FXUS66 KMTR 101931
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1231 PM PDT Fri Apr 10 2026

...New AVIATION...

.KEY MESSAGES...
Updated at 1220 PM PDT Fri Apr 10 2026

 - Rain and thunderstorms through the weekend 

 - Gradual warming and drying trend next week

&&

.SHORT TERM...
Issued at 1220 PM PDT Fri Apr 10 2026
(This evening through Saturday)

A mid/upper level low pressure system remains about 100 miles off of 
the northern California coast. This feature has resulted in 
widespread rain showers across our region the past 24 hours with the 
North Bay picking up between 0.25"-1.25". Lesser amounts have been 
reported south of the North Bay, but some coastal and mountain 
locations have received up to 0.75". Overall, this has been greater 
than originally forecasted. This band of rain showers continues to 
shift inland and the threat for rain showers and thunderstorms will 
persist throughout the afternoon and evening, especially as day time 
heating increases surface based CAPE to between 500-1000 J/kg. Any 
thunderstorm will be capable of producing lightning, locally heavy 
rainfall, erratic/gusty winds, and small hail. Weak low-level wind 
shear does not support a mention of rotation that would lead to 
tornadoes and/or waterspouts through this evening. Rain showers and 
a slight chance of thunderstorms will continue into the night, yet 
chances for both trend downward overnight. 

An approaching mid/upper level low is forecast to drop out of the 
Gulf of Alaska on Saturday and move inland Sunday afternoon across 
northern California. This is when we have all three ingredients for 
thunderstorms: lift, instability, and moisture. Some of the higher 
resolution and conviction-allowing models (CAMs) such as the RRFS 
indicate the potential for a narrow cold-frontal rainband (NCFR) to 
move across the Bay Area and Central Coast Saturday afternoon and 
evening. This will be when we have the greatest potential for 
rotating cells that may produce waterspouts and/or weak tornadoes. 
In coordination with the Storm Prediction Center, we have been 
upgraded to a Marginal Risk of severe thunderstorms on Saturday. The 
greatest potential being the threat of wind exceeding 40 knots. 

From previous forecaster: "Anglers should take special note of the 
expected weather and have a plan to reach safe harbor quickly when 
the weather turns. Even without thunderstorms, the marine conditions 
will deteriorate through the day Saturday. If thunderstorms develop, 
the associated wind gusts are capable of capsizing small vessels. 
Fishing leads to more lightning deaths in the U.S. than any other 
activity. When thunder roars, head indoors!"

&&

.LONG TERM...
Issued at 1220 PM PDT Fri Apr 10 2026
(Saturday night through next Thursday)

The rainfall amounts continue to trend higher today through Sunday 
with 0.50"-0.75" in the southern Salinas Valley, 1"-2" across much 
of the Bay Area and Central Coast, and up locally up to 4" in the 
coastal ranges. However, this rainfall will be mostly beneficial 
with no widespread river flooding anticipated. However, we can still 
see ponding of water on roadways, minor urban and small stream 
flooding, and flooding of poorly drained areas. This will be 
especially so if any heavier showers and/or thunderstorms develop 
and train over any one given area.  

Post-frontal rain showers and isolated thunderstorm will continue 
into Sunday as a colder air mass settles into the region. This is 
when we may see snow fall across the higher peaks across the region, 
however little to no snow accumulation is expected. Lingering rain 
showers and isolated thunderstorms may persist into early Monday 
morning before a warming and drying trend resumes by Monday 
afternoon. Slightly below normal temperatures are expected Monday 
afternoon before rebounding to near seasonal averages by Thursday 
and Friday. 

&&

.AVIATION...
(18Z TAFS)
Issued at 1230 PM PDT Fri Apr 10 2026

It's a challenging day for TAFs, as we have scattered showers 
moving through the region leaving mix of IFR to VFR ceilings and 
visibility. Expect skies to remain partly to mostly cloud for the 
next few hours, with perhaps some clearing this afternoon. Given the 
lingering moisture and the potential for some sunshine there may be 
a renewed push for isolated to scattered showers this afternoon and 
evening. The big question will be thunderstorm chances. The SPC 
mesoanalysis page currently shows decent surface CAPE, around 500-
1000 J/kg, low level lapse rates around 6.5-7.5 C/km, and LI's 
around 0 to -1. In terms of shear, aka as lift, we currently have 
around 20-30kt. This would support thunderstorm potential if 
conditions continue to hold or continue to become more favorable for 
development. For now, there is no mention of VCTS or TS in the TAFs, 
excluding LVK, but my current thinking is that timing would look to 
be between 20-3Z for Bay Area terminals. Here the chance of 
thunderstorms range from  30-50%, favoring the interior North and 
East Bay areas. 

Vicinity of SFO...VFR to MVFR conditions are forecast this afternoon 
and evening due to lingering clouds and showers moving through the 
region. As noted above conditions are becoming favorable for 
thunderstorms. KSFO has the about a 30-40% chance for thunderstorms 
from 18-0Z this afternoon with chances falling to 15-20% until 3-4Z. 
For now, there is no mention of VCTS or TS/TSRA in the TAF, but it 
will be something to monitor this afternoon and evening. After that, 
there might be some showers that pass through tonight and into 
tomorrow morning. Winds begin to increase tomorrow afternoon and 
into the evening, as the next storm system arrives. 20-25kt gusts 
are possible from 21-0Z on Saturday.  

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...A mix of sun and clouds should lead to VFR 
conditions through the afternoon. Showers, roughly a 20-30% chance, 
and perhaps a rogue thunderstorm, around 15-20%, will be possible 
through 0Z. The forecast becomes tricky once again, with models 
showing additional rounds of -SHRA or VCSH this evening and into the 
early overnight hours. MVFR cigs would be expected with these 
conditions, but also have the potential to occur without rain.

&&

.MARINE...
(Tonight through next Wednesday)
Issued at 1220 PM PDT Fri Apr 10 2026

Isolated to scattered showers and a chance of thunderstorms 
remain in the forecast today. The next round of precipitation 
arrives late Saturday into Sunday, as the next weather system 
arrives. Increasing winds are expected, with isolated gale force 
gusts from Pigeon Point to Point Pinos. High pressure builds 
behind the system with fresh northwest winds developing early next
week.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from 9 AM to 9 PM PDT Saturday for Mry Bay-
     Pigeon Pt to Pt Pinos 0-10 nm-Pt Pinos to Pt Piedras 
     Blancas 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm-SF Bay N of 
     Bay Bridge.

     Small Craft Advisory from 9 AM to 3 PM PDT Saturday for Pt Arena 
     to Pt Reyes 0-10 nm.

     Small Craft Advisory from 3 PM to 9 PM PDT Saturday for Pigeon 
     Pt to Pt Pinos 10-60 NM.

&&

$$

SHORT TERM...RGass
LONG TERM....RGass
AVIATION...KR
MARINE...KR

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Prepared by Boulder-Creek.com Weather at: Fri Apr 10 14:30:02 PDT 2026