LakeEffect Snow Storms

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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

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A Lake-Effect Snow Storm on Satellite
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A Lake-Effect Snow Storm on Radar
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A Lake-Effect Snow Storm on Radar
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Geographic Preferences
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Geographic Preferences
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Geographic Preferences
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Great Lakes Snowfall Climatology
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Zooming In The Average Annual Snowfall (inches)
Over the Eastern Great Lakes
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Record Event
37.9 inches at the Buffalo Airport in 24 h
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(No Transcript)
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The Lake-Effect Season
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Basic Concepts of Formation
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Basic Concepts of Formation
The atmosphere upwind of thelake is
characterized by a verystrong temperature
inversion, witharctic air near the ground. Air
isblowing from the land toward thewater.
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Basic Concepts of Formation
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Basic Concepts of Formation
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Basic Concepts of Formation
The warm water provides thermalenergy and
moisture to theoverlying cold air
rememberthat thermal energy transportis from
warm to cold. The warmair rises to form clouds.
Note thatit also raises the height of
thecapping inversion.
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Basic Concepts of Formation
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Basic Concepts of Formation
Note how the inversion has risen in altitude and
thelower-levels of the atmosphere have moistened.
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Basic Concepts of Formation
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Basic Concepts of Formation
The rising air condenses to formprecipitation,
and snow fallsdownwind of the shore line.
Thegreater the air-water temperaturecontrast,
the heavier the snowfall
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Formation of Bands
Looking down the wind direction, from west
toeast, the clouds tend to form into
bands, usually oriented parallel to the long axis
of the lake
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1
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A Lake-Effect Snow Storm on Radar
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2
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Formation of Bands
Note the rising and sinking motion
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Formation of Bands
Clouds are suppressed in between bands
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Formation of Bands
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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

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The Temperature Difference on a Thermodynamic
Diagram
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Water Temperatures are Available
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The State of the Water and Land is Critical
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The State of the Water and Land is Critical
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Ingredient 2 for Formation

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

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Wheres the Beef?
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Ingredient 3 for Formation

• Directional wind shear
• Small amounts of directional wind change with
  height (lt 30 degrees) below the inversion favors
  horizontal roll convection
• Highly sheared environments (gt 60 degrees)
  disrupt and diminish the efficiency of rolls,
  leading only to flurries

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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

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Demonstration of Fetch
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Ingredient 5 for Formation

• Sufficiently moist upstream air
• RH gt 70 below the inversion favors heavy
  lake-effect snow
• RH lt 50 usually means little snow
• Often upstream RH is the factor that kills
  potentially heavy lake-effect events

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Orographic Lift Can Make a HUGE Difference!
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Effect of Orography
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Shoreline Orientation Can Make a HUGE Difference!
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Shoreline Orientation Can Make a HUGE Difference!
Change in surfacefriction as air passes from
land to water causesconvergence in theregion
shown by a
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Shoreline Orientation Can Make a HUGE Difference!
First bandforms in theconvergenceregion.
Notedivergence- nearby
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Shoreline Orientation Can Make a HUGE Difference!
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This Theory in Action
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This Theory in Action
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If Atmosphere is SufficientlyUnstable,
Thundersnowstorms Can Form