Snow Ratios Explained

Data from NOAA

Snow Ratios Explained

Snow ratios (also called snow-to-liquid ratio, snow ratio, or snow density ratio) refer to the amount of snow (in inches) produced from a given amount of liquid precipitation (in inches of water equivalent). It tells you how "fluffy" or "dense" the snow will be.


Typical Snow Ratios in Winter Weather

  • High ratio (light, fluffy snow) 15:1 to 25:1 or higher:
    • Very cold temperatures (below ~10 to 15F at the surface and through the cloud layer)
    • Low moisture content in the air (dry air)
    • Dendritic (star-shaped) snowflakes form best in this range
    • Common in deep cold air masses, lake-effect snow in very cold air, or high elevations
  • Average ratio (typical "normal" snow): 10:1 to 15:1:
    • Moderate cold (surface temps ~15 to 28F)
    • Most common in many winter storms across the U.S.
    • Balanced dendritic + plate/column snowflakes
  • Low ratio (heavy, wet snow): 5:1 to 10:1:
    • High moisture content, often near rain/snow line or in warm advection
    • Snow is dense, packs easily, great for snowballs but hard to shovel
    • Common in Southeast U.S. winter storms or coastal events
  • Very low ratio (wet slushy snow or sleet): Greater than 5:1 (sometimes 3:1 or 2:1)
    • Temps close to freezing (30 to 35F)
    • Often mixes with sleet or freezing rain
    • Snow is very heavy and wet → major power line/tree damage risk

Factors That Influence Snow Ratio

  • Temperature profile through the cloud layer (especially 0C to -15C range) - dendritic growth zone is around -12C to -18C (10F to 0F), This zone is generally between 850 mb (~4,800 feet) and 700 mb (~9,900 feet)
    • Moisture content (dry air = higher ratio; moist air = lower ratio)
    • Vertical motion (strong lift can produce denser snow)
    • Surface temperature (if warmer than ~32F, snow melts on contact if lower effective ratio)
    • Wind and turbulence (can break dendrites into lower ratio)

Snowflake Shapes by Temperature

  • The shape of a snowflake depends heavily on the temperature of the layer in which it grows:
    • 32°F to 25°F: Thin hexagonal plates
    • 25°F to 21°F: Needles
    • 21°F to 14°F: Hollow columns
    • 14°F to 10°F: Sector plates
    • 10°F to 3°F: Dendrites (classic branching, stellar shapes)

Examples in Southeast / North Georgia Winter Storms

  • 1989 Christmas Storm (very cold): 15:1 to 20:1 ratios — light, fluffy snow, high accumulation from modest liquid.
  • January 2011 north Georgia storm: 10:1 to 15:1 in mountains/foothills (fluffy), 8:1 to 10:1 in Atlanta metro (denser).
  • Snowmageddon 2014: Very high ratios (15:1 to 20:1+) due to extreme cold - 0.15 to 0.25 inches liquid equivalent produced 6–10 inches snow in north Georgia.
  • Typical Southeast marginal events (e.g., 1994 ice storm spillover): 5:1 to 8:1 - heavy, wet snow or sleet.
  • Wind and turbulence (can break dendrites into lower ratio)
  SNOW RATIO CHART
Liquid 3:1 5:1 8:1 9:1 10:1 12:1 14:1 16:1 18:1 20:1
0.01 0.0 0.1 0.1 0.1 0.1 0.1 0.1 0.2 0.2 0.2
0.02 0.1 0.1 0.2 0.2 0.2 0.2 0.3 0.3 0.4 0.4
0.03 0.1 0.2 0.2 0.3 0.3 0.4 0.4 0.5 0.5 0.6
0.04 0.1 0.2 0.3 0.4 0.4 0.5 0.6 0.6 0.7 0.8
0.05 0.2 0.3 0.4 0.5 0.5 0.6 0.7 0.8 0.9 1.0
0.06 0.2 0.3 0.5 0.5 0.6 0.7 0.8 1.0 1.1 1.2
0.07 0.2 0.4 0.6 0.6 0.7 0.8 1.0 1.1 1.3 1.4
0.08 0.2 0.4 0.6 0.7 0.8 1.0 1.1 1.3 1.4 1.6
0.09 0.3 0.5 0.7 0.8 0.9 1.1 1.3 1.4 1.6 1.8
0.10 0.3 0.5 0.8 0.9 1.0 1.2 1.4 1.6 1.8 2.0
0.15 0.5 0.8 1.2 1.4 1.5 1.8 2.1 2.4 2.7 3.0
0.20 0.6 1.0 1.6 1.8 2.0 2.4 2.8 3.2 3.6 4.0
0.25 0.8 1.3 2.0 2.3 2.5 3.0 3.5 4.0 4.5 5.0
0.30 0.9 1.5 2.4 2.7 3.0 3.6 4.2 4.8 5.4 6.0
0.35 1.1 1.8 2.8 3.2 3.5 4.2 4.9 5.6 6.3 7.0
0.40 1.2 2.0 3.2 3.6 4.0 4.8 5.6 6.4 7.2 8.0
0.45 1.4 2.3 3.6 4.1 4.5 5.4 6.3 7.2 8.1 9.0
0.50 1.5 2.5 4.0 4.5 5.0 6.0 7.0 8.0 9.0 10.0
0.60 1.8 3.0 4.8 5.4 6.0 7.2 8.4 9.6 10.8 12.0
0.70 2.1 3.5 5.6 6.3 7.0 8.4 9.8 11.2 12.6 14.0
0.80 2.4 4.0 6.4 7.2 8.0 9.6 11.2 12.8 14.4 16.0
0.90 2.7 4.5 7.2 8.1 9.0 10.8 12.6 14.4 16.2 18.0
1.00 3.0 5.0 8.0 9.0 10.0 12.0 14.0 16.0 18.0 20.0


Snow Ratio Climatology


Image from St. Louis University