883
FXUS66 KMTR 122052
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
152 PM PDT Sun May 12 2024

...New SYNOPSIS, SHORT TERM, LONG TERM...

.SYNOPSIS...
Issued at 146 PM PDT Sun May 12 2024

Slight decrease in daytime highs today and tomorrow as a result of
weak troughing. Temperatures warm little into the mid week as
ridging resumes. Coastal stratus will continue to bring overcast
skies for coast and bay shorelines in the early portions of the
day, then clearing in the afternoons. Hints at a cooling trend in
the late week.

&&

.SHORT TERM...
(This evening through Monday)
Issued at 146 PM PDT Sun May 12 2024

Its a quiet day, with a relatively quiet forecast in store, so lets
have some fun with this morning`s discussion and learn a little bit
about why we saw the cloud cover we did near the coast.

The 12Z sounding from KOAK this morning revealed a strong inversion,
a condition in which air temperature rises with increasing height
instead of falls, as well as a deeply saturated layer reaching just
shy of 950mb beneath this inversion layer. What is 950mb you ask?
Well, as you go higher in the atmosphere, pressure begins to fall.
950mb simply describes in the atmosphere a certain pressure level.
However, the actual altitude at which particular pressures are
found is always changing as a result of the atmosphere
continuously evolving as troughs and ridges build and decay. But
enough about that, lets move on.

If you were to glance at satellite imagery this morning, you would
have seen abundant cloud cover near the coast, as well as it
penetrating further inland into coastal valleys and bay communities
than in mornings previous. This cloud cover is represented by the
saturated layer within the sounding where the temperature and
dewpoint lines meet, with the inversion acting as a lid or a cap on
top, limiting the altitude to which these coastal clouds could
reach. A glance at the Ft. Ord profiler which examines the depth and
altitude of the marine layer shows the maximum altitude of the
marine layer reaching only to about 1400` approximately. Therefore,
if you live at a higher elevation near the coast, say 1500` and
above, you did not see overcast skies this morning from the marine
stratus, but rather, probably looked down on a blanket of grey and
white below. Meanwhile, coastal communities lying below 1400` feet
or so were enveloped in clouds, leading to grey skies. However, at
this time, coastal cloud cover has begun to recede as daytime solar
heating helps to warm air near the surface and the clouds. As this
warmer air rises, it will help to sap moisture, or humidity, from
the saturated layer, aka the clouds, and effectively evaporate them
until clear skies are achieved.

So what does this all mean in short? We saw extensive cloudy and
grey conditions near the coast, bays, and even reaching into coastal
valleys this morning as a result of total saturation being reached
in the lower levels of the atmosphere. These clouds reached their
maximum altitude at about 1400` before they hit a cap and could not
lift any higher. As the sun rose and began to warm the Earth, clouds
began to dissipate as warmer air was mixed into them and helped to
evaporate or rid the lower levels of moisture. As this warming
continues, cloud cover will begin to recede, leading to clear skies
for much of the region.

So there you have it! Perhaps you just wanted to hear what the
temperatures were going to be today, or what the *potential* aurora
viewing conditions might be tonight. Instead you got an unsolicited
meteorology lesson. Well, don`t fret, we`ll cover those other things
too.

Warm temperatures continue today, though will be just a few degrees
cooler than what was seen yesterday as weak troughing aloft begins
to build into the region. Expect daytime highs in the mid to lower
80s today for interior regions, and upper 50s to low 60s along the
coast. Tomorrow, those daytime highs drop to upper 70s to very low
80s, and mid to upper 50s, respectively. As this troughing regime
begins, this should allow the marine layer to deepen and for
coastal stratus to push a bit further inland tonight as air rises
and is able to surpass coastal mountains and elevated terrain
easier. That being said, if you`re looking to do some aurora
scouting, you`re going to need to go higher up in elevation, and
further inland. For more on geomagnetic storms and aurora
forecasts, please visit the Space Weather Prediction Center`s
website at spaceweather.gov. Or visit their Twitter/X account
@NWSSWPC.

&&

.LONG TERM...
(Monday night through next Saturday)
Issued at 146 PM PDT Sun May 12 2024

High pressure, or ridging, will begin to build towards
Tuesday, allowing temperatures to begin to warm up once again.
However, with the main ridge axis staying out over the northern
Pacific ocean, we are not likely to see temperatures warm
significantly, and likely not become as warm as we saw them Friday
and Saturday of this past week. For interior regions of our area,
daytime highs will likely be in the low 80s, topping out into the
mid 80s. Coastlines and bay shores will see high temps in the upper
50s to low 60s as onshore winds help to keep things cooler at the
coast. Minor heat risk for the most sensitive populations will be
present through much of the week. Stratus is expected to bring
cloudy conditions at the coast most mornings, then generally
clearing into the afternoons each day.

Towards the late week and next weekend, the end of the
forecast period, it appears the ridge begins to break down, and
troughing begins with decent agreement, though not perfect, amongst
models, hinting at a bit of a cool off for most locations. All
for now.

&&

.AVIATION...
(18Z TAFS)
Issued at 1055 AM PDT Sun May 12 2024

Generally a repeat of yesterday in terms of the extent of marine
stratus. As expected, saw slightly less FG impacts and higher cigs
this morning due to marine layer expansion. However, many
locations still dealing with IFR cigs and slow to clear this
morning. Expecting stratus to linger along coastal areas through
the day today with CLR conditions over land. High confidence in a
relatively early return of stratus to most terminals tonight.

Vicinity of SFO...Clearing conditions to VFR late this morning.
Marine stratus will likely linger along the coast, Golden Gate,
and near the San Bruno Gap most of the day. High confidence in IFR
cigs returning overnight, though timing for them to make it around
to the terminal remains moderate confidence. Otherwise typical
diurnal onshore flow.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Fairly effective clearing of stratus for
much of the areas away from the immediate coastline. Expecting
inland areas to remain mostly CLR today, but marine stratus
will linger along coastal areas through much of today. Some areas
along the coast, especially the southern Monterey Bay, may see
periodic recurrence of IFR cigs through this afternoon as an eddy
that has formed in the Bay could essentially waft the clouds back
and forth over the terminals.

&&

.MARINE...
(Today through Friday)
Issued at 1055 AM PDT Sun May 12 2024

Fair weather continues for the waters of Central California
through the week as high pressure builds over the Eastern Pacific.
Northwest winds begin to increase this evening to a fresh breeze.
Seas build to 12 to 15 feet by Tuesday before gradually abating
through the rest of the week.

&&

.BEACHES...
Issued at 719 PM PDT Fri May 10 2024

Long period southwest swell will lead to slightly elevated chances
for sneaker wave and rip current development this weekend.
Conditions are expected to stay below Beach Hazards Statement
criteria as swell height will only be between 1-2 feet. However, in
light of anomalously warm temperatures and increased likelihood of
people traveling to the coast, visitors to the beach should remember
to take safety precautions to prevent being caught by an unexpected
large wave and to never turn your back on the ocean.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from 3 PM to 9 PM PDT Monday for Mry Bay-Pt
     Pinos to Pt Piedras Blancas 0-10 nm.

     Small Craft Advisory until 9 PM PDT this evening for Pigeon Pt
     to Pt Pinos 0-10 nm-Pt Arena to Pt Reyes 0-10 nm.

     Small Craft Advisory until 3 AM PDT Monday for Pt Pinos to Pt
     Piedras Blancas 0-10 nm.

     Small Craft Advisory until 9 AM PDT Tuesday for Pt Arena to Pt
     Reyes 10-60 NM.

&&

$$

SHORT TERM...AC
LONG TERM....AC
AVIATION...Behringer
MARINE...Behringer

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