Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

000 
FXUS66 KMTR 290908
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
208 AM PDT Thu Jun 29 2017

.SYNOPSIS...Seasonable summer pattern in place with a marine layer
along the coast leading to areas of night and morning low clouds
followed by sunny afternoons away from the coast. These conditions
are expected to continue through the 4th of July Holiday.

&&

.DISCUSSION...as of 2:08 AM PDT Thursday...Satellite imagery 
shows low clouds have spread into the Salinas valley as well as 
across the San Francisco Bay to the East Bay Hills, with less 
coverage over the North Bay except for Marin County. The marine 
layer depth has compressed somewhat and is now around 1100 feet 
per the Fort Ord profiler, but low clouds and fog are still 
expected to form even in the North Bay valleys by sunrise. Onshore
flow is still strong, with 3.3 mb between SFO and SAC last hour. 

An upper level trough remains over the Great Basin with high
pressure aloft over the Eastern Pacific. This ridge is forecast to
build in over California over the next couple of days resulting in
a slight warming trend, especially across inland areas where high
temperatures will once again approach 100 degrees in the warmest
locations. There will be a steep temperature gradient to the coast
where 60s to lower 70s will be the rule through the forecast
period, with continued marine influence. 

An upper level trough is progged to approach the coast by the end
of the week which will deepen the marine layer and increase
onshore flow. Thus, cooler temperatures will filter inland as
well. 

By early next week, the upper level high will center over the
desert southwest. Differences in model output regarding the
position of this ridge mean either high temperatures warm once 
again across our southern inland areas, or if the ridge remains 
farther east, continued seasonable weather. The latest ECMWF still
keeps the ridge farther east with a deepening trough off the 
coast. The current forecast trend is more in line with this 
solution. 

&&

.AVIATION...As of 10:47 PM PDT Wednesday...For 06z TAFs. A
moderate northerly gradient continues across the region and has
kept the north coast mostly clear of low clouds. The marine layer
is currently around 1800 ft and will only see minimal
fluctuations. Low clouds will fill in across area terminals as the
night progresses. Moderate onshore flow around 10 to 15 kt with 
locally higher gusts will gradually ease overnight. 

Moderate confidence. 

Vicinity of KSFO...MVFR cigs will lower to IFR around 800 feet 
after 09z tonight. Low clouds will scatter out around 17z-18z 
Thursday morning. Moderate west winds around 10 to 15 kt with 
gusts to around 20 kt will gradually diminish overnight.

SFO Bridge Approach...Similar to KSFO. 

Monterey Bay Terminals...IFR cigs will lower to LIFR overnight. 
Low clouds will scatter out around 18z-21z Thursday morning. 
Light west winds around 5 to 10 kt will prevail through the night.

&&

.MARINE...as of 8:59 AM PDT Thursday...Building high pressure off
the California coast will maintain strong and gusty northerly 
winds through the remainder of the week and into the upcoming 
weekend. Steep wind waves and fresh swell will dominate the 
coastal waters as a result of the strong winds. Persons operating 
small crafts should use extra caution along the Central California
Coast and Bays through at least the forthcoming weekend.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...SCA...Pigeon Pt to Pt Pinos 0-10 nm
             SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm
             SCA...Pt Reyes to Pigeon Pt 0-10 nm until 3 AM
             SCA...Mry Bay from 3 PM

&&

$$

PUBLIC FORECAST: Sims
AVIATION: CW
MARINE: CW


Visit us at www.weather.gov/sanfrancisco

National Weather Service Glossary of Abbreviations