782
FXUS66 KMTR 110551
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1051 PM PDT Wed Jul 10 2024

...New AVIATION, MARINE...

.SYNOPSIS...
Issued at 334 AM PDT Wed Jul 10 2024

Last peak of the heat wave starts today and lasts through
Friday. Cool down through the weekend with near normal temps by the
start of next week.

&&

.UPDATE...
Issued at 957 PM PDT Wed Jul 10 2024

A warm core 500 mb high pressure system (geopotential heights 597
decameters) remains nearly stationary over the western CONUS. The
high is very slow to move since it`s situated over land, locked
in place with strong diurnal surface heating (a positive feedback
loop). Our forecast area remains over the western periphery of
this high pressure system, 31.1 Celsius 925 mb and 27.3 Celsius
850 mb temperatures on the evening Oakland upper air sounding are
near the max moving average for early-mid July. There were no record
highs at the long term stations today, but it was again above to
well above normal inland far removed from any undercutting i.e.
surface to near surface cooling coastal breezes. Compressional
warming is also seen on the Bodega Bay and Fort Ord profilers,
with maritime air only ~ 800 feet deep in the vicinity of Fort
Ord.

The northerly pressure gradient is 6.5 mb ACV-SFO, strengthened
today to 7 mb, there`s also a southerly SMX-SFO 2.3 mb pressure
gradient and the SFO-SAC gradient is 2.6 mb. The NAM is under-
forecasting both ACV-SFO and SMX-SFO gradients, the strength of
both need to be closely monitored, an increasing northerly
gradient and wind will strengthen downsloping warming, drying and
bring the lower level temperature inversion closer to sea level,
in turn sharply turning temperatures upwards again post sunrise
(high solar angle). A strengthened southerly gradient will help
keep a surface trough along the coast assisting the onshore wind
as long as both gradients maintain.

Added record highs for July 11th below. 110F Livermore daytime
high forecast tomorrow e.g. will near tomorrow`s record high 111F
July 11, 1961.

&&

.SHORT TERM...
(This evening through Thursday)
Issued at 110 PM PDT Wed Jul 10 2024

Today begins another warm up with temperatures across the interior
reaching 103-109 degrees while it remains in the 60`s and 70`s near
the coast. Excessive Heat Warnings remain in effect for the interior
areas where major HeatRisk are expected (isolated areas of extreme
HeatRisk) through Friday evening. Elsewhere, Heat Advisories are in
effect with temperatures expected in the 80`s to mid 90`s (away from
the immediate coastline). Tonight, conditions cool in the lower
elevations into the 50`s for most locations while is stays in the
upper 60`s to lower 80`s in the higher elevations.

Tomorrow is expected to be the peak of this heat event with
afternoon maximum temperatures expected to be a few to several
degrees warmer than today as the marine layer compresses slightly.
It is worth noting that conditions away from the marine influence
will remain very dry with early morning (highest elevations) and
afternoon humidity dropping into the upper single digits to low
twenties, elevating fire weather concerns.

&&

.LONG TERM...
(Thursday night through next Tuesday)
Issued at 110 PM PDT Wed Jul 10 2024

Ever so slight cooling is expected on Friday with temperatures near
what we will see Wednesday afternoon, still very warm to hot across
the interior with the advisories and warnings remaining the same.
That said, people sensitive to heat and those recreating/working
outdoors remain at greatest risk for heat-related illnesses.

Remember these heat safety tips:

* Stay hydrated and drink plenty of fluids.
* Wear lightweight, light-colored clothing.
* Reduce time spent outdoors or stay in the shade.
* Never leave people or pets unattended in vehicles.
* Use sunscreen if going to the coast or the pool.

By the weekend, HeatRisk and temperatures start their decline as the
ridge migrates to the east and a deep mid/upper level low digs into
the Gulf of Alaska. This should bring more of an onshore flow to the
region with slightly cooler temperatures, better humidity
recoveries, and more onshore breezes by the afternoon hours.
Temperatures are expected to be near to slightly above seasonal
averages by the start of next week.

&&

.AVIATION...
(06Z TAFS)
Issued at 1051 PM PDT Wed Jul 10 2024

Mix of VFR and LIFR conditions across the board. Current satellite
guidance shows less widespread stratus than yesterday and the Fort
Ord profiler shows a more compressed marine layer. HREF guidance
shows stratus primarily staying concentrated along the Central Coast
and directly along the coast of the SF peninsula. Stratus may extend
into portions of the SF Bay and North Bay later tonight with IFR to
LIFR CIGs developing but confidence remains low to moderate. Any
stratus that does develop will dissipate by mid to late morning with
stratus to return along the Central Coast by the late evening. Light
winds out of the west to northwest persist overnight with winds
strengthening and becoming more moderate during the day.

Vicinity of SFO...VFR through the TAF period. Low confidence that
stratus will reach SFO tonight due to a more compressed marine layer
and lack of model consensus. FEW to SCT low level clouds may move
over the airport overnight through the morning hours. Onshore flow
persists with winds gradually weakening overnight before moderate to
at times gusty winds return during the day.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...IFR to LIFR conditions persist through the
late morning. Satellite shows a small eddy near MRY which is
temporarily leading to FEW/SCT CIGs compared to BKN/OVC. IFR CIGs
are expected to prevail at MRY as this eddy dissipates but will
continue to monitor. Stratus will continue through the late morning
before VFR conditions return in the afternoon. Moderate uncertainty
about timing of stratus return tomorrow evening - for now leaning
towards a stratus return in the late evening between 02-04Z.

&&

.MARINE...
(Tonight through next Tuesday)
Issued at 1051 PM PDT Wed Jul 10 2024

Gusty northwest winds becoming more widespread over the coastal
waters, particularly over the northern outer coastal waters and
lingering through the weekend. Occasional gusts near gale force
may be possible over the far northern outer waters Thursday into
Friday. Significant wave heights will build to between 10 to 12
ft, on average, over the outer coastal waters. Portions of the
northern outer coastal waters will see wave heights peak between
12 to 14 feet during the late week. Significant wave heights,
sustained wind speeds, and wind gusts begin to subside over the
weekend.

&&

.CLIMATE...
Issued at 342 PM PDT Wed Jul 10 2024

Record high temperatures at the long term climate stations for
July 11.

Station          July 11th record high

Santa Rosa       113 in 1913
Kentfield        112 in 1913
Napa             106 in 1961, 1913
Livermore        111 in 1961
San Francisco     92 in 1983
SFO Airport       93 in 1983
Redwood City     104 in 1961, 1959
Half Moon Bay     74 in 1959
Oakland downtown  98 in 1983
San Jose         103 in 1913
Salinas Airport   87 in 1934
King City        107 in 1983

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory until 8 PM PDT Friday for CAZ502-503-506-508-512-
     516-528.

     Excessive Heat Warning until 8 PM PDT Friday for CAZ504-510-
     513>515-517-518.

PZ...Small Craft Advisory until 3 PM PDT Friday for Pt Arena to Pt
     Reyes 10-60 NM.

     Small Craft Advisory until 3 AM PDT Thursday for Pigeon Pt to Pt
     Pinos 10-60 NM.

&&

$$

SHORT TERM...RGass
LONG TERM....RGass
AVIATION...Kennedy
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