Winter Weather in Greenwich Connecticut, United StatesDaily high temperatures decrease by 4°F, from 47°F to 43°F, rarely falling below 24°F or exceeding 59°F. The lowest daily average high temperature is 37°F on January 23. Daily low temperatures decrease by 6°F, from 35°F to 29°F, rarely falling below 10°F or exceeding 46°F. The lowest daily average low temperature is 24°F on January 29. 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. The figure below shows you a compact characterization of the hourly average winter temperatures. 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. 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). CloudsThe winter 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 season. The highest chance of overcast or mostly cloudy conditions is 53% on February 28. The clearest day of the winter 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%. PrecipitationA 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 the winter is essentially constant, remaining around 25% throughout. 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 the winter in Greenwich, the chance of a day with only rain decreases from 24% to 17%, the chance of a day with mixed snow and rain increases from 3% to 5%, and the chance of a day with only snow remains an essentially constant 3% throughout. RainfallTo show variation within the season and not just the monthly totals, we show the rainfall accumulated over a sliding 31-day period centered around each day. The average sliding 31-day rainfall during the winter in Greenwich is rapidly decreasing, starting the season at 3.5 inches, when it rarely exceeds 5.8 inches or falls below 1.4 inches, and ending the season at 2.4 inches, when it rarely exceeds 4.9 inches or falls below 0.9 inches. The lowest average 31-day accumulation is 2.0 inches on February 6. SnowfallAs with rainfall, we consider the snowfall accumulated over a sliding 31-day period centered around each day. The average sliding 31-day snowfall during the winter in Greenwich is rapidly increasing, starting the season at 2.2 inches, when it rarely exceeds 6.8 inches or falls below -0.0 inches, and ending the season at 6.0 inches, when it rarely exceeds 17.4 inches. The highest average 31-day accumulation is 7.5 inches on January 26. SunOver the course of the winter in Greenwich, the length of the day is rapidly increasing. From the start to the end of the season, the length of the day increases by 1 hour, 49 minutes, implying an average daily increase of 1 minute, 13 seconds, and weekly increase of 8 minutes, 34 seconds. The shortest day of the winter is December 21, with 9 hours, 13 minutes of daylight and the longest day is February 28, with 11 hours, 15 minutes of daylight. The latest sunrise of the winter in Greenwich is 7:19 AM on January 3 and the earliest sunrise is 50 minutes earlier at 6:29 AM on February 28. The earliest sunset is 4:25 PM on December 7 and the latest sunset is 1 hour, 19 minutes later at 5:44 PM on February 28. Daylight saving time is observed in Greenwich during 2024, but it neither starts nor ends during the winter, so the entire season 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. 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. MoonThe figure below presents a compact representation of key lunar data for the winter of 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. HumidityWe 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 the winter, 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. WindThis 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 increasing during the winter, increasing from 8.3 miles per hour to 9.3 miles per hour over the course of the season. 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. The highest daily average wind speed during the winter is 9.4 miles per hour on February 26. The hourly average wind direction in Greenwich throughout the winter is predominantly from the west, with a peak proportion of 46% on December 29. Water TemperatureGreenwich 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 very rapidly decreasing during the winter, falling by 13°F, from 51°F to 38°F, over the course of the season. The lowest average surface water temperature during the winter is 37°F on February 22. Growing SeasonDefinitions 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 winter in Greenwich is reliably fully outside of 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 very rapidly decreasing during the winter, decreasing by 3,349°F, from 3,359°F to 10°F, over the course of the season. Solar EnergyThis 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 increasing during the winter, rising by 1.4 kWh, from 1.9 kWh to 3.4 kWh, over the course of the season. The lowest average daily incident shortwave solar energy during the winter is 1.7 kWh on December 23. TopographyFor 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%). Data SourcesThis 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 PointThere 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 DataAll 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. DisclaimerThe 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. Please review our full terms contained on our Terms of Service page. |