FXUS66 KMTR 071840
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1140 AM PDT Tue Apr 7 2026

...New SHORT TERM, LONG TERM, AVIATION, MARINE...

.KEY MESSAGES...
Updated at 1038 AM PDT Tue Apr 7 2026

 - Marine layer clouds in the morning with clear skies in the
   afternoon Tue - Wed

 - Unsettled weather with widespread light to moderate rain 
   Friday through Saturday

 - Thunderstorms possible Friday and Saturday

&&

.SHORT TERM...
Issued at 1038 AM PDT Tue Apr 7 2026
(This afternoon through Wednesday)

The weather is mostly quiet in the short term. The marine layer 
deepened to 2,200 feet according to the 12Z sounding. That was 
enough to bring stratus to the coast and bay adjacent valleys. 
Those clouds are now clearing, and the cooler humid air will 
retreat back to the immediate coast this afternoon. Temperatures 
today will climb into the 70s across the interior, while the coast
is stuck in the low to mid 60s. A building short wave ridge will 
cause a subtle pattern shift through Wednesday. The most obvious
impact will be some compression of the marine layer under the 
higher pressure. This will cause less extensive stratus coverage 
Wednesday morning compared to what we saw this morning. Otherwise 
conditions will be very similar to today with a gentle NW breeze,
comfortable temperatures, and mostly clear skies in the afternoon.

&&

.LONG TERM...
Issued at 1038 AM PDT Tue Apr 7 2026
(Wednesday night through next Monday)

The pattern starts to change on Thursday. A mature, vertically 
stacked, cut-off low pressure system over the Eastern Pacific 
will slowly drift East towards the coast through the day. The 
first indications of this system will be increasing high clouds 
and a wind shift from NW to SW. The North Bay may get some light 
prefrontal rain in the afternoon or evening, and it's possible 
that an outer rain band could bring a lightning strike or two, but
for most it will be a nice day. As the low continues to drift 
towards the coast, rain will become more widespread Friday morning
and continue, off- and- on, through the day. The biggest question
of the forecast is thunderstorm chances. Cut-off lows making 
landfall have surprised us in the past, so it's certainly worth a 
deep investigation as we get closer to the event. Since there is 
no obvious steering mechanism, it's hard to pin down what path 
these cut-off lows will take. That's important as the maximum 
lift, wind shear, and vorticity will all line up right near the 
low pressure center. The timing also plays a role, with maximum 
instability during the warmest temperatures in the afternoon.

The thunderstorm chances are revitalized Friday as a reinforcing
trough digs down from the Gulf of Alaska. Whether we get storms 
or not remains in question, but an associated cold front will more
than likely bring additional rain to the region. Right now the 
afternoon looks like the wettest period, but that could still 
change. All told we expect to get somewhere between 0.25-0.75" 
across the valleys, and up to 1.5" in the coastal mountains. From 
a rainfall perspective, that puts this event firmly in the 
beneficial category, with no flooding impacts expected. The only 
caveat is if thunderstorms or strong showers do develop, the 
storm motion will likely be relatively slow, so any associated 
downpours could cause localized flooding, especially in urban 
areas. A drying trend will probably start on Sunday, but the 
ensemble clusters disagree on the pattern next week. There's 
currently a 60% chance for a warm dry ridge, and a 40% chance for 
a cool, wet trough.

&&

.AVIATION...
(18Z TAFS)
Issued at 1038 AM PDT Tue Apr 7 2026

The marine layer stratus has cleared across all terminals,
including Half Moon Bay this time. The stratus bank has mostly
pulled well offshore, increasing the confidence that it won't be
back for an early return. That being said, there is still a very
good chance for stratus to return overnight, but a compressing
marine layer will limit the areal extent compared to yesterday.

Vicinity of SFO...Moderate to strong WNW winds are expected to
develop by the early afternoon and persist through the evening before
slowly tapering off overnight. There is about a 40% chance for
stratus to return to the terminal Wednesday morning. The chances
are very good that a cloud filled marine layer makes it to the
coast and spills through the Golden Gate, but the wind direction
and compressing marine layer both suggest SFO itself may stay in 
a clear pocket this time. If ceilings do develop, expect high IFR 
or low MVFR heights.

SFO Bridge Approach...Clear this afternoon. Similar to SFO
Wednesday.

Monterey Bay Terminals...The skies have cleared and VFR conditions
will remain through the day. The exact timing of the stratus
return is hard to pin down. While I was surprised by how early 
the clouds returned last night, the marine layer is compressing 
and the clouds have pulled back well off the coast. GFSLAMP 
probabilistic guidance shows there is only a 20% chance of 
ceilings before 06Z tonight. They are, however, very likely to be 
in place by 12Z, with high IFR or low MVFR bases.

&&

.MARINE...
(Today through Sunday)
Issued at 1038 AM PDT Tue Apr 7 2026

A gentle to moderate NW breeze and slight to moderate seas will
prevail through Tuesday. Winds will remain moderate while
gradually shifting to a SW direction from Wednesday through
Thursday ahead of a low pressure system. This system will will
bring disturbed weather with possible thunderstorms on Friday.
Winds will increase to a strong NW breeze this weekend as
subtropical high pressure builds over the Eastern Pacific.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 3 AM PDT Wednesday for Pt Pinos to Pt 
     Piedras Blancas 0-10 nm.

&&

$$

SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...Flynn
MARINE...Flynn

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Prepared by Boulder-Creek.com Weather at: Tue Apr 7 14:30:02 PDT 2026