709
FXUS66 KMTR 070505
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1005 PM PDT Tue May 6 2025

...New AVIATION, MARINE...

.SYNOPSIS...
Issued at 1123 AM PDT Tue May 6 2025

Overall the weather is pretty quiet. There will be a
modest warming trend late week before a cold front brings gusty
winds and a significant cooling trend from Sunday-Monday.

&&

.UPDATE...
Issued at 846 PM PDT Tue May 6 2025

No significant forecast updates planned for this evening. Upper
low near Las Vegas kept convection confined to the southern
Sierra. Locally our weather was and continues to be most impacted
by a southerly wind reversal that brought clouds to the coastal
locations that usually see sunny skies under NW wind flow pattern.
The strong winds pushed through the Golden Gate and out into the
Delta with continued breezy winds at this hour from Napa out
towards Vacaville. Meanwhile SFO is currently showing an odd
southerly wind (Half Moon Bay too) for the evening hours in
response to all of this. NAM model shows the southerly wind flow
continuing over the near shore waters while more typical NW winds
persist offshore which has produced some interesting stratus movement
this afternoon and evening. The 00z Oakland sounding showed a well
defined inversion layer around 2200 feet and the SFO-Sac gradient
of 3.6 mb is allowing the cool marine air to ooze inland with
early evening satellite trend showing the stratus filling in rapidly
for most locations including through the Petaluma gap for the North
Bay, in-situ for the Berkeley redwoods as well as the Monterey Bay
region and northern Salinas Valley. The nosing ridge of high
pressure aloft with 850 mb temps 14-15 celsius is only acting to
strengthen the low level inversion layer. In general temps to
remain seasonably mild for Weds before a more noted warming trend
starts Thursday and kicks into gear for inland areas Friday and
Saturday. Any warm to hot weather will be short lived as the
longwave pattern remains active and high confidence for a noted
dry cold frontal passage on Sunday with rapid cooling trend for
2nd half of the weekend and into early next week.

&&

.SHORT TERM...
(This afternoon through Wednesday)
Issued at 1123 AM PDT Tue May 6 2025

A southerly surge has brought the marine layer back to the coast and
the Ft. Ord profiler is measuring the depth around 2,000 feet. As
these winds are south-southeasterly, the San Francisco Peninsula
was mostly spared from the stratus this morning. Even if you
managed to stay out of the clouds, temperatures are much colder
for virtually everybody today. The average 24 hour change is
around -7F. While the SFO-WMC gradient has relaxed from -6.7
to -3.6 mb over the last 24 hours, there are still some lingering
offshore winds in northern Napa County. Otherwise the NE winds
have subsided as the 500 mb ridge becomes the dominant feature.
According to high resolution guidance, the southerly surge will
likely persist through Wednesday morning before more typical NW
winds return. Expect more extensive stratus coverage tomorrow
morning.

&&

.LONG TERM...
(Wednesday night through next Monday)
Issued at 1123 AM PDT Tue May 6 2025

As the ridge builds a warming trend will kick off from Wednesday
through Friday. There is high confidence that the 850 mb temperature
is expected to exceed 17C by Friday, which is the 90th percentile
for this time of year. Temperatures are expected to climb into the
mid to upper 80s for many inland areas, with upper 60s to low 70s
along most of the coast. The Southern Salinas Valley looks like the
warmest spot with King City temperatures in the 90s. Santa Cruz
looks like the warmest coastal location with temperatures in the mid
to upper 70s due to terrain driven adiabatic warming. There is still
some uncertainty with how deep the following trough or cut-off low
will be, but it looks likely that the warming trend will reverse
sharply starting Sunday. Broadly speaking, our current forecast
brings inland temperatures from 10 degrees above normal to 15 below
normal from Saturday - Monday. The associated cold front also
brings a slight chance for light rain and some gusty winds to
start next week.

&&

.AVIATION...
(06Z TAFS)
Issued at 1005 PM PDT Tue May 6 2025

MVFR-IFR stratus is expanding into the coastal valleys and will
cover most terminals during the early morning hours on Wednesday.
Breezy onshore winds continue to diminish with light and variable
winds overnight. Stratus mixes out late Wednesday morning with the
immediate coast remaining socked in through the 24-hour TAF period,
with breezy onshore flow resuming in the afternoon.

Vicinity of SFO... VFR continues into the early overnight hours,
with MVFR stratus over the terminal after midnight through late
Wednesday morning. Northwest flow continues to diminish with light
and variable winds overnight before breezy onshore flow resumes
Wednesday afternoon. Clouds return to the terminal area Wednesday
evening, but confidence is low to moderate for a ceiling at the
terminal. OAK has a higher confidence for ceilings late Wednesday
evening before the end of the TAF period.

SFO Bridge Approach... Confidence is low in stratus impacts on
Wednesday evening before the end of the TAF period. Otherwise
similar to SFO.

Monterey Bay Terminals... MVFR-IFR stratus currently covers SNS and
is expected to impact MRY over the next couple of hours. Light
drainage winds prevail overnight before breezy onshore winds resume
Wednesday afternoon. High confidence that SNS clears out, and
moderate confidence that MRY scatters out, late Wednesday morning,
with moderate confidence in an early return of MVFR-IFR stratus to
MRY early Wednesday evening.

&&

.MARINE...
(Tonight through next Monday)
Issued at 1005 PM PDT Tue May 6 2025

Moderate to fresh northwest winds will continue over the northern
outer waters from Point Arena to Point Reyes through the night
before diminishing early Wednesday morning. Elsewhere, gentle
southerly winds will turn northwesterly through Wednesday morning.
Seas have subsided with moderate seas to continue through the end
of the forecast period. Northerly winds strengthen late this week
with widespread fresh to strong gusts expected through the end of
the forecast period.

&&

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

     Small Craft Advisory from 9 PM Wednesday to 3 AM PDT Thursday
     for Pt Arena to Pt Reyes 10-60 NM.

&&

$$

SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...DialH
MARINE...DialH

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