Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
441 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 3:20 am PDT Monday...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 4:41 am PDT Monday...satellite imagery reveals a
patch of low clouds over the Monterey Bay as well as a few high
clouds streaming in from the northwest. Winds are expected to
remain light through the morning hours then increase in the
afternoon as moderately strong and gusty winds develop. Mostly
clear skies expected through the day with increasing high clouds
expected through the afternoon.
Vicinity of ksfo...VFR. Light winds expected through the morning
hours. Moderate west winds around 15 to 25 knots with gusts to 30 knots
possible this afternoon through early evening.
Sfo bridge approach...similar to ksfo.
Monterey Bay area terminals...VFR. Light winds expected through
the morning hours. Moderate west winds around 15 knots with gusts to
20 knots possible this afternoon through early evening. LIFR to
vlifr conditions expected to bounce around through 17z this morning.
Clearing expected around 17z.
Marine...as of 03:00 am PDT Monday...moderate northwest winds will
continue across the coastal waters through Monday as an
approaching cold front maintains a tight gradient over the region.
Stronger winds are expected Tuesday night into Wednesday as an
area of high pressure builds over the eastern Pacific producing
gale force winds across portions of the coastal waters.
... 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 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 0-10 nm from 9 am
Small Craft Advisory...pt pinos to pt Piedras Blancas 10-60 nm from 3 PM
Public forecast: dykema
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