Scientific Forecaster Discussion
fxus66 kmtr 232045
Area forecast discussion
National Weather Service San Francisco Bay area
145 PM PDT Mon Oct 23 2017
Synopsis...a rapid warming trend that got underway today will
persist into Tuesday with the potential for record to near record
breaking daytime temperatures. Temperatures cool slightly as
offshore flow and the high pressure aloft weakens by midweek, yet
temperatures look to remain above seasonal averages through late
week. In addition, ongoing dry conditions will likely persist
through the end of the month.
Discussion...as of 01:45 PM PDT Monday...a strong ridge of high
pressure building in from the south and west has resulted very
warm to hot conditions across the region. Afternoon temperatures
are forecast to be around 15 to 20 deg f above seasonal averages
and will likely warm by a few more degrees on Tuesday as weak
offshore flow persists. With this type of late season heat event,
temperatures will be evenly spread from near the coast in the 80s
to 90s inland this afternoon. The warmest and driest air mass
appears to remain placed over Southern California and up into the
central coast where afternoon temperatures will potentially reach
into the middle/upper 90s on Tuesday afternoon. Cannot even rule
out lower 90s in and around the Monterey area as well as Santa
Cruz. These warm temperatures may reach or exceed current record
values for the calendar date, both today and on Tuesday.
The heat will result in concerns for our more heat sensitive
populations such as the elderly, Young and homeless with heat risk
levels reaching into the low to moderate category, especially across
the central coast. However, long October nights and clear skies will
allow for sufficient overnight cooling with lows generally in the 50s
for most urban areas while higher elevations only cool into the 60s
and lower 70s.
By midweek, a slight cooling trend is likely as the mid/upper level
ridge retreats back out over the Pacific in response to trough
digging into the Great Basin and Central Plains. While onshore flow
returns at the coast, weak offshore flow will persist inland to help
maintain temperatures that are above seasonal averages at least on
Wednesday and Thursday.
Stronger onshore flow is then anticipated late in the week into early
next week which will help cool inland areas as well. However, look
for values to remain on the warm side of normal through early next
week. Will have to watch for the return of overnight/early morning
coastal clouds late in the week as the boundary layer moistens up.
Otherwise, ongoing dry weather conditions are likely to persist
through the end of the month.
Aviation...as of 10:17 am PDT Monday for 18z tafs...VFR
conditions are expected to prevail at taf sites through the
forecast period. Winds are forecast to remain fairly light at most
sites. Forecast confidence is high.
Vicinity of ksfo...VFR conditions expected to prevail. Generally
light winds expected with speeds up to around 10 kt this
Sfo bridge approach...similar to ksfo.
Monterey Bay terminals...VFR conditions expected to prevail.
Locally breezy southeast winds will continue for another few
hours in the parts of the Salinas valley, and will decrease in
Fire weather...as of 2:50 am PDT Monday...light to moderate
offshore wind event seems to be unfolding about as expected.
Humidity values staying moist through 3 am with just a few of the
North Bay hill sites showing signs of drying. More rapid drying
will occur through the afternoon with poor humidity recovery
forecast tonight. The strongest winds are currently remaining over
the highest hills and not see much evidence or trend for mixing
those down early this morning. None the less we still have warm,
dry and breezy conditions on tap today. Probability of new
ignitions will remain high the next few afternoons with near
record warmth and drying of the fine fuels. At this time just plan
to run generic headlines in the fire weather forecast to raise
awareness without issuing any specific watches or warnings.
Marine...as of 08:54 am PDT Monday...northwest winds will
continue to gradually diminish through the day. Additionally, the
northwest swell will decrease through the middle of the week, but
then increase again late week as another long-period swell
... Arena to Pigeon pt 10-60 nm until 9 PM
Public forecast: rgass
fire weather: rww
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