Scientific Forecaster Discussion
fxus66 kmtr 181104
Area forecast discussion
National Weather Service San Francisco Bay area
404 am PDT sun Mar 18 2018
Synopsis...dry weather conditions and a slight warming trend can be
expected Sunday into Monday ahead of our next storm system. This
system will bring widespread rainfall to our region from Tuesday
through Thursday, along with the potential for periods of heavy
rain and locally strong southerly winds.
Discussion...as of 04:01 am PDT Sunday...temperatures are
running a few to as much as 9 deg f cooler compared to 24 hours
ago as mainly clear sky conditions prevail over the region.
Remnant low level moisture is helping to keep temperatures from
cooling too much and should prevent most locations from reaching
the freezing mark. With that said, patchy fog is already being
reported in the North Bay valleys as well as the far southern
Salinas valley as surface temperatures have cooled to dewpoint
values (generally in the middle 30s). In the Santa Clara and East
Bay valleys, low clouds have developed early this morning. After a
cool start to the morning, temperatures will warm into the upper
50s to lower 60s as a short-wave ridge builds off of the coast.
Dry conditions along with additional warming is forecast for
Monday with most areas warming into the lower to upper 60s under a
mostly sunny sky.
A developing storm system well offshore is forecast to approach the
West Coast by the midweek with deeper moisture advecting into the
California coast. With this, cloud cover will be on the increase
late Monday into Tuesday morning with widespread rain likely to
impact the region around or slightly after sunrise Tuesday morning.
The latest WRF and NAM forecast output shows moderate rain spreading
across the region with precipitable water values of 1.25" - 1.50" pointed toward
central and Southern California through Tuesday afternoon. At this
time, the forecast models do point the deepest moisture into
Monterey County southward (southern california). Regardless,
additional rainfall will likely impact the entire region again on
Wednesday as a weak mid/upper level disturbance approaches northern
California. The core of the mid/upper level trough will then rotate
across the region Thursday with continued changes for rain turning
to showers Thursday afternoon/evening into Friday. Exact details on
the timing of each passing system and placement of the atmospheric
river remains difficult to Pin-Point at this time. Given the
uncertainly, folks should prepare for the potential for periods of
moderate to locally heavy rainfall and breezy winds during the
middle portion of the upcoming week.
While dry conditions will develop over the region late Friday
into Saturday, showers may linger across the northern portion of
the region during this time frame as one last mid/upper level
disturbance pushes inland across northern California. Be sure to
to check back for the latest forecast information in the coming
days we continue to sort out the details.
Aviation...as of 10:35 PM PDT Saturday...showers have diminished
rapidly leaving just a few clouds this evening. Low level
moisture remains near the surface which will allow for MVFR cigs
to develop around the sfo Bay area after 12z.
Vicinity of ksfo...possible MVFR cigs after 12z. Any cigs that
develop will be patchy in nature and should burn off after 16z.
Sfo bridge approach...similar to ksfo.
Monterey Bay terminals...some low clouds remain along the coastal
range which will keep brief MVFR cigs to mry through 08z. Drainage
wind will clear out the clouds after 08z. Otherwise VFR.
Marine...as of 04:01 am PDT Sunday...high pressure over the
coastal waters will bring light northwest winds today and tonight.
Winds will shift to southerly on Monday and increase Tuesday as a
deep low tracks northeast across the offshore waters. Along with
gusty winds seas will become mixed Tuesday through Thursday.
Public forecast: rgass
aviation: west pi
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