Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus66 kmtr 231801 

Area forecast discussion
National Weather Service San Francisco Bay area
1001 am PST Mon Jan 23 2017

Synopsis..scattered to numerous showers will continue to impact
the region through late this evening with a potential for embedded
thunderstorms. Brief heavy rainfall within stronger showers and/or
thunderstorms will pose a threat for flash flooding of area creeks
and urban areas. Showers will then taper off late tonight into
Tuesday morning. Mainly dry Tuesday afternoon through Wednesday.
Latest models now show a very weak front with light rain late
Wednesday night into early Thursday morning. Long range forecast
looks dry with a warming trend throughout the weekend while
overnight lows will be seasonably cool.

&& of 9:08 am PST Monday...shower activity
continues across the region with core of cold air aloft passing
over the region. Isolated thunder possible today with small hail
the main impact. Another well defined shortwave with a surface low
off the coast will pass through the region tonight into early
Tuesday morning. This will bring another renewed period of showers
and isolated thunderstorms. Will keep the Flash Flood Watch in
place as is through 6 PM this evening due to the fact that brief
heavy rain is still causing issues for mudslides, roads and on
small creeks seeing rapid rises. Showers could linger Tuesday
morning but mainly over the ocean waters. A drying trend Tuesday
afternoon through weds but seasonably cool with highs in the mid

The 12z NAM is showing another weak boundary late weds night into
early Thursday morning. A weak front may move through and drop
another 0.10 of rain. Will be adjusting grids and forecasts to
account for this shortly. After 18z Thursday there is good model
consistency that a strong ridge will build. Daytime highs this
weekend should warm into the 60s but overnight lows could be
chilly with some upper 20s Saturday morning. Will also have to be
on the lookout that easterly flow brings Tule fog in from the
Central Valley but we've got a few days to fine tune those
details. The immediate coast should see temps well into the 60s
with full sunshine this weekend as 583 dm ridge builds over the


Previous of 03:13 am PST Monday...the entire region
remains in an unstable, Post-frontal environment with showers
moving inland into the San Francisco Bay area and central coast
early this morning. This activity will continue through much of
the day as the main mid/upper level low off of the Pacific
northwest coast slides southward down the California coast. Cannot
rule out a few thunderstorms through the day as well as the air
mass aloft continues to cool and remains unstable. While
widespread heavy rainfall is not anticipated, any stronger showers
or thunderstorms that produce brief, heavy downpours will pose a
threat for flash flooding of area streams as well as urban areas.
Thus, a Flash Flood Watch remains in effect through late
afternoon/evening given the supersaturated soils and elevated
levels of local creeks, rivers and reservoirs.

By late tonight, the upper level low will weaken off our coast
with the trough axis beginning to shift inland. This will allow
for showers to diminish in coverage from north to south through
early Tuesday morning. With lingering moisture in place and the
proximity of the trough, showers will remain possible over the
souther portion of the central coast into Tuesday morning. Tuesday
afternoon will give way to mostly dry conditions region-wide with
breaks in cloud cover also likely as an upper level ridge builds
across the eastern Pacific. By late Wednesday into Thursday
morning, the models show a weak upper level disturbance dropping
into northern California. This system appears to remain weak and
have limited moisture to work with as it pushes inland. However,
cannot rule out light rain over the coastal waters and into the
North Bay from Wednesday night into Thursday morning. Otherwise,
most areas will remain dry as this system pushes inland to our

The models are in good agreement late in the forecast period with
dry weather conditions likely region-wide Thursday through at
least the upcoming weekend. With the ridge over the eastern
Pacific building inland across the state, temperatures will likely
warm to above seasonal averages with low to mid 60s possible
during the afternoon hours Saturday and Sunday. Given clearing
skies Tuesday into Wednesday, cool/chilly overnight temperatures
are expected before moderating a bit late in the week as the ridge
builds aloft.

&& of 10:02 am PST Monday...showers expected today
along with a possible thunderstorm or two as a system moves down
from the northwest. Very difficult to time things so went with general
vcsh mvrf/VFR combinations in almost all cases. Conditions improve
after 14z tomorrow. Low to moderate confidence.

Vicinity of ksfo....VFR generally although dropping to MVFR at
times with stronger cells. Therefore, timing is general with many
updates likely through the day. Concern then switches to possible
easterly winds tomorrow morning which could impact operations. Low
to moderate confidence.

Sfo bridge approach...similar to sfo.

Monterey Bay terminals...VFR generally with mvrf possible due to
any showers. Moderate confidence.

&& of 09:46 am PST Monday...a low pressure system will
move through our region later today with scattered showers and
possible thunderstorms. The low will then reach Southern
California later Tuesday. Large westerly swell will persist
through Tuesday morning.


Mtr watches/warnings/advisories...
... Flood Watch...caz006-505>513-516>518-528>530
high surf advisory...caz006-505-509-529-530
Small Craft Advisory...mry Bay
Small Craft Arena to pt Reyes 0-10 nm
Small Craft Reyes to Pigeon pt 0-10 nm
Small Craft Advisory...Pigeon pt to pt pinos 0-10 nm
Small Craft pinos to pt Piedras Blancas 0-10 nm
Small Craft Arena to Pigeon pt 10-60 nm
Small Craft Advisory...Pigeon pt to pt Piedras Blancas 10-60 nm
Small Craft Advisory...rough bar advisory for sf bar



Public forecast: rww
aviation: Bell
marine: Bell

National Weather Service Glossary of Abbreviations