Scientific Forecaster Discussion
fxus66 kmtr 222205
Area forecast discussion
National Weather Service San Francisco Bay area
205 PM PST Mon Jan 22 2018
Synopsis...central coast lingering showers will quickly end this
evening. Otherwise look for partly cloudy skies tonight with
patchy fog developing in the valleys. Dry and seasonably cool
weather forecast Tuesday. Next front arrives weds morning or
midday in the North Bay and then spreads rain southward later weds
afternoon into weds night for the Bay area into the central
coast. Steady rain quickly turns to showers before sunrise
Thursday. A round of more organized showers is possible Thursday
afternoon as the upper low moves inland. Dry weather forecast
Friday through the weekend and into early next week.
Discussion...as of 2:05 PM PST Monday...kmux radar picking up
the last few showers across the central coast as the frontal band
that passed through the area last night and this morning
dissipates. Short term concern for tonight will be some fog
development with moist boundary layer and high pressure building
in which should strengthen valley inversions.
Outside of morning fog no real weather concerns for Tuesday with
dry and seasonably cool weather forecast as high pressure briefly
Run of the mill Pacific frontal passage on tap for weds. As has
been the trend of late, the models seem to be showing a less
robust frontal passage. Latest timing would bring steady frontal
rains into the North Bay later weds morning or around midday.
Front will then slide southward through the Bay area weds
afternoon and evening. Similar to todays front, the rain will
weaken and become more disorganized by the time it reaches the
central coast. The North Bay coastal hills will be the winners
once again with 1-2 inches of rain possible while amounts will
drop off sharply over the Bay area and central coast. Winds
associated with the front will be fairly light too, some gusts in
the 25-35 mph range as the front passes through.
Any steady rain will quickly turn to showers before sunrise
Thursday. Cold air aloft and an associated shortwave are forecast
to pass through on Thursday afternoon. This should produce an
organized area of rain and isolated thunderstorms, especially
focused from about the Santa Cruz mtns northward. Some brief heavy
rain and small hail will be possible as this feature passes
Dry weather returns Thursday night into Friday. Latest model
trends show above average confidence for dry conditions Friday
through the weekend and into early next week. Some of the GFS
solutions keep the storm track just to our north but ensembles
suggest another West Coast ridge could become entrenched so the
Wed-Thu rain may be the last significant rainfall for awhile.
Aviation...as of 10:20 am PST Monday...for 18z tafs. Satellite
imagery and radar shows rapidly weakening frontal cloud band,
with some lingering embedded showers, now moving into the
Monterey Bay region. Ceilings are lifting up out of the MVFR range
from the northwest behind it, followed by clearing skies.
However, ceilings are expected to lower back to MVFR once again
tonight, along with fog development in the North Bay valleys.
Vicinity of ksfo...ceilings have lifted out of the MVFR range
with VFR conditions now expected to prevail the remainder of the
day and through the evening rush. Winds will generally be out of
the west and less than 15 kt.
Sfo bridge approach...similar to ksfo.
Monterey Bay terminals...currently MVFR at ksns with VFR cigs at
kmry. Still a few light showers in the area but should end
entirely by early afternoon. Expect ceilings to be close to the
MVFR/VFR margin the rest of the day and into the evening, then
lower somewhat overnight.
Marine...as of 01:42 PM PST Monday...switch to northwesterly
winds is progressing down the coast behind the cold front, now
located near Pigeon Point. These winds will slowly diminish as
the day progresses. Small craft advisories remain in place mainly
due to hazardous sea conditions caused by large swells. These
swells will gradually decrease through Tuesday. The next frontal
system is set to arrive mid-week bringing back southerly winds
and increasing northwest swell.
... Arena to pt Reyes 0-10 nm
Small Craft Advisory...pt Reyes to Pigeon pt 0-10 nm
Small Craft Advisory...Pigeon pt to pt pinos 0-10 nm
Small Craft Advisory...pt pinos to pt Piedras Blancas 0-10 nm
Small Craft Advisory...pt 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
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