FXUS66 KMTR 052318
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
418 PM PDT Sun Apr 5 2026

...New AVIATION, MARINE...

.KEY MESSAGES...
Updated at 1253 PM PDT Sun Apr 5 2026

 - Above normal temperatures continue today; cooling trend begins
   tomorrow

 - Beneficial rain and a low potential for thunderstorms mid to 
   late week

&&

.SHORT TERM...
Issued at 1253 PM PDT Sun Apr 5 2026
(This evening through Monday)

Another warm day is on the books for today. Temperatures are running 
around 15 to 20 degrees above normal across the interior and around 
10 to 15 degrees above normal along the coast. Highs today will 
largely be in the 80s across the interior and 70s along the 
coastline. The pattern shifts quite notably heading into Monday as 
upper level ridging exits eastward and weak shortwave upper level 
troughing moves in. This will allow the marine layer to develop 
(albeit a shallow one between 1000-1500 ft) and we will see a 
"southerly surge" of stratus along the coast. If you live along the 
coast, tomorrow morning will feel very different than today due to 
the much cooler temperatures and low level stratus. There may even 
be some potential for coastal drizzle early Monday morning. Offshore 
winds are expected to become onshore again this afternoon/evening 
with onshore winds to then prevail through the remainder of the 
forecast. Temperatures cool much more noticeably on Monday with 
interior highs dropping into the low to mid 70s and coastal highs 
into the upper 50s to low 60s. Interior temperatures will still be 
running a few degrees above normal while coastal temperatures are 
fairly seasonal. 

&&

.LONG TERM...
Issued at 1253 PM PDT Sun Apr 5 2026
(Monday night through next Saturday)

Cooler, wetter weather remains on track to arrive mid to late week 
as our next system arrives. Upper level ridging tries to rebuild on 
Tuesday, but, remains compressed due to a deep upper level low 
moving into the PNW. This results in Tuesday's forecast staying 
rather similar to Monday's with interior highs in the 70s and 
coastal highs in the 50s to 60s. By Wednesday, we start to see our 
next rainmaker on the horizon. The upper level trough over the PNW 
will exit eastwards into the Central United States with a second low 
pressure system approaching California from the west. This system 
has some characteristics of a cut-off low with cluster guidance 
starting to come into better agreement about it. The upper level low 
looks to move southwards parallel to California's coastline before 
moving inland over Baja California. This upper level low originates 
from the Gulf of Alaska and is bringing down a much cooler airmass. 
As the cooler airmass arrives, it will bring a return of more 
seasonal temperatures in the 60s to 70s across the entire region. 
Originally rain looked likely to return on Wednesday but guidance 
has shifted with the bulk of the rain now returning Thursday and 
Friday. Current guidance suggests rain showers will be fairly 
widespread across our CWA but they will be more showery than 
stratiform (uniform over a large area) in nature. Ensemble guidance 
has trended upwards recently in terms of how much precipitation we 
are expected. Overall the rain is still classified as light and 
beneficial but we can expected between 0.5-0.75" across the coastal 
mountains and Santa Clara Hills while the lower elevations see 
around 0.25-0.35". The highest amounts look to be farther south over 
the Central Coast in the Santa Cruz Mountains and the Santa Lucia 
Range. Locally breezy onshore winds are expected across the higher 
elevations and mountain gaps/passes but these are expected to stay 
well below Wind Advisory criteria. 

As mentioned yesterday, there is a non-zero chance of thunderstorms 
across much of the area Thursday and Friday. The probability of 
thunderstorms has increased across the region with a 15-20% chance 
of thunderstorms on Thursday and Friday. In terms of support, low 
level lapse rates are decent (7-8 C/km) with several hundred joules 
of low level MUCAPE but low level shear is fairly negligible. Our 
thunderstorm chances and rain totals will largely depend on where 
the surface low pressure system moves inland and how progressive the 
upper level system is. If the surface low maintains its current path 
and moves into the Bay Area, thunderstorms will be more likely south 
of the North Bay and across the Central Coast. Comparatively, if it 
shifts more southerly (i.e. moving in over SLO), our thunderstorm 
chances would largely go away. Given the increase in forecast 
precipitation totals, dry lightning concerns with this system have 
largely abated. The majority of locations are now expected to see 
wetting rains (precipitation totals greater than or equal to 0.1") 
which alleviates the risk of fires started by lightning. All in all, 
there is some potential for thunderstorms with this upcoming system 
but confidence is not quite there yet. Make sure to stay up to date 
as we continue to narrow in precipitation totals and the potential 
for thunderstorms. 

&&

.AVIATION...
(00Z TAFS)
Issued at 418 PM PDT Sun Apr 5 2026

VFR conditions continue through the evening hours with breezy 
onshore winds prevailing, counterbalanced by lingering light onshore 
flow inland. As the winds diminish this evening, MVFR-IFR stratus 
comes in from the Pacific and the impacts the coast, spreading 
inland through the early morning hours on Monday. Greatest 
confidence at the immediate coast, through moderate confidence in 
stratus impacts at the interior terminals. Stratus will retreat to 
the immediate coast through Monday morning, with onshore flow 
resuming in the afternoon.

Vicinity of SFO... VFR conditions with breezy northwest winds 
continue through the evening hours. MVFR stratus will begin to flow 
through the Golden Gate overnight, with moderate confidence in the 
exact timing of the stratus impacts, but high confidence that they 
develop by 12Z. Stratus will dissipate Monday morning with breezy 
west-northwest winds in the afternoon. Some stratus will flow 
through the Golden Gate Monday evening, but the highest confidence 
for impacts at SFO comes after the end of the TAF period.

SFO Bridge Approach... Similar to SFO.

Monterey Bay Terminals... VFR conditions with breezy northwest winds 
continue through the evening hours. IFR ceilings develop late this 
evening, with the stratus clearing through Monday morning before 
breezy northwest winds develop in the afternoon. Some high 
resolution models are depicting stratus returning near the end of 
the TAF period, but the greatest confidence lies afterward.

&&

.MARINE...
(Tonight through next Friday)
Issued at 418 PM PDT Sun Apr 5 2026

Light to moderate winds continue over the coastal waters for much
of  next week. Locally fresh winds will briefly develop early to
midweek  across the coastal waters with locally stronger winds
possible along  the Big Sur Coast. Unsettled weather returns mid
to late week and  brings with it light showers, a slight chance of
thunderstorms, and  moderate seas. Winds increase next weekend
with a fresh breeze  expected over the northern coastal waters.

&&

.CLIMATE...
Issued at 110 PM PDT Fri Apr 3 2026

The following are the record high temperatures at the long term 
stations for April 5th.

Location           April 5th 

Santa Rosa         90 in 1939
Kentfield          88 in 1924
San Rafael         87 in 1957
Napa               86 in 1989, 1957
Richmond           83 in 1989
Livermore          84 in 1989, 1916
San Francisco      88 in 1989
SFO Airport        84 in 1989
Redwood City       87 in 1989
Half Moon Bay      74 in 2016
Oakland Museum     85 in 1989  
San Jose           89 in 1989
Salinas Airport    95 in 1989

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from 3 PM Monday to 3 AM PDT Tuesday for Pt 
     Pinos to Pt Piedras Blancas 0-10 nm.

&&

$$

SHORT TERM...Kennedy
LONG TERM....Kennedy
AVIATION...DialH
MARINE...Kennedy

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Prepared by Boulder-Creek.com Weather at: Sun Apr 5 20:30:03 PDT 2026