Portland
Maine, USA
Long-term weather forecast
Long-term weather forecast

December weather forecast and climate
Portland, ME

Dusk view of the lit skyscrapers of the Portland city in Maine
Dusk view of the lit skyscrapers of the Portland city in Maine
December, the first month of the winter, in Portland, is also a wintry month, with average temperature varying between 37.2°F (2.9°C) and 20.5°F (-6.4°C).

Temperature

In December, the average high-temperature decreases, from a frosty 48°F (8.9°C) in November, to a cold 37.2°F (2.9°C). The average low-temperature, in December, is 20.5°F (-6.4°C).

Humidity

In December, the average relative humidity in Portland is 70.2%.

Rainfall

In December, in Portland, the rain falls for 11.5 days. Throughout December, 4" (102.1mm) of precipitation is accumulated. Throughout the year, there are 130.9 rainfall days, and 47.3" (1200.3mm) of precipitation is accumulated.

Snowfall

Months with snowfall in Portland are January through April, November and December.

Ocean temperature

In Portland, the average seawater temperature is 45.3°F (7.4°C). Swimming in 45.3°F (7.4°C) is considered dangerous. Unprotected immersion in temperatures below 50°F (10°C) causes quickly maximum intensity cold shock with hyperventilation.

Daylight

With an average of 9h of daylight, December has the shortest days of the year in Portland.

Sunshine

December has the least sunshine of the year, with an average of 4.5h of sunshine.

UV index

January and December, with an average maximum UV index of 1, are months with the lowest UV index. A UV Index value of 2, and less, symbolizes a low health risk from unprotected exposure to the Sun's UV rays for the ordinary person.
The daily maximum UV index of 1 interpret into the following advice:
Most people can stay in the Sun for up to 1 hour without burning, apart from children that always must be protected from sun exposure. The solar radiation is most powerful near the mid-day, so the exposure to the direct Sun should be reduced accordingly. Sun-protective clothing, a long-sleeved shirt and pants, a wide-brimmed hat, and UVA and UVB-blocking sunglasses are particularly helpful in blocking UV radiation's harmful effects. Caution! The reflection of snow can nearly double the intensity of the Sun's UV radiation.

What is the temperature in December in Portland?

The average high-temperature, in December, is 37.2°F (2.9°C), while the average low-temperature is 20.5°F (-6.4°C).

What is the average humidity in December in Portland?

The average relative humidity in December in Portland, Maine, is 70.2%.

How many days does it rain in December in Portland?

In Portland, in December, during 11.5 rainfall days, 4" (102.1mm) of precipitation is typically accumulated.

How much does it snow in Portland in December?

In Portland, Maine, in December, during 6.1 snowfall days, 13.2" (335.3mm) of snow is typically accumulated.

What is the water temperature in December in Portland?

In December, the average ocean temperature is 45.3°F (7.4°C). Swimming in 45.3°F (7.4°C) is considered life-threatening. Even a few minutes in 55.4°F (13°C) water is uncomfortable, and swimming below 50°F (10°C) may cause total loss of breathing control and cold shock, depending on a person's physique.

What is the month with the shortest days in Portland?

December has the shortest days of the year in Portland, Maine, with an average of 9h of daylight.

What is the average length of the day in December in Portland?

In December, the average length of the day is 9h.

What is the month with the least sunshine in Portland?

The month with the least sunshine in Portland, Maine, is December, with an average of 4.5h of sunshine.

How many hours of sunshine does Portland have in December?

In Portland, the average sunshine in December is 4.5h.

What is the month with the lowest UV index in Portland?

Months with the lowest UV index in Portland are January and December, with an average maximum UV index of 1.

What is the UV index reading in December in Portland?

In December, the average daily maximum UV index in Portland is 1. A UV Index estimate of 2, and below, represents a low health risk from unsafe exposure to the Sun's UV rays.
Average temperature in December - Portland, ME
  • Average high temperature in December: 37.3°F

The warmest month (with the highest average high temperature) is July (78.8°F).
The month with the lowest average high temperature is January (31.2°F).

  • Average low temperature in December: 20.4°F

The month with the highest average low temperature is July (59.4°F).
The coldest month (with the lowest average low temperature) is January (13.4°F).

Average humidity in December - Portland, ME
  • Average humidity in December: 70.2%

The month with the highest relative humidity is September (76.7%).
The month with the lowest relative humidity is February (65.2%).

Average rainfall in December - Portland, ME
  • Average rainfall in December: 4"

Wettest months (with the highest rainfall) are October and November (4.9").
The driest month (with the lowest rainfall) is August (3.1").

Average rainfall days in December - Portland, ME
  • Average rainfall days in December: 11.5 days

The month with the highest number of rainy days is May (12.6 days).
The month with the lowest number of rainy days is September (9.2 days).

Average snowfall in December - Portland, ME
  • Average snowfall in December: 13.2"

The month with the highest snowfall is January (19.2").
Months with the lowest snowfall are May, June, July, August, September and October (0").

Average snowfall days in December - Portland, ME
  • Average snowfall days in December: 6.1 days

The month with the highest number of snowfall days is January (7.9 days).
Months with the lowest number of snowfall days are May, June, July, August, September and October (0 days).

Average sea temperature in December - Portland, ME
  • Average sea temperature in December: 45.3°F

The best month for swimming (with the highest average sea temperature) is August (63.7°F).
The coldest month (with the lowest average sea temperature) is March (38°F).

Average daylight in December / Average sunshine in December - Portland, ME
  • Average daylight in December: 9h

The month with the longest days is June (Average daylight: 15.4h).
The month with shortest days is December (Average daylight: 9h).

  • Average sunshine in December: 4.5h

The month with most sunshine is July (Average sunshine: 9.1h).
The month with least sunshine is December (Average sunshine: 4.5h).

Average UV index in December - Portland, ME
  • Average UV index in December: 1

Months with the highest UV index are June and July (UV index 8).
Months with the lowest UV index are January and December (UV index 1).