Scientific Forecaster Discussion
fxus66 kmtr 240535
Area forecast discussion
National Weather Service San Francisco Bay area
1035 PM PDT Mon Oct 23 2017
Synopsis...look for another round of very warm to hot weather 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
Discussion...as of 9:20 PM PDT Monday...as expected it was a very
warm day across our entire region with many locations in the mid
80s to the lower 90s. With plenty of offshore flow in place even
coastal locations where able to warm to the same levels.
Interesting to note that unlike many Summer days where we can see
a 50 degree variation across our County Warning Area for high temperatures, today
was just around 10 degrees. Even the usually cool Half Moon Bay
soared to 87.
Temperatures have been slow to cool tonight with light offshore
winds keeping values up. In fact many spots are running 5 to 15
degrees ahead of this time yesterday. With dewpoints in the 40s
to mid 50s, clear skies, and light winds, we should see a nice
drop in temperatures overnight. Lows will mostly be in the 50s to
the lower 60s. Tomorrow will be a near repeat of today with the
potential for a few degrees of additional warming. In general mid
80s to mid 90s can be expected. Not out of possibilities that an
isolated triple digit reading will happen. Experimental heat risk
program shows generally low risk for urban locations due to cooler
overnight temperatures. A moderate risk is indicated for some of
the higher elevation locations.
Current forecast appears to be on track.
Previous discussion...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 10:40 PM PDT Monday...VFR through the entire
period for all tafs due to an offshore flow in place. No cigs
forecast. Winds will generally be under 12 knots. High confidence.
Vicinity of ksfo...VFR through the period with no cigs forecast.
Winds forecast to be under 10 knots. Direction will be variable at
first then mostly 280 to 310 after 19z. High confidence.
Sfo bridge approach...similar to ksfo.
Monterey Bay terminals...VFR through the period with sky clear
conditions. Stronger winds near ksns with speeds over 10 knots
possible starting after 12z. Winds at kmry generally under 6kt.
Fire weather...as of 5:00 PM PDT Monday...winds are anticipated
to decrease later this afternoon and evening for the North Bay and
East Bay hills. Otherwise, generally light offshore wind will
continue for all other zones through tomorrow. Another hot and dry
day tomorrow, with single digit humidity values possible for
parts of Monterey and San Benito counties. Humidity values
increase by Wednesday. With cooler conditions slated for our
entire region by Thursday.
Marine...as of 9:20 PM PDT Monday... generally light
northwesterly winds will prevail over the coastal waters through
Tuesday. Additionally, the northwest swell will decrease through
the middle of the week, but then increase again late week as
another long- period swell arrives.
Public forecast: Bell/rgass
fire weather: BAM
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