Maine weather and outdoor projects
Maine has a short, mild summer and long, cold winters. The coast around Portland is moderated by the ocean, while northern Maine around Caribou has one of the shortest frost-free seasons in the eastern U.S. The outdoor project season runs roughly from late May to late September, and less in the north.
Coastal fog and dew can leave surfaces wet until late morning, so wait for them to dry before painting or staining. Many Maine homes have wood siding and shingles that need regular finishing, and the best stretch is usually July to early September. Plan concrete pours well before the first fall frost.
Frost dates in Maine
In Portland, the median last spring freeze (32°F) is around April 26 and the median first fall freeze is around October 15, a frost-free season of about 170 days.
In Caribou, the median last spring freeze (32°F) is around May 7 and the median first fall freeze is around October 1, a frost-free season of about 143 days.
Frost dates matter for concrete, which must not freeze in its first 48 hours, for paint and caulk that need nights above their minimum, and for lawn care, since crabgrass preventer goes down as the soil warms in spring. See how late in fall you can stain, paint or seal.
Best time to stain a deck in Maine
In Portland, the most reliable months are June–September. May and October can also work on the right days. November–April is too cold, with average highs around 42°F. In May, nights average about 46°F, so finish early on mild days and check the overnight low. October is cool, with highs around 60°F, so choose the warmest afternoons.
In Caribou, the most reliable months are June and August. May, July and September can also work on the right days. October–April is too cold, with average highs around 35°F. In May and September, nights average about 44°F, so finish early on mild days and check the overnight low. July averages about 8 wet days a month, so wait for a clear stretch.
Check this week’s hour-by-hour verdict with the deck staining forecast.
Best time to paint outside in Maine
In Portland, the most reliable months are May–September. April and October can also work on the right days. November–March is too cold, with average highs around 39°F. April is cool, with highs around 54°F, so choose the warmest afternoons. In October, nights average about 41°F, so finish early on mild days and check the overnight low.
In Caribou, the most reliable months are June and August–September. May, July and October can also work on the right days. November–April is too cold, with average highs around 32°F. In May, nights average about 41°F, so finish early on mild days and check the overnight low. July averages about 8 wet days a month, so wait for a clear stretch. October is cool, with highs around 53°F, so choose the warmest afternoons.
Check this week’s hour-by-hour verdict with the exterior painting forecast.
Best time to pour concrete in Maine
In Portland, the most reliable months are May–September. October can also work on the right days. November–April averages about 23 nights a month at or below 32°F, so fresh concrete needs blankets or heated enclosures. October brings about 6 freezing nights a month, so pick a mild spell and keep curing blankets on hand.
In Caribou, the most reliable months are June–August. May and September can also work on the right days. October–April averages about 25 nights a month at or below 32°F, so fresh concrete needs blankets or heated enclosures. May and September bring about 3 freezing nights a month, so pick a mild spell and keep curing blankets on hand.
Check this week’s hour-by-hour verdict with the concrete pouring forecast.
Best time to seal a driveway in Maine
In Portland, the most reliable months are June–September. May can also work on the right days. October–April is too cold, with average highs around 44°F. May is cool, with highs around 64°F, so choose the warmest afternoons.
In Caribou, the most reliable months are August. June–July and September can also work on the right days. October–April is too cold, with average highs around 35°F. In May, nights average about 41°F, too cold for the coating to dry and cure overnight. In June, nights average about 51°F, so finish early on mild days and check the overnight low. July averages about 8 wet days a month, so wait for a clear stretch. September is cool, with highs around 67°F, so choose the warmest afternoons.
Check this week’s hour-by-hour verdict with the driveway sealing forecast.
Best time to fertilize or treat a lawn in Maine
In Portland, the most reliable months are May–September. April and October can also work on the right days. November–March is too cold, with average highs around 39°F. April and October are cool, with highs around 57°F, so choose the warmest afternoons.
In Caribou, the most reliable months are May–September. October can also work on the right days. November–April is too cold, with average highs around 32°F. October is cool, with highs around 53°F, so choose the warmest afternoons.
Check this week’s hour-by-hour verdict with the lawn fertilizer forecast.
How the weather differs across Maine
| Place | Hottest month avg high | Coldest month avg low | Rain per year | Last spring freeze | First fall freeze |
|---|---|---|---|---|---|
| Portland | 80°F | 16°F | 48 in | April 26 | October 15 |
| Caribou | 77°F | 3°F | 41 in | May 7 | October 1 |
Of the places above, Portland has the most good months for staining, painting and concrete combined (14 job-months), and Caribou has the fewest (8). If you live between them, expect something in between, and higher ground to be cooler with a shorter season.
Monthly weather in Portland
| Month | Avg high | Avg low | Wet days* | Rain | 3 PM humidity | Freezing nights |
|---|---|---|---|---|---|---|
| January | 32°F | 16°F | 7 | 3.5 in | 55% | 29 |
| February | 35°F | 17°F | 7 | 3.5 in | 51% | 26 |
| March | 42°F | 26°F | 7 | 4.1 in | 51% | 25 |
| April | 54°F | 35°F | 7 | 4.4 in | 49% | 12 |
| May | 64°F | 46°F | 7 | 3.7 in | 55% | 1 |
| June | 74°F | 55°F | 7 | 4.2 in | 58% | 0 |
| July | 80°F | 61°F | 7 | 3.4 in | 59% | 0 |
| August | 79°F | 60°F | 5 | 3.6 in | 58% | 0 |
| September | 71°F | 52°F | 5 | 3.8 in | 59% | 0 |
| October | 60°F | 41°F | 7 | 5.3 in | 58% | 6 |
| November | 48°F | 32°F | 7 | 4.3 in | 56% | 18 |
| December | 38°F | 22°F | 8 | 4.5 in | 58% | 27 |
*Days with at least 0.1 inch of rain or melted snow. Freezing nights: average nights a month at or below 32°F. Humidity is calculated from NOAA hourly normal temperature and dew point at 3 PM.
Monthly weather in Caribou
| Month | Avg high | Avg low | Wet days* | Rain | 3 PM humidity | Freezing nights |
|---|---|---|---|---|---|---|
| January | 21°F | 3°F | 7 | 3.0 in | 66% | 30 |
| February | 24°F | 4°F | 6 | 2.4 in | 59% | 28 |
| March | 34°F | 16°F | 6 | 2.8 in | 52% | 29 |
| April | 48°F | 29°F | 8 | 3.0 in | 46% | 21 |
| May | 63°F | 41°F | 9 | 3.5 in | 44% | 4 |
| June | 72°F | 51°F | 8 | 3.9 in | 50% | 0 |
| July | 77°F | 56°F | 8 | 4.2 in | 54% | 0 |
| August | 76°F | 54°F | 8 | 3.6 in | 53% | 0 |
| September | 67°F | 46°F | 7 | 3.4 in | 55% | 2 |
| October | 53°F | 36°F | 8 | 4.0 in | 59% | 12 |
| November | 40°F | 26°F | 7 | 3.4 in | 65% | 24 |
| December | 28°F | 12°F | 8 | 3.6 in | 70% | 30 |
Use the averages, then check the forecast
These ratings describe a typical month, not a particular week. A warm spell in a “poor” month can give you a good day, and a wet week can spoil a “good” one. Use this page to plan the season, then check the 7-day forecast for your ZIP code before you buy materials or book help. Each project forecast checks the hours after you finish too: overnight lows, dew and rain that would ruin fresh stain, paint, sealer or concrete.
About this data
Monthly temperatures, rain days, snowfall and freeze dates are NOAA National Centers for Environmental Information (NCEI) U.S. Climate Normals for 1991–2020 at PORTLAND INTL JETPORT, CARIBOU MUNI AP. Ratings apply the same temperature limits as our forecasts (for example, 50°F or warmer for deck stain and driveway sealer, and no freezing nights for new concrete) to the average month. Your product label always takes priority.
Frequently asked questions
When is the best time to stain a deck in Maine?
In Portland, June–September. In Caribou, June and August. Look for at least 24 dry hours before and after, and nights above about 40°F. The deck staining forecast checks your exact week.
When is the last frost in Maine?
Portland: around April 26; Caribou: around May 7. These are median dates from NOAA 1991–2020 normals, so a freeze after them happens in about half of years. Low spots and valleys freeze later in spring.
Can you pour concrete in winter in Maine?
Yes, but it needs cold-weather practices. Portland averages about 82 freezing nights from December to February, so fresh concrete needs insulated blankets, a heated enclosure or an accelerated mix, and must not freeze in the first 48 hours. Many homeowners wait for spring.
What months are best for sealing a driveway in Maine?
In Portland, June–September. In Caribou, August. Most sealers need 50°F or warmer for 24 hours and a dry day after. See the driveway sealing forecast.