321
FXUS66 KMTR 100811
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
111 AM PDT Fri May 10 2024

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

.SYNOPSIS...
Issued at 0105 AM PDT Fri May 10 2024

A moderate HeatRisk will exist for the warmest inland areas for
today and Saturday as afternoon temperatures reach the 80s to
around 90. Cooler along the coast with onshore breezes. A slight
cooldown will occur by early next week.

&&

.SHORT TERM...
(Today and tonight)
Issued at 0105 AM PDT Fri May 10 2024

The large-scale pattern features high pressure aloft from the
northeast Pacific through the Pacific Northwest, with a weak cutoff
low over the Great Basin. Surface high pressure will remain
prominent across much of the west, with weak coastal troughing along
CA. 925 mb winds will maintain a north/northeast component today
providing a continuation of warm/low humidity conditions for inland
areas and the hills. However surface winds along the coast will
develop a more onshore (west/southwest) component through the day.
This will keep coastal temperatures more moderated, while still
relatively mild. A very shallow marine layer under 300 feet is noted
via the Fort Ord profiler this morning and this layer may deepen
slightly across southern portions of the coast today. The most
likely forecast outcome suggests that stratus/fog development
should remain relatively limited in this pattern, but wouldn`t be
surprised to see at least some patchy areas around the coast and
bays this morning. Elsewhere, there remains a little bit of mid-
level moisture and elevated instability such that we can`t rule of
the development of a shower or two over the inland mountains of
southeast Monterey and San Benito Counties. The most likely
forecast outcome is probably just some cumulus development, but
it`s worth noting that a few of the high resolution models and
HREF ensemble members show some simulated reflectivity returns
over these areas this afternoon. For now just something to watch.
Otherwise today`s main forecast concern is temperatures. And our
warmer inland areas will certainly be heating up. Probabilistic
forecasts indicate a high (70%+) probability for high temperatures
to reach 80 degrees or warmer for almost all areas, sans the
coast and coastal marine-influenced valleys. Typically warmer
places such as the Santa Clara Valley, southern Salinas Valley, and
the North/East Bay valleys will see temperatures well into the
80s, with the warmest spots eclipsing the 90 degree mark.
Locations with a 50% or greater probability for reaching 90
degrees today include the Sonoma Valley, Santa Rosa area, and
portions of the East Bay bordering the Sacramento Valley. This
will produce a moderate HeatRisk for these areas, with a minor
risk elsewhere. There will be some overnight relief however, as
temperatures tonight dip into the 50s for most areas, except for
some lower 60s in the interior hills.

Given the warm interior temperatures here`s a reminder of some 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.

&&

.LONG TERM...
(Saturday through Thursday)
Issued at 0105 AM PDT Fri May 10 2024

The upper ridge will remain prominent through Saturday, but will
weaken into early week as weak troughing encompasses the
Intermountain West. This will result in gradually cooling
temperatures, albeit still above normal inland. A moderate HeatRisk
will exist for the warmer areas on Saturday so it`s still a good
idea to practice heat safety. Otherwise high temperatures this week
will generally be in the 80s inland, 70s within the marine-
influenced valleys, and 60s on the beaches. Upper ridging looks to
re-establish across portions of the west for late week bringing
another possible warmup heading into next weekend.

&&

.AVIATION...
(06Z TAFS)
Issued at 1044 PM PDT Thu May 9 2024

Currently VFR at all terminals. VFR through the TAF period. As the
upper-level ridge weakens as it moves through the Pacific Northwest,
winds will slowly be allowed to increase and return to onshore flow
by tomorrow afternoon.

Vicinity of SFO...Currently VFR with breezy northwesterly flow. VFR
through the TAF period. Winds will become offshore by mid-morning
before slowly increasing and returning to westerly flow by tomorrow
afternoon.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Currently VFR and calm at MRY and VFR with
westerly flow at SNS. Confidence remains low that MVFR conditions
will return to the terminals during the TAF period. MRY will see a
transition from drainage flow to northwesterly flow overnight before
westerly winds prevail tomorrow afternoon. Northwesterly winds will
prevail through the TAF period at SNS.

&&

.MARINE...
(Tonight through next Wednesday)
Issued at 1044 PM PDT Thu May 9 2024

High pressure system brings light to moderate winds over the
waters. Winds will become more southerly along the Big Sur and
Monterey Bay region into Friday. Otherwise, gentle breezes out of
the north and northwest continue through the weekend first portion
of the weekend creating relatively calm conditions over the
waters. Dry weather continues through the forecast period as high
pressure dominates.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&

$$

SHORT TERM...SPM
LONG TERM....SPM
AVIATION...Sarment
MARINE...SO

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