Beach Hazards Statement 10, NWS San Francisco Bay Area, CA

708 
WHUS46 KMTR 281658
CFWMTR

COASTAL HAZARD MESSAGE
National Weather Service SAN FRANCISCO CA
858 AM PST Sat Dec 28 2019

CAZ006-505-509-529-530-281800-
/O.EXP.KMTR.BH.S.0010.000000T0000Z-191228T1700Z/
San Francisco-
Coastal North Bay Including Point Reyes National Seashore-
San Francisco Peninsula Coast-Northern Monterey Bay-
Southern Monterey Bay and Big Sur Coast-
858 AM PST Sat Dec 28 2019

...BEACH HAZARDS STATEMENT WILL EXPIRE AT 9 AM PST THIS MORNING...

The long period northwest swell which prompted the Beach Hazards
Statement has decreased, and the threat of sneaker waves and rip
currents has also decreased. However, waves at the beach will 
continue to be larger than normal and beachgoers should exercise 
caution near the water. Never turn your back to the ocean!

$$

Area Forecast Discussion
National Weather Service San Francisco Bay Area
1001 PM PST Fri Dec 27 2019

.SYNOPSIS...Cool and dry conditions will continue across the
region through Saturday night. Frost is likely late tonight and
early Friday in most areas away from the immediate coast. By
Saturday night, frost is expected to be confined to only the
colder inland valleys. Rain returns Sunday and Sunday night, as a
weather system drops south along the coast. There is also a slight
chance of thunderstorms, mainly near the coast. Dry weather will
likely return by Monday, and then persist through at least
Thursday of next week.

&&

.DISCUSSION...As of 9:20 PM PST Friday...Skies remain mostly
clear across our region this evening, except for a few patches of
low clouds along the San Mateo County Coast. Evening temperatures
at most locations are similar to what they were at this time last
evening, except as much as 13 degrees cooler at the Napa Airport
where the 9 pm temperature was already a chilly 36 degrees.
However, surface dewpoints are slightly higher in the North Bay
Valleys compared to last evening which may help hold temps up a
bit overnight. The most likely outcome is that overnight lows
tonight will be similar to last night. Frost is expected for a few
hours around sunrise Saturday in most locations away from the
coast. The coldest locations will likely be the North Bay Valleys
and the valleys of southern Monterey County where morning lows are
forecast to be as cold as the upper 20s. The low levels remain
dry enough to keep fog from being a significant weather impact
late tonight and Saturday morning, although patchy fog could
develop.

Weather conditions on Saturday are expected to be much like today.
After a chilly start, look for afternoon highs to be mostly in the
mid and upper 50s, and a few degrees cooler than today due to
increased high cloud cover. Increasing cloud cover on Saturday
night, as well as increasing boundary layer relative humidity as
low level onshore flow develops, will result in moderating
nighttime temperatures. Only the cooler inland valleys are
expected to see frost late Saturday night and early Sunday. But
there will be a greater potential for fog tomorrow night and
Sunday morning.

Evening satellite currently shows a cold weather system centered
south of the Aleutian Islands. The models have come into better
agreement on the track of this system, as well as precipitation
timing and amounts, as it impacts our area later in the weekend.
An upper low is forecast to approach the coast of the Pacific
Northwest by early Sunday morning, and then dive south just off
the California coast from late Sunday morning through Sunday
night. The models have sped up the timing of precipitation onset,
and it now looks as though rain will begin to spread into the
North Bay by mid morning Sunday and develop as far south as the
Santa Clara Valley and Monterey Bay by mid afternoon. Showers will
continue through much of Sunday night and taper off from north to
south late Sunday night and early Monday.

Because the track of this system has more over water trajectory
than previous model runs, model QPF has trended upward. The NAM,
GFS, and ECMWF all generally forecast about a half inch of rain
across our area, with local amounts as high as an inch and as low
as a tenth of an inch. Rain rates may be briefly heavy,
especially if convection develops, with seems likely as the cold
and unstable airmass associated with the upper low tracks close
to the coast. Slight thunderstorm chances are currently in our
forecast for most of our area on Sunday afternoon and evening, but
thunderstorm chances appear highest over the coastal waters and
near the coast.

The coldest air with this system is expected to remain offshore
until after most precipitation ends. Even so, we could see light
snow accumulation above 4000 feet by late Sunday night.

Winds are not expected to be a factor with this system, although
brisk northwest winds are forecast to develop near the coast in
the wake of the the upper low late on Sunday afternoon and into
Sunday evening.

Aside from a few lingering showers in the far southern part of
our area on Monday morning, Monday should be a dry day as the
upper low quickly drops to our south. Dry weather is then
expected to continue through much of the rest of next week as an
upper ridge over the Eastern Pacific noses inland over California.
The GFS is dry throughout next week, but the 12Z ECMWF weakens
the ridge over California by Thursday and brings rain into our
area by Thursday night and Friday.

&&

.AVIATION...As of 9:50 PM PST Friday...Dry airmass will keep VFR
conditions through Saturday with the exception of patchy fog
around STS after 12Z. Light onshore winds.

Vicinity of KSFO...VFR.

SFO Bridge Approach...Same as KSFO.

Monterey Bay Terminals...VFR conditions expected. NAM model has
backed off bringing low cigs into MRY early Saturday morning.

&&

&&

.MARINE...as of 09:36 PM PST Friday...A 1026 mb high off the
California coast will weaken on Saturday as a low pressure system
moves into the Pacific Northwest waters. On Sunday the low will
move south along the west coast bringing a chance of rain and a
slight chance of thunderstorms to the coatsal waters. Northwest
winds will increase Sunday night and Monday after the system
passes. A long period northwest swell will continue through
Saturday.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm
             SCA...Pt Arena to Pt Reyes 0-10 nm until 2 AM
             SCA...Pt Reyes to Pigeon Pt 0-10 nm until 2 AM
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm until 2 AM

&&

PUBLIC FORECAST: Dykema
AVIATION: W Pi
MARINE: W Pi

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