Scientific Forecaster Discussion
fxus66 kmtr 271800
Area forecast discussion
National Weather Service San Francisco Bay area
1000 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 8:30 am PST Monday...a few lingering showers
are still around southern portions of our region with just light
echos being detected. Models are in good agreement that mostly
dry weather can be expected by this afternoon with highs only in
Quiet weather remains on tap through the work week with
temperatures forecast to increase especially starting on
Wednesday. 12z GFS just coming in does indicate a return to
wetter weather on Sunday which is similar to the 06z run. 0z
European model (ecmwf) from last night keep the rain farther to the north, so will
be interesting to see if the European model (ecmwf) trends more to the GFS.
No major updates planned.
Previous discussion...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 evening.
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 10:00 am PST Monday...for 18z tafs. Widespread
VFR expected today with a few vcsh off the coast and over
southern Monterey/San Benito counties. Cumulus development will
predominately be vertically limited and over the higher terrain.
Vicinity of ksfo...VFR. Northwest-west winds generally 15kt or less.
Sfo bridge approach...similar to sfo.
Monterey Bay terminals...VFR. Northwest-west winds generally 11kt or less.
Marine...as of 09:57 am PST Monday...gradually increasing
northwest winds this afternoon through tonight then weakening
tomorrow... except along the Big Sur coast where breezy winds
will continue. Northwest winds will increase to become moderate
again Thursday through Friday. A moderate northwest swell will
move through the waters this week.
... Arena to Pigeon pt 10-60 nm from 3 PM
Public forecast: Bell/dykema
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