Scientific Forecaster Discussion
Area forecast discussion...corrected
National Weather Service San Francisco Bay area
1026 PM PST Sat Mar 8 2014
Synopsis...a Pacific weather system will spread considerable
cloudiness over our region tonight and Sunday and perhaps produce
a few sprinkles. Rain will eventually develop across the North
Bay late Sunday and Sunday night...and into the remainder of the
San Francisco Bay area late Sunday night and early Monday. Showers
are expected to end by midday Monday. Dry and mild weather is then
forecast from late Monday through the remainder of next week.
Discussion...as of 8:50 PM PST Saturday...upper level ridging
strengthened across California today in advance of an approaching
Pacific weather system. Subsidence warming under this ridge pushed
temperatures higher across our region today...even with increasing
high clouds filtering the sun to some extent. Afternoon temperatures
warmed well into the 60s and lower 70s across the San Francisco
Bay area and from the upper 60s to lower 80s in the Monterey Bay
area. Highs today were anywhere from 5 to 15 degrees above normal.
Clouds are lowering and thickening this evening as moisture
streams in off the Pacific and warm advection continues. Since
late afternoon radar has been showing weak returns off the coast
and across Sonoma County. But these returns are at 12k feet and
above. If light rain is falling out of these middle-level clouds...it
almost certainly is not reaching the ground. We may see a few
isolated sprinkles overnight...but measurable rainfall is not
expected in the short-term and is not forecast by any of the
models through at least midday Sunday.
The approaching system has a rich supply of moisture with precipitable waters up
around 1.5 inches offshore near 130w. Most of that moisture is
currently riding up and over the ridge and into the Pacific northwest. The
frontal boundary will sag south into northwest California later
tonight and Sunday morning and rain may reach as far south as
Sonoma County on Sunday afternoon. But for the most part...Sunday
should be another dry day across our region. Skies should be cloudy
across most of the San Francisco Bay area with some sunny breaks
possible farther to the south.
Rainfall is not expected to make it south of Sonoma County until
Sunday night when a shortwave trough approaches and kicks the
frontal rain band south across the rest of the North Bay...and
perhaps as far south as Santa Cruz and San Jose by daybreak Monday
morning. The front is forecast to rapidly weaken by Monday morning
and measurable rainfall appears highly unlikely from Monterey
southward. Rain totals through Sunday night are forecast to range
from 0.25 to 1.25 in across Sonoma County...0.10 to 0.50 across
the rest of the North Bay and into the city of San Francisco...and
a tenth of an inch or less for most areas south of San Francisco.
Widely scattered showers may linger through late Monday
morning...but the models agree that all precipitation will end by midday
Monday. Monday afternoon should be mostly sunny and dry with brisk
northwest winds developing as surface high pressure rapidly
builds offshore. A forecast update was recently completed to
remove all shower chances from Monday afternoon.
Upper level ridging is forecast to quickly develop over California
on Monday night and Tuesday. This ridge is then expected to
persist through the remainder of next week and into the following
weekend...resulting in an extended period of dry and mild weather
across our entire area. Offshore flow will develop by late Monday
night as northwest winds veer to the north. Northerly winds could
gust locally up to 40 miles per hour in the hills from late Monday night into
Aviation...as of 10:15 PM PST Saturday...high clouds are
streaming into the area ahead of a frontal system and radar is
picking up a few echoes off San Francisco. Aside from a few
sprinkles tonight this system will not impact the area until
Sunday night. Dry airmass at the surface will allow for one more
night of VFR conditions.
Vicinity of ksfo...VFR.
Ksfo bridge approach...VFR.
Monterey Bay area terminals...VFR.
Public forecast: dykema
aviation: west pi
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