Lafayette, California 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

847
FXUS66 KMTR 041905
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1205 PM PDT Mon May 4 2026

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

.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...
(18Z TAFS)
Issued at 1130 AM PDT Mon May 4 2026

An upper low west of Monterey is allowing for showers to rotate
off the Sierra and towards the Bay Area. Isolated showers and
t-storms possible this afternoon but best chance of stratiform
precip will occur between 05z-12z Tuesday over the the North Bay
and SF Bay terminals. Cigs mainly VFR through 05z this evening
then lowering at times. Morning overcast Tuesday should clear by
17-18z as the low moves eastward and high pressure builds.

Vicinity of SFO...Cigs mainly above 3000 feet this afternoon due
to instability of nearby low. Best chance of showers occurs
between 07-14z Tuesday with lowering of cigs. Clearing trend by
18z Tuesday as upper low ejects and drier NW flow returns with
building high pressure.

SFO Bridge Approach...Similar to SFO under this synoptic pattern
with clouds developing over the SF Peninsula but blowing over the
bridge approach this afternoon/evening.

Monterey Bay Terminals...Cig heights mainly above 3000 feet the
rest of this afternoon and evening.

&&

.MARINE...
(Today through Saturday)
Issued at 438 AM PDT Mon May 4 2026

A light to gentle breeze continues over the waters with winds to
become more moderate by Tuesday. A weak upper level disturbance
lingers over the region through midweek. This disturbance will
bring light, scattered showers and a non-zero chance of
thunderstorms Monday into Tuesday. Northerly winds and seas
strengthen Thursday into next weekend as high pressure rebuilds.

&&

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

$$

SHORT TERM...DialH
LONG TERM....DialH
AVIATION...RW
MARINE...RW

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