Scientific Forecaster Discussion
fxus66 kmtr 160431
Area forecast discussion
National Weather Service San Francisco Bay area
931 PM PDT Mon Oct 15 2018
Synopsis...light offshore winds are forecast to persist through
midweek with temperatures near or above seasonal averages. Onshore
winds increase a bit late in the week which will help moisten
conditions while temperatures remain seasonably mild.
Discussion...as of 9:30 PM PDT Monday...upper level low over
western Arizona combined with upper level ridging over the Pacific
northwest is bringing offshore flow to the area. Temperatures
along the coast warmed to the mid 70s today while inland areas
reached the mid 80s.
Offshore gradients have eased a little tonight as the upper low
has advanced slightly eastward. North to northeast winds are
expected to increase over the North Bay hills tonight but not as
much as last night. Gusts to 35 mph can be expected over the hills
of Napa and Sonoma counties during the early morning hours of
Tuesday. There is the possibility of local fog in the mry Bay area
tonight otherwise clear skies are expected. Cooling is expected
Tuesday but only by a few degrees at most.
The upper low lifts northeast Tuesday and Wednesday but a weak
trough persists from the Salt Lake southwestward into Southern
California. This will keep a weak offshore component over the
area through the week. However by Thursday and Friday an onshore
flow may develop near the surface bringing some cooling.
Models indicate a Rex block over the west this weekend with upper
level high moving over the Pacific northwest and a weak low over
Southern California. A light and dry east to northeast flow
persists aloft over our area. Medium range models indicate an end
to the blocking pattern by next Monday and Tuesday as a weather
system moves into the Pacific northwest bringing a chance for rain
in the northern part of the County Warning Area. The synoptic-scale pattern
indicates a long wave trough may be moving closer to the West
Coast and could bring better rain chances by the end of the month.
Aviation...as of 4:38 PM PDT Monday...for 00z tafs. Northerly
winds have maintained mainly clear skies across the region today.
Light winds and clear skies are expected to prevail through the
Vicinity of ksfo...VFR. Light onshore flow will turn offshore
Sfo bridge approach...similar to ksfo.
Monterey Bay terminals...VFR. Light onshore flow will turn
Fire weather...as of 01:57 PM PDT Monday...wind speeds across the
region, even in the highest peaks of far eastern Sonoma County and
Napa County have fallen below 10 mph, even with wind gusts at or
below 15 mph. This was well forecast and so are the very dry
conditions that prevail. While the winds have diminished,
critically dry conditions prevail with many locations across the
interior at or below 10%. Wind speeds may increase a bit again
late this evening and overnight in the North Bay mountains,
primarily in the highest peaks/ridges. The dry air mass will
remain in place through mid week with poor overnight humidity
recoveries, especially in the hills above 1,000 feet.
Should see conditions moisten slightly late in the week as onshore
winds increase a bit. Overall, this should help limit fire weather
concerns region-wide. Will need to closely monitor these
conditions however as the ongoing dry, breezy/windy conditions
have further dried fuels.
Marine...as of 08:46 PM PDT Monday...light to moderate northerly
winds will prevail over the coastal waters. Mixed swell will
continue with a long period southerly swell through mid week and
a more moderate period northwest swell. A longer period northwest
swell will arrive during the second half of the week.
Public forecast: west pi
fire weather: dykema
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