Scientific Forecaster Discussion
fxus66 kmtr 271130
Area forecast discussion
National Weather Service San Francisco Bay area
330 am PST Mon Feb 27 2017
Synopsis...a weather system will continue to produce widely
scattered showers today, mainly across areas south of San Jose. A
few showers will linger into this evening. Isolated snow showers
are likely in the hills above 3000 feet today. Dry weather will
return by Tuesday. Dry conditions will then persist through the
end of the work week, along with a warming trend. A system moving
into the Pacific northwest this upcoming weekend may produce rain
in the North Bay, but elsewhere dry and mild weather will persist.
Discussion...as of 3:05 am PST Monday...a cold upper trough is
currently digging south across eastern California and into the
Great Basin. This weather system is producing widely scattered
showers in our area, with most shower activity currently confined
to areas south of the Golden Gate. Some of the heavier showers
have produced brief periods of small hail. Model consensus
indicates that shower activity will continue to gradually shift to
the south as the day progresses, with most precipitation likely
confined to areas south of San Jose after sunrise and then
shifting south of Monterey Bay by afternoon. Rainfall accumulation
today will be on the order of a quarter inch or less. Snow levels
will be as low as 2500 feet and a dusting of snow is possible on
the higher peaks of the Santa Cruz Mountains and across the Diablo
Range. Up to an inch or two of snow may accumulate at the higher
elevations of the Santa Lucia mountains in Monterey County by this
Showers are expected to end by late this evening and dry weather
is forecast to return to all areas by Tuesday. This system is
bringing a cold airmass into northern and central California,
with 850 mb temperatures expected to drop as low as -3 deg c. This
will result in 2 to 3 cold nights across our region starting
tonight. Tonight's lows will mostly be in the 30s and lower 40s
and the colder inland valleys will probably see temperatures drop
to around freezing for a few hours around sunrise Tuesday morning.
Similar temperatures are expected on Tuesday night, or even a bit
cooler. Most model guidance indicates Tuesday night will be the
coldest night of the week. Nighttime temperatures will begin to
moderate by Wednesday night and especially late in the week and
into next weekend. Daytime temperatures will gradually warm during
the week as an upper ridge builds over California, with highs
expected to be mostly in the 60s during the second half of the
week. This ridge will maintain dry conditions across our entire
area through the end of the week.
A system moving into the Pacific northwest next weekend may dip
far enough south to bring rain to at least the northern part of
our forecast area by late in the weekend. But on this point
forecast confidence decreases due to model differences. The trend
of the GFS has been to shift next weekend's system farther south.
The 00z GFS brought a cold front and associated precip as far
south as the San Francisco peninsula by late Saturday night and
Sunday. The 06z GFS is even more robust with this system,
spreading light to moderate rain across nearly our entire forecast
area by late Sunday. However, the 00z European model (ecmwf) keeps all rain just
to the north of Sonoma County. Given the trend of the GFS, have
increased pops across the North Bay Saturday night and Sunday. But
in deference to the ECMWF, have kept areas south of the Golden
Gate dry. Also, it's Worth noting that cpc's 6-10 and 8-14 day
outlooks both favor drier than normal conditions across our area.
Aviation...as of 03:30 am PST Monday...for 12z tafs. Current
radar returns showing scattered showers across the region moving
southeast. Expecting generally VFR conditions throughout the forecast
period with possibility of MVFR cigs and vis during heavier
showers. As Showers Pass over wind gusts around 15 to 20 kt are
possible. Showers should taper off from north to south this
morning. Sts bouncing between VFR and IFR/LIFR vis this morning.
Vicinity of ksfo...VFR except possibly briefly down to MVFR
during a shower. West to northwest winds generally less than 10/15
kt with possible gusts into the 15 to 20 kt range with a passing
shower. Moderate confidence. Dry VFR conditions expected to
prevail during the day on Monday.
Sfo bridge approach...similar to sfo.
Monterey Bay terminals...VFR prevailing except possibly briefly
down to MVFR vis during a shower. Winds generally less than 10 kt
with possible gusts to around 15 kt during a passing shower.
Moderate confidence. Dry VFR conditions expected to prevail by
late morning on Monday.
Marine...as of 02:08 am PST Monday...currently seeing scattered
showers across the coastal waters tonight as a weak cold front
moves through from the north. Showers will continue into today
tapering off from north to south. Winds are expected to hover
around small craft criteria through the period. No significant
swell trains are expected this week.
... Arena to Pigeon pt 10-60 nm from 3 PM
Public forecast: dykema
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