Exterior Painting Weather in San Francisco, CA: 10-Day Windows & Best Months

Q: What temperature can you paint outside?

Standard latex: 50–90°F with nights of 40°F+; low-temperature formulas are rated down to 35°F and the engine marks 35–50°F highs as MARGINAL for exactly that reason. San Francisco's edge months live in that band — April averages 63°F highs over 50°F nights.

Q: How many dry hours does exterior paint need before rain?

About 24 — a 0.05"+ shower inside that window streaks or washes fresh latex. San Francisco offers those 24-hour dry runs most reliably in August (rain on just 3% of days); February is the gamble at 38%.

Q: Why does dew ruin fresh paint?

Because a film that hasn't coalesced can't shed water: on cooling San Francisco siding, dew flat-spots the sheen and drags surfactants out in streaks. It forms when the wall reaches the dew point — the engine wants a 5°F spread from 6–11 p.m. Finish 2 hours before sunset and latex gets its lead time.

Q: Can you paint in high humidity?

The label limit is ~80% relative humidity, and it compounds: humid air slows the cure, which pushes wet film into dew hours. The engine flags 80–83% and fails beyond. In San Francisco, the drier August air makes this a non-issue; muggy spells make it the day-killer.

Q: What is surface temperature vs air temperature?

The forecast reports air; the label limits the wall. In direct sun a wall runs 20°F+ hotter — a 66°F San Francisco July day can put a west wall past the 90°F ceiling by mid-afternoon. Follow the shade around the house and check the surface by hand or IR thermometer.

Q: When does painting season end in San Francisco?

It doesn't, quite: every San Francisco month averages 8+ workable days, though January thins to 20. Watch nights and dew more than the calendar.

San Francisco is one of the rare places where exterior painting weather never fully closes: every month averages 8 or more workable days by NOAA 1991–2020 normals. August leads the calendar with 30 workable days: average high 68°F, low 56°F, rain on 3% of days. Below: today through day 10 against the label rules, then the year at a glance.

GOOD — every label check passes MARGINAL — one soft fail NO — hard fail or several soft

The rules this check uses

These rows are what the San Francisco strip checks hour by hour: consensus paint-can requirements, plus the low-temp-formula band the engine marks MARGINAL.

Typical label thresholds for exterior painting — the ruleset behind every San Francisco verdict above.
Check	Threshold	Why it matters
Air temperature	50–90°F (low-temp formulas from 35°F)	The film (or mix) chemistry runs on temperature — both while you work and for the first hours after.
Overnight low	≥35°F during the first 24 h (≥40°F preferred)	Curing continues after dark; the first night can undo a perfect afternoon.
Dry before	≤0.05" rain in the prior 12 h; watch back to 24 h	Checked backward from your start hour using the two look-back days in the forecast data.
Dry after	<0.05" rain for 24 h after	The engine sums forecast rain hour by hour through the cure window for San Francisco.
Evening dew-point spread	≥5°F from 6–11 pm	When air temperature meets the dew point, water condenses on your fresh work first.
Daytime humidity	≤80%	Read as the daytime maximum, 10 a.m.–5 p.m.; within 3 points of the limit counts as marginal.
Wind	≤15 mph (brush only up to 20 mph)	Wind dries the leading edge too fast and carries overspray.

Always follow your product label — formulas vary. The table above is the typical range across major manufacturers, not a promise about your can.

Best months for exterior painting in San Francisco

San Francisco's calendar, scored: each month's days passing the temperature rules, discounted by that day's historical rain odds (NOAA 1991–2020). Not a forecast.
Month	Avg high	Avg low	Rain odds/day	Workable days
January	58°F	47°F	36%	20
February	60°F	48°F	38%	18
March	62°F	49°F	34%	20
April	63°F	50°F	23%	23
May	64°F	51°F	13%	27
June	66°F	53°F	6%	28
July	66°F	54°F	3%	30
August	68°F	56°F	3%	30
September	70°F	56°F	4%	29
October	70°F	54°F	12%	27
November	64°F	51°F	26%	22
December	58°F	47°F	36%	20

There is no off-season to plan around in San Francisco — the planning question is week-to-week, not month-to-month. The leanest stretch is January (20 workable days, average high 58°F); the richest is August with 30. The California table ranks every listed city by the same math.

San Francisco has a real wet/dry rhythm: February brings rain on 38% of days versus 3% in August. When the calendar gives you a August-side window, the dry-before and dry-after rules nearly take care of themselves.

Related check: roof coating in San Francisco — same 50–90°F chemistry, but roofs hit the dew point first and wind is a safety stop.

Source honesty: every monthly figure on this page is the 1991–2020 normal at San Francisco Dwtn, Ca Us, 2.3 km from San Francisco's center — your block's shade lines and wind exposure sit on top of that baseline. Scoring details are on the methodology page.

San Francisco by the numbers

Hottest month: September — 70°F average high, 0 days topping 90°F.
The cold floor is January at 58°F afternoons and 47°F overnight.
Measurable rain: February leads at 38% of days; August is the quiet end at 3%.
Bottom line for San Francisco: roughly 295 workable exterior painting days a year.

Prep checklist

Two clean days beat one perfect one: 24 h of dry cure and a 40°F+ night — August is San Francisco's highest-odds month (30 days).
Scrape, then wash: loose paint and chalk go first, because latex only grips solid substrate.
Give washed siding 24 hours — north walls in San Francisco can need double after a February-grade soak.
Read the wall, not the app: an ir surface thermometer on sunlit siding shows 20°F+ over San Francisco's reported 68°F.
Bare wood gets primer, stains get stain-blocker, gaps get caulk — in that order, on dry substrate.
Follow the shade around the house — never a wall in direct midday sun.
Cut in with an angled brush set, roll a wet edge, and drop the sprayer plan over 15 mph.
Stop 2 hours before sunset: with August lows near 56°F, San Francisco's siding meets the dew point before the late news.

Gear that saves a window

Transparency note: gear links here become affiliate links only when the program is enabled — today they are plain references. See the affiliate disclosure.

Extension pole
Second-story reach without moving the ladder every pass.
IR surface thermometer
Reads the wall, not the air — sun-baked siding runs hotter.
Canvas drop cloths
Grips ladders and won't shred like plastic.
Angled brush set
Control at trim, corners, and cut-in lines.

FAQ

What temperature can you paint outside?

Standard latex: 50–90°F with nights of 40°F+; low-temperature formulas are rated down to 35°F and the engine marks 35–50°F highs as MARGINAL for exactly that reason. San Francisco's edge months live in that band — April averages 63°F highs over 50°F nights.

How many dry hours does exterior paint need before rain?

About 24 — a 0.05"+ shower inside that window streaks or washes fresh latex. San Francisco offers those 24-hour dry runs most reliably in August (rain on just 3% of days); February is the gamble at 38%.

Why does dew ruin fresh paint?

Because a film that hasn't coalesced can't shed water: on cooling San Francisco siding, dew flat-spots the sheen and drags surfactants out in streaks. It forms when the wall reaches the dew point — the engine wants a 5°F spread from 6–11 p.m. Finish 2 hours before sunset and latex gets its lead time.

Can you paint in high humidity?

The label limit is ~80% relative humidity, and it compounds: humid air slows the cure, which pushes wet film into dew hours. The engine flags 80–83% and fails beyond. In San Francisco, the drier August air makes this a non-issue; muggy spells make it the day-killer.

What is surface temperature vs air temperature?

The forecast reports air; the label limits the wall. In direct sun a wall runs 20°F+ hotter — a 66°F San Francisco July day can put a west wall past the 90°F ceiling by mid-afternoon. Follow the shade around the house and check the surface by hand or IR thermometer.

When does painting season end in San Francisco?

It doesn't, quite: every San Francisco month averages 8+ workable days, though January thins to 20. Watch nights and dew more than the calendar.

Other projects in San Francisco

Exterior Painting nearby

Guides

Climatology: NOAA 1991–2020 normals via SAN FRANCISCO DWTN, CA US (2.3 km from San Francisco center, elevation 150 ft); live outlook by Open-Meteo.