FXUS66 KMTR 050452
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
952 PM PDT Mon May 4 2026
...New AVIATION, MARINE...
.KEY MESSAGES...
Updated at 1204 PM PDT Mon May 4 2026
- Cooler temperatures and cloudy mornings through Tuesday with
light rain expected tonight through Tuesday morning for the SF
Bay Area
- Warmer and drier conditions return for the middle of the week
through the weekend
&&
.SHORT TERM...
Issued at 1204 PM PDT Mon May 4 2026
(This evening through Tuesday)
The satellite image shows some lingering low and mid-level clouds
throughout the Bay Area and Central Coast, accompanied by a east-to-
west band of high clouds entering the North and East Bays. Zooming
out to the synoptic level pattern, an upper level low is crawling
into the state, centered near the coast of Monterey County. This is
bringing cool conditions throughout the region and rain across the
SF Bay Area through Tuesday morning, as warm air advection driven by
the low pressure system interacts with the cooler air aloft. As
noted by the previous forecaster, lower surface pressures over the
Great Basin are practically canceling the offshore flow effects that
a east-to-west flow over the Sierra Nevada would typically produce.
In fact, the SFO-WMC pressure gradient is strongly positive (that
is, much higher pressure at the San Francisco Airport compared to
Winnemucca in north-central Nevada -- 9.8 mb higher as of 11 AM) and
will remain so through the overnight period. The rain band will come
into Sonoma and Napa Counties this afternoon into the evening
commute, steadily moving into the SF Bay Area this evening and
overnight before dissipating Tuesday morning. Rain totals have
continued to trend upwards, and the latest forecast now has totals
of around half an inch for the interior mountains of the North Bay,
around a quarter to half an inch for the North Bay in general, and a
tenth to a quarter of an inch south of the Golden Gate through the
southern reaches of San Mateo and Alameda counties. Localized rain
totals near one inch, as suggested by some high-resolution model
output, are very possible if the rain band overproduces. In
addition, there remains a 5 to 10% chance for thunderstorms through
the early part of Tuesday morning, with the chance for enhanced
rainfall intensity where storms set up.
Temperatures remain rather cool today with highs in the middle to
upper 60s across the inland valleys, and the upper 50s to lower 60s
along the coast. There may be a slight warm up in the most interior
valleys on Tuesday as highs go into the lower 70s, but otherwise
similar conditions are expected on Tuesday.
&&
.LONG TERM...
Issued at 1204 PM PDT Mon May 4 2026
(Tuesday night through next Sunday)
By Wednesday, the upper level low moves into the Great Basin and
southern Rockies with ridging building back behind it, leading to a
warming and drying trend across the region. Highs in the inland
valleys will steadily climb from the middle 70s to lower 80s on
Wednesday up to the middle 80s to the lower 90s for the upcoming
weekend, while locations near the Bays will warm from the middle 60s
to lower 70s on Wednesday, to the lower 70s to the lower 80s for the
weekend. These rising temperatures could bring Moderate HeatRisk for
the inland valleys on Sunday, corresponding to a moderate chance for
heat-related illnesses in sensitive populations (including children,
the elderly, pregnant women, and people who work or live outdoors).
Towards the latter part of the work week, a decaying front will
sweep through the far northern parts of California, which may bring
gusty conditions for the coast, ridgelines, and favorably oriented
valleys and passes Thursday through Saturday.
The CPC extended outlook shows that temperatures above the seasonal
averages are likely to persist through the middle of May, while
precipitation totals lean below the seasonal average. For context,
the seasonal average high in downtown San Francisco is around 64
degrees, while the seasonal average precipitation total for the May
11 to 17 period, as covered in the CPC 8-14 day outlook, falls a
shade under two tenths of an inch for the same station.
&&
.AVIATION...
(06Z TAFS)
Issued at 921 PM PDT Mon May 4 2026
Precip is finally trending southward toward SF Bay and ending for
the N Bay. Despite some precip CIGs remain rather high with VFR
and occasional MVFR. Will keep this trend through early Tuesday
AM. The farther south the precip moves it will begin to fade more
too. SJC will only have VCSH and MRY/SNS remain dry. Some
clearing expected Tuesday with VFR. Tuesday evening residual
moisture will bring a lot of strato-cu to the region with MVFR
CIGs.
Vicinity of SFO...VFR this evening with light rain and MVFR CIGs
possible by Tuesday AM. VFR expected for Tuesday afternoon with a
few CU. MVFR CIGs return Tuesday evening.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...VFR and dry. No precip expected later,
but some MVFR CIGs possible then VFR Tuesday afternoon with nearby
CU.
&&
.MARINE...
(Tonight through next Sunday)
Issued at 921 PM PDT Mon May 4 2026
Unsettled weather over the northern waters with passing showers
due to a weak weather system moving through early Tuesday. light
to gentle northerly breezes will persist Tuesday. Light wind and
seas continue through Wednesday as high pressure builds. Northerly
wind and seas increase Thursday into the weekend as more typically
strong springtime onshore surface pressure gradients develop over
the waters.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&
$$
SHORT TERM...DialH
LONG TERM....DialH
AVIATION...MM
MARINE...MM
Visit us at www.weather.gov/sanfrancisco
Follow us on Facebook, X, and YouTube at:
www.facebook.com/nwsbayarea
x.com/nwsbayarea
www.youtube.com/nwsbayarea
Prepared by Boulder-Creek.com Weather at: Mon May 4 22:30:03 PDT 2026
From the National Weather Service
|