Wildfire in California, November 3 to 15, 2018

Area Forecast Discussion
National Weather Service San Francisco Bay Area
905 PM PDT Sat Nov 3 2018

.SYNOPSIS...Gusty offshore winds and a very dry airmass will
continue to elevate fire danger in the hills through early Sunday
morning, particularly in the North and East Bay Hills. Despite a
slight cool down over the next few days, warmer than normal
daytime temperatures will persist on Sunday and through the
upcoming work week, along with dry weather.

&&

.DISCUSSION...As of 9:05 PM PDT Saturday...Saturday was another
day and warm autumn day across our region. Afternoon highs were
generally 10 to 20 degrees warmer than seasonal averages, except
some coastal locations that were only about 5 degrees warmer than
normal. Primary forecast concern in the short-term continues to be
very low relative humidity values overnight combined with locally
gusty offshore winds in the hills, continuing to produce Red Flag
conditions in the North and East Bay Hills. See Fire Weather
Discussion below for more details.

A shortwave trough will track across the Pacific Northwest
tonight and Sunday. This trough will weaken the ridge slightly
over California, but more importantly weaken offshore flow across
our area. Thus, expect at least modest cooling in most areas on
Sunday (cooling of about five degrees or so). Even so, afternoon
highs tomorrow will be well above normal in most locations,
particularly inland and in the hills.

The models agree that the synoptic-scale pattern across North
America and the eastern Pacific will change very little through
next week, with an upper trough dominating the central portion of
North America and an upper ridge holding firm off the West Coast.
In between, over California, dry northwesterly flow will persist
aloft and either neutral or light offshore flow will dominate
near the surface. Daytime temperatures next week are not expected
to be as warm as they were today, but will still be anywhere from
5 to 10 degrees warmer than normal in most areas. Clear skies, dry
air, and long autumn nights will mean rather chilly nights,
particularly in the interior valleys. Based on a consensus of
model data, no rain is expected anywhere in our forecast area
through next week and into the following weekend.

&&

.AVIATION...as of 4:35 PM PDT Saturday...Surface high over the
eastern Pacific extends into the Pacific Northwest coast. This
will keep dry offshore flow over the SFO Bay Area. Humidities were
a little higher along the coast this morning and some low clouds
made it into MRY. Expect similar conditions tonight while VFR
continues in the SFO Bay Area.

Vicinity of KSFO...VFR. West winds to 15 kt through 04Z.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR except for brief periods of patchy
fog and low clouds between 10Z and 16Z.

&&

.FIRE WEATHER...As of 8:50 PM PDT Saturday...A very dry airmass
has swept across the district from the north and relative humidity
values this evening are about 30 percent below where they were at
the same time last evening. Relative humidity (RH) values in the
hills of the North and East Bay are currently in the teens and
20s, with isolated higher elevation locations around 10 percent.
00Z NAM and latest local WRF model indicate very little RH
recovery overnight. North to northeast winds in the hills remain
gusty this evening, especially in the North and East Bay Hills where
gusts of between 20 and 45 mph are currently being reported. This
combination of very dry air and gusty winds in the hills will
continue to produce critical fire weather conditions overnight. A
Red Flag Warning remains in effect for the North Bay Mountains and
East Bay Hills until 6 am Sunday. Winds are forecast to gradually
subside in the hills overnight and it's likely that Red Flag
conditions will end by late tonight and that the Red Flag Warning
will be allowed to expire at 6 am. But dry air will remain over
the area through Sunday.

Better overnight humidity recoveries are forecast for Sunday
night, which will help ease fire weather concerns. However, RH
values are then forecast to decrease once again by late Monday
and continue low through much of the rest of the week due to light
offshore flow. Currently, offshore winds are not expected to be
strong enough to meet Red Flag Criteria after tonight, except
perhaps on isolated high ridges and peaks. But will need to
continue to monitor forecast models closely for any signs of
upward trends in strength of offshore flow during the upcoming
week. Longer range models continue to show dry conditions
persisting through the next 7 to 10 days.

&&

.MARINE...As of 8:41 PM PDT Saturday...High pressure off the
California coast will keep gusty northwest winds through
Wednesday. Winds over the southern waters may decrease Tuesday and
Wednesday as the high shifts northward. A light west swell will
mix with a minor longer period south swell.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...SCA...Pigeon Pt to Pt Pinos 0-10 nm
             SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Reyes to Pigeon Pt 0-10 nm
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm

&&

PUBLIC FORECAST: Dykema
AVIATION: DRP
MARINE: W Pi
FIRE WEATHER: Dykema

Visit us at www.weather.gov/sanfrancisco

Follow us on Facebook, Twitter, and YouTube at:
www.facebook.com/nwsbayarea
www.twitter.com/nwsbayarea
www.youtube.com/nwsbayarea