944
FXUS66 KMTR 221756
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1056 AM PDT Sun Sep 22 2024

...New AVIATION...

.SYNOPSIS...
Issued at 337 AM PDT Sun Sep 22 2024

Temperatures will continue to warm this afternoon, with highs in the
low 90s inland across the North Bay, East Bay and higher elevations
above the marine layer extending south into Monterey County and San
Benito County. The heat builds further Monday and Tuesday, with
areas of moderate HeatRisk possible for inland locations not under
the influence of the marine layer.

&&

.UPDATE...
Issued at 853 AM PDT Sun Sep 22 2024

Extensive stratus coverage has developed across the valleys this
morning, beginning to mix out along the very fringes of the
stratus deck. The 24-hour temperature trends show temperatures
across the region running near or slightly above those seen this
time yesterday. Still expecting a warming trend to continue today
and Monday, but possibly not as dramatic as the current forecast
shows. Will evaluate the trends throughout the rest of the
morning, taking a closer look at the short-term temperature
forecast with the afternoon forecast package.

DialH

&&

.SHORT TERM...
(Today and tonight)
Issued at 337 AM PDT Sun Sep 22 2024

Low level ridging below a slow developing upper level weakness in
the H50 height fields will result in warmer temperatures today and
then climb even higher tomorrow to start the work week with moderate
HeatRisk possible for inland locations away from the marine layer.
Deterministic guidance has consistently advertised the weakly forced
upper level disturbance, though the exact location and evolution
over the next couple days has been difficult to pin down. It has
likely limited the impacts of the heat somewhat over the next few
days, but highs on Monday will still be in the mid 90s to near 100
inland across the North, South and East Bay, also farther south into
Monterey County above the marine layer and San Benito County.

&&

.LONG TERM...
(Monday through Saturday)
Issued at 337 AM PDT Sun Sep 22 2024

The potential for moderate HeatRisk will extend into Tuesday under a
stagnant airmass between a developing upper low offshore to our west
and building ridge over the Intermountain West. By Wednesday, the
offshore upper low merges with a strengthening trough over the
Pacific Northwest. The upper troughing to our north will spread
cooler temperatures aloft over our region, resulting in lower
surface temperatures closer to normal for this time of year for
Wednesday and beyond, while another upper level disturbance develops
offshore of SOCAL and remains quasi-stationary into next weekend.

&&

.AVIATION...
(18Z TAFS)
Issued at 1042 AM PDT Sun Sep 22 2024

Tricky forecast earlier this morning with amendments and
adjustments to many TAFS. The reason? A compressing marine layer
through sunrise allowing for expansion of the marine layer, but
also patchy fog/reduced visibility. As of the 18Z TAF package
issuance, vis satellite shows rapid thinning of stratus layer
yielding VFR all terminals by 18Z or shortly thereafter. VFR this
afternoon/this evening with low stratus hugging the coastline. Do
expect the lurking stratus to move inland again tonight. However,
building high pressure will leading to further compression.
Extent of stratus will not be as much as this morning.
Additionally, NE flow begins to develop late night just above the
marine layer. Earlier clearing of stratus for Monday AM rush.

Vicinity of SFO...Clearing over terminal by 1815Z. Stratus
lingering SE and E of runways. Onshore flow developing later this
afternoon. IFR to LIFR late tonight.  Earlier clearing tomorrow.

SFO Bridge Approach...Stratus layer clearing from the
edges...therefore some stratus will linger longer over the
approach than SFO.

Monterey Bay Terminals...VFR this afternoon. CIGS return early
this evening.

&&

.MARINE...
(Today through Friday)
Issued at 853 AM PDT Sun Sep 22 2024

High pressure over the Eastern Pacific and low pressure over
California will lead to breezy northwesterly flow over the coastal
waters through at least Monday. Winds will be strongest over outer
waters north of Point Reyes. The locally stronger winds will
result in a steeper fresh swell. Northwesterly breezes decreasing
and seas abating Tuesday. Seas rebuilding to become rough in the
outer waters towards the end of the forecast period.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 9 AM PDT Monday for Pt Arena to Pt
     Reyes 10-60 NM.

&&

$$

SHORT TERM...JM
LONG TERM....JM
AVIATION...MM
MARINE...MM

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