Scientific Forecaster Discussion
fxus66 kmtr 231757
Area forecast discussion
National Weather Service San Francisco Bay area
957 am PST Thu Nov 23 2017
Synopsis...chance of rain over the North Bay today while the
rest of the district should remain dry with continued warmer than
normal temperatures. Dry weather is expected to return to all
areas on Friday and continue through most of Saturday. Rain will
return to our region late Saturday through Sunday.
Discussion...as of 9:00 am PST Thursday...area radars continue to
show weak echoes moving into the northern portion of Sonoma
County. A few hundredths have been picked up by automated rain
gauges in the North Bay over the past 6 hours. Latest computer
models don't indicate much precip with the weak impulse moving
across northern California now. Otherwise, the rest of the
district will see another mild day with high temperatures slightly
above normal with highs ranging from the lower 80s in parts of
Monterey County to the upper 60s around the San Francisco Bay
High pressure will rebuild over the state on Friday for dry and
continued mild conditions through most of the weekend. Rain
chances will return to the district as a cold front impacts the
area. Rainfall is expected to begin in the North Bay Saturday
evening. The cold front will move to the south and east spreading
rainfall across our entire area through Sunday. Rain will briefly
switch to showers behind the front with dry weather returning
again early next week. Rainfall amounts are forecast to range from
generally 1/4" to 1/2" for most urban locations, with coastal
ranges seeing 1/3" to 2/3", and possibly some areas getting up to
an inch. In addition to the rain, southerly winds will increase
with gusts over 20 mph possible with the frontal passage.
Next week is expected to be dry and mild as another ridge of high
pressure builds over the west.
Aviation...as of 9:56 am PST Thursday...for 18z tafs. Mid and
high clouds from an upper level trough continue to stream over the
San Francisco Bay area. Rain and showers associated with this
system will stay confined to the North Bay. Isolated showers are
still possible at ksts through at least early afternoon, despite
hi-res forecast models keeping things relatively dry. Light and
variable winds this morning will turn onshore this afternoon,
between 5-10 knots. Biggest question mark of the tafs will be
timing and coverage of low cigs this evening/overnight across the
district. Latest mtrwrf model is a little more aggressive than
previous run about bringing in low clouds tonight, especially
across the sf Bay area. Needless to say, not very confident with
Low-moderate forecast confidence.
Vicinity of ksfo...VFR through this evening. Northwest/west-northwest winds this
afternoon, around 10 kt. Current thinking is MVFR cigs roll in by
Sfo bridge approach...similar to ksfo.
Monterey Bay terminals...VFR this afternoon, with IFR cigs
possible around midnight; low confidence on ceiling timing. Light to
moderate northwest winds this afternoon, 5-10 kt.
Marine...as of 8:27 am PST Thursday...coastal troughing in
Southern California will increase northernly winds over the
southern coastal waters late this morning through this evening.
Otherwise, weak high pressure off the California coast will keep
light to moderate northerly winds through Friday. Southerly winds
will increase Saturday as a low pressure system moves into the
Pacific northwest waters. Rain will spread over the area Saturday
night and Sunday.
... Pinos to pt Piedras Blancas 0-10 nm from 10 am
Public forecast: Sims
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