Presentation Transcript
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 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 ( 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 Sufficiently Unstable, Thundersnowstorms Can Form: If Atmosphere is Sufficiently Unstable, Thundersnowstorms Can Form