047
FXUS66 KMTR 061852
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1152 AM PDT Sat Jul 6 2024

...New AVIATION, MARINE...

.SYNOPSIS...
Issued at 103 AM PDT Sat Jul 6 2024

Day 5 of the heat wave and triple digit temperatures will return
to inland areas this afternoon. A slight cool down begins Sunday,
but hot weather will continue through next week. Red Flag
Warnings remain in effect through Saturday night.

&&

.UPDATE...
Issued at 902 AM PDT Sat Jul 6 2024

Near term analysis - morning satellite imagery shows a shallow
marine layer had nosed its way inland overnight, but it`s already
retreating back the coast. Even though it`s retreating it won`t
disappear and will likely hug the coast through the day. As a
result, we`ll likely see some large temperature spreads from the
coast to the interior of 30-40 degs. Speaking of large
temperatures spreads, we`ve already seen some impressive
temperatures spreads in the vertical this morning too. Higher
elevations didn`t really cool off overnight as the marine layer
came in over lower elevations. Marin Headlands and Big Sur coast
are two great examples of temps in the 50s and 80/90s over nearby
higher elevations.

No update needed this morning...heat and fire are still the main
weather topics.

MM

&&

.SHORT TERM...
(Today and tonight)
Issued at 103 AM PDT Sat Jul 6 2024

A few daily records will likely fall this afternoon as the second
peak of this heat wave continues. Some inland areas will be in
the triple digits including Santa Rosa (101), Livermore (106),
and King City (105). Coastal areas will continue to enjoy nature`s
air conditioning as the marine layer fills up with stratus this
morning. These coastal clouds will come and go over the weekend,
but the cooler weather will remain.

Not much change to the short term forecast tonight as Saturday
continues to look like one of the hotter days in this prolonged
heat wave. The 850 mb temperature (measured at 27.5C at 00Z) will
likely peak today, with both the ECMWF and GEFS ensemble means
near 30C at 07/00Z. That benchmark has only been hit 6 times out
of roughly 56,000 weather balloon observations going gback to
1948. There`s even an outside chance (5% or so) that the all-time
record of 31C will be hit. Either way, we are continuing to deal
with historic heat, especially at higher elevations.

&&

.LONG TERM...
(Sunday through Friday)
Issued at 103 AM PDT Sat Jul 6 2024

There is a little bit of good news in the long term forecast.
The strong, persistent ridge will finally slide east, with the
axis crossing California on Sunday. This will bring marginally
cooler temperatures. Inland areas will trade low 100s for mid to
upper 90s. Those slightly more mild conditions will then persist
through next week. I know everyone is looking for the end of this
heat wave, but the best we are going to get is a minor
improvement. While there won`t be many 100 degree thermometers
outside of southern Monterey and San Benito Counties (including
Pinnacles Nat`l Park), we are still way above seasonal averages.
In the short term section I mentioned the chance for 30C 850 temps
today. While we are glad to see that will start to come down next
week, it likely won`t drop below 24C until next weekend. 24C is
certainly better than 30C, but it`s still in the top 10% for this
time of year. So when will the heat wave actually end? There is
some indication that a cold front is possible next Friday. It`s
still early, and the models don`t yet agree, but there is hope.

This has been a long heat wave, and there is still much more to
come. Please continue to taking the following precautions to keep
yourself, family, friends and pets safe from the heat:

-Stay inside in an air conditioned environment between 10am and 7pm.
-Suspend unnecessary outdoor activities during the extreme heat, but
if you must be outdoors, take frequent breaks in the shade  or AC
and drink cool water.
-Know the signs and symptoms of Heat Exhaustion vs. Heat Stroke!
Heat Stroke can be deadly if not treated immediately by a medical
professional. Call 911 if you suspect someone is suffering from Heat
Stroke.
-Wear a lifejacket, swim near a lifeguard, and check conditions
before entering the water if going to a river or ocean to cool off.
Rivers and the ocean are extremely cold, and Cold Water Shock can
turn into paralysis and drowning if you are not careful.
-Use a cool and damp towel on your body if you do not have AC and
are feeling hot. Or, take a cool shower or bath.
-Do not leave kids or pets in a parked car.
-Ensure pets and livestock have access to shade and water.

&&

.AVIATION...
(18Z TAFS)
Issued at 1152 AM PDT Sat Jul 6 2024

A strong lower level temperature inversion is present under
strong mid to upper level high pressure i.e. sinking, compressing
air, 925 mb (~ 2500 feet) and 850 mb (~5000 feet) level temperatures
on today`s 12z Oakland upper air sounding were 34.8 Celsius and
30 Celsius which tied 4th warmest at the 925 mb level and is 6th
warmest at the 850 mb level for the period of record since 1948.
Lower level temperatures within the temperature inversion will
hold either steady or warm a little more during the day. The SFO-SAC
pressure gradient (onshore wind) is weak at 1.3 mb however it does
prevail over the 0.7 mb ACV-SFO and 0.4 mb SFO-SMX pressure gradients
therefore allowing a marine layer intrusion of coastal fog, stratus
/LIFR-IFR conditions/, including patchy light drizzle this morning.
Inland it`s VFR.

Wildfire smoke and haze from the Lake Fire to our southeast may
lower slant range visibility aloft tonight and Sunday per recent
vertically integrated HRRR smoke forecasts. Northwest to west surface
winds will otherwise help keep good surface visibilities continuing
through today and this evening at least.

Recent HRRR and HREF output show coastal fog and stratus /LIFR-IFR/
redeveloping and moving locally inland tonight and Sunday morning,
otherwise VFR for inland terminals and stratus and fog mixing out
/VFR/ back to the coastline by late Sunday morning.

Vicinity of SFO...VFR. Light northeast wind becoming westerly and
increasing during the afternoon and early evening with gusts to
20 to 23 knots. Light west to northwest wind tonight and Sunday
morning, becoming west 15 to 20 knots Sunday afternoon.

SFO Bridge Approach...Similar to SFO. Slant range visibility likely
lowering by tonight and Sunday, lowest during sunset/sunrise.

Monterey Bay Terminals...Northwest winds over the coastal waters
is transporting fog and stratus /IFR/ conditions to the coastline
around the Monterey Bay. Still have late morning and afternoon
maximum mixing to erode stratus and fog back to VFR. Between early
and mid evening stratus and fog /LIFR-IFR/ will move back inland
for the overnight and Sunday morning then mixing out to VFR by late
Sunday morning and afternoon.

&&

.MARINE...
(Today through Thursday)
Issued at 1028 AM PDT Sat Jul 6 2024

High pressure continues through the forecast period. Winds
continue to diminish with moderate to fresh northwest winds
persisting through the early work week. By midweek, northwest
winds strengthen with moderate to fresh sustained winds and strong
gusts possible across the coastal waters. Significant wave
heights will build to 10 to 13 feet by mid to late week.

&&

.FIRE WEATHER...
Issued at 920 AM PDT Sat Jul 6 2024

Just finished up coordination calls with agency fire partners and
neighboring offices. No updates needed for ongoing fire
headlines. Red Flag Warnings remain in effect for the North Bay
Interior Mountains, East Bay Hills and Santa Cruz Mountains until
9 PM Saturday. Red Flag Warnings are also in effect for the Santa
Lucia Mountains, San Benito County, and the Southern Salinas
Valley until 9 PM Saturday as well.

Marine layer brought some overnight relief for lower elevations,
but higher elevations (specifically Red Flag Locations) saw no
relief with temps in the 80s/90s and RH less than 30 percent.
Winds are breezy at times too. Needless to say critical fire
weather conditions.

While the Red Flag Warning is set to expire this evening with
weakening winds, lack of humidity recovery tonight over higher
elevations will lead to near critical conditions.

For Sunday, areas of concern will be focused away from the coast
with another hot and dry day. Area of greatest concern will be the
East Bay were afternoon gusty pass/gap winds combined with hot/dry
conditions will lead to isolated pockets of critical fire weather.
Not widespread enough for another Red Flag, but critical
nonetheless.

MM

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Excessive Heat Warning until 11 PM PDT Wednesday for CAZ502>504-
     506-510-512>518.

     Red Flag Warning until 9 PM PDT this evening for CAZ504-512-
     515>518.

     Heat Advisory until 11 PM PDT Wednesday for CAZ508-528-529.

PZ...None.
&&

$$

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

Visit us at www.weather.gov/sanfrancisco

Follow us on Facebook, Twitter, and YouTube at:
www.facebook.com/nwsbayarea
www.twitter.com/nwsbayarea
www.youtube.com/nwsbayarea