Scientific Forecaster Discussion
fxus66 kmtr 222049
Area forecast discussion
National Weather Service San Francisco Bay area
149 PM PDT sun Oct 22 2017
Synopsis...after a seasonably mild afternoon across the region
today, very warm to hot temperatures are likely on Monday and
Tuesday afternoons. Along with the heat, dry conditions will persist
through the first half of the week as a result of weak offshore
winds. A gradual cooling trend is then forecast during the second
half of the week, yet temperatures will remain above seasonal
Discussion...as of 01:47 PM PDT Sunday...high pressure continues
to build in over the region from the south and will strengthen
through midweek. As the air mass aloft warms, surface temperatures
will also increase with afternoon highs reaching 15 to 20 deg f
above seasonal averages on Monday and Tuesday. This combined with
weak offshore flow will result in temperatures reaching into the
80s at the coast with Lower/Middle 90s inland. With this event,
the warmest temperatures are forecast to occur on Tuesday across
the central coast where the warmest and driest air mass will be in
place. Cannot rule out a few of the warmest inland areas such as
Pinnacles National Park reaching into the upper 90s.
Overall, winds are forecast to remain light for most urban locations
but may become breezy and locally gusty at times in the peaks and
ridges beginning tonight before gradually tapering off Monday night
into Tuesday. These conditions will raise fire weather concerns to
some extent, but rainfall late last week is providing some temporary
relief, at least initially. By the time conditions dry out late
Monday and Tuesday, wind speeds are forecast to be weaker.
Heat risks will also increase into the moderate category both Monday
and Tuesday afternoon, mainly from the Santa Cruz Mountains southward
through the central coast. However, longer nights and modest
overnight cooling under clear skies will limit the overall heat
risks region-wide through this heat event. Thus, folks are urged to
remain vigilant and use extra caution during the peak heating of the
day through early this week.
The mid/upper level ridge is then forecast to weaken and shift back
offshore by midweek in response to an upper level trough digging
southward across the Great Basin and Central Plains. This will allow
for a cooling trend from Wednesday through at least Friday, yet
temperatures are forecast to remain above seasonal averages. In
addition, medium to longer range models maintain dry weather
conditions and near to slightly above average temperatures heading
through the end of October.
Aviation...as of 10:45 am PDT Sunday...VFR. Generally light
variable winds in the mornings and overnight with light
afternoon/evening onshore sea breeze generally of up to 15 kt.
Inland valley locations could see sunrise fog develop, esp near
Vicinity of ksfo...VFR.
Sfo bridge approach...similar to ksfo.
Monterey Bay terminals...VFR.
Fire weather...as of 3:20 am PDT Sunday...gradual warming and
drying will continue across the district today. Offshore flow is
then forecast to develop tonight, resulting in much warmer and
drier conditions by Monday and Tuesday. Locally moderate and gusty
north to northeast winds are forecast in the hills late tonight
and Monday morning. The latest WRF has scaled back on the
magnitude of wind speeds in the hills tonight and Monday morning.
Even so, local gusty winds are likely over the higher ridges and
peaks of the North Bay, particularly across eastern Napa County
where gusts up to 40 mph are possible. In addition, nighttime
humidity recoveries will be poor in the hills tonight. Were it not
for the recent wetting rains on Thursday night, these
developments may have resulted in critical fire weather
conditions. However, finer fuels are expected to retain enough
moisture in the short term to mitigate fire weather concerns to
some extent. Will continue to draw attention to local gusty winds
and drying conditions with headlines in the fire weather planning
Fuels are expected to dry significantly by late Monday.
Fortunately, winds in the hills on Monday night are not expected
to be as strong as tonight, with only some isolated patches of
gusty winds expected at the higher elevations of the North Bay.
Will continue to monitor fuel moisture over the next few days to
determine if critical fire weather conditions may occur. Winds are
expected to subside in all areas by Tuesday afternoon, but very
warm and dry conditions will continue through midweek. Slight
cooling is expected during the second half of the week as high
pressure over California weakens.
Marine...as of 10:44 am PDT Sunday...moderate northwest swells
to subside through day. Small craft advisories in effect for
hazardous seas primarily in the outer waters. A frontal system
will move into the Pacific northwest today with northwest winds
increasing tonight behind the front. Winds will decrease Monday
through Wednesday except over the northern outer waters as high
pressure builds into the Great Basin creating offshore flow.
... Arena to pt Reyes 0-10 nm until 3 am
Small Craft Advisory...pt Reyes to Pigeon pt 0-10 nm until 3 am
Small Craft Advisory...Pigeon pt to pt pinos 0-10 nm until 3 am
Small Craft Advisory...pt pinos to pt Piedras Blancas 0-10 nm until 3 am
Small Craft Advisory...pt Arena to Pigeon pt 10-60 nm until 3 am
Small Craft Advisory...Pigeon pt to pt Piedras Blancas 10-60 nm until 3 am
Public forecast: rgass
fire weather: dykema
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