National Weather Service Raw Text Product

400 
FXUS66 KMTR 130457
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
857 PM PST Sun Feb 12 2017

.SYNOPSIS...Dry weather conditions along with seasonable
temperatures will persist across the region through the first half
of the upcoming workweek as high pressure dominates the weather
pattern. Unsettled conditions then return by late Wednesday into
Thursday with periods of rain and wind likely to continue through
next weekend.

&&

.DISCUSSION...as of 8:57 PM PST Sunday...No updates needed
tonight with just some high clouds spreading over the North Bay.
After a chilly start Monday morning expect another mostly sunny
and seasonably mild Feb day with high pressure over the region.
Main theme for Monday through Weds will be dry weather to allow
storm clean up and preparations for the next round of storms to
impact the region and state starting Weds night and likely
continuing on and off through at least next Weds.

By Weds afternoon clouds should thicken and southerly winds will
start to be on the increase. Rain looks to start in the North Bay
around 06z Thursday (10 pm Weds night). The trend on the models has
been faster as there is a 180 kt East-Asian jet developing over
the central Pacific. The main frontal rains are timed to move
through the Bay Area for the Thursday morning commute. For now
would characterize this first system as weak to moderate in
strength as it'll be the first system to knock into the ridge.
Impacts early on will probably be minor as it'll likely be the
impact of multiple storms over days that will once again stress
the rivers, creek and hillsides of the Bay Area.

The initial system should race through pretty quickly on Thursday.
Next storm will be quick on the heels with the last few gfs runs
keeping the best jet stream energy and dynamics focused on
southern California while the Bay Area would see rain, but lighter
rainfall amounts overall. Will be interesting to see the trends on
tonights ECMWF run.

The 00z gfs run shows what appears to be five frontal passages
from Weds night through next Weds. The first passes through
Thursday morning, another on Friday (but focused on SoCal). Third
system on Sunday, the fourth on Presidents Day and then a final
cold core trough by about next Tues and Weds. Gfs storms totals
currently show on average 2 inches for the valleys with 4-6 inches
in the hills. The first system looks to be tied to an AR on the
leading edge but the systems look to have strong jet dynamics
(more wind) be faster moving and with more well defined surface
cold front versus some of the warm frontal episodes we've seen so
far this winter. So it looks like rain but perhaps of a different
variety but on top of very wet soils and fast responding rivers
and streams. Will assess the Euro for the overnight package.

&&

.PREV DISCUSSION...as of 01:45 PM PST Sunday...Aside from a few high
clouds advancing inland across the region this afternoon, mostly
sunny skies prevail region-wide. With this, and thanks to building
high pressure along the West Coast, temperatures have warmed into
the upper 50s to lower 60s so far this afternoon for most
locations. Expecting these conditions to persist into the start of
next week with overnight lows dropping into the upper 30s to mid
40s on Monday morning.

The ridge will remain the dominate weather feature across the region
through the start of the workweek and allow for a slight warming
trend to persist. Meanwhile, do expect an increase in high level
clouds as a more moist westerly flow develops. This too should bring
overnight temperatures up a bit by Tuesday morning when widespread
40s will be most common. With that said, do expect dry weather
conditions to persist as precipitation remains well north and west
of the region. 

By Wednesday, the latest forecast models continue to show rain
returning to the North Bay as early as the morning hours as moisture
advection increases ahead of an approaching frontal boundary. These
chances for rain will then spread inland and southward Wednesday
night into Thursday morning as the cold front advances across the
region. Rainfall along the frontal band will likely be moderate to
briefly heavy at times as the system moves from north to south
across the region Wednesday night into Thursday. Southerly winds
will also increase and become breezy to gusty at times ahead of and
along the cold front. The GFS and ECMWF continue to be progressive
with this system and show only lingering showers in wake of the
frontal passage Thursday afternoon/evening. 

While the forecast models are in good agreement with an unsettled
pattern likely to persist from late in week into the weekend, they
differ on the specifics. The last GFS and ECMWF models now both show
a mid/upper level low pushing inland somewhere along the central or
southerly California coast on Friday. I more direct track would
likely spread additional precipitation across much of the region
while a track further south may result in mostly dry weather
conditions or our region. Additional storm systems are forecast to
impact the central California coast through this upcoming weekend
and potentially into the early part of the following week. With low
forecast confidence beyond the Wednesday/Thursday system, folks are
urged to keep up to date with the latest forecast information
through the upcoming workweek. Regardless of exact timing and
rainfall amounts, unsettled conditions appear likely and will have
the potential to exacerbate flooding concerns across the region. 

&&

.AVIATION...As of 7:50 PM PST Sunday...VFR persists this evening except
beginning to see patchy low clouds developing on the immediate coast.
Boundary layer humidity fairly moist supports possible additional 
developing low clouds and/or fog tonight. Ended up fairly clear most
spots last night. Winds generally light to moderate.

Vicinity of KSFO...VFR. Westerly winds gradually subsiding this evening,
becoming light/variable wind late.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR with light winds.

&&

.MARINE...as of 6:29 PM PST Sunday...High pressure over the
eastern Pacific will maintain light to moderate northerly winds
along the central coast through Tuesday. A longer period swell is
forecast to arrive later tonight. Southerly winds will develop
Tuesday night into Wednesday as a frontal system slowly approaches
the coast.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...None.

$$

PUBLIC FORECAST: RWW
AVIATION: Canepa
MARINE: MM


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