269
FXUS66 KMTR 070855
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
155 AM PDT Sun Jul 7 2024

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

.SYNOPSIS...
Issued at 1236 AM PDT Sun Jul 7 2024

Day 6 of the inland heat wave. The peak of the event is finally
behind us and some minor relief is on the way this week before a
more substantial cool-down next weekend.

&&

.SHORT TERM...
(Today and tonight)
Issued at 1236 AM PDT Sun Jul 7 2024

ACARS data from Oakland flights are showing the 850 mb temperature
is 31C. The highest 850 mb temperature ever observed from the
Oakland weather balloon is 31.0C. This means we are experiencing
the hottest low level heat since records began 75 years ago.
Inland areas reached triple digits yesterday with a few over 110.
Higher elevations are seeing some of the hottest daily max and
min temps on record. For example Pinnacles National Park reached
116 degrees yesterday (all time record 117 9/6/20), and Mallory
Ridge (north of Livermore @ 1948 ft) only got down to 90 Saturday
morning before jumping back up to 106 in the afternoon.
Fortunately onshore winds and a shallow marine layer are keeping
coastal areas cool.

As the ridge axis moves across California, temperatures will begin
to cool a bit Sunday. The only record we are threatening is at
King City (105 forecast). Otherwise, most inland areas will stay
out of the 100s today. Higher elevations are still seeing very
warm conditions, but they will also begin to cool a few degrees
Sunday. Coastal areas will be much cooler (similar to yesterday)
with marine layer clouds breaking in the afternoon and returning
in the evening.

&&

.LONG TERM...
(Monday through Saturday)
Issued at 1236 AM PDT Sun Jul 7 2024

The cool-down will continue through Tuesday as the ridge continues
to slide east. While this is certainly welcome, it is not a
drastic improvement. To put it in perspective, the 850 mb temp is
currently in the top 99.99% (30.2 C) of historical observations.
We are anxiously awaiting it to drop back to the the 98% (25 C) by
Tuesday. We are still going to be well above average this week with
inland areas remaining in the 90s. By Wednesday, the cooling
trend flattens, and temps may tick back up a few degrees Wed-Fri
before a more substantial cool-down arrives this weekend.

This heat wave has been going for 5 days now and we are just now
getting on the back nine. The warm mornings and back-to-back
record breaking temperatures can cause cumulative effects that
make the situation more dangerous. Heat is the number 1 weather
related killer in the United States. Unfortunately lives will be
lost during this heat wave. Follow these tips to protect yourself,
your loved ones, and your animals.

-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. You can put your
 cellphone/wallet or even your shoe in the back seat as a reminder.
-Ensure pets and livestock have access to shade and water.

&&

.AVIATION...
(06Z TAFS)
Issued at 1108 PM PDT Sat Jul 6 2024
Mix of IFR to LIFR expected tonight at most airports with only SJC
and LVK expected to remain VFR through the TAF period. Confidence is
increasing that stratus will return farther inland tonight with
elevated fog potential in the North Bay and Central Coast.
Visibility is expected to decrease overnight but confidence remains
low to moderate as to how far visibility will decrease at STS.
Guidance indicates elevated fog potential at STS but ensemble
guidance currently keeps visibilities above 1SM. Winds will remain
onshore at all stations through the TAF period with lighter
overnight winds anticipated to become more moderate by tomorrow
afternoon. Haze and smoke may be visible from terminals, but it is
not expected to result in a reduction in flight category.

Vicinity of SFO...VFR transitioning to IFR overnight. Moderate
confidence that IFR CIGs will develop overnight with low to moderate
confidence as to how far visibility will decrease. Ensemble guidance
shows a few models (NBM, GLAMP) with visibilities dropping to 2SM
but other models (HRRR) do not show visibilities decreasing much
below 6SM. For now, continuing the thinking that visibilities will
decrease but leaning towards visibility only decreasing to 4SM.
Onshore flow persists with light overnight winds becoming more
moderate and gusty during the afternoon.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...LIFR becoming VFR by late tomorrow morning.
Night Fog shows low level stratus blanketing MRY and SNS with
observations reporting CIGs at 300 ft. Elevated potential for fog
development and visibility is expected to decrease to a 1/2SM. LIFR
conditions will persist through the night and into tomorrow morning
before VFR conditions briefly return. Stratus and LIFR conditions
will return by tomorrow evening. Onshore flow persists through the
period with light overnight winds becoming more moderate during the
day.

&&

.MARINE...
(Tonight through next Friday)
Issued at 1108 PM PDT Sat Jul 6 2024

Surface high pressure over the Pacific Ocean will continue  to be
the dominating feature through the period. Northwesterly  breezes
will prevail through the period, increasing tomorrow  afternoon as
the pressure gradient tightens. Significant wave  heights begin to
build to 10-13 feet in the outer waters by  Wednesday.

&&

.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.

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

PZ...Small Craft Advisory from 3 PM this afternoon to 9 AM PDT Monday
     for Pt Arena to Pt Reyes 10-60 NM.

&&

$$

SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...Kennedy
MARINE...Sarment

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