Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA
FXUS66 KMTR 200030
Area Forecast Discussion
National Weather Service San Francisco Bay Area
430 PM PST Thu Jan 19 2017
.SYNOPSIS...Scattered showers can be expected today before the next
front arrives tonight into Friday with another round of wind and
rain. Lingering showers Saturday before the final front brings
more wind and rain Sunday before tapering to showers Sunday night
into Monday and possibly Tuesday.
.DISCUSSION...as of 02:55 PM PST Thursday...KMUX radar imagery
continues to show a few lingering showers, some of them heavy,
moving W to E across the Bay Area. Given the low snow levels of 4k
feet any stronger cells may have small hail associated with it.
Expect the convective showers to taper off after 00Z.
Storm number two in a series of three storms will impact the Bay
Area starting tonight. The next storm system is forecast to spread
rain over the North Bay 03-06Z tonight then increase in coverage
and intensity with the cold front and large scale ascent by 12z
Friday. The combination of PWATs approaching one inch, 150+kt jet
aloft, sfc cold front and orographic lift will likely lead to a
period of moderate to heavy rain overnight into early Friday
morning. The heavier rain will gradually diminish from N to S
through the day and become more showery in nature. Thunderstorms
will be possible as well with increasingly unstable airmass.
Rainfall amounts have not changed that much from previous
forecast. Generally speaking, 1.5-3" for the North Bay and coastal
mountains. Lower elevations and urban areas 0.5-1" possible. Given
all the recent rains local rivers and streams will be quick to
respond, especially if thunderstorms develop.
As mentioned above snow levels remain around 4k feet. Latest
guidance suggest very little change into the weekend with the snow
levels. That being said, accumulating snow will be possible over
the higher peaks of Monterey/San Benito through Sunday morning.
When it is all said and done several inches are possible over Cone
Pk, Junipero Serra Pk, Chew`s Ridge.
In addition to the rain, southerly winds will increase ahead and
with the frontal passage. Southerly winds of 20 to 30 mph with
gusts 40 to 50 mph will be possible. A wind advisory has been
issued for the coast and the hills tonight through Friday morning.
Showery regime holds for Friday night and into Saturday. Conf is
not that great, but there could be a discernible break in the
action Saturday afternoon before storm three rolls in. The third
system is still on track for Saturday night into Sunday. The third
system appears to have the most moisture associated with
it...PWATs greater than 1". That being said, it will likely have
the most rainfall as well. Rainfall amounts Saturday night into
Sunday will be a little higher than tonight`s storm system. Most
notably over the higher terrain of Santa Cruz and Monterey. Given
the accumulative impact of rain, hydro concerns will be greatest
with the third system. Winds will also be stronger with the third
storm. If the forecast holds true a high wind warning may be
needed Saturday night into Sunday. Gust to 60 mph possible.
showers early next week with drying there afternoon.
.AVIATION...As of 3:55 PM PST Thursday...Scattered showers and
isolated thunderstorms with possible lightning and gusty south
winds will continue to impact the region through this evening.
Decreased vsbys possible with moderate to heavy showers. The next
system is anticipated to move in late tonight bringing with it
widespread rain and strong and gusty southerly winds. Wind gusts
are expected to reach 30 to 40 kt overnight. As this system moves
across the region cigs will lower to MVFR around 1500 ft after
06z tonight. The main frontal band is forecast to move through after
12z. Moderate to brief heavy rain showers expected Friday during
the morning rush. IFR cigs/vsbys possible with heaviest showers.
Isolated thunderstorms with small hail possible with this next
system as well. However confidence is low therefore it is not
included in the TAF.
Vicinity of KSFO....Isolated showers will persist through the
evening with mainly MVFR cigs expected. An isolated thunderstorm
cannot be ruled out. South to southwest winds around 10 kt
expected through this evening. Winds will increase late tonight
(around 06z)becoming southeasterly ahead of a cold front.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Isolated showers will persist through the
evening with mainly MVFR/VFR cigs expected. An isolated
thunderstorm cannot be ruled out. South to southwest winds around
10 kt expected through this evening. Winds will increase late
tonight (around 07z-08z)becoming southeasterly ahead of a cold
.MARINE...as of 2:12 PM PST Thursday...Rough and hazardous seas
are forecast to continue through tonight. winds will increase and
turn southerly by late tonight. gale force wind gusts up to 45 kt
are possible ahead of a cold front that will pass through the
waters early tomorrow morning. winds will shift westerly but
remain moderate to gusty...even behind the front. winds will
increase again saturday night as another frontal system
approaches. very large swells arrive friday afternoon with swell
heights building to 25 to 30 feet friday night and saturday. rouge
waves of 30 feet or greater are possible during this timeframe.
SCA...Pigeon Pt to Pt Pinos 0-10 nm
SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm
SCA...Pt Arena to Pt Reyes 0-10 nm
SCA...Pt Reyes to Pigeon Pt 0-10 nm
SCA...Pt Arena to Pigeon Pt 10-60 nm
SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm
SCA...Rough Bar Advisory for SF Bar
SCA...SF Bay from 12 AM
PUBLIC FORECAST: MM
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