Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA
FXUS66 KMTR 240951
Area Forecast Discussion
National Weather Service San Francisco Bay Area
251 AM PDT Fri Mar 24 2017
...Rain and gusty southerly winds return today...
.SYNOPSIS...Rain and wind will spread southward today across the
forecast area as a cold front moves across the region. A break in
the rain is expected Saturday with showers anticipated to return
Sunday afternoon and night as a low pressure system moves through.
.DISCUSSION...as of 2:51 AM PDT Friday...The approaching system is
taking its time reaching us, but KMUX radar is starting to fill in
with stronger reflectivities off the coast. So far, only a couple
hundredths of an inch have been picked up by rain gauges in the
Latest model runs indicate a slightly slower solution with the
main rain band intensifying over the North Bay after sunrise, then
spreading south through the remainder of the Bay Area during the
morning. The HRRR keeps the Monterey Peninsula rain-free until
early afternoon. Satellite-estimated precipitable water values
still exceed 180-200% of normal offshore, with over 1.5" of PW in
the moisture plume aimed currently aimed at the Northern
California coast. Thus, once this system moves through, episodes
of locally heavy rain are possible, especially over coastal hills.
Rainfall totals through Saturday morning are forecast to range
from 1-3" in the North Bay and coastal hills and from 0.25-0.75"
in the lower elevations. Rain to turn to showers this afternoon
and end overnight.
In addition to rain, southerly winds are expected to ramp up in
advance of and with the front. Winds will be strongest over the
higher terrain from Santa Cruz county northward, as well as some
coastal areas. A wind advisory will be issued for these areas for
much of today. Downed limbs, trees and power lines seem likely.
Precip will turn showery by Friday night and end in the pre-dawn
hours of Saturday. Saturday looks dry but seasonably cool.
Another system will bring rain chances back to the area late
Sunday. This system does not look to be as wet, but an additional
0.25-0.50" with local amounts 0.75 inches possible. This rain is
expected to be east of the area by midday Monday.
Beyond that the remainder of next week now looks dry.
.AVIATION...As of 10:40 PM PDT Thursday...For 06z TAFs. VFR
conditions are expected to persist the next several hours across
the Bay Area through about 10 to 14Z before showers associated
with an approaching front push onshore. Rain is expected to reach
the San Francisco Bay Area terminals by Thursday morning with a
steady rain mid/late morning that will continue into the afternoon
and evening hours. Expect ceilings to become MVFR as the rain
reaches the terminals. Medium confidence on timing of the rain.
Winds are becoming southerly tonight and can expect breezy conditions
by mid morning at many locations. Gusts are likely to exceed 20
to 25 kt by 18Z. High confidence on wind direction, medium
confidence on the timing and gust magnitude.
Vicinity of KSFO...VFR through about 9 to 10Z, and then
transitioning to MVFR ceilings and with rain by Friday morning.
Southerly winds will increase by morning with gusts exceeding 20
kt by 18Z and continuing into the afternoon and evening.
SFO Bridge Approach...Same as KSFO.
Monterey Bay Terminals...VFR overnight with generally light winds.
Rain showers are expected to begin impacting after 18Z with MVFR
ceilings and increasing southerly winds.
.MARINE...as of 2:21 AM PDT Friday...Occasional gale force gusts
are possible through the day as a storm system impacts the region
with strong southerly winds and rain. Seas will be rough with the
frontal passage, but should begin to decrease by this evening.
Expect northwest winds to return by Saturday morning before
briefly becoming southerly on Sunday as another weak system
moves over the waters.
.Tday...Wind Advisory...North Bay Mountains from 6 AM this
morning to 3 PM PDT this afternoon
Wind Advisory...San Francisco Peninsula Coast-East Bay
Hills and the Diablo Range-Santa Cruz Mountains from
10 AM this morning to 7 PM PDT this evening
SCA...Pigeon Pt to Pt Pinos 0-10 nm
SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm
SCA...Pt Arena to Pigeon Pt 10-60 nm until 9 AM
SCA...Pt Reyes to Pigeon Pt 0-10 nm
SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm
SCA...Pt Arena to Pt Reyes 0-10 nm until 3 PM
SCA...Mry Bay from 9 AM
PUBLIC FORECAST: Sims
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