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December Weather in Greenwich Connecticut, United States

Daily high temperatures decrease by 7°F, from 47°F to 40°F, rarely falling below 27°F or exceeding 59°F.

Daily low temperatures decrease by 7°F, from 35°F to 28°F, rarely falling below 15°F or exceeding 46°F.

For reference, on July 20, the hottest day of the year, temperatures in Greenwich typically range from 68°F to 84°F, while on January 29, the coldest day of the year, they range from 24°F to 37°F.

Average High and Low Temperature in December in Greenwich

Average High and Low Temperature in December in GreenwichDec112233445566778899101011111212131314141515161617171818191920202121222223232424252526262727282829293030313110°F10°F15°F15°F20°F20°F25°F25°F30°F30°F35°F35°F40°F40°F45°F45°F50°F50°F55°F55°F60°F60°F65°F65°F70°F70°FNovJanDec 147°FDec 147°F35°F35°FDec 3140°FDec 3140°F28°F28°FDec 1144°FDec 1144°F32°F32°FDec 2141°FDec 2141°F29°F29°F
The daily average high (red line) and low (blue line) temperature, with 25th to 75th and 10th to 90th percentile bands. The thin dotted lines are the corresponding average perceived temperatures.

The figure below shows you a compact characterization of the hourly average temperatures for the quarter of the year centered on December. The horizontal axis is the day, the vertical axis is the hour of the day, and the color is the average temperature for that hour and day.

Average Hourly Temperature in December in Greenwich

Average Hourly Temperature in December in GreenwichDec112233445566778899101011111212131314141515161617171818191920202121222223232424252526262727282829293030313112 AM12 AM2 AM2 AM4 AM4 AM6 AM6 AM8 AM8 AM10 AM10 AM12 PM12 PM2 PM2 PM4 PM4 PM6 PM6 PM8 PM8 PM10 PM10 PM12 AM12 AMNovJanfreezingfreezingvery coldcoldcool
frigid 15°F freezing 32°F very cold 45°F cold 55°F cool 65°F comfortable 75°F warm 85°F hot 95°F sweltering
The average hourly temperature, color coded into bands. The shaded overlays indicate night and civil twilight.

Constanţa, Romania (4,840 miles away); Karabudakhkent, Russia (5,596 miles); and Nagano, Japan (6,712 miles) are the far-away foreign places with temperatures most similar to Greenwich (view comparison).

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The month of December in Greenwich experiences essentially constant cloud cover, with the percentage of time that the sky is overcast or mostly cloudy remaining about 51% throughout the month.

The clearest day of the month is December 2, with clear, mostly clear, or partly cloudy conditions 51% of the time.

For reference, on February 28, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 53%, while on September 22, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 64%.

Cloud Cover Categories in December in Greenwich

Cloud Cover Categories in December in GreenwichDec11223344556677889910101111121213131414151516161717181819192020212122222323242425252626272728282929303031310%100%10%90%20%80%30%70%40%60%50%50%60%40%70%30%80%20%90%10%100%0%NovJanDec 151%Dec 151%Dec 3148%Dec 3148%Dec 1149%Dec 1149%Dec 2148%Dec 2148%clearmostly clearpartly cloudymostly cloudyovercast
0% clear 20% mostly clear 40% partly cloudy 60% mostly cloudy 80% overcast 100%
The percentage of time spent in each cloud cover band, categorized by the percentage of the sky covered by clouds.

A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In Greenwich, the chance of a wet day over the course of December is gradually decreasing, starting the month at 28% and ending it at 25%.

For reference, the year's highest daily chance of a wet day is 36% on August 2, and its lowest chance is 22% on January 29.

Over the course of December in Greenwich, the chance of a day with only rain decreases from 24% to 16%, the chance of a day with mixed snow and rain remains an essentially constant 4% throughout, and the chance of a day with only snow increases from 1% to 5%.

Probability of Precipitation in December in Greenwich

The percentage of days in which various types of precipitation are observed, excluding trace quantities: rain alone, snow alone, and mixed (both rain and snow fell in the same day).

Rainfall

To show variation within the month and not just the monthly total, we show the rainfall accumulated over a sliding 31-day period centered around each day.

The average sliding 31-day rainfall during December in Greenwich is rapidly decreasing, starting the month at 3.5 inches, when it rarely exceeds 5.8 inches or falls below 1.4 inches, and ending the month at 2.5 inches, when it rarely exceeds 4.2 inches or falls below 0.7 inches.

Average Monthly Rainfall in December in Greenwich

The average rainfall (solid line) accumulated over the course of a sliding 31-day period centered on the day in question, with 25th to 75th and 10th to 90th percentile bands. The thin dotted line is the corresponding average snowfall.

Snowfall

As with rainfall, we consider the snowfall accumulated over a sliding 31-day period centered around each day.

The average sliding 31-day snowfall during December in Greenwich is rapidly increasing, starting the month at 2.2 inches, when it rarely exceeds 6.8 inches or falls below -0.0 inches, and ending the month at 6.0 inches, when it rarely exceeds 15.6 inches or falls below 0.4 inches.

Average Monthly Snowfall in December in Greenwich

The average snowfall (solid line) accumulated over the course of a sliding 31-day period centered on the day in question, with 25th to 75th and 10th to 90th percentile bands. The thin dotted line is the corresponding average rainfall.

Over the course of December in Greenwich, the length of the day is essentially constant. The shortest day of the month is December 21, with 9 hours, 13 minutes of daylight and the longest day is December 1, with 9 hours, 26 minutes of daylight.

Hours of Daylight and Twilight in December in Greenwich

Hours of Daylight and Twilight in December in GreenwichDec11223344556677889910101111121213131414151516161717181819192020212122222323242425252626272728282929303031310 hr24 hr4 hr20 hr8 hr16 hr12 hr12 hr16 hr8 hr20 hr4 hr24 hr0 hrNovJanDec 219 hr, 13 minDec 219 hr, 13 minnightnightdaydayDec 19 hr, 26 minDec 19 hr, 26 min
The number of hours during which the Sun is visible (black line). From bottom (most yellow) to top (most gray), the color bands indicate: full daylight, twilight (civil, nautical, and astronomical), and full night.

The earliest sunrise of the month in Greenwich is 7:00 AM on December 1 and the latest sunrise is 19 minutes later at 7:19 AM on December 31.

The earliest sunset is 4:25 PM on December 7 and the latest sunset is 10 minutes later at 4:36 PM on December 31.

Daylight saving time is observed in Greenwich during 2024, but it neither starts nor ends during December, so the entire month is in standard time.

For reference, on June 20, the longest day of the year, the Sun rises at 5:22 AM and sets 15 hours, 8 minutes later, at 8:30 PM, while on December 21, the shortest day of the year, it rises at 7:16 AM and sets 9 hours, 13 minutes later, at 4:29 PM.

Sunrise & Sunset with Twilight and Daylight Saving Time in December in Greenwich

Sunrise & Sunset with Twilight and Daylight Saving Time in December in GreenwichDec112233445566778899101011111212131314141515161617171818191920202121222223232424252526262727282829293030313112 AM2 AM4 AM6 AM8 AM10 AM12 PM2 PM4 PM6 PM8 PM10 PM12 AMNovJan7:00 AM7:00 AMDec 14:26 PMDec 14:26 PM7:19 AM7:19 AMDec 314:36 PMDec 314:36 PM7:09 AM7:09 AMDec 114:26 PMDec 114:26 PM7:16 AM7:16 AMDec 214:29 PMDec 214:29 PMSolarMidnightSolarMidnightSolarNoonSunriseSunset
The solar day over the course of December. From bottom to top, the black lines are the previous solar midnight, sunrise, solar noon, sunset, and the next solar midnight. The day, twilights (civil, nautical, and astronomical), and night are indicated by the color bands from yellow to gray.

The figure below presents a compact representation of the sun's elevation (the angle of the sun above the horizon) and azimuth (its compass bearing) for every hour of every day in the reporting period. The horizontal axis is the day of the year and the vertical axis is the hour of the day. For a given day and hour of that day, the background color indicates the azimuth of the sun at that moment. The black isolines are contours of constant solar elevation.

Solar Elevation and Azimuth in December in Greenwich

Solar Elevation and Azimuth in December in GreenwichDec112233445566778899101011111212131314141515161617171818191920202121222223232424252526262727282829293030313112 AM12 AM2 AM2 AM4 AM4 AM6 AM6 AM8 AM8 AM10 AM10 AM12 PM12 PM2 PM2 PM4 PM4 PM6 PM6 PM8 PM8 PM10 PM10 PM12 AM12 AMNovJan0010102020001010202030
northeastsouthwest
Solar elevation and azimuth over the course of December 2024. The black lines are lines of constant solar elevation (the angle of the sun above the horizon, in degrees). The background color fills indicate the azimuth (the compass bearing) of the sun. The lightly tinted areas at the boundaries of the cardinal compass points indicate the implied intermediate directions (northeast, southeast, southwest, and northwest).

The figure below presents a compact representation of key lunar data for December 2024. The horizontal axis is the day, the vertical axis is the hour of the day, and the colored areas indicate when the moon is above the horizon. The vertical gray bars (new Moons) and blue bars (full Moons) indicate key Moon phases. The label associated with each bar indicates the date and time that the phase is obtained, and the companion time labels indicate the rise and set times of the Moon for the nearest time interval in which the moon is above the horizon.

Moon Rise, Set & Phases in December in Greenwich

Moon Rise, Set & Phases in December in GreenwichDec112233445566778899101011111212131314141515161617171818191920202121222223232424252526262727282829293030313112 AM12 AM4 AM4 AM8 AM8 AM12 PM12 PM4 PM4 PM8 PM8 PM12 AM12 AMNovJanNov 18:48 AMNov 18:48 AMNov 154:29 PMNov 154:29 PMDec 11:22 AMDec 11:22 AMDec 154:02 AMDec 154:02 AMDec 305:28 PMDec 305:28 PMJan 135:28 PMJan 135:28 PMJan 297:37 AMJan 297:37 AM7:34 AM7:34 AM5:40 PM5:40 PM4:10 PM4:10 PM7:48 AM7:48 AM7:39 AM7:39 AM4:24 PM4:24 PM3:29 PM3:29 PM7:50 AM7:50 AM7:28 AM7:28 AM4:05 PM4:05 PM4:24 PM4:24 PM8:09 AM8:09 AM7:32 AM7:32 AM5:21 PM5:21 PM
The time in which the moon is above the horizon (light blue area), with new moons (dark gray lines) and full moons (blue lines) indicated. The shaded overlays indicate night and civil twilight.
Dec 2024IlluminationMoonriseMoonsetMoonriseMeridian PassingDistance
1
0%7:39 AMSE4:24 PMSW-12:01 PMS245,378 mi
2
2%8:40 AMSE5:15 PMSW-12:58 PMS243,295 mi
3
7%9:35 AMSE6:16 PMSW-1:56 PMS241,162 mi
4
13%10:22 AMSE7:24 PMSW-2:53 PMS239,015 mi
5
21%11:00 AMESE8:36 PMWSW-3:48 PMS236,874 mi
6
31%11:31 AMESE9:49 PMWSW-4:40 PMS234,757 mi
7
42%11:58 AMESE11:02 PMWSW-5:29 PMS232,700 mi
8
50%12:21 PME--6:16 PMS230,776 mi
9
65%-12:14 AMW12:44 PME7:03 PMS229,097 mi
10
76%-1:27 AMW1:08 PME7:51 PMS227,819 mi
11
86%-2:43 AMWNW1:33 PMENE8:42 PMS227,113 mi
12
93%-4:00 AMWNW2:04 PMENE9:37 PMS227,142 mi
13
98%-5:20 AMWNW2:41 PMENE10:35 PMS228,017 mi
14
100%-6:38 AMNW3:29 PMNE11:37 PMS229,760 mi
15
100%-7:50 AMNW4:27 PMNE--
16
99%-8:50 AMNW5:34 PMNE12:40 AMS232,281 mi
17
95%-9:37 AMNW6:45 PMENE1:40 AMS235,382 mi
18
90%-10:14 AMWNW7:56 PMENE2:34 AMS238,790 mi
19
82%-10:43 AMWNW9:04 PMENE3:24 AMS242,208 mi
20
74%-11:07 AMWNW10:09 PMENE4:09 AMS245,353 mi
21
64%-11:27 AMW11:10 PME4:51 AMS247,985 mi
22
50%-11:46 AMW-5:30 AMS249,921 mi
23
45%12:10 AME12:04 PMW-6:09 AMS251,048 mi
24
36%1:11 AME12:23 PMWSW-6:48 AMS251,322 mi
25
27%2:12 AMESE12:45 PMWSW-7:29 AMS250,769 mi
26
18%3:14 AMESE1:10 PMWSW-8:12 AMS249,476 mi
27
11%4:19 AMESE1:40 PMWSW-9:00 AMS247,583 mi
28
6%5:25 AMSE2:18 PMSW-9:52 AMS245,268 mi
29
2%6:29 AMSE3:06 PMSW-10:48 AMS242,730 mi
30
0%7:28 AMSE4:05 PMSW-11:46 AMS240,170 mi
31
1%8:18 AMSE5:12 PMSW-12:45 PMS237,763 mi

We base the humidity comfort level on the dew point, as it determines whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid. Unlike temperature, which typically varies significantly between night and day, dew point tends to change more slowly, so while the temperature may drop at night, a muggy day is typically followed by a muggy night.

The chance that a given day will be muggy in Greenwich is essentially constant during December, remaining around 0% throughout.

For reference, on August 1, the muggiest day of the year, there are muggy conditions 50% of the time, while on November 20, the least muggy day of the year, there are muggy conditions 0% of the time.

Humidity Comfort Levels in December in Greenwich

Humidity Comfort Levels in December in GreenwichDec11223344556677889910101111121213131414151516161717181819192020212122222323242425252626272728282929303031310%0%10%10%20%20%30%30%40%40%50%50%60%60%70%70%80%80%90%90%100%100%NovJanDec 10%Dec 10%Dec 310%Dec 310%Dec 110%Dec 110%Dec 210%Dec 210%drydryhumidhumidcomfortablecomfortable
dry 55°F comfortable 60°F humid 65°F muggy 70°F oppressive 75°F miserable
The percentage of time spent at various humidity comfort levels, categorized by dew point.

This section discusses the wide-area hourly average wind vector (speed and direction) at 10 meters above the ground. The wind experienced at any given location is highly dependent on local topography and other factors, and instantaneous wind speed and direction vary more widely than hourly averages.

The average hourly wind speed in Greenwich is gradually increasing during December, increasing from 8.3 miles per hour to 8.8 miles per hour over the course of the month.

For reference, on February 26, the windiest day of the year, the daily average wind speed is 9.4 miles per hour, while on July 31, the calmest day of the year, the daily average wind speed is 5.6 miles per hour.

Average Wind Speed in December in Greenwich

The average of mean hourly wind speeds (dark gray line), with 25th to 75th and 10th to 90th percentile bands.

The hourly average wind direction in Greenwich throughout December is predominantly from the west, with a peak proportion of 46% on December 29.

Wind Direction in December in Greenwich

Wind Direction in December in GreenwichDec11223344556677889910101111121213131414151516161717181819192020212122222323242425252626272728282929303031310%100%20%80%40%60%60%40%80%20%100%0%NovJanwestsouthnortheast
northeastsouthwest
The percentage of hours in which the mean wind direction is from each of the four cardinal wind directions, excluding hours in which the mean wind speed is less than 1.0 mph. The lightly tinted areas at the boundaries are the percentage of hours spent in the implied intermediate directions (northeast, southeast, southwest, and northwest).

Greenwich is located near a large body of water (e.g., ocean, sea, or large lake). This section reports on the wide-area average surface temperature of that water.

The average surface water temperature in Greenwich is decreasing during December, falling by 7°F, from 51°F to 44°F, over the course of the month.

Average Water Temperature in December in Greenwich

The daily average water temperature (purple line), with 25th to 75th and 10th to 90th percentile bands.

Definitions of the growing season vary throughout the world, but for the purposes of this report, we define it as the longest continuous period of non-freezing temperatures (≥ 32°F) in the year (the calendar year in the Northern Hemisphere, or from July 1 until June 30 in the Southern Hemisphere).

The growing season in Greenwich typically lasts for 7.2 months (220 days), from around April 2 to around November 8, rarely starting before March 16 or after April 20, and rarely ending before October 25 or after November 23.

The month of December in Greenwich is reliably fully outside of the growing season.

Time Spent in Various Temperature Bands and the Growing Season in December in Greenwich

Time Spent in Various Temperature Bands and the Growing Season in December in GreenwichDec11223344556677889910101111121213131414151516161717181819192020212122222323242425252626272728282929303031310%100%10%90%20%80%30%70%40%60%50%50%60%40%70%30%80%20%90%10%100%0%NovJanDec 12%Dec 12%Dec 31-0%Dec 31-0%Dec 110%Dec 110%Dec 21-0%Dec 21-0%50%Nov 850%Nov 8Nov 2310%Nov 2310%freezingvery coldcoldcoolfrigidcomfortable
frigid 15°F freezing 32°F very cold 45°F cold 55°F cool 65°F comfortable 75°F warm 85°F hot 95°F sweltering
The percentage of time spent in various temperature bands. The black line is the percentage chance that a given day is within the growing season.

Growing degree days are a measure of yearly heat accumulation used to predict plant and animal development, and defined as the integral of warmth above a base temperature, discarding any excess above a maximum temperature. In this report, we use a base of 50°F and a cap of 86°F.

The average accumulated growing degree days in Greenwich are essentially constant during December, remaining within 7°F of 3,366°F throughout.

Growing Degree Days in December in Greenwich

The average growing degree days accumulated over the course of December, with 25th to 75th and 10th to 90th percentile bands.

This section discusses the total daily incident shortwave solar energy reaching the surface of the ground over a wide area, taking full account of seasonal variations in the length of the day, the elevation of the Sun above the horizon, and absorption by clouds and other atmospheric constituents. Shortwave radiation includes visible light and ultraviolet radiation.

The average daily incident shortwave solar energy in Greenwich is essentially constant during December, remaining within 0.1 kWh of 1.8 kWh throughout.

The lowest average daily incident shortwave solar energy during December is 1.7 kWh on December 23.

Average Daily Incident Shortwave Solar Energy in December in Greenwich

Average Daily Incident Shortwave Solar Energy in December in GreenwichDec11223344556677889910101111121213131414151516161717181819192020212122222323242425252626272728282929303031310.0 kWh0.0 kWh0.5 kWh0.5 kWh1.0 kWh1.0 kWh1.5 kWh1.5 kWh2.0 kWh2.0 kWh2.5 kWh2.5 kWh3.0 kWh3.0 kWh3.5 kWh3.5 kWh4.0 kWh4.0 kWhNovJanDec 231.7 kWhDec 231.7 kWhDec 11.9 kWhDec 11.9 kWhDec 111.8 kWhDec 111.8 kWh
The average daily shortwave solar energy reaching the ground per square meter (orange line), with 25th to 75th and 10th to 90th percentile bands.

For the purposes of this report, the geographical coordinates of Greenwich are 41.026 deg latitude, -73.628 deg longitude, and 92 ft elevation.

The topography within 2 miles of Greenwich contains only modest variations in elevation, with a maximum elevation change of 243 feet and an average elevation above sea level of 77 feet. Within 10 miles contains only modest variations in elevation (715 feet). Within 50 miles contains significant variations in elevation (1,657 feet).

The area within 2 miles of Greenwich is covered by artificial surfaces (59%), water (20%), and trees (18%), within 10 miles by water (37%) and trees (32%), and within 50 miles by trees (36%) and water (31%).

This report illustrates the typical weather in Greenwich, based on a statistical analysis of historical hourly weather reports and model reconstructions from January 1, 1980 to December 31, 2016.

Temperature and Dew Point

There are 4 weather stations near enough to contribute to our estimation of the temperature and dew point in Greenwich.

For each station, the records are corrected for the elevation difference between that station and Greenwich according to the International Standard Atmosphere , and by the relative change present in the MERRA-2 satellite-era reanalysis between the two locations.

The estimated value at Greenwich is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Greenwich and a given station.

The stations contributing to this reconstruction are:

To get a sense of how much these sources agree with each other, you can view a comparison of Greenwich and the stations that contribute to our estimates of its temperature history and climate. Please note that each source's contribution is adjusted for elevation and the relative change present in the MERRA-2 data.

Other Data

All data relating to the Sun's position (e.g., sunrise and sunset) are computed using astronomical formulas from the book, Astronomical Algorithms 2nd Edition , by Jean Meeus.

All other weather data, including cloud cover, precipitation, wind speed and direction, and solar flux, come from NASA's MERRA-2 Modern-Era Retrospective Analysis . This reanalysis combines a variety of wide-area measurements in a state-of-the-art global meteorological model to reconstruct the hourly history of weather throughout the world on a 50-kilometer grid.

Land Use data comes from the Global Land Cover SHARE database , published by the Food and Agriculture Organization of the United Nations.

Elevation data comes from the Shuttle Radar Topography Mission (SRTM) , published by NASA's Jet Propulsion Laboratory.

Names, locations, and time zones of places and some airports come from the GeoNames Geographical Database .

Time zones for airports and weather stations are provided by AskGeo.com .

Maps are © OpenStreetMap contributors.

Disclaimer

The information on this site is provided as is, without any assurances as to its accuracy or suitability for any purpose. Weather data is prone to errors, outages, and other defects. We assume no responsibility for any decisions made on the basis of the content presented on this site.

We draw particular cautious attention to our reliance on the MERRA-2 model-based reconstructions for a number of important data series. While having the tremendous advantages of temporal and spatial completeness, these reconstructions: (1) are based on computer models that may have model-based errors, (2) are coarsely sampled on a 50 km grid and are therefore unable to reconstruct the local variations of many microclimates, and (3) have particular difficulty with the weather in some coastal areas, especially small islands.

We further caution that our travel scores are only as good as the data that underpin them, that weather conditions at any given location and time are unpredictable and variable, and that the definition of the scores reflects a particular set of preferences that may not agree with those of any particular reader.

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