Portland, Maine Weather
Fireflies rise from the lawn. Day 78 of spring. Read this microseason across nine climate regions →
Portland weather forecast — hour by hour, 7-day outlook, NOAA radar
- TodayJun 4Clear——88°53°—
- FridayJun 5Overcast——84°57°-4°
- SaturdayJun 6Light Drizzle31%0.05″67°55°-17°
- SundayJun 7Drizzle64%0.02″80°53°+13°
- MondayJun 8Overcast23%—80°50°0°
- TuesdayJun 9Overcast——87°58°+7°
- WednesdayJun 10Overcast——93°64°+6°
AQI 61 (Moderate), driven by PM2.5. AQI up 13 over the last 6 hours (gradual rise). PM2.5 at 11.6 µg/m³ (AQI 56) with a 0.79 fine-to-coarse ratio and 5 mph wind — combustion smoke trapped in calm air, not road dust.
OK No precautions needed for the general population; unusually sensitive individuals may consider limiting prolonged outdoor exertion.
What's driving it
Ozone × UV × Sky
Ozone at AQI 38. Overcast through the UV peak window (cloud cover ~100%) — afternoon ozone should stay flat.
- Present
- AQI 38
- UV peak
- 0.0 at 1 PM
- Sky at peak
- overcast
- Projected peak
- AQI 5
PM × Wind × Precip
PM2.5 at 11.6 µg/m³ (AQI 56) with a 0.79 fine-to-coarse ratio and 5 mph wind — combustion smoke trapped in calm air, not road dust.
- PM2.5/PM10
- 0.79
- Wind
- light
- Recent rain
- 0h in last 6h
- Pattern
- stagnant smoke
Trends
Seven days of AQI and PM2.5.
Hourly air-quality data from the Copernicus Atmosphere Monitoring Service, charted across the past and next several days. Dashed lines mark the AQI breakpoints at 50 (Good → Moderate) and 100 (Moderate → Unhealthy for Sensitive Groups).
The higher the clouds, the finer the weather.
- Moonrise
- 3:50 AM
- Moonset
- 1:35 PM
- In sign
- ♒︎ Aquarius
Fireflies rise from the lawn
Portland at a glance
- Today vs. normal: 6°F below the seasonal normal for this latitude
- Last frost: May 8 (climatological average for this latitude)
- Microseason: Jun 1–5
- Planting window: Harvest spring lettuce before it bolts. Sow heat-tolerant greens.
Right now in the garden
Peak growing season
As of June 5, the growing season is at its peak — frost is months away. Continue succession-planting beans and summer squash. Start fall brassicas (broccoli, cabbage, kale) from seed indoors for transplanting in late summer.
SPC Convective Outlook
Storm Prediction Center — Portland
SPC has placed Portland in the Marginal Risk category for severe thunderstorms day after tomorrow.
- TODAYNONENo severe risk
- TOMORROWNONENo severe risk
- DAY 3MRGLMarginal Risk
Isolated severe storms possible. Limited threat for hail or damaging wind.
Source: NOAA / NWS Storm Prediction Center categorical convective outlook. Outlooks are re-issued multiple times per day; this page reflects the most recent SPC polygons covering the city’s coordinates.
Planting calendar
| Month | Plant | Harvest |
|---|---|---|
| January | — | — |
| February | — | — |
| March | — | — |
| April | — | — |
| May | lettuce, peas, spinach, radishes | lettuce, peas, radishes |
| June | lettuce, peas, spinach, radishes, tomatoes, peppers, beans, squash | lettuce, peas, radishes |
| July | tomatoes, peppers, beans, squash | tomatoes, beans, summer squash |
| August | tomatoes, peppers, beans, squash, fall brassicas, garlic (overwinter), carrots | tomatoes, beans, summer squash |
| September | fall brassicas, garlic (overwinter), carrots | tomatoes, beans, summer squash |
| October | — | winter squash, tomatoes (last) |
| November | — | — |
| December | — | — |
A year in weather
July brings Portland's warmest temperatures at roughly 70°F mean, while January delivers the coldest at around 24°F. October sees peak rainfall with 5.3 inches, contrasting with July's drier 3.4 inches.
| Month | Mean temp | Precip | Rainy days |
|---|---|---|---|
| January | 24° | 3.5″ | 7 |
| February | 26° | 3.5″ | 7 |
| March | 34° | 4.1″ | 7 |
| April | 45° | 4.4″ | 7 |
| May | 55° | 3.7″ | 7 |
| June | 64° | 4.2″ | 7 |
| July | 70° | 3.4″ | 7 |
| August | 69° | 3.6″ | 5 |
| September | 62° | 3.8″ | 5 |
| October | 50° | 5.3″ | 7 |
| November | 40° | 4.3″ | 7 |
| December | 30° | 4.5″ | 8 |
Regional context
Portland falls within the warm-summer humid continental climate region, sharing temperature ranges, seasonal patterns, and growing conditions with other nearby cities in this climate zone.
Similar climates: Lewiston, ME, Bangor, ME, South Portland, ME, Auburn, ME, Biddeford, ME.
Naturalist notes
Late May brings the first ruby-throated hummingbirds to Portland's gardens, their migration timed with the blooming of native honeysuckle.
Apple trees across the region typically reach full bloom by mid-May, marking the transition from spring's cool nights to the approaching warmth of early summer.
Frequently asked
- When does it freeze in Portland?
- Portland's last spring frost typically occurs around mid-May, while the first fall frost returns around mid-October.
- What is the rainy season in Portland?
- October receives the most rainfall with approximately 5.3 inches on average; the city sees roughly 48 inches total annually.
- What is the warmest month in Portland?
- July typically records the warmest temperatures, averaging about 70°F.
- What is the coldest month in Portland?
- January typically brings the coldest weather, averaging about 24°F.
- When can I start a vegetable garden in Portland?
- Cool-season crops like peas and lettuce can be planted around the last spring frost in mid-May; warm-season crops such as tomatoes and peppers should wait 1–2 weeks after.
- How many rainy days does Portland get?
- Portland experiences about 80 rainy days per year on average.
- What hardiness zone is Portland?
- Portland's USDA hardiness zone depends on its lowest average winter temperature; use the USDA's online lookup tool with the city ZIP code for the current zone designation.
Climate
Portland, Maine experiences a warm-summer humid continental climate. Winter brings January temperatures that hover near 24°F, while summer peaks in July with averages around 70°F — creating a 46°F seasonal swing.
Annual precipitation totals about 48 inches, falling across roughly 80 rainy days throughout the year.
Geography drives Portland's weather patterns through its latitude of 43.7°N, proximity to large water bodies, and elevation. These factors determine what grows in the region, when frost threatens, and how daily weather unfolds.