995
FXUS66 KMTR 181750
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1050 AM PDT Tue Aug 18 2026

...New AVIATION...

.KEY MESSAGES...
Updated at 428 PM PDT Mon Aug 17 2026

 - Slight warming trend continues through Wednesday

 - Marine layer remains compressed through mid week

 - Light winds continue to be mitigating factor for
   Timber Fire

&&

.UPDATE...
Issued at 950 AM PDT Tue Aug 18 2026

Water vapor imagery continues to show a trough of low pressure
over the Eastern Pacific, with multiple areas of low pressure
rotating around this trough. One of this areas of low pressure is
retrograding a bit, which is allowing the high pressure system
over the Desert Southwest to expand more over California today.
That said, the upper level flow over California remains out of the
southwest, and we continue to see high clouds streaming through
this flow into Central California. These clouds are not going to
limit heating today, and given the building ridge, expect inland
areas to warm 3 to 5 degrees today over yesterday.

Meanwhile, did once again see a good marine layer push this
morning, despite it being slightly shallower, around 1500 feet. We
also some drizzle along the immediate coast in San Mateo and
Monterey County this morning, with 0.01 inch reported. Given the
marine layer being slightly shallower, it is clearing more
quickly this morning. However, expect it to once again to linger
along the coast today, with some areas struggling to see the sun.
Therefore, expect coastal areas to remain at or below normal for
this time of year, while the inland areas see the warmer
conditions.

One other note is that we did see significant nocturnal drying in
the higher elevations last night. In fact, we had widespread
fair to moderate with areas of poor recoveries, especially down
in the Santa Lucia, where several sites struggled to recover to 30
percent. Expect these overnight recovery conditions to continue to
worsen tonight, as the ridge takes hold, and the marine layer
compresses even more.  Palmer

&&

.SHORT TERM...
Issued at 1145 PM PDT Mon Aug 17 2026
(Today and tonight)

Mid/upper level clouds continue to stream from southwest to
northeast across our area with mild temperatures expected once again
overnight into early Tuesday morning. The mild start to the day will
help bump temperatures at least a few degrees (away from the marine
layer) higher from Mondays values as the influence from upper level
ridging over the Four Corners nudges west. H85 temperatures will be
around 23-24C by peak heating which is in the 90th percentile for
this time of year. With that, the warmest temperatures will be at
higher elevations, especially the East Bay Hills and Santa Lucias,
including higher portions of the Timber Fire. Fortunately, light
winds continue to be a mitigating factor to more rapid spreading of
the fire.

&&

.LONG TERM...
Issued at 1145 PM PDT Mon Aug 17 2026
(Wednesday through Monday)

Warmer temperatures persist Wednesday under the influence of the
aforementioned ridging aloft, however the troughing over the EPAC
pushes back east and slightly north by Thursday with a sharpening
trough axis well offshore. The cool down for Thursday through the
remainder of the extended forecast will be subtle and gradual.
There are at least two tropical waves that will pass well to our
south, the first on Thursday followed by a more organized wave
with tropical development possible by the end of the weekend into
the beginning of next week. We`ll be keeping an eye on any
midlevel moisture advection north from either of the two waves.

&&

.AVIATION...
(18Z TAFS)
Issued at 1049 AM PDT Tue Aug 18 2026

Seeing typical retreat of stratus to the coastline this morning
with most interior sites returning to VFR through the afternoon.
Onshore winds are forecast to increase late this morning and
persist through the early evening before diminishing after sunset.
Going with a persistence forecast for this evening and into
Wednesday morning. Thus, moderate to high confidence for IFR to
LIFR conditions to return to the coast by mid-to-late evening and
then spreading across the Bay Area terminals late evening into
early Wednesday morning. Expecting stratus to retreat to the
coastline by mid-to-late Wednesday morning.

Vicinity of SFO...MVFR. Stratus is forecast to clear by between
18Z- 19Z and give way to VFR conditions through late evening. In
addition, moderate to fresh west-northwestery breeze is forecast
this afternoon and early evening. High confidence for MVFR and
moderate to high confidence for IFR returning late this evening
and persisting through late morning on Wednesday.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Mix of LIFR to IFR conditions currently.
VFR conditions briefly return this afternoon before IFR to LIFR
conditions redevelop early this evening into Wednesday morning.
Gentle breeze is forecast this afternoon before diminishing after
sunset.

&&

.MARINE...
(Today through Sunday)
Issued at 950 AM PDT Tue Aug 18 2026

A fresh to strong northwest breeze will develop across the outer
waters through the day and extend into the inner waters tonight
into Wednesday. Winds then remain elevated through the end of the
forecast period. Locally stronger winds are possible in the
coastal jet regions north of Point Reyes and along the Big Sur
coast. Seas build to 7 to 9 feet Tuesday and Wednesday before
subsiding late week.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 3 PM PDT Wednesday for Pt Arena to Pt
     Reyes 10-60 NM.

&&

$$

SHORT TERM...JM
LONG TERM....JM
AVIATION...RGass
MARINE...RGass

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