Exterior Painting Weather: 10-Day Windows & Best Months

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Or browse by state below — every city page runs the live 10-day check against the rules on this page.

The canonical ruleset

The engine scores each day against this table — typical latex-label requirements, with the 35–50°F band flagged for low-temperature formulas.

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

Why the forecast decides the paint job

Exterior latex does not dry the way a puddle dries. It cures in two stages: first the water leaves the film, then the acrylic binder particles fuse together — coalescence — into a continuous plastic skin. That second stage is temperature-driven. Below roughly 50°F, standard latex binder is too stiff to fuse properly, and the film that forms is weak no matter how dry it looks. The film also keeps forming for hours after it is tack-free, which is why the overnight low matters as much as the afternoon high. Paint applied at 2 p.m. is still curing at 2 a.m.

Three numbers control every rule on this page: air temperature, surface temperature, and dew point. They are not the same number. A south- or west-facing wall in direct midday sun can run 20°F or more hotter than the air — a 75°F forecast can mean a 95°F+ wall, which is over the label ceiling even though the thermometer says go. The reverse happens in the evening: siding radiates heat to a clear sky and drops below air temperature, which is exactly how it reaches the dew point while the forecast still reads "dry."

Dew point is the temperature at which the air's moisture condenses onto a surface. When a freshly painted wall cools to within a couple of degrees of the dew point, water beads on the uncured film. The label chemistry that applies here is the same chemistry behind deck staining and roof coating — water-based films, 50°F floors, evening dew as the silent killer. The thresholds below are typical product-label requirements distilled into one checklist; formulas vary, so always follow YOUR can.

Reading a 10-day forecast against the can

WorkWindow scores every forecast day against seven checks. A hard fail on any one of them makes the day a NO-GO. A soft fail flags the day MARGINAL — and the engine tolerates at most one soft fail per day. Two soft fails together drop the day to NO-GO. Conditions are scored across working hours, 8 a.m. to 6 p.m., except where noted. Full scoring logic is on the methodology page.

Work temperature: 50–90°F, with a 35°F asterisk

Standard latex wants 50°F or better while you apply and for the first hours of dry time. The ceiling is 90°F — above that, the film skins before it levels. The asterisk: some low-temperature formulas are rated down to 35°F, so a day with a high between 35 and 50°F is scored MARGINAL rather than dead. That marginal call is a formula question, not a judgment call — see the next section.

Overnight low: 35°F hard, 40°F soft

The engine checks the low across a 24-hour window after application, because the film keeps curing overnight. A low under 40°F stalls standard latex — soft fail, acceptable only if you are running a low-temp formula. A low under 35°F is a hard fail for everything; even cold-rated paint has hit its floor.

Rain before: 12 hours hard, 24 hours soft

The surface must be dry to the touch and out of a recent soak. 0.05 inches or more of rain inside the past 12 hours is a hard fail. The same amount inside the past 24 hours earns a soft flag, because siding — wood especially — can read dry on the surface while the substrate underneath still holds water. Paint traps that moisture, and trapped moisture becomes blisters.

Rain after: 24 clean hours, no exceptions

Rain of 0.05 inches or more inside the first 24 hours after application can streak or wash fresh paint. There is no soft version of this rule. The engine also does not require certainty to count rain against you: a forecast with a 60% or higher probability of at least 0.02 inches is treated as rain when scoring. A "chance of showers tomorrow afternoon" is not a technicality — it is a blocked cure window.

Dew-point spread: 5°F soft, 2°F hard

The surface should stay at least 5°F above the dew point while the film forms. The engine checks the spread through the evening hours, 6 p.m. to 11 p.m., because that is when siding cools fastest. A spread under 5°F is a soft fail; under 2°F is a hard fail — at that margin, dew on the fresh film is close to certain.

Humidity: 80% daytime limit

Daytime relative humidity above 80% is a hard fail; readings within 3 points of the limit get the marginal flag. High humidity does not stop cure the way cold does — it stretches it. Recoat windows that read 4 hours on the can become all-day waits, and paint that stays open longer collects more dust, more bugs, and more risk of evening dew.

Wind: 15 mph brush-only, 20 mph stop

Above 15 mph, spraying is off the table — overspray drifts onto cars, windows, and the neighbor's fence, and the leading edge of your wet film dries too fast, leaving lap marks. Above 20 mph, spraying is unsafe and even brushing is fighting the weather. Sitewide, no task scores a go above 28 mph regardless of method.

The 35–50°F band: what MARGINAL means here

This is the one rule where the answer depends on which can you bought. Standard exterior latex carries a 50°F minimum, and below that the binder cannot coalesce — the failure is invisible on day one and obvious by spring. Low-temperature formulas modify the binder and coalescent package to fuse at lower temperatures, and their labels are rated down to 35°F.

The engine splits the difference honestly. A forecast high between 35 and 50°F is scored MARGINAL: a real window if your can says 35°F, a NO-GO if it says 50°F. Check the fine print on the can before trusting the flag — a low-temperature rating is always stated explicitly, usually on the back panel next to the recoat times. Two more things change in that band even with the right paint. First, the overnight low still has to hold 35°F or better for the full 24-hour cure window. Second, everything slows down: recoat times stretch, and a film that stays soft into the evening is more exposed to the dew-spread rule above. Cold-weather painting is legal in that band; it is not fast. Where those shoulder weeks land on the calendar depends on where you live — see best months by region.

Season strategy by region

The same seven rules produce very different calendars depending on where the house sits. General patterns, not city forecasts:

• North (cold winters, four seasons). The standard-latex season runs roughly late spring through early fall, bounded by the 50°F floor and the 35°F hard night low. Low-temperature formulas buy real shoulder weeks on both ends — those 35–50°F MARGINAL days in mid-spring and mid-fall are exactly what the formula exists for, provided nights hold above 35°F. Watch the overnight low more than the afternooon high; a 55°F day with a 33°F night is still a NO-GO.
• South (hot summers, mild winters). The problem inverts: the 90°F ceiling and sun-heated walls block midsummer afternoons, not the calendar. Spring and fall are the wide windows. In summer, the job becomes morning-only — beat the ceiling, then stop before surfaces cook. Mild-winter regions can pick up December-to-February windows that northern crews never see, if lows cooperate.
• Coastal / humid. Temperature is rarely the blocker; the 80% humidity limit and the 5°F dew-point spread are. Marine-layer mornings leave siding damp past mid-morning — start later, after the surface is genuinely dry, and expect the evening dew check to close the day earlier than inland. Stretched recoat times mean a two-coat wall can take two days instead of one.
• Desert / arid. Humidity almost never fails, but the 90°F ceiling, surface temperatures 20°F+ above air, and wind do. Large day-night temperature swings can trip the 40°F soft night low even when afternoons are warm. The winning tactic is chasing shade around the house all day and treating wind, not moisture, as the forecast line that kills windows.

What each ignored rule costs you

Every threshold above maps to a specific, recognizable failure. This is what shows up when a rule gets skipped:

• Painting below 50°F with standard latex. Poor coalescence. The film looks fine, but it never fused — expect cracking, chalking, poor scrub resistance, and peeling that starts the following season. This is the most expensive failure on the list because it usually means full removal and repaint.
• Ignoring the overnight low. Cure stalls at night, then dew lands on the stalled film. The visible result is surfactant leaching — brown or glossy streaks weeping down the wall — plus uneven sheen that no amount of waiting fixes.
• Painting inside the 12-to-24-hour lookback. Paint over a damp substrate seals the moisture in. It comes back out as blisters and, on wood, as adhesion failure that peels in sheets down to bare material.
• Rain inside the 24-hour cure window. Streaking, wash-off on fresh edges, and surfactant runs. Best case is a visible second coat; worst case is stripping the washed areas.
• Dew spread under 5°F. Condensation flat-spots the finish — dull patches in a satin or gloss film, gloss haze, and water spotting that telegraphs every place the dew sat.
• Humidity above 80%. Sags and runs on vertical surfaces as the film stays open too long, plus a recoat schedule that quietly slides a one-day job into three.
• Wind above 15–20 mph. Overspray drift claims on anything downwind, lap marks where the leading edge flashed off, and grit embedded in the wet film.
• Painting a wall in direct midday sun. With the surface 20°F+ hotter than the air, the paint skins before it levels — brush marks lock in, adhesion suffers, and blisters form where solvent boiled under the skin.

Prep and timing tactics that widen the window

A marginal forecast often contains a good working day inside it. How to find it:

1. Find the 2.5-day dry block first. The full requirement is 12 clean hours before (24 to clear the soft flag), the working day itself, and 24 clean hours after. Scan the 10-day forecast for that block before anything else — remembering that a 60% chance of 0.02 inches counts as rain.
2. Start mid-morning, not dawn. Dew burned off is the trigger, not the clock. The scored working window runs 8 a.m. to 6 p.m., but siding wet with morning dew fails the same way rain does. Touch the surface; if the back of your hand comes away damp, wait.
3. Follow the shade around the house. East walls in the afternoon, west walls in the morning, north walls in the middle of the day. Never a wall in direct midday sun — that 20°F+ surface premium turns a legal 75°F day into an over-ceiling wall.
4. Stop about 2 hours before sunset. The film needs to set before the 6 p.m.–11 p.m. dew window opens. A last panel brushed at dusk is the one that flat-spots.
5. Match method to wind. Under 15 mph, spray if you like. 15–20 mph, brush and roll only. Above 20 mph, load the truck and go home.
6. In the 35–50°F band, verify the can. The MARGINAL flag assumes a low-temperature formula. If the label says 50°F, the flag does not apply to you, and neither does the window.

These are typical label numbers, not a substitute for the ones printed on your paint. When the can and this page disagree, the can wins.

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