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

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FXUS66 KMTR 201148
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
348 AM PST Sun Jan 20 2019

.SYNOPSIS...An approaching cold front will spread precipitation
across the North Bay beginning in the predawn hours, and then
south across most of the rest of the forecast area by this
afternoon. Showers and a slight chance of thunderstorms are
expected late this afternoon and evening, diminishing overnight
and ending by Monday morning. Gusty west to northwest winds are
expected from late this afternoon through much of tonight,
especially near the coast. Dry conditions, cool overnight
temperatures, and progressively warmer days are then forecast
through the end of the week and into next weekend as strong high
pressure builds over the West Coast.

&&

.DISCUSSION...As of 3:05 AM PST Sunday...Periods of light rain
have persisted in the North Bay overnight, mainly across Sonoma
and Marin Counties. Elsewhere, clouds have been on the increase
as a weather system approaches from the northwest. Rainfall will
become more widespread in the North Bay a few hours before sunrise
as a surface cold front approaches. The front is forecast to
spread rain south to San Francisco and Oakland by mid morning, to
Santa Cruz and San Jose by midday, and to Monterey and Hollister
by early afternoon. Numerous showers will follow the front through
the evening hours and our area may also see a few late afternoon
and evening thunderstorms with small hail as a cold and unstable
airmass moves in behind the front. Showers are then forecast to
taper off late tonight and mostly end by daybreak Monday.

Rain rates with this system are forecast to be mostly light.
However, satellite measurements indicate respectable
precipitable water values of around one inch just ahead of the
frontal boundary. So there will likely be a least a brief period
of moderate rain rates as the front moves through. Afternoon and
evening showers and isolated thunderstorms may produce brief heavy
downpours. Rainfall totals through tonight are forecast to
generally range from a quarter to a half inch in most urban,
valley, and coastal locations (except a tenth of an inch or less
in southern inland valleys). In the hills, rain totals through
tonight are projected to range from a half inch to an inch, with
highest amounts likely in the North Bay Mountains. Behind the cold
front, snow levels are forecast to drop as low as 3500 feet by
late tonight, and some of the higher elevations of Monterey and
San Benito County may see some light snow accumulation. However,
most precipitation is forecast to end in the SF Bay Area before
snow levels drop low enough for snow to fall on Bay Area peaks.

South to southwest winds will increase somewhat ahead of the
approaching front, but winds won`t really be a factor until after
frontal passage when winds turn to the west and increase. Blustery
conditions are expected to develop by evening, especially near the
ocean and bays where gusts of 35 to 45 mph are likely starting
around sunset and continuing through at least midnight. This
looks to be a marginal Wind Advisory scenario. However, saturated
soil from recent rain events have left trees more vulnerable to
topple during gusty winds. Therefore, a wind advisory will be
issued for most coastal zones from 6 pm this evening through 4 am
Monday morning.

A few showers may linger across the southern portion of our area
into early Monday morning. Otherwise Monday is forecast to be a
partly cloudy, dry, and seasonably cool day with brisk winds at
the coast.

Models have been very consistent and in very good agreement in
forecasting a significant pattern change during the first half of
this week. A high amplitude upper ridge is forecast to develop
near the West Coast by midweek and then persist for an extended
period of time. The result will be dry weather through the week
and upcoming weekend, and quite likely through the end of the
month. Nights will be cool through midweek, especially in the
valleys where cool air from the departing system will remain for a
few days. Otherwise, expect a warming trend through the week.
Daytime temperatures will warm 5 to 10 degrees above normal by the
second half of the week and into the weekend.

&&

.AVIATION...as of 3:49 AM PST Sunday...MVFR except IFR in
occasional light rain in the North Bay early this morning. Light
rain and lowering ceilings and visibilities then spreading
elsewhere today and tonight. Gusty winds developing later this
afternoon and evening.

Vicinity of KSFO...MVFR with light rain. Gusty west winds
developing this afternoon and evening. Gusts to 34 knots.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR early, becoming MVFR with light rain
this morning. Gusty west winds this evening.

&&

.MARINE...As of 2:35 AM PST Sunday...Northwest winds will
increase across the waters in the wake of the frontal passage with
occasional gale force gusts possible over the outer waters late
Sunday night. West swell will continue to gradually diminish over
the weekend before a northwest swell arrives early next week.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...Coastal Flood Advisory...CAZ006-505-506-508-509-529-530
             SCA...Pigeon Pt to Pt Pinos 0-10 nm from 3 PM
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm from 3 PM
             SCA...Pt Arena to Pigeon Pt 10-60 nm from 10 AM
             SCA...Pt Arena to Pt Reyes 0-10 nm from 1 PM
             SCA...Pt Reyes to Pigeon Pt 0-10 nm from 1 PM
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm from 1 PM
             SCA...SF Bay from 1 PM
             SCA...Mry Bay from 3 PM

&&

$$

PUBLIC FORECAST: Dykema
AVIATION: Sims
MARINE: Sims

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