FXUS66 KMTR 131310
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
610 AM PDT Wed May 13 2026
...New AVIATION...
.KEY MESSAGES...
Updated at 1200 AM PDT Wed May 13 2026
- Cooling trend continues today
- Warming and drying trend resumes Thursday through the weekend
&&
.SHORT TERM...
Issued at 1204 AM PDT Wed May 13 2026
(Today and tonight)
A disjointed marine layer is trying to reform overnight per
satellite fog product. Where it is reforming it's rather deep at
1500-2000 ft. The complicating factor in development of the marine
layer is the passing upper low well to the north in OR and a
trailing vort max/shortwave trough passing over region. Lastest
guidance continues to advertise some expansion of the marine layer
through sunrise, but it never completely fills in the "standard"
marine layer footprint. Morning low clouds will give way to
afternoon sunshine, even the coastal locations. The coastal
clearing today will be enhanced by the increasing northerly
gradients and stronger winds. SFO-ACV will ramp up to over 5 mb,
which is decent. Winds will be strongest over the coastal waters
this afternoon and immediate coastline with gusts of 25-45 mph
possible. Despite some sunshine temperatures will be close to or
below normal for mid May with highs in the 60s to lower 70s
coast/bays and 70s to mid 80s inland. It will be the coldest day
of the next seven.
For tonight, not expecting a ton of marine stratus due to
lingering stronger northerly flow and a departing upper level
trough.
&&
.LONG TERM...
Issued at 1204 AM PDT Wed May 13 2026
(Thursday through Tuesday)
By Thursday zonal flow develops over the region as high pressure
begins to build, but is tampered by a trough near the Gulf of AK.
The semi-zonal flow will continue through Friday. As such, a
gradual warming and drying trend will develop. A blip in the
longwave pattern with a sagging upper level trough over CA on
Saturday will drop temperatures back to near or below seasonal
averages. The sagging trough deepens and develops a low that
sweeps into the Great Basin. Why is this important for our area?
Pattern recognition points to bursts of offshore flow over the
higher terrain each night into morning hours beginning Sunday
into next week. This will lead to marginal humidity recovery at
night. Not a big fire concern at this point, but something we'll
need to monitor over the next few days. ERC charts are catching on
with a trend line back toward daily maxes.
More uncertainty for next week is around max temps Mon/Tue. While
the longwave pattern shows troughing to the east and a ridge over
the EPac it doesn't scream heat. The NBM is showing some rather
warm temps with interior 90s again. Call it recency bias, but 850
mb not 20C+ gives me pause on max temps from the NBM. Other ens
guidance is on the colder side and did verify better during our
most recent warm spell. That being said, we'll need to watch this
as well and trend temps down if needed. Stay tuned...
&&
.AVIATION...
(12Z TAFS)
Issued at 610 AM PDT Wed May 13 2026
.AVIATION...
Widespread moderate winds will impact the Bay throughout the day due
to the tightening pressure gradient driven by the dry cold front
passing through our region. Currently MVFR-IFR ceilings for most
terminals that will scatter out by 17-19Z (10am-12pm PDT). Model
guidance is not giving a strong signal on the return of a expansive
marine layer tonight. There may be some low-level stratus in the
coastal areas this evening though the marine layer is not expected
to expand far inland.
Vicinity of SFO...Borderline MVFR-IFR ceilings persist through late
morning Wednesday with moderate to fresh breezes. Wednesday
afternoon will bring gusts up to 30kts that will continue through
the evening. VFR conditions are expected throughout the day with
some low-level clouds beginning to creep in overnight. Winds should
also ease overnight.
SFO Bridge Approach...Current satellite (13Z) is showing a gap
amidst surrounding MVFR-IFR ceilings. Should become completely VFR
by the late morning and winds should match the general pattern of
KSFO with gusts up to 25kts.
Monterey Bay Terminals...MVFR ceilings persist through Wednesday
morning and are expected to mix out by the afternoon. Westerly winds
are also expected to increase through the day with VFR conditions
forecast through the end of the TAF period. Low to medium confidence
that a prominent marine layer will re-develop Wednesday evening as
we are currently in a transitional period. GFS LAMP and MOS guidance
are leaning more pessimistic meanwhile HREF is leaning towards a
few to scattered stratus deck. KMRY will continue to experience low
clouds Wednesday evening due to its proximity to the coast, though
it is unclear whether KSNS will join them.
&&
.MARINE...
(Tonight through next Sunday)
Issued at 443 PM PDT Tue May 12 2026
Hazardous marine conditions develop midweek and will continue into
next week. Winds increase through the remainder of the week with
strong to near gale force winds and occasional gale force gusts
Wednesday and Thursday. Wind driven seas will build to between 10
to 12 feet Wednesday and Thursday. Surface high pressure will
then strengthen over the eastern Pacific Friday into next week.
This will result in a strong coastal jet, widespread gale force
to potentially severe gale winds, and very high, wind driven seas
between 12 to 17 feet expected.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 3 AM PDT Thursday for Mry Bay.
Small Craft Advisory until 9 AM PDT Thursday for Pt Arena to Pt
Reyes 0-10 nm.
Gale Warning from 9 AM Thursday to 3 AM PDT Friday for Pt Arena
to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM.
Small Craft Advisory until 3 AM PDT Friday for Pt Pinos to Pt
Piedras Blancas 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm.
Small Craft Advisory until 3 AM PDT Friday for Pigeon Pt to Pt
Pinos 0-10 nm-Pigeon Pt to Pt Pinos 10-60 NM.
Small Craft Advisory until 9 AM PDT Thursday for Pt Arena to Pt
Reyes 10-60 NM.
&&
$$
SHORT TERM...MM
LONG TERM....MM
AVIATION...Navarrete
MARINE...JM
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Prepared by Boulder-Creek.com Weather at: Wed May 13 06:30:03 PDT 2026
From the National Weather Service
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