FXUS66 KMTR 080612
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1112 PM PDT Tue Apr 7 2026

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

.KEY MESSAGES...
Updated at 1111 PM PDT Tue Apr 7 2026

 - Above normal temperatures and dry conditions with a marine
   layer Wednesday

 - Unsettled weather returns as early as Thursday and continues 
   through the weekend with light to moderate rainfall

 - Thunderstorms possible Friday through Sunday

&&

.SHORT TERM...
Issued at 1111 PM PDT Tue Apr 7 2026
(Tonight through Wednesday night)

Wednesday's weather is brought to you by upper-level shortwave 
ridging. The aforementioned ridge's axis across the state and a 
cutoff low right behind it is supporting onshore flow. A modest 
marine layer of 1,500 feet was observed on the 00Z April 8th 
sounding - this may actually undergo some deepening tonight as 
heights ever so slightly begin to fall ahead of the approaching 
cutoff low. Nonetheless, a cloudy start can be expected along the 
coast and in the valleys with temperatures warming to 5-10 degrees 
above normal by the afternoon.

&&

.LONG TERM...
Issued at 1111 PM PDT Tue Apr 7 2026
(Thursday through next Tuesday)

The aforementioned cutoff low near 38 N, -138 W in the Eastern 
Pacific Ocean will kickoff our pattern change on Thursday. Due to 
its independence from the jet stream, its exact location and timing 
is difficult to say with certainty. Thus, this is a boom or bust 
forecast by nature which is evident in the spread between the 10th 
and 90th percentiles. For example, 72-hour accumulation for Santa 
Rosa between now and 5 PM Friday is forecast to be 0.22" with a 10th 
percentile of 0.03" and a 90th percentile of 0.40". No matter how 
you slice it, it's not a lot of rain; however, this provides insight 
that rainfall totals will be highly dependent on where rain 
showers/thunderstorms develop. The trend has been for an even slower 
progression of the surface low to the east. While rain and 
thunderstorms on Thursday cannot be completely ruled out with the 
outer rain bands, the best thunderstorm chances are now expanding 
from Friday into Sunday. Point forecast soundings illustrate that 
the profile will be characterized by conditionally unstable lapse 
rates yielding low CAPE, high 0-6 km shear, and PWAT values near the 
90th percentile. It also shows that thunderstorms will likely be 
diurnally driven by surface heating with the most unstable parcel 
being the surface parcel. Thunderstorm hazards include lightning, 
locally heavy rainfall, erratic/gusty winds, and small hail. Due to 
the slow steering motion and training effect of cutoff lows, 
localized flooding will be possible if a rain shower/thunderstorm 
were to develop. There is high confidence that the cutoff low gets 
absorbed with the help of a digging upper-level longwave trough from 
the Gulf of Alaska late Friday, but global ensemble clusters diverge 
by Saturday on the depth, strength, and type of troughing across the 
state. Deterministic ECMWF and GFS are both advertising a surface 
low digging down the West Coast and cutting inland in Northern 
California. The close proximity to the low would maintain rain and 
thunderstorm chances over the weekend. Rainfall totals on the order 
of 0.50"-1.00" are expected with up to 2.00" in the coastal ranges. 
Heights will begin to rise Monday, kicking off at least a brief 
warming and drying trend.

&&

.AVIATION...
(06Z TAFS)
Issued at 957 PM PDT Tue Apr 7 2026

Gentle to moderate onshore pattern wind flow will continue to 
diminish through the evening hours. MVFR stratus is developing at 
the immediate coast and should eventually cover the coastal regions 
and parts of the East Bay near OAK, but a compressed marine layer 
should allow for less inland development than last night, 
particularly in the North Bay interior valleys. Stratus should 
retreat to the immediate coast on Wednesday morning with moderate 
onshore flow resuming in the afternoon. Expecting more stratus 
coverage to develop Wednesday night as an incoming system promotes 
the growth of the marine layer.

Vicinity of SFO... Moderate westerly winds continue for a couple 
more hours with winds becoming light overnight. Moderate confidence 
that the terminal remains VFR overnight, although some low scattered 
clouds could intrude into the terminal area. Confidence for stratus 
impacts is slightly higher at OAK. Any stratus that develops in the 
vicinity will dissipate through Wednesday morning, with the west-
northwest winds returning in the afternoon, with a moderate 
confidence for stratus returning in the evening hours into Thursday 
morning.

SFO Bridge Approach... Similar to SFO.

Monterey Bay Terminals... Light winds overnight through Wednesday 
morning. MVFR-IFR stratus has developed in patches near MRY and will 
expand across the terminals through the night, with impacts 
continuing through Wednesday morning. Breezy northwest winds resume 
in the afternoon, with MVFR-IFR stratus returning late Wednesday 
evening.

&&

.MARINE...
(Tonight through next Monday)
Issued at 957 PM PDT Tue Apr 7 2026

A gentle to moderate northwest breeze and slight to moderate seas
prevail through the night. Winds will remain moderate while
gradually shifting to the southwest from Wednesday through
Thursday ahead of a low pressure system. This system will will
bring disturbed weather with possible thunderstorms on Friday
through Sunday. Winds will increase to a strong NW breeze by
Sunday as subtropical high pressure builds over the Eastern
Pacific.

&&

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

&&

$$

SHORT TERM...Sarment
LONG TERM....Sarment
AVIATION...DialH
MARINE...DialH

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: Wed Apr 8 00:30:02 PDT 2026