National Weather Service Raw Text Product

Displaying AFOS PIL: AFDMTR Received: 2017-11-14 18:14 UTC


941 
FXUS66 KMTR 141814
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
1014 AM PST Tue Nov 14 2017

...Windy and rainy weather returns for Wednesday into Thursday...

.SYNOPSIS...Look for mostly dry conditions today before a storm 
system brings widespread rainfall and breezy to locally gusty 
winds during the day Wednesday to the North Bay and through the 
remainder of the region Wednesday night. After another period of 
dry conditions, a third system is possible late in the upcoming 
weekend.

&&

.DISCUSSION...as of 9:07 AM PST Tuesday...Areas of fog developed 
in the early morning hours across the North Bay, bringing 
visibilities down to a quarter-mile in some locations such as 
Santa Rosa, Petaluma, and Napa. Visible satellite imagery still 
shows this fog lingering in parts of Napa Valley as well as along 
parts of the Highway 101 corridor. Motorists are encouraged to 
slow down, keep headlights on, and allow for extra time to reach 
their destination.

The main concern over the next few days will be the incoming 
system that will bring moderate to locally heavy rainfall to parts
of the region. 12Z forecast guidance is trickling in right now, 
and a first glance shows similar solutions to the 00Z guidance. 
The heaviest rain still appears like it will occur over the Santa 
Cruz Mountains where 3 to 4+" inches of rain is forecast to fall. 
Additionally, there are concerns for the North Bay Mountains and 
Valley zones where the recent burn scars give the area increased 
potential for mudslides, debris flows, and flash flooding. We'll 
be evaluating the latest forecast guidance as it comes in through 
the morning and make any necessary adjustments to bulletins and 
products. Aside from a few adjustments with sky cover, no major 
changes are planned to the short-term forecast for today. For 
additional details with the upcoming system and beyond, please 
refer to the previous discussion section.

&&

.PREV DISCUSSION...as of 2:45 AM PST Tuesday...A cold front went 
through our region overnight and brought varying amounts of 
rainfall to the San Francisco and Monterey Bay Region. Most urban 
locations ended up with less than 2/10" while coastal ranges saw 
amounts from a few hundredths all of the way to around an inch. 
With the front continuing to dissipate and progress to the south, 
mostly dry weather is forecast today. Highs will mostly be in the 
60s along with clearing from north to south.

Main forecast concern centers around Wednesday into Thursday as a
moderate system will bring widespread rainfall to our area. 
Models indicate that a surface and upper level low will move to 
the BC coastline while an associated cold front will progress down
the coast of California. The front will have ample moisture to 
use (IVT values possibly over 750 kg/m/s) increasing the risk of 
higher rain rates and possible flooding. Rainfall will move back 
to the Sonoma coast early on Wednesday and slowly progress into 
San Francisco Bay then into Monterey Bay. Biggest concern will be 
if the front stalls leading to high rain amounts occuring over the
same location for several hours. The front should be to the south
by Thursday morning with post-frontal showers likely into the 
afternoon. 

Rainfall amounts will range from 3-5" for many coastal ranges to 
1-2" for many urban spots. Only the far southeastern part of our 
CWA will likely see lesser amounts. One good note, the main band 
of rain is forecast to go through after the evening rush on 
Wednesday. In fact, the bulk of the rain will likely occur after 
sunset.

Wind will be the other concern. As the front approaches southerly
winds will pick up with higher elevation areas likely to see gusts
over 40 mph at time. Favored spots in the North and East Bay hills
will likely see gusts over 50 mph. A wind advisory has been
issued.

Drier weather will return on Friday and hold at least into early
Sunday. After that another system will bring rain back to our
region. Amounts from that should be less than what we will see 
Wednesday into Thursday.

&&

.AVIATION...As of 10:15 AM PST Tuesday...For 18z Tafs. CIGS will 
improve through midday and into the early afternoon with 
widespread VFR. An initial shot of moisture will arrive over the 
North Bay late tonight, bringing lower ceilings (BKN TO OVC 
040-060) and vcsh/-shra to some TAF sites through tomorrow 
morning. Brief improvement in conditions late tomorrow morning 
through early afternoon before second main round of precipitation 
and lowering cigs/visbys arrives by Wednesday evening.

Vicinity of KSFO...VFR. Winds generally light today. For tonight,
VFR with BKN-OVC at 050-080 by sunrise Wednesday with a few
vicinity showers to the north. Increasing southerly winds through
the day tomorrow ahead of approaching front. Precipitation from
next frontal band arrives around 03Z THU. 

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...A few clouds around the Monterey Bay will
dissipate by late morning. Otherwise, VFR through the TAF period,
with increasing high clouds tomorrow morning. Next precipitation
arrives around 09Z THU.  

&&

.MARINE...as of 10:08 AM PST Tuesday...Light winds today will
gradually increase and turn southerly tonight and tomorrow ahead
of a frontal boundary arriving later Wednesday. Winds ease and
turn more westerly in the wake of the front. Moderate seas.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...NONE.

&&

$$

PUBLIC FORECAST: Rowe/Bell
AVIATION: DRP
MARINE: DRP

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