Ingredient

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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