Lake Effect Snow Storms

Lake-Effect Snow Storms: 

Lake-Effect Snow Storms Intense, highly localized snow storms that form near major bodies of water Usually take the shape of narrow bands downwind of the shore Can produce tens of inches of snow in a single day Require a specific set of conditions involve the atmosphere and land & water surface

A Lake-Effect Snow Storm on Satellite: 

A Lake-Effect Snow Storm on Satellite

A Lake-Effect Snow Storm on Radar: 

A Lake-Effect Snow Storm on Radar

A Lake-Effect Snow Storm on Radar: 

A Lake-Effect Snow Storm on Radar

Geographic Preferences: 

Geographic Preferences

Geographic Preferences: 

Geographic Preferences

Geographic Preferences: 

Geographic Preferences

Great Lakes Snowfall Climatology: 

Great Lakes Snowfall Climatology

Slide9: 

Zooming In – The Average Annual Snowfall (inches) Over the Eastern Great Lakes

Record Event: 

Record Event 37.9 inches at the Buffalo Airport in 24 h

The Lake-Effect “Season”: 

The Lake-Effect “Season”

Basic Concepts of Formation: 

Basic Concepts of Formation

Basic Concepts of Formation: 

Basic Concepts of Formation The atmosphere upwind of the lake is characterized by a very strong temperature inversion, with arctic air near the ground. Air is blowing from the land toward the water.

Basic Concepts of Formation: 

Basic Concepts of Formation

Basic Concepts of Formation: 

Basic Concepts of Formation

Basic Concepts of Formation: 

Basic Concepts of Formation The warm water provides thermal energy and moisture to the overlying cold air – remember that thermal energy transport is from warm to cold. The warm air rises to form clouds. Note that it also raises the height of the capping inversion.

Basic Concepts of Formation: 

Basic Concepts of Formation

Basic Concepts of Formation: 

Basic Concepts of Formation Note how the inversion has risen in altitude and the lower-levels of the atmosphere have moistened.

Basic Concepts of Formation: 

Basic Concepts of Formation

Basic Concepts of Formation: 

Basic Concepts of Formation The rising air condenses to form precipitation, and snow falls downwind of the shore line. The greater the air-water temperature contrast, the heavier the snowfall

Formation of Bands: 

Formation of Bands Looking down the wind direction, from west to east, the clouds tend to form into bands, usually oriented parallel to the long axis of the lake 1 2

A Lake-Effect Snow Storm on Radar: 

A Lake-Effect Snow Storm on Radar 1 2

Formation of Bands: 

Formation of Bands Note the rising and sinking motion

Formation of Bands: 

Formation of Bands Clouds are suppressed in between bands

Formation of Bands: 

Formation of Bands

Ingredient #1 for Formation: 

Ingredient #1 for Formation Sufficient temperature difference between the lake surface and overlying air Represents a measure of instability, similar to the lifted index in the context of thunderstorms At least 13 C difference between water and 850 mb This is approximately the dry adiabatic lapse rate between 1000 mb (surface) and 850 mb

The Temperature Difference on a Thermodynamic Diagram: 

The Temperature Difference on a Thermodynamic Diagram

Water Temperatures are Available: 

Water Temperatures are Available

The State of the Water and Land is Critical: 

The State of the Water and Land is Critical

The State of the Water and Land is Critical: 

The State of the Water and Land is Critical

Ingredient #2 for Formation: 

Ingredient #2 for Formation Sufficiently deep cold air mass at the surface One of the most important aspects when considering intensity Inversion heights < 3000 ft preclude heavy lake-effect snows Inversion heights > 7500 ft strongly support heavy lake-effect snows In some cases, an inversion may not be present or obvious

Where’s the Beef?: 

Where’s the Beef?

Ingredient #3 for Formation: 

Ingredient #3 for Formation Directional wind shear Small amounts of directional wind change with height (< 30 degrees) below the inversion favors horizontal roll convection Highly sheared environments (> 60 degrees) disrupt and diminish the efficiency of rolls, leading only to flurries

Ingredient #4 for Formation: 

Ingredient #4 for Formation Adequate Fetch Fetch is the distance traveled by air over water Long fetch promotes more heating of the air and a higher inversion A minimum fetch of 100 miles is needed for significant lake-effect snow Flow over multiple lakes can help

Demonstration of Fetch: 

Demonstration of Fetch

Ingredient #5 for Formation: 

Ingredient #5 for Formation Sufficiently moist upstream air RH > 70% below the inversion favors heavy lake-effect snow RH < 50% usually means little snow Often upstream RH is the factor that kills potentially heavy lake-effect events

Orographic Lift Can Make a HUGE Difference!: 

Orographic Lift Can Make a HUGE Difference!

Effect of Orography: 

Effect of Orography

Shoreline Orientation Can Make a HUGE Difference!: 

Shoreline Orientation Can Make a HUGE Difference!

Shoreline Orientation Can Make a HUGE Difference!: 

Shoreline Orientation Can Make a HUGE Difference! Change in surface friction as air passes from land to water causes convergence in the region shown by a “+”

Shoreline Orientation Can Make a HUGE Difference!: 

Shoreline Orientation Can Make a HUGE Difference! First band forms in the convergence region. Note divergence “-” nearby

Shoreline Orientation Can Make a HUGE Difference!: 

Shoreline Orientation Can Make a HUGE Difference!

This Theory in Action: 

This Theory in Action

This Theory in Action: 

This Theory in Action

If Atmosphere is SufficientlyUnstable, Thundersnowstorms Can Form: 

If Atmosphere is Sufficiently Unstable, Thundersnowstorms Can Form