Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
1032 am PDT Monday Mar 30 2015
Synopsis...mostly clear and mild weather will continue through
today. A dry weather system will sweep into the area beginning
Tuesday...bringing much cooler conditions Tuesday and
Wednesday...along with locally gusty winds. Temperatures will then
warm slightly by the end of the week. Dry weather is forecast at
least through Saturday. Rain may develop by late in the weekend.
Discussion...as of 8:30 am PDT Monday...morning satellite loop
plus surface observation show most places with sunny conditions outside of a
couple of pockets of clouds near the coast. Highs are expected to
be a few degrees cooler for the northern two thirds of the County Warning Area compared
to yesterday due to an increase in the onshore flow at the
surface. Southern Monterey County plus San Benito County still
expecting another warm day with upper 70s to upper 80s.
Cooler weather forecast by Tuesday as a cold front GOES across.
This will usher in colder temperatures for the remainder of the week with
highs confined to the 60s and 70s. Most locations will be 10
to 15 degrees cooler compared to last weekend. Will need to keep
an eye on overnight lows for the North Bay valleys since some of
the guidance indicates possible middle to upper 30s later in the week.
Previous discussion...except for some patchy low clouds near
Monterey Bay...skies remain mostly clear early this morning.
Current conditions are similar to what they have been the past few
days. However...changes are expected to get underway today that
will put an end to the unseasonably warm weather our are
experienced over the weekend.
Water vapor satellite imagery shows a broad upper trough over the
eastern Pacific...centered along 150w. This trough is forecast to
approach the West Coast by later today...triggering an increase
in onshore flow. This will result in cooler conditions across our
region. Temperatures will be about five degrees cooler than
yesterday...but will still remain warmer than normal.
A cold front will move inland across the Pacific northwest and far northern
California tonight as the initial shortwave trough arrives...but all precipitation
associated with that front will remain well to our north. Low
level moisture will increase in our area as the remnants of that
front dissipate over the coastal waters. So we can expect an
increase in low clouds tonight...with perhaps some patchy fog and
drizzle near the coast late tonight and Tuesday morning. The
cooling trend will continue on Tuesday with high temperatures
dropping another five to ten degrees. In addition...locally
blustery conditions will develop with gusty west to northwest
winds expected. The marine layer that is expected to develop
tonight will mix out by Tuesday afternoon as a much cooler airmass
sweeps in aloft.
Breezy and relatively cool conditions will continue into
Wednesday as a second shortwave trough moves into northern California.
Although temperatures on Tuesday and Wednesday will be
significantly cooler than what we've seen lately...temperatures are only
expected to cool back to near normal.
Shortwave ridging will develop over California by Thursday...and
result in continued dry weather from Thursday through
Saturday...along with warming temperatures.
There continues to be a great deal of uncertainty concerning the
evolution of the weather pattern during at the end of our extended
forecast period and beyond. The European model (ecmwf) appears to be settling on a
wet solution...with a cold upper trough dropping south just
offshore along 130w and delivering widespread soaking rains to our
region beginning in the North Bay by late Sunday night and
spreading south through the remainder of our region by next
Tuesday morning. The 00z GFS shows a much different
scenario...swinging the system inland to our north and east and
keeping our area entirely dry. It should be noted that yesterday's
00z European model (ecmwf) was forecasting a dry scenario much like the current
GFS...while past runs of the GFS have indicated at least some
rain. Clearly the medium range models are having a difficult time
with this pattern evolution and forecast confidence will remain
low until better run-to-run consistency and model agreement
Aviation...as of 10:28 am PDT Monday...VFR conditions through
this evening. Patchy low ceilings along the coast...but at this time
do not think they will impact terminals this afternoon.
Otherwise...gusty winds will be poss this afternoon.
Vicinity of ksfo...VFR. Moderate west winds around 15 to 25 knots
with gusts to 30 knots possible this afternoon through early evening.
Will bring ceilings back overnight with ceilings impacting Tuesday morning rush.
Sfo bridge approach...similar to ksfo.
Monterey Bay area terminals...VFR. Moderate west winds around 15
knots with gusts to 20 knots possible this afternoon through early
evening. Ceilings return again tonight...but thinking more ceilings and
less fog for Tuesday morning.
Marine...as of 10:27 am PDT Monday...northerly flow will persist
along the central coast today as a cold front approaches the
region. Wind will increase further on Tuesday into Wednesday
behind the cold front as high pressure builds. A mixed swell will
also continue with a long period southerly swell.
... Bay from 3 PM
Small Craft Advisory...Pigeon pt to pt pinos 0-10 nm from 3 PM
Small Craft Advisory...pt Arena to pt Reyes 0-10 nm
Small Craft Advisory...pt Reyes to Pigeon pt 0-10 nm
Small Craft Advisory...pt pinos to pt Piedras Blancas 0-10 nm
Small Craft Advisory...pt Arena to pt Reyes 10-60 nm
Small Craft Advisory...Pigeon pt to pt pinos 10-60 nm
Small Craft Advisory...pt Reyes to Pigeon pt 10-60 nm
Small Craft Advisory...pt pinos to pt Piedras Blancas 10-60 nm from 3 PM
Public forecast: Bell/dykema
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