. VFR conditions north of the Monterey Bay through
late tonight before the marine layer is expected to deepen some
bringing the potential for low clouds around the SF Bay taf sites.
Monterey terminals can expect low clouds and occasional fog
through mid morning with IFR/LIFR/VLIFR conditions prevailing.
Winds have diminished for the most part overnight with light winds
through the morning before the afternoon sea breeze kicks in
increasing winds to around 10-15 kt, locally higher.

Vicinity of KSFO...VFR with some low clouds along the coast west
of the airport. At this time, not expecting stratus to move into
the terminal. Light winds this morning around or under 10 kt.
Onshore winds will increase again this afternoon to around 15-20
kt. Models and guidance show the potential for low clouds to move
further inland late tonight.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...As anticipated, low clouds have filled
back into the Monterey Bay and have moved over the Peninsula and
down the Salinas Valley. IFR/LIFR/VLIFR conditions through mid
morning due to low clouds and occasional fog. VFR conditions
forecast by late this morning and prevailing through this evening.
Expect low clouds to return tonight. Light winds this morning
increasing and turning onshore this afternoon.

&& of 02:22 AM PDT Sunday...Moderate to locally breezy
northwest winds will continue across the waters tonight, though
will weaken slightly. Expect winds to gradually increase tomorrow
afternoon and evening. Winds will then pick up further early next
week as a disturbance moves down from the Pacific Northwest into
northern California. Near gale force gusts may be possible over
the northern waters by late Monday. Elevated winds will persist
through mid week. These winds will produce steep wind waves
creating hazardous seas conditions, particularly for smaller
vessels. Moderate northwest swell through the period along with a
lighter longer period southerly swell.


     .Tday...SCA...Pigeon Pt to Pt Pinos 0-10 nm from 3 PM
             SCA...Pt Arena to Pt Reyes 0-10 nm from 3 PM
             SCA...Pt Arena to Pigeon Pt 10-60 nm from 3 PM
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm until 5 AM




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NWS MTR Office Area Forecast Discussion