FXUS66 KMTR 190705
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
1205 AM PDT Sat Sep 19 2026
...New SHORT TERM, LONG TERM...
.KEY MESSAGES...
Updated at 1202 AM PDT Sat Sep 19 2026
- Warming trend continues today
- Brief cooling on Sunday into Monday
- Warming trend resumes on Tuesday
&&
.SHORT TERM...
Issued at 1202 AM PDT Sat Sep 19 2026
(Today and tonight)
Marine layer stratus has developed along the coast and is flowing
into the SF Bay Area and Monterey Bay regions. Some patches of
radiational stratus have also developed inland. Further expansion
is expected across most of the valleys tonight before stratus
retreats to the immediate coast after sunrise.
The weather pattern places an upper level ridge over the West Coast
today, allowing for the warming trend over the last couple of days
to continue. The upper level trough that brought us cool
temperatures and widespread clouds is crawling over southern Idaho,
and as it does, the pressure gradients will start to support some
northeasterly offshore flow in the higher elevations of the North
Bay and East Bay, with gusts to 20 to 30 mph possible through the
morning hours. At midnight, the SFO-WMC gradient has turned negative
at -1.3 mb, and will peak around -2 or -3 mb during the 6-9 AM
timeframe. High temperatures in the inland valleys will reach the
80s to the lower 90s, while the Bays reach the upper 60s to the
lower 80s and the Pacific coast hovers in the lower to middle 60s.
Afternoon breezes should be similar to those seen yesterday with
gusts of 20 to 30 miles per hour along the coast, through favored
gaps and passes, and within the Salinas Valley.
&&
.LONG TERM...
Issued at 1202 AM PDT Sat Sep 19 2026
(Sunday through Friday)
On Sunday, a cutoff low heads into the state and interrupts the
warming trend, cooling the inland valleys by around 5 to 10 degrees
for Sunday and Monday such that highs will be in the middle 70s to
the lower 80s, rising to the middle 80s up to the lower 90s in the
interior parts of the North Bay and Central Coast, with the Bays see
highs in the middle 60s to the middle 70s. By Monday morning, the
core of the low should set up right over the Central Coast, giving
us a slight chance for drizzle.
Upper level ridging returns by Tuesday, and a warming trend resumes
with the current forecast showing Moderate HeatRisk returning to a
fair swath of the interior by Wednesday and Thursday, most notably
the interior East and South Bays and the Santa Lucia range. This
would correspond to a moderate risk for heat related illnesses
within sensitive populations (children, the elderly, pregnant women,
people with chronic diseases, and people who work or live outdoors
without adequate cooling or hydration). Inland highs for Wednesday
and Thursday are expected to be in the 90s, which is supported by
ensemble models continuing to show that 850 mb temperatures above
20C (or temperatures around 1500 ft above sea level above 68F) are
likely to nearly certain for those two days, with an average around
21-22C, close to the 90th percentile for this time of year. This is
a shade cooler than the last forecast update, so we will be watching
how the situation evolves as we go through the weekend.
&&
.AVIATION...
(06Z TAFS)
Issued at 1014 PM PDT Fri Sep 18 2026
Stratus is making its way inland bringing a mix of MVFR to IFR
ceilings to most terminals tonight. Onshore winds ease overnight
with their wind direction largely influenced by local terrain. By
Saturday morning, winds shift onshore again and increase to moderate
through the day. Most terminals will develop borderline MVFR-IFR
ceilings and may intermittently jump between the two categories.
Relied on persistence for STS with model guidance showing a high
chance for another round of fog early Saturday morning. Low to
medium confidence on whether APC, HAF, OAK, and MRY will drop to
LIFR overnight. Current TAF hints at the possibility of borderline
IFR-LIFR ceilings at the previously mentioned sites. Overall, medium
confidence on the exact ceiling heights and clearing times. HAF
might be the only terminal who does not clear on Saturday. If it
does, it will be for a short period.
Vicinity of SFO...Ceiling heights may jump between MVFR-IFR through
the course of the night with light onshore breezes. Medium
confidence on exact clearing time on Saturday as ceilings may
persist as late as 20Z (1 PM). Moderate westerly winds increase
through the afternoon and ease by sunset. Saturday evening shows a
promising return for stratus as early as sundown, though low to
medium confidence on the exact return time.
SFO Bridge Approach...Delayed arrival of stratus tonight compared to
SFO. Though, ceilings and wind pattern will generally be similar to
SFO.
Monterey Bay Terminals...IFR ceilings have already filled over MRY
and are slowly making their way over to SNS via current satellite
imagery. LIFR ceilings may develop intermittently overnight with
slight impacts to visibility. Onshore winds become light and
variable overnight. As stratus clears tomorrow morning, a moderate
onshore flow will develop through the afternoon. A similar stratus
pattern is expected again Saturday evening.
&&
.MARINE...
(Tonight through next Thursday)
Issued at 908 PM PDT Fri Sep 18 2026
Moderate to fresh northwest winds persist through the weekend.
Strong gusts up to 30 kt are possible across the northern coastal
waters, Big Sur coastal jet region, and the Monterey Bay region
through Saturday. Winds briefly diminish across the southern
coastal waters Saturday morning, but increase again to fresh by
Saturday afternoon. Slight to moderate wind driven seas prevail
this weekend and steadily build to rough early next week.
&&
.FIRE WEATHER...
Issued at 429 AM PDT Fri Sep 18 2026
The marine layer is expected to begin redeveloping itself through
the day as a ridge develops over the state. By the evening hours the
marine layer should be around 1000-1500 feet, along with attendant
impacts of stratus development below the marine layer inversion and
poor overnight humidity recoveries within and above the thermal
belts. As the ridge develops, weak offshore flow is possible
Saturday morning, particularly across the higher elevations of the
North and East Bay.
DialH
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 3 AM PDT early this morning for Mry
Bay-Pigeon Pt to Pt Pinos 0-10 nm-Pt Pinos to Pt Piedras
Blancas 0-10 nm.
Small Craft Advisory until 3 AM PDT Sunday for Pigeon Pt to Pt
Pinos 10-60 NM-Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt
Reyes 10-60 NM.
Small Craft Advisory from 3 PM this afternoon to 3 AM PDT Sunday
for Pigeon Pt to Pt Pinos 0-10 nm-Pt Pinos to Pt Piedras
Blancas 0-10 nm.
&&
$$
SHORT TERM...DialH
LONG TERM....DialH
AVIATION...Navarrete
MARINE...Navarrete
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Prepared by Boulder-Creek.com Weather at: Sat Sep 19 00:30:05 PDT 2026
From the National Weather Service
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