Wildfire in California, November 1 to 6, 2019

Area Forecast Discussion
National Weather Service San Francisco Bay Area
1038 PM PDT Thu Oct 31 2019

.SYNOPSIS...A Freeze Warning has been issued for tonight for
the North Bay Valleys and interior portions of Monterey and San
Benito Counties. Cool to cold overnight temperatures will
continue for the next several nights. Otherwise, generally quiet
weather is anticipated for the next week with warm daytime highs.
Mainly light winds and dry conditions are expected through at
least the end of next week.

&&

.DISCUSSION...as of 10:16 PM PDT Thursday...A Freeze Warning for
the North Bay Valleys and interior portions of Monterey and San
Benito counties is valid until 9 am Friday.

Compared to this morning the cooling effects tonight into Friday
morning look a bit more favorable with the current synoptic
pattern. Light mixing surface winds interacting with low level
thermal belts or low level temperature inversions this morning
likely resulted in surface or valley floor temperatures from
falling like they could have in the absence of inversions. Plus
the evening atmosphere is the driest it has been since late last
Sunday, the 00z Oakland sounding precipitable water was only 0.18
inches. Thus after more inspection into whether or not the
aforementioned thermal belt warming effects would happen again
tonight, it appears the answer is generally no, not as much,
including other factors in the synoptic pattern. Present forecast
lows look good except only decided to nudge downward by a few
degrees far inland valley forecast low temperatures where the
coldest air has the best chance of pooling Friday morning. 24 hour
trends on the mesowest also support this downward temperature
adjustment. No changes were made to low temperature forecasts
nearest the ocean or bays.

For additional info on the forecast please see the previous
discussion.

&&

.PREV DISCUSSION...as of 02:00 PM PDT Thursday...A deep upper trough
remains over the center of the country while an upper ridge
continues to be parked over the northeastern Pacific. A weak upper
trough is situated south of the ridge, setting up a Rex Block
over the eastern Pacific. Building high pressure over the area
has led to another day of sunny skies and temperatures which have
rapidly warmed since this morning. Higher pressure at the surface
persists inland and light offshore flow continues this afternoon.
This is bringing warm afternoon temperatures all the way to the
coast in many cases with Monterey recording a temperature of 74
degrees at 1 pm. Highs today will reach into the upper 60s and
70s across the board with an isolated 80 degree reading or two
possible in the warmer valley locations. The atmosphere remains
very dry with relative humidity in the teens and 20s. Thus even
though winds have decreased fire danger remains elevated.

The airmass tonight will remain dry with clear skies and light
winds. This will allow for good radiational cooling once again
with freezing temperatures expected across the North Bay Valleys
and interior portions of Monterey and San Benito Counties. A
Freeze Warning has been issued for these locations from 2 am to 9
am Friday. Other isolated mountain valley locations across the
North Bay, East Bay, and Santa Cruz Mountains will also see
temperatures dipping below freezing tonight. Patchy frost will
be possible but the atmosphere may still be too dry for
widespread frost. Elsewhere, cool overnight temperatures are
expected again tonight with widespread readings in the mid 30s to
mid 40s. A warming airmass aloft will allow hilltop temperatures
to remain in the 50s overnight.

The upper ridge off the West Coast will very slowly shift eastward
into the weekend and through much of next week. As a result the
weather is expected to change little from day to day. Low
temperatures will moderate as the airmass gradually warms and low
level moisture slowly increases. High temperatures will range from
the upper 60s to lower 80s through the end of next week. Winds
will generally be light with periods of very light offshore flow.
This will make for very pleasant weather for any outdoor plans
through the entire week.

The question on everyone's mind is when rain will return to the
forecast. The latest ensemble forecasts have trended down in
regards to the chance of rain returning next weekend, with the
majority of the ECMWF/GEFS ensemble members remaining dry through
the next 15 days. Stay tuned to the latest forecast for any
updates regarding rain chances.

&&

.AVIATION...as of 10:38 PM PDT Thursday...Airmass remains very
dry under light offshore flow. Impacts from the Kincade Fire smoke
expected to be minimal.

Vicinity of KSFO...VFR. Light winds.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR. Southeast winds to 10 kt in the
Salinas Valley after 09Z diminishing after 17Z.

&&

.MARINE...as of 10:30 PM PDT Thursday...High pressure covers the
Great Basin and the waters off the Pacific Northwest. Winds will
be mostly light northwest through Tuesday but will occasionally
switch briefly to offshore. The seas remain light and mixed with
two moderate period  northwest swells with a smaller southerly
swell.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...Freeze Warning...CAZ506-516>518

&&

PUBLIC FORECAST: Canepa/ST
AVIATION: W Pi
MARINE: W Pi

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