Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS66 KMTR 060439
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
939 PM PDT Wed Oct 5 2022

.SYNOPSIS...A gradual warming trend and dry conditions are expected
through the week as high pressure builds over the region. Slight
cooling and unsettled weather are possible during the early to mid
portion of next week as upper troughing approaches the region.

&&

.DISCUSSION...as of 09:14 PM PDT Wednesday...Continuing to see a
warming trend in the daytime highs across the region. Today`s
highs peaked in the 70s along most of the coast with 70s and 80s
around the Bay shorelines then mid 80s to mid 90s inland. The
hottest locations were in their typical spots: Eastern portion of
Napa county along with the far East Bay (Concord-Livermore and
eastward) were in the upper 80s to low 90s...interior Central CA
at Pinnacles National Park and Parkfield were 97 and 95,
respectively. Overall, those hotter interior areas ranged about 4
to 8 degrees warmer than yesterday`s max temps.

This is all thanks to the high pressure ridge sitting over the CA
coast which has brought a warmer airmass while also compressing
the marine layer to limit the cooling effect of ocean air. What`s
interesting is that cities closer to the coast like Santa Rosa,
San Francisco, and San Jose all showed a similar warming trend
around 3 to 8 degrees because the marine layer is more compressed
up north. The Bodega Bay profiler has a marine layer depth of only
300 feet. Meanwhile, to the south in Central CA, cities like Santa
Cruz, Salinas, and Monterey were similar to yesterday`s highs
within a few degrees (some warmer, some cooler). The Fort Ord
profiler has a deeper marine layer at around 1000 ft so the ocean
air was able to mitigate the warming trend from the ridge aloft.

On the nighttime satellite imagery, we see a blanket of stratus
over the ocean and butting up to the coastline. Since the marine
layer is more compressed up north, there`s only a slight intrusion
of stratus near Pt Reyes moving inland about 10 miles. Around
Monterey Bay, that slightly deeper marine layer has stratus all
around the Monterey Bay shoreline pushing inland and filling the
Salinas Valley towards King City (over 40 miles from the shore).

As overnight temperatures cool, we could see patchy fog develop
overnight into early morning hours due to the compressed marine
layer. So be on the lookout for periods of reduced visibility if
you`re driving late at night and into the morning commute hours.

&&

.PREV DISCUSSION...as of 02:48 PM PDT Wednesday...

Warm up accompanied by dry conditions continues into this weekend
as robust upper ridge remains situated over the west coast states.
The marine layer will be compressed under large-scale subsidence due
to the high pressure aloft, leading to patchy dense fog impacts
persisting into the mid-to-late morning into the weekend. Fog and
low clouds will mix out by the afternoons, giving way to sunny
afternoons with high temps slightly above normal. Coastal areas
will remain closer to seasonal temps.

As we move towards the start of next week, hints of a large-scale
pattern change are beginning to make their way into view. Cool down
starts Sunday as the ridge axis shifts to our west, making way for
an upper low to make its way southward along the western CONUS by
the Tuesday-Wednesday timeframe. Considerable model uncertainty
remains regarding the timing and placement of the low, but focus is
on a possible offshore wind event. As ensemble guidance comes to a
better agreement over the next few days, expect forecast details to
become more clear. The impact from last month`s rain are non-negligible
in some areas, but most heavier fuels remain dry. Given the warm
and dry conditions expected this weekend, will continue to monitor
the response of finer fuels and adjust forecast details accordingly
regarding critical fire weather conditions.

&&

.AVIATION...As of 5:31 PM Wednesday... For the 00Z TAFs. Some
coastal terminals, such as KMRY and KSFO, experience some
lingering clouds off the coast, but all sites are VFR. Satellite
shows the marine layer is hugging the coastline near the San
Francisco Peninsula and Southern parts of Monterey Bay. With a
persistent shallow marine layer (~700 feet at Bodega Bay and ~1100
feet at Fort Ord), chances are high for stratus to return with
IFR/LIFR cigs starting around 08Z near coastal valleys and along
the coastline. The NBM and the HREF did not have complete
agreement on timing of the return of stratus for KSTS and KAPC,
therefore less confident whether cigs will roll back in ~1-2 hours
sooner/later than expected near 07-09Z.

High confidence near KOAK on cigs but lower confidence on timing of
cigs to return, therefore tempo is in place for 07Z to 09Z.

Moderate onshore winds prevail throughout the rest of the day as the
high pressure ridge lingers over the region.

Vicinity of SFO... Although the satellite shows the marine layer
remains relatively close near to KSFO near the coastline, models
show VFR conditions for the area terminals. High confidence that VFR
will prevail into the evening. High confidence that stratus will
return near 12Z then start to dissipate mid morning. VFR conditions
return near 17Z as the diurnal heating takes into affect.

KSFO Bridge Approach... Similar to SFO.

Monterey Bay... KMRY shows IFR conditions for most of the TAF period
till about 06z, where LIFR conditions prevail until 17Z. Less
confidence on clearing of cigs and if there is any possible haze
near 21Z. This will be dependent on a combination of diurnal warming
and vertical mixing.

&&

.MARINE...as of 09:14 PM PDT Wednesday...High pressure will remain
nearly stationary over the eastern Pacific through late week
resulting in gusty northwest winds mainly across the northern
waters. Gusty northwest winds will  create choppy seas and
hazardous conditions for small craft.  Lighter winds are forecast
this weekend. Mixed northwest and  southerly swell continue
through the week.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...SCA...Pt Arena to Pt Reyes 0-10 nm until 3 AM
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm until 3 AM
             SCA...Pt Arena to Pigeon Pt 10-60 nm

&&

$$

PUBLIC FORECAST: Bingaman
AVIATION: SO
MARINE: Canepa

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


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.