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000 
FXUS66 KMTR 210145
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
545 PM PST Wed Nov 20 2019

.SYNOPSIS...Gusty and dry offshore flow will continue through the 
night over the North and East Bay Hills/Mountains. Dry conditions, 
along with seasonable temperatures, are forecast from Thursday 
through the upcoming weekend. Rain chances return next week possibly 
impacting the Thanksgiving holiday.

&&

.DISCUSSION...as of 01:46 PM PST Wednesday...Offshore flow is 
well underway across the region, especially the North and East Bay
where breezy and locally gusty north to northeast winds persist. 
While humidity levels have been slow to lower, they have been on a
downward trend with values in the 20% to 40% across much of 
greater San Francisco Bay Area away from the immediate coast. Wind
speeds in the higher elevations have weekend slightly, yet are 
forecast continue to gust in the 35 to 45 mph through the evening 
with locally higher gusts upwards of 50 to 60 mph. As a result, 
will keep the current Red Flag Warning in place for the North and 
East Bay Hills/Mountains at this time. If conditions trend in a 
more positive direction through the evening, the Red Flag Warning 
may need to be dropped earlier than the current end time of 7 AM 
Thursday. 

Winds are forecast to diminish region-wide by early Thursday morning 
with a slight increase in humidity. The local WRF model also 
continues to point a southerly surge working northward along the Big 
Sur Coast early Thursday morning. This would spread northward and 
impact places in the northern Monterey Bay such as Santa Cruz during 
the day Thursday. Thus, low clouds and fog may advect inland across 
these regions resulting a rapid change in weather conditions. This 
too could hold temperatures down along coastal areas on Thursday. 
Overall, dry weather conditions will persist through late week with 
temperatures near seasonal averages. Of greatest impact to the 
region, colder overnight temperatures are likely with middle to 
upper 30s in the region's colder interior valleys and higher 
elevations while widespread 40s are likely elsewhere through late 
week.

A ridge of high pressure will then build briefly over the region 
this upcoming weekend which will result in a slight warming trend 
across the interior. Overnight temperatures will remain chilly for 
much of the region as well. The focus moves to Monday and Tuesday as 
another offshore wind event appears possible in response to another 
trough dropping into the Great Basin and then down into the Desert 
Southwest. Will need to closely monitor this situation as widespread 
rainfall is not likely leading up to this next offshore event. 
Details will come more into focus as we head into the weekend.

The medium range models continue to point toward a shift in the 
pattern that will result in the potential for more active weather. 
Folks are urged to remain up-to-date with the latest forecast 
information during the holiday week, especially if any travel is 
expected. At this time, run to run consistency is lacking so 
confidence is marginal on the details. Regardless, there is at least 
a chance of precipitation during middle to late next week. Stay 
tuned...

&&

.AVIATION...as of 5:34 PM PST Wednesday...Dry conditions with 
offshore flow resulting in near high confidence VFR. Low level 
wind shear over the North Bay and East Bay tonight, NE winds
easing early Thursday morning.

Vicinity of KSFO...VFR. West wind has diminished to near 10 knots,
light wind tonight becoming NE early Thursday morning.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR. Mainly light west wind diminishing
to light E-SE wind this evening. E-SE wind near 10 knots in the 
Salinas Valley overnight and Thursday morning. Increasing SW wind
possible at KMRY and NW wind at KSNS Thursday afternoon and early
evening due to a southerly surge on the coast.

&&

.FIRE WEATHER....As of 5:45 PM PST Wednesday...Gusty north winds
in the hills of the North and East Bay have subsided since earlier
today, but gusts of between 25 and 35 mph continue early 
Wednesday evening, with local gusts up to 50 mph on the highest 
peaks in the North Bay. Relative humidity values have been 
gradually lowering through the day and poor overnight recoveries 
are expected at the higher elevations of the North and East Bay 
tonight. Based on latest models, gusty offshore winds will persist
overnight. Although winds tonight aren't expected to be as strong
as last night and this morning, they will likely be strong enough
to generate critical fire weather conditions when combined with
poor overnight humidity recovery and very dry fuels. Thus, will 
maintain the Red Flag Warning for the North and East Bay Hills 
tonight. The Red Flag Warning will almost certainly be allowed to
expire at 7 am Thursday since models indicate much lighter winds 
by Thursday morning. 

Fire weather concerns will return early next week as medium range 
models suggest another round of offshore flow impacting the region 
and be potentially more widespread. Hot dry windy index shows 
values increasing to nearly 400 by Monday. Stay tuned - fire 
season is definitely not over until the region receives 
widespread wetting rainfall. 

&&

.MARINE...as of 5:18 PM PST Wednesday...Northwest winds will
gradually diminish across the coastal waters this afternoon and
evening. A moderate northwesterly fresh swell will continue
tonight then diminish Thursday. A long period northwest swell is
forecast to move into area waters on Friday.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...Red Flag Warning...North Bay Mountains and East Bay Hills
             GLW...Pt Arena to Pigeon Pt 10-60 nm until 9 PM
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm until 9 PM
             SCA...Pt Arena to Pt Reyes 0-10 nm until 6 PM
             SCA...Pt Reyes to Pigeon Pt 0-10 nm until 6 PM

&&

$$

PUBLIC FORECAST: RGass
AVIATION: Canepa
MARINE: CW
FIRE WEATHER: Dykema/MM

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