The question of whether it will snow in December is complex, depending entirely on location and atmospheric conditions. December marks the beginning of meteorological winter in the Northern Hemisphere, a three-month period characterized by the lowest average temperatures. While this time brings the potential for snow across many latitudes, the actual occurrence of winter precipitation is a delicate balance of temperature, moisture, and large-scale weather patterns. Local geography and global climate forces are the primary determinants of a snowy start to the season.
The Meteorological Requirements for December Snow
For precipitation to fall as snow rather than rain, specific atmospheric conditions must align from the clouds down to the ground. Snowflakes originate when the air temperature high in the atmosphere is at or below freezing (0°C or 32°F). Water vapor freezes onto tiny particles, forming ice crystals that aggregate into snowflakes. Sufficient moisture is also necessary, as very cold air is often dry, meaning areas with extremely low temperatures may rarely receive snow.
For snow to reach the ground intact, the temperature profile throughout the atmosphere must remain below freezing or only slightly above it. Snow can still fall if the air temperature near the ground is between 0°C and 2°C, because the melting process cools the surrounding air through evaporative cooling. However, accumulation is unlikely if the ground temperature is warmer than 5°C.
Global December Snowfall Zones
The probability of December snowfall varies dramatically across the globe, allowing regions to be categorized based on their likelihood of seeing winter precipitation.
High Probability Zones
These areas, including the Arctic, Northern Canada, Siberia, and high-altitude mountain ranges like the Rockies and the Alps, consistently maintain the sub-freezing temperatures required for snow formation and retention throughout the month.
Moderate Probability Zones
Regions such as the Mid-Atlantic United States and Central Europe experience a more temperamental December. Cold air masses frequently clash with moisture from nearby oceans, but the temperature often hovers around the freezing point, making the precipitation type difficult to predict.
Low Probability Zones
These zones encompass regions like the coastal Mediterranean, the Deep Southern United States, and the Southern Hemisphere, where December falls during the meteorological summer. Temperatures here are typically too warm to support snow.
Analyzing Regional Variability and Historical Norms
The reliability of December snow is heavily influenced by localized geographic features and established climate oscillations. Proximity to large bodies of water, for instance, can lead to lake-effect snow. This occurs when cold air masses move across warmer lake waters, picking up moisture that falls as heavy, localized snow on the downwind shore. Similarly, high elevation areas often have a near-certain chance of snow because temperatures decrease with altitude, ensuring the air remains below freezing.
Large-scale atmospheric patterns also introduce significant variability into December’s weather. The North Atlantic Oscillation (NAO), a fluctuation in the pressure difference between the Icelandic Low and the Azores High, strongly influences the storm track across the eastern United States and Europe. A negative phase of the NAO weakens the polar jet stream, allowing frigid Arctic air to dip further south, increasing the likelihood of snowy December conditions. Conversely, El Niño conditions, characterized by warmer sea surface temperatures in the central and eastern Pacific, lead to milder temperatures and a lower likelihood of early-season snowfall across the northern United States.
Modern Trends in December Snowfall
Long-term warming trends are altering the typical patterns of December snowfall, particularly in moderate probability zones. Climate change is causing winter to be the fastest-warming season for much of the United States, directly impacting when and how precipitation falls. A warmer atmosphere holds more moisture, but if temperatures remain above freezing, this moisture falls as rain instead of snow.
This shift results in a shrinking snow season, often delaying the onset of reliable snowfall until later in January and February. Snowfall amounts have decreased in many regions, with some areas seeing a reduction of over 50% in average annual snowfall between the 1961–1990 and 1991–2020 periods. While some very cold areas may see an increase in heavy snow events due to increased atmospheric moisture, the overall trend is a decrease in the frequency and duration of December snow cover across the mid-latitudes.