FXUS66 KMTR 202054
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
154 PM PDT Mon Jul 20 2026

...New SHORT TERM, LONG TERM, FIRE WEATHER...

.KEY MESSAGES...
Updated at 154 PM PDT Sun Jul 19 2026

 - Approximately 15% chance of high based showers through Tuesday.

 - Breezy onshore winds return for the second half of the week.

 - Temperatures will hover around normal through the week.

&&

.SHORT TERM...
Issued at 154 PM PDT Mon Jul 20 2026 (This evening through 
Tuesday night)

Afternoon satellite and radar show clouds and showers streaming
over the area from post tropical storm Elida. The showers are 
high based, meaning the bottoms of the the showers are around 
5-8000 feet. At this elevation in summer months, the rain coming
out of the showers typically evaporated before hitting the ground.
Even so, with the forecast cycle, showers were added into much of
the area with QPF limited to 0.01", which is generous. Really 
showers will be lucky to reach a trace.

The overall pattern is fairly interesting with a broad ridge over
the western US, trying to flex into the west coast, but challenged
by trough over the eastern Pacific. This trough is the exit route
for post tropical storm Elida, riding up and over the edge of the
ridge. This is where the complexities creep in. The strength of
the ridge and trough are not static and models are trying to
project them, but only offer about a 80% vision rate. Meaning,
there is still error in the forecast. The error is showing up in
the POP and QPF fields and trying to play with temps as well. As
stated, the POP forecast has from NBM and other model guidance for
the next 36 hours as Elida passes by. QPF will remain low, unless
there is a wobble eastward of the remnant system. Models are
showing nice vorticity bands (at 500, 700, and 850 mb) spinning 
off the remnant low, heading our way on Wednesday. This comes into
play as it could provide a focus point for more intense showers, 
if there remains enough moisture in the area at that time, and 
right now that does not look probable. This will be something to 
watch as this system can still make a wobble. At this time there
is no expectation of dry thunderstorms or even lightning. The
depth of any convection just doesn't look deep enough to reach the
hail growth zone needed to exchange charges and generate
lightning. There would need to be a substantial shift in the
pattern to find better areas of instability and even then, the
system would need to intensify as undergoes extratropical
transition, which it is showing no signs of. No mention of dry
thunderstorms in the forecast.

Models continue to show Tuesday as the warmest day of the week
with temps running about 5ish degrees above normal. However, the
remnant low may provide more clouds than expected and cap
temperatures to around normal. Confidence is high that in the wake
of the remnant low temps will cool slightly, around 5ish degrees
below normal. By the weekend the four corners high will try to
press into the area again causing more warming.

Summary: Post tropical storm or remnant low Elida will continue to
make the forecast challenging with respect to nearly all sensible
weather elements. Keep an eye on an ever changing forecast.

&&

.LONG TERM...
Issued at 154 PM PDT Mon Jul 20 2026 (Wednesday through next 
Sunday)

In the wake of the remnant low confidence is high that temps will
cool slightly, around 5ish degrees below normal, as troughing
prevails. By the weekend the four corners high will try to press 
into the area again causing more warming. This will take us from a
deeper marine layer for the second half of the workweek to a more
compressed one for the weekend. The one thing to watch for as the
trough makes it self known is onshore winds. Winds from the ocean
on to land will increase each afternoon. Some key locations like
Petaluma gap, Altamont, and through the Golden Gate will gust each
afternoon. Strength will depend on where you are at.

&&

.AVIATION...
(18Z TAFS)
Issued at 1049 AM PDT Mon Jul 20 2026

Mid to high level clouds continue to stream across the region from
the southwest this morning. These clouds helped eroding the 
stratus deck below with most terminals having scattered out at 
this hour. Showers accompanying these mid/high clouds may produce
a shower here and there however most will not hit the ground and
fall as virga. VFR conditions and diurnal winds will prevail 
this afternoon. High confidence in the return of IFR conditions to
coastal terminals tonight with low confidence elsewhere due to 
the shallow nature of the marine layer.

Vicinity of SFO...VFR conditions and northwesterly flow will
prevail. Low confidence on the return of an IFR cigs tonight,
however current thinking brings IFR cigs in around 05z over KOAK
and between 13z-17z over KSFO.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR conditions will prevail with 
moderate northwesterly winds kicking in by this afternoon. 
Moderate to high confidence on IFR cigs returning tonight. 
Current thinking has IFR cigs returning around 02z.

&&

.MARINE...
(Today through Saturday)
Issued at 1049 AM PDT Mon Jul 20 2026

Light to locally moderate northwesterly winds will prevail 
through midweek, becoming moderate Thursday into Friday. Slight  
to moderate seas will prevail. Tropical cyclone activity in the 
Eastern Pacific Ocean will spur several rounds of moderate period 
southerly swells; hazardous conditions from mixed seas may result.
Instability from the remnants of the tropical cyclone will also 
bring a slight chance of convection that may bring showers as well
as gusty and erratic outflow winds that would be result in 
hazardous conditions to small craft.

&&

.FIRE WEATHER...
Issued at 154 PM PDT Mon Jul 19 2026

No significant impacts expected as sub-tropical moisture moves
over the Bay Area and Central Coast. There has been some
discussion of dry thunderstorms, but as of this afternoon models
are not indicating an environment that would support their
development. At this point I would give dry thunderstorms a 
probability of less than 1% this week. What should be expected is
an isolated shower here or there with little to no accumulation. 
The marine layer will remain fairly well mixed out through Tuesday
afternoon, but should start to build back in late Tuesday and 
Tuesday night. Expect it to reach around 1000 feet by midweek.
Strong onshore winds will develop each afternoon for the second
half of the week. They typical places will gusts like they do
every summer afternoon.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&

$$

SHORT TERM...BFG
LONG TERM....BFG
AVIATION...CW
MARINE...CW

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Prepared by Boulder-Creek.com Weather at: Mon Jul 20 14:30:03 PDT 2026