320
FXUS66 KMTR 021156
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
456 AM PDT Tue Jul 2 2024

...New AVIATION, MARINE...

.SYNOPSIS...
Issued at 1258 AM PDT Tue Jul 2 2024

A significant and prolonged heat wave begins today and will last
through the weekend. Inland areas will have dangerous record
breaking heat this week. Red Flag Warnings are in effect for some
higher elevations due to low humidity and gusty offshore winds.
Skip the fireworks this year. Wildfires will be easy to start and
quick to spread.

&&

.SHORT TERM...
(Today and tonight)
Issued at 1258 AM PDT Tue Jul 2 2024

The high pressure dome is building, causing the marine layer to
compress. Most areas will start the day cloud-free, though some
areas along the immediate coast or northern Salinas Valley may
have some fog or mist during the morning commute. Temperatures
are already 5-10 degrees warmer than 24 hours ago, and that trend
will accelerate after sunrise. Some inland areas will reach the
90s by 11 AM and 100s before 1 PM. The max temperature forecast
has increased by a degree or two for most of the area. San
Francisco will have a sharp gradient across the city with mid to
upper 80s expected Downtown, and mid 60s at Ocean Beach. San Jose
has a 40% chance of reaching 100 degrees today. The Red Flag
Warning recently began, and wind gusts of 15-30 mph have already
been observed in the mountains this morning. Low temperatures
tonight will be several degrees warmer than they are currently,
and well above average with many inland areas remaining in the
upper 60s or low 70s. There won`t be much relief overnight.

&&

.LONG TERM...
(Wednesday through Monday)
Issued at 1258 AM PDT Tue Jul 2 2024

The record breaking heat isn`t going anywhere. The high pressure
dome will linger over California for at least a week, with more
long range guidance suggesting that timeline may even be
optimistic. A very slow moving ridge of high pressure is causing
air to descend. Descending air warms and dries on the way down.
This leads to cloud free skies and hot, dry air at the surface.
Fortunately, as the high pressure gradually meanders east and
becomes centered directly over California, the moderate offshore
winds will abate by mid week as gentle onshore flow returns. This
will help with fire weather concerns and allow coastal areas to
cool off a bit. However, with the strong high pressure in place,
these onshore winds will only cool off areas very close to the
coast, as the marine layer will remain compressed under 1,000 ft.

The temperature ticked up a degree or two with the updated
forecast for most areas. The deterministic NBM is well below the
mean, especially for max temps in coastal areas such as San
Francisco and Santa Cruz. The difference is less obvious for
inland areas, but still noticeable. The forecast leans heavily
towards the ensemble mean, rather than the deterministic NBM, based
on past performance during similar heat waves. The overall message
is the same, inland areas will have dangerous heat extending
through the weekend at least.

The previous discussion mentioned that we have a chance to break
the all-time record temperature at 850mb (roughly 5,000 ft)
measured by the OAK weather balloon this weekend. The current
record is 31C with observations dating back to 1948. While that
remains a possibility, another important point to demonstrate the
length of this heat wave is the amount of time we are expected to
stay above 25C at 850mb. This threshold is only reached 1.8% of
the time, so we`ll call it the 98th percentile of low level
atmospheric temperatures. With greater than 90% certainty, the
current GEFS and ECMWF ensembles predict that we will climb above
the 98th percentile Tue or Wed, and reamin above this threshold
for at least 6 days. At that point the GEFS shows a 10% chance of
dipping below 25C, but on the flip side, there is also a 10%
chance of a new all time record of 32C at that time. This spread
demonstrates that the confidence is certainly lower next week, but
the most likely timeline for relief (when the ensemble means dip
below the 25C) doesn`t occur until Saturday the 13th. That`s 12
days in the 98th percentile of 850mb temps.

*While we have all seen temperatures like this before, this event
 may end up approaching the upper end of what we`ve seen
 historically, in terms of longevity. Heat is the #1 weather-
 related killer in the United States. This is a significant heat
 wave, especially for inland areas. Please take the proper
 precautions, as impacts will only worsen day-by-day. A bit on
 heat safety below.

HEAT SAFETY AND IMPACTS:

By now youre well aware that it is going to be extremely hot this
week with well-above normal temperatures; now lets talk about the
impacts of excessive heat and actions we can take to minimize those
impacts: With extreme heat, and especially prolonged heat events, it
is a marathon, and not a sprint. Our bodies, infrastructure, pets,
and livestock will be under duress from heat over the span of days
as opposed to just a day or two. Given that there is little
overnight relief expected throughout this event, this is where it
really becomes a marathon, and precautionary measures are
necessitated in order to prevent adverse results such as heat
exhaustion and stroke. This is not just for individuals sensitive to
heat, but rather, the entire population. Heat for this duration and
at these temperatures can be dangerous for everyone. Do your body a
favor and if you can, suspend outdoors activities between the hours
of 10am and 7pm on days where Heat Advisories or Excessive Heat
Warnings are in effect. Remain in air conditioning if you have that
available to you in your residence, or seek out air conditioned
environments such as stores, movie theaters, restaurants, libraries,
and cooling shelters.

If you cannot access air conditioned environments, must be outside,
work outdoors, or otherwise, there are other precautionary measures
you can take to keep yourself and your loved ones safe (including
pets!) during excessive heat. Take frequent breaks in the shade and
ensure that you are drinking plenty of cool water, or other
hydrating beverages such as sports drinks with electrolytes. Avoid
DEHYDRATING drinks such as alcohol or caffeinated beverages. That
aside, visiting your city public pool or a lake, river, or ocean can
also help keep you cool, but dont forget the life jacket! If
planning on swimming, stick to where there is a lifeguard, and know
the ocean or river conditions before you get in. Although outside of
our area, its worth repeating: rivers can run fast and cold with
snowmelt in the Sierra Nevada mountains, and cold water shock can
set in quickly, which can lead to loss of muscle control, and
ultimately, drowning. Cold water shock can also set in for ocean-
goers. Have fun at the water, but be smart, be safe, and Know Before
You Go!

Finally, if you do not have air conditioning or cannot access it,
and also cannot access a body of water to stay cool: consider taking
cold showers or baths, turn on those sprinklers or garden hose and
have a fun time in your own makeshift water park, or lay a damp,
cool towel across your head or body. Even just dipping your hands
and feet in cool water can help to abate feelings of excessive heat.
For pets and livestock, make sure they have access to shade
structures or areas, and have clean water freely available to them
at all times. They do not have the same resources or ability to
notify of feeling heat-stressed as we do, so check in on them! If
theyre permanently outdoors, consider giving them a quick rinse-
down with the hose or set up misters, as the evaporation will help
to keep them cool as well.

&&

.AVIATION...
(12Z TAFS)
Issued at 426 AM PDT Tue Jul 2 2024

IFR-LIFR ceilings continue at the immediate Central Coast and into
the Salinas Valley, expected to retreat to the coast later this
morning. Light winds this morning will develop into breezy onshore
flow in the afternoon and evening. Stratus is expected to build at
the coast this evening but lower confidence in impacts to the
MOnterey bay terminals. Marginal LLWS concerns continue during the
overnight periods in the North Bay.

Vicinity of SFO...High confidence of VFR through the TAF period.
Light winds overnight, building to a breezy west-northwest flow this
afternoon with gusts up to 20-25 knots. Winds diminish in the
evening.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Rather perplexingly, while fog has
developed at SNS and is expected to continue through the morning,
MRY has cleared out for extended periods this morning. Such a
development is rather humbling and speaks to the challenges of
forecasting on the West Coast. Ceilings have returned to MRY, and
have kept the ceilings in the TAF, but will monitor observations
for the rest of the morning. Breezy northwest flow develops this
afternoon. In another puzzling twist, updated model output has MRY
and SNS potentially staying clear through the night tonight into
Wednesday morning.

&&

.MARINE...
(Today through Sunday)
Issued at 426 AM PDT Tue Jul 2 2024

  Fresh to strong northerly winds continue over the outer coastal
waters today, with gale force gusts possible in the northern outer
waters. Winds will diminish and become moderate to fresh by mid-
week as surface high pressure strengthens and moves eastward.
North to northwest winds prevail through the forecast period but
wind  direction may become more variable by late week as winds
weaken.  Elevated significant wave heights between 10-12 feet
continue  through mid- week before abating by the late week.
Portions of the northern outer waters may see peak wave heights
between 12-16  feet through mid-week.

&&

.FIRE WEATHER...
Issued at 330 PM PDT Mon Jul 1 2024

A Red Flag Warning will be in effect starting at 11pm tonight for
some elevated locations in the North Bay Hills, East Bay Hills,
Marin and Sonoma Coastal Ranges through late tomorrow evening  with
the North Bay Hills RFW continuing until 5pm Wednesday. RH  values
are generally in the teens with gusty north/northeast offshore flow.
As the hot and dry pattern persists, fuels continue to dry. ERCs are
drying in to the 70-90 percentile range across our region.
Combine that with the expected surge of campers over the long
holiday weekend and obvious risks of fireworks, putting our area
in a combustible situation through next weekend. Fireworks should
not be used this year, and campers should be very careful with
anything dragging from trailers and securing campfires.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Coastal Flood Advisory until 11 PM PDT Wednesday for CAZ006-506-
     508.

     Heat Advisory from 11 AM this morning to 7 PM PDT Wednesday for
     CAZ006.

     Red Flag Warning until 11 PM PDT this evening for CAZ502-503-512-
     515.

     Excessive Heat Warning from 11 AM this morning to 8 PM PDT
     Sunday for CAZ502>504-506-510-512>518.

     Red Flag Warning until 5 PM PDT Wednesday for CAZ504.

     Heat Advisory from 11 AM this morning to 8 PM PDT Sunday for
     CAZ508-528-529.

PZ...Small Craft Advisory until 3 AM PDT Wednesday for Pt Arena to Pt
     Reyes 0-10 nm.

     Gale Warning until 3 AM PDT Wednesday for Pt Arena to Pt Reyes
     10-60 NM.

     Small Craft Advisory until 9 AM PDT this morning for Pigeon Pt
     to Pt Pinos 10-60 NM.

&&

$$

SHORT TERM...Flynn
LONG TERM....Flynn/Clouser
AVIATION...DialH
MARINE...DialH

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