Is it good to paint in Portland, ME this week?
A live 7-day go/no-go calendar for exterior paint in Portland, built from the local forecast against the 5°F-above-dew-point rule. We lead with the signal a weather app misses: overnight condensation risk.
- Dew margin
- -2.4°F
- Overnight dew
- High
- Rain
- 2%
- Window
- —
High condensation risk overnight — surface dips to within -2.4°F of the 56°F dew point (low 54°F, 100% cloud, 1 mph wind). A fresh paint can blush/blister. Stop 4h before dew falls.
- Dew margin
- 1.6°F
- Overnight dew
- High
- Rain
- 8%
- Window
- —
High condensation risk overnight — surface dips to within 1.6°F of the 60°F dew point (low 61°F, 73% cloud, 8 mph wind). A fresh paint can blush/blister. Stop 4h before dew falls.
- Dew margin
- 1°F
- Overnight dew
- High
- Rain
- 40%
- Window
- —
High condensation risk overnight — surface dips to within 1°F of the 58°F dew point (low 53°F, 100% cloud, 7 mph wind). A fresh paint can blush/blister. Stop 4h before dew falls.
- Dew margin
- 6.7°F
- Overnight dew
- Low
- Rain
- 2%
- Window
- 8am–5pm
Clear to paint: temps 60–68°F, RH under 64%, surface stays 6.7°F+ above the dew point, no rain in the cure window.
- Dew margin
- 0.8°F
- Overnight dew
- High
- Rain
- 10%
- Window
- —
High condensation risk overnight — surface dips to within 0.8°F of the 53°F dew point (low 53°F, 100% cloud, 1 mph wind). A fresh paint can blush/blister. Stop 4h before dew falls.
- Dew margin
- 4.8°F
- Overnight dew
- Watch
- Rain
- 10%
- Window
- 10am–3pm
Watch overnight dew — surface comes within 4.8°F of the dew point (margin is 5°F). Time the coat to dry well before evening.
- Dew margin
- 15.9°F
- Overnight dew
- Low
- Rain
- 1%
- Window
- 11am–5pm
Cold mornings (down to 43°F, floor is 50°F) — wait for the surface to warm past midday before you paint.
- High condensation risk overnight — surface dips to within -2.4°F of the 56°F dew point (low 54°F, 100% cloud, 1 mph wind). A fresh paint can blush/blister. Stop 4h before dew falls.
- Humidity peaks at 100% — well above the 85% ceiling; cure stalls and moisture gets trapped.
Hold off. These are forecast numbers — confirm the surface temperature on-site before you start.
Why these thresholds
Overnight dew condensing on a fresh coat causes blistering, surfactant leaching and peeling — the cause of 40%+ of exterior paint failures.
- • Surface temp must stay 5°F above the dew point through application and cure (ASTM D3276 / ISO 8502-42).
- • Air + surface in the 50–85°F band (low-temp lines to 35°F).
- • Humidity under 85%; ideally under 70%.
- • No rain for 24h after application.
- • We use the forecast ground-surface temperature as a surface-temp proxy — confirm on-site with an IR thermometer.
Free in the beta
Watch this job site 24/7
Get an email the moment overnight dew, rain, or an out-of-range stretch threatens a fresh coat — and a morning digest with the best window ahead. No app to check; we watch the forecast for you.