Snow & Ice

Frozen Precipitation & Winter Phenomena

Formation

Freezing Water - Forms when water vapor condenses directly to ice or when liquid precipitation freezes

Types

Multiple Forms - Snow crystals, ice pellets, freezing rain, sleet, hail, and glaze ice

Impact

Major Hazards - Slippery surfaces, reduced visibility, weight damage, avalanches

Snow Formation

Snow forms when water vapor condenses directly into ice crystals at temperatures below 0°C (32°F). This process, called deposition, occurs without passing through the liquid phase. Snow crystals grow by collecting water vapor until they become heavy enough to fall as snowflakes.

Crystal Formation Process:

1. Ice nucleation - Water vapor condenses on dust/salt particles
2. Crystal growth - Additional water vapor deposits on nucleus
3. Snowflake development - Complex shapes form (dendrites, needles, plates)
4. Fall - Crystal becomes heavy enough to overcome air resistance

Snowflake Types

Dendrites: Six-sided crystals with branches, form 15-25°F

Plates: Flat hexagonal shapes, form below 0°F

Needles: Long thin crystals, form 0-10°F

Graupel: Pellets of frozen precipitation, very icy

Snow Depth & Water Content

Snow-to-Water Ratio: 10:1 typical (10 inches snow = 1 inch water)

Wet Snow: 5:1 ratio, heavier and denser

Dry Snow: 15:1 ratio, light and fluffy

Powder: 20:1 or higher, ideal for skiing

Ice & Frozen Precipitation

Freezing Rain & Glaze Ice

Formation: Rain falls from warm layer above through freezing air near surface

Impact: Instant freezing creates thin glass-like coating

Hazard: Extremely slippery, heavy ice weight breaks branches and power lines

Severity: Even small accumulations (0.5 inch) cause significant problems

Sleet & Ice Pellets

Formation: Raindrops freeze in mid-air as they fall through freezing layer

Characteristics: Small hard pellets that bounce on impact

Hazard: Creates icy surfaces, accumulates in drifts

Sound: Distinct pinging sound as pellets strike surfaces

Hail (Winter & Summer)

Formation: Ice particles cycle through freezing and wet zones in thunderstorms, adding layer upon layer

Size: Ranges from pea-sized (small hail) to softball-sized (giant hail)

Winter Role: Part of severe winter storms when embedded in snow

Damage: Severe hail causes billions in damage to crops, vehicles, structures annually

Snow & Ice Hazards

Travel Hazards

Black Ice: Thin transparent ice difficult to see
Reduced Friction: Tires lose traction, skidding occurs
Visibility: Heavy snow reduces sight distance
Accidents: Increased crashes and multi-vehicle pileups
Flights: Delays and cancellations common

Property Damage

Weight: Heavy snow and ice loads break branches and roofs
Power Lines: Ice accumulation collapses lines causing outages
Pipes: Frozen pipes burst causing water damage
Foundation: Ice heave damage from freeze-thaw cycles
Cost: Billions annually in winter storm damage

Natural Hazards

Avalanches: Massive snow slides down mountains
Blizzards: Combination of heavy snow and wind
Glacial Hazards: Calving icebergs, ice shelves collapse
Lake Effect: Extreme localized snow from lake evaporation

Human Health

Hypothermia: Body temperature drops to dangerous levels
Frostbite: Tissue freezes, potential amputation
Snow Blindness: Sun reflection on snow causes eye damage
Deaths: Cold-related deaths increase during winter

Snow Records & Extremes

Annual Snow Records:

• Mt. Baker, WA: 1,140 inches (1998-99)
• Mt. Rainier, WA: 1,125 inches (1971-72)
• Paradise, WA: ~500 inches typical annual
• Greatest US accumulation: 37 feet (1921 in CA)

Single Event Records:

• Most in 24 hours: 75.8 inches (CA, 1951)
• Most in 1 hour: 14 inches (documented in Canada)
• Greatest on ground: 37 feet (Tamarack, CA)

Winter Safety

Before Winter Arrives

✓ Winterize vehicle (snow tires, wipers, fluid)
✓ Insulate pipes to prevent freezing
✓ Have emergency supplies (blankets, food, water)
✓ Stock sand/salt for icy areas
✓ Trim tree branches over structures
✓ Test heating systems

During Snow & Ice

✓ Reduce travel speed on slippery surfaces
✓ Increase following distance dramatically
✓ Avoid sudden movements (accelerating, braking, turning)
✓ Stay indoors if possible during severe weather
✓ Layer clothing for outdoor activities
✓ Cover exposed skin to prevent frostbite