FXUS66 KMTR 121500
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
800 AM PDT Tue May 12 2026
...New UPDATE...
.KEY MESSAGES...
Updated at 1216 AM PDT Tue May 12 2026
- Gradual cooling trend develops today through midweek
- Warming and drying trend midweek and beyond
&&
.UPDATE...
Issued at 758 AM PDT Tue May 12 2026
Satellite imagery shows extensive stratus coverage across the
valleys with high clouds aloft, with the Bodega Bay profiler
showing an marine layer around 1500-2000 ft deep this morning.
Stratus should gradually pare back to the coastal regions through
the day with some inland development expected this evening. Gusty
onshore winds this afternoon and evening will contribute to the
potential for elevated fire weather threat in the farthest
interior regions of Monterey and San Benito Counties, particularly
the areas adjacent to the Central Valley where daytime relative
humidities are low and overnight recoveries are poor. Although the
threat is not widespread enough for fire weather products, any
well-aligned grass fires that start may take hold and spread
quickly. People in these interior regions should take care to
properly dispose of cigarettes and matches and avoid using
equipment that creates sparks.
DialH
&&
.SHORT TERM...
Issued at 1216 AM PDT Tue May 12 2026
(Today and tonight)
The pattern shift discussed on yesterday's AFD is upon us. A quick
snapshot of the longwave pattern over the West shows a ridge
sneaking off to the east and settling over the Desert SW and
knocking on CA is an upstream upper trough and associated cut-off
low. Onshore flow plus lower 500 mb heights equals a deep marine
layer presences this morning. Satellite fog product shows a decent
marine layer with way more inland intrusion than 24 hours ago.
Marine layer depth will vary from 1000-1500 feet this morning.
Light mist or drizzle will be possible along the immediate
coastline through this morning.
Deeper marine layer and onshore flow will lead to a later
clearing time of inland stratus for Tuesday. The coast on the
other hand may not see much in the way of clearing today.
Noticeable cooldown for Max Temps today bringing readings closer
to seasonal averages. Max Temps 60s to 70s coast/bays and 70s to
lower 90s interior.
If we follow the trend is your friend logic: the upstream upper
low has been trending more north and continues to do so. As such,
the chance for widespread drizzle and/or light rain has now been
removed from the forecast late Tuesday night into Wednesday. That
being said, still expecting another push of marine stratus
overnight.
&&
.LONG TERM...
Issued at 1216 AM PDT Tue May 12 2026
(Wednesday through Monday)
The upper low will sweep through Oregon during the day on
Wednesday. While the forecast has trended drier temperatures will
still be on the cool side. Wednesday will be coolest day of the
forecast. Additionally, expect some breezy onshore winds through
out the day. Winds will be strongest along the coast and inland
gaps/passes.
Quiet weather returns for the second half of the work week and
into the weekend with zonal flow, warming temps, night/morning
clouds.
&&
.AVIATION...
(12Z TAFS)
Issued at 600 AM PDT Tue May 12 2026
.AVIATION...
The stratus intrusion onshore has brought IFR-LIFR ceilings to most
terminals which should scatter out by late morning Tuesday. The
lower cloud ceilings are impacting the visibility at a few airports,
though are expected to improve by 17Z. Light winds will increase to
moderate strength by the afternoon with some terminals experiencing
gusts up to 20-25kts. The marine layer is expected to move back
onshore by Tuesday evening, though it won't be as expansive.
Vicinity of SFO...Moderate onshore winds will persist through the
TAF period with gusts reaching up to 25-27 kts Tuesday afternoon.
The moderate winds combined with high-level clouds should help mix
out the stratus layer and shift back to VFR conditions by 18Z. The
stratus deck is expected to return overnight (02-03Z) but should
remain MVFR through Wednesday morning.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...LIFR ceilings are causing misty conditions
which is impacting the visibility across the terminals this morning.
Conditions are expected to improve by 16-18Z with VFR conditions
forecast by 19Z. Light, variable winds are expected to become
moderate and onshore by the afternoon. Another night of stratus is
also anticipated to return by Wednesday evening.
&&
.MARINE...
(Tonight through next Sunday)
Issued at 949 PM PDT Mon May 11 2026
Occasional strong gusts continue through tonight across the far
northern outer waters. Otherwise, a moderate to fresh northwest
breeze will continue over the waters through midweek. Seas subside
but remain moderate with 4 to 6 foot seas through midweek. Winds
increase and seas build starting mid-week with gale force winds
and wave heights in excess of 10 feet likely starting Friday and
continuing through the weekend.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from 9 AM to 3 PM PDT Wednesday for Mry Bay-
Pigeon Pt to Pt Pinos 0-10 nm-Pigeon Pt to Pt Pinos 10-60
NM-Pt Arena to Pt Reyes 10-60 NM.
Small Craft Advisory from 3 PM this afternoon to 3 PM PDT
Wednesday for Pt Arena to Pt Reyes 0-10 nm-Pt Reyes to
Pigeon Pt 0-10 nm.
Small Craft Advisory from 3 AM to 3 PM PDT Wednesday for Pt
Pinos to Pt Piedras Blancas 0-10 nm.
&&
$$
SHORT TERM...MM
LONG TERM....MM
AVIATION...Navarrete
MARINE...Kennedy
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Prepared by Boulder-Creek.com Weather at: Tue May 12 10:30:03 PDT 2026
From the National Weather Service
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