Exterior Painting Weather in Ann Arbor, MI: 10-Day Windows & Best Months

Q: What temperature can you paint outside?

50–90°F for standard formulas, 35°F+ for low-temp lines, and the wall itself must stay 5°F above the dew point. In Ann Arbor the practical range is set by nights: the 40°F overnight floor arrives around May and leaves after September.

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

Plan 24 rain-free hours after the last coat; the engine fails any day that can't deliver them. With Ann Arbor's rain odds swinging from 34% of days in August to 58% in January, the strip above is mostly a search for that dry pair.

Q: Why does dew ruin fresh paint?

Fresh latex needs hours before it can take standing water; evening condensation gets there first on cooling siding. The check: air minus dew point from 6–11 p.m., 5°F or better. Humid January evenings in Ann Arbor are when GOOD afternoons hide failing nights.

Q: Can you paint in high humidity?

Up to about 80% daytime RH — above that, dry times stretch until the film meets the evening dew. 80–83% reads MARGINAL on the engine; more is a fail. Pair humidity with Ann Arbor's dew-point spread rule and paint mornings-into-early-afternoons in the humid months.

Q: What is surface temperature vs air temperature?

Two different numbers: air (what the app shows) and the wall (what the paint feels). Sun adds 20°F or more; evening radiational cooling subtracts. That's why the engine checks the 90°F top on Ann Arbor's hot afternoons and the dew-point spread after sunset — both are surface problems the air forecast hides.

Q: When does painting season end in Ann Arbor?

When nights stop clearing 40°F — in Ann Arbor that's typically after September, when average lows hit 50°F and falling. Low-temp formulas (35°F rated) buy a few extra weeks; the engine shows them as MARGINAL days before the hard close.

The exterior painting season in Ann Arbor runs May through September — 5 months averaging at least 8 workable days by NOAA 1991–2020 normals. The single best month is August, averaging 20 days that clear every check — highs of 82°F, lows near 58°F, and a 34% daily rain chance. 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 Ann Arbor 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 Ann Arbor 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 Ann Arbor.
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 Ann Arbor

Ann Arbor'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	32°F	16°F	58%	0
February	35°F	16°F	53%	0
March	45°F	25°F	46%	0
April	58°F	34°F	46%	0
May	70°F	46°F	46%	16
June	80°F	56°F	41%	18
July	84°F	59°F	36%	20
August	82°F	58°F	34%	20
September	75°F	50°F	36%	19
October	62°F	39°F	42%	7
November	48°F	30°F	44%	0
December	36°F	22°F	54%	0

Figure 100 workable days a year in Ann Arbor, spread across May through September. Shoulder months turn on the overnight rule: an afternoon at 70°F passes, but the 40°F night floor is what actually opens the season in May. The Michigan table ranks every listed city by the same math.

The rain odds swing hard across the year — 34% of days in August up to 58% in January. Season the plan accordingly: prep in the wet months, apply in the dry ones.

If the walls pass, the roof might too: roof coating in Ann Arbor uses the same film chemistry with tighter dew and wind limits.

Source honesty: every monthly figure on this page is the 1991–2020 normal at Ann Arbor Se, Mi Us, 4.9 km from Ann Arbor's center — your block's shade lines and wind exposure sit on top of that baseline. Scoring details are on the methodology page.

Ann Arbor by the numbers

Hottest month: July — 84°F average high, 0 days topping 90°F.
The cold floor is January at 32°F afternoons and 16°F overnight.
Measurable rain: January leads at 58% of days; August is the quiet end at 34%.
The 40°F-night season spans May–September here.
Bottom line for Ann Arbor: roughly 100 workable exterior painting days a year.

Prep checklist

Find application day plus 24 dry hours with nights at 40°F+; Ann Arbor offers that pairing most often in August (20 workable days).
Scrape, then wash: loose paint and chalk go first, because latex only grips solid substrate.
Give washed siding 24 hours — north walls in Ann Arbor can need double after a January-grade soak.
An ir surface thermometer settles arguments: label limits bind the wall surface, which outruns Ann Arbor's air by 20°F+ in sun.
Bare wood gets primer, stains get stain-blocker, gaps get caulk — in that order, on dry substrate.
Sequence walls so you always paint in shade; midday sun skins latex before it levels.
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 58°F, Ann Arbor'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.
Angled brush set
Control at trim, corners, and cut-in lines.
Exterior paint + primer
One-coat hide on sound, prepped siding.

FAQ

What temperature can you paint outside?

50–90°F for standard formulas, 35°F+ for low-temp lines, and the wall itself must stay 5°F above the dew point. In Ann Arbor the practical range is set by nights: the 40°F overnight floor arrives around May and leaves after September.

How many dry hours does exterior paint need before rain?

Plan 24 rain-free hours after the last coat; the engine fails any day that can't deliver them. With Ann Arbor's rain odds swinging from 34% of days in August to 58% in January, the strip above is mostly a search for that dry pair.

Why does dew ruin fresh paint?