Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus66 kmtr 151133 
afdmtr

Area forecast discussion
National Weather Service San Francisco Bay area
433 am PDT sun Sep 15 2019

Synopsis...the cooling trend that began in coastal areas on
Saturday will spread inland today and Monday as a weather system
moves in from the northwest. There is also a chance of rain on
Monday, mainly across the northern half of the area. A second
weather system may bring renewed rain chances around the middle of
next week, and also keep temperatures on the cool side of normal
through much of the week.

&&

Discussion...as of 3:30 am PDT Sunday...temperatures have cooled
back to normal across area airports, with current readings in the
50s to lower 60s. The marine layer has Bee steadily ramping up
over the past 24 hours, and now is over 1000 feet. More notable is
the tightening of the onshore surface pressure gradient over the
past 24 hours, with 3.0 mb from sfo to SAC, as compared to 0.8 mb
yesterday at this time. These factors are in response to an
approaching upper trough, and as a result, inland areas today
will enjoy much cooler temperatures as was already observed near
the coast yesterday. Highs today are forecast to range from the
mid 60s to lower 70s at the coast, to the 70s and 80s inland.
Warmest inland locations should only reach the lower 90s.

Meanwhile, the approaching upper level trough is robust enough to
bring rainfall to northern California on Monday, possibly as far
south as the Monterey Bay. There are still differences in model
solutions regarding rainfall amounts as well as how far south it
will occur. Models have been trending drier each day as the event
approaches, however, the 06z NAM is now more bullish, with San
Francisco getting over a quarter of an inch by mid day Monday. The
00z GFS and European model (ecmwf) both have around a tenth of an inch for that
timeframe.

Medium range models indicate another trough bringing rain chances
to the northern portion of the area on Wednesday. Have added
chance or slight chances of rain to mainly the North Bay for this
time frame. This trough will keep temps cool. In the longer
range, models indicate rising heights for slightly warmer temps
again by next weekend.

&&

Aviation...as of 04:33 am PDT Sunday...for 12z tafs. The marine
layer has deepened to around 1200-1500 ft above ground level per The Fort Ord
profiler. Satellite imagery shows stratus along the coast and over
the bays with high clouds streaming overhead. MVFR/IFR conditions
for coastal sites through this morning (~16z-18z) with VFR
elsewhere. Expect additional cloud layers to develop later today
and into tomorrow as a cold front approaches. Winds currently vary
between SW to northwest across the region at around 10 kt. Winds to turn
more onshore this afternoon 10-15 kt with locally higher gusts at
ksfo. Chances of showers will increase late tonight from north to
south.

Vicinity of ksfo...IFR cigs continue but may lift to MVFR later
this morning before clearing. Clearing expected between 17z-19z,
although confidence is low. VFR conditions this afternoon and
evening before cloud layers arrive tonight with showers
approaching early tomorrow morning. SW to west winds 10-15 kt with
gusts 20-25 kt in the afternoon.

Sfo bridge approach...similar to ksfo.

Monterey Bay terminals...IFR cigs through late this morning.
Currently a patch of clearing over kmry, but satellite still shows
stratus surrounding the Airport over the peninsula. Do expect IFR
cigs to fill back in at some point this morning. VFR this
afternoon with low clouds returning early this evening.

&&

Marine...as of 2:51 am PDT Sunday...light to moderate northwest
winds will persist over the coastal waters today. Expect locally
breezy afternoon and evening winds along the inner coastal waters
south of Pigeon Point and over the bays. Winds will ease early
this week as high pressure over the eastern Pacific weakens. A
cold front will move through the waters on Monday bringing a
chance of showers. Mixed seas will continue with moderate period
northwest swell and a slightly longer period southerly swell.

&&

Mtr watches/warnings/advisories...
... Arena to pt Reyes 0-10 nm until 3 PM
Small Craft Advisory...Pigeon pt to pt pinos 0-10 nm from 11 am
Small Craft Advisory...sf Bay from 2 PM
Small Craft Advisory...mry Bay from 2 PM
Small Craft Advisory...pt pinos to pt Piedras Blancas 0-10 nm

&&

$$

Public forecast: Sims
aviation: as
marine: as

Visit US at www.Weather.Gov/sanfrancisco

National Weather Service Glossary of Abbreviations