Hail in California, April 12, 2018

Area Forecast Discussion
National Weather Service San Francisco Bay Area
1034 AM PDT Thu Apr 12 2018

.SYNOPSIS...A few residual showers will linger into the morning
hours. A slight chance of showers will remain in the North Bay
through this afternoon. Dry conditions are expected Thursday night
through Saturday with warmer temperatures. Precipitation chances
and cooler temperatures return Sunday and Monday.

&&

.DISCUSSION...as of 09:15 AM PDT Thursday... The cold front that
brought an intense, narrow band of rain (often referred to as a
narrow cold frontal rain band aka NCFR), wind gusts locally up to
61mph (at Atlas Peak), and locally up to around 4/5" of an inch
of rain (but more generally around 1/4") has now passed. Rain
rates were intense through this band (over .01"/minute), but very
brief (generally around 5 minutes in total duration).

Remote sensing data shows a few weak, isolated showers lingering
along the Sonoma and Marin coastlines, plus farther offshore of the
San Mateo coast in the wake of the cold front. These showers will
weaken as the day progresses, however, a single shower or two could
possibly push onshore and persist into early afternoon, however,
only a very small fraction of the area/population would be impacted.
Today will see temperatures generally 7 to 13 degrees below normal
in the wake of yesterdays cold front. Overnight lows will generally
range in the upper 30s to low 40s for most areas, which is about 2
to 6 degrees below normal for our nightly lows. Tonight will be the
coldest night through at least this upcoming weekend.

High pressure will bring a gradual warming and drying trend to the
region through Saturday afternoon. Temperatures will peak Saturday
afternoon, with highs in the upper 60s through upper 70s
regionwide, or about 2 to 6 degrees above normal per location.
This short term warming/drying trend will end on Sunday as a low
pressure system descends from the Gulf of Alaska to bring cooler
temperatures, breezy winds, and a chance of rain. The main focus
of todays forecast package will be to fine tune tonights low and
the probability of precipitation for the system on Sunday. No
major updates planned for this morning, see previous discussion
for more information on the current (overnight) forecast package.

.PREVIOUS DISCUSSION...As of 3:00 AM PDT Thursday...Radar
indicates a few showers embedded in the moist northwest flow.
Showers will diminish later this morning over the SFO and MRY Bay
Areas but a surface trough moving into the Pacific Northwest will
keep a slight chance of showers in the North Bay through this
afternoon. All areas should be dry tonight through Saturday as
upper level ridging moves over the area and weak offshore flow
develops at the surface. Thursday night will be unseasonably cool
with lows into the upper 30s in the coldest inland valleys. But it
will warm up quickly Friday and Saturday and by Saturday inland
temperatures are expected to be in the 70s.

The ridge pushes east on Sunday as an upper level trough
approaches the Pacific Northwest coast. Models indicate a frontal
system will bring rain to the North Bay Sunday afternoon
spreading to the MRY Bay Area Sunday night. The upper trough is
forecast to deepen as it moves onshore which should provide good
support for showers on Monday. Snow levels should drop down
enough that there could be a couple of inches of snow in the
highest peaks. It is too early to determine the convective
potential for Monday but there is certainly a possibility.

Long range models one more chance of rain for the district midweek
before the storm track shifts north.

&&

.AVIATION...As of 10:34 AM PDT Thursday...For 18z tafs. VFR
conditions at all terminals this morning. A few showers are
possible across the North Bay (KSTS), but impact would be brief.
Otherwise, impacts would be occasional passing clouds 2500-4000
ft,which may drop visuals or MVFR cat. Winds will be gusty at
times as well.

Vicinity of KSFO...VFR conditions. Passing clouds could briefly
impact the airport. Gusty westerly winds this afternoon up to 25
kt.

SFO Bridge Approach...Similar to KSFO. Wrong place wrong time type
of cloud day.  May impact visuals.

Monterey Bay Terminals...VFR through the period. Gusty onshore
winds this afternoon 20-25 kt.

&&

.MARINE...as of 10:28 AM PDT Thursday...Moderate to locally strong
winds will prevail across the coastal  waters through tonight.
Steep fresh northwest swell will build  today across the coastal
waters creating hazardous seas. Increased shoaling is possible
near bars, reefs and harbor entrances.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Reyes to Pigeon Pt 0-10 nm
             SCA...Pigeon Pt to Pt Pinos 0-10 nm
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Rough Bar Advisory for SF Bar
             SCA...Mry Bay
             SCA...SF Bay from 3 PM

&&

PUBLIC FORECAST: DRP
AVIATION: MM
MARINE: MM

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