lecture 5 lake effect storms
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Lecture 5 Lake Effect Storms. 13.1. Snow climatology highly influenced by lake effects. Why Lake Effect?. In Fall season, lakes are warm, advancing polar air comes across with cold air and strong winds

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Presentation Transcript
slide2
13.1

Snow climatology highly influenced by lake effects

why lake effect
Why Lake Effect?
  • In Fall season, lakes are warm, advancing polar air comes across with cold air and strong winds
    • Thermal contrast, together with strong winds across water whips up strong surface fluxes of heat and moisture
    • Near surface warming gives rise to static instability, i.e. near surface warm, moist air underlies cold advancing air above
    • Strong unstable overturning results, producing progressively deeper clouds as air traverses lake
    • If clouds and their precipitation process is sufficiently mature as air approaches lee shore, precipitation reaches surface on lee shore
    • When advancing polar air is sufficiently cold, precipitation will be snow
cold air moving over water surface steam fog
Cold Air Moving Over Water Surface – Steam Fog
  • Cold air off continent moves over relatively warm water surface
  • Fluxes of heat and moisture from water into air (bulk formulae):
lake effect storm types
Lake Effect Storm Types
  • Wind/Shear Parallel Bands
  • Shore Parallel Bands
    • Shore based
    • Midlake
  • Mesoscale Vortex
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13.3

Lake effect clouds become deeper and feature and increasingly mature precipitation process as flow traverses lake

visible satellite loop
Visible Satellite Loop
  • Cloud rolls over water
  • Spectacular Cloud streets over land
  • Effect of lake shoreline
  • Gravity waves perpendicular to flow

1704 UTC - 1748UTC

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13.6b

Water Temperature

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Longer wind Fetch will produce more mature clouds and precipitation process and so more snow. Therefore more snow downwind of where lake is wider13.9
predicting wind parallel lake effect storms
Predicting Wind Parallel Lake Effect Storms
  • Lake temperature minus 850 mb temperature >13C
  • Wind fetch >100 km
  • Wind speed moderate to high, i.e. >10 m/s
shore parallel bands
Shore Parallel Bands
  • Land breeze mesoscale circulation
  • Deeper than wind parallel bands ( up to 4 km AGL)
  • Very intense precipitation over a small area
  • May be short lived or last several days
shore parallel bands1
Shore Parallel Bands
  • Wind blows roughly parallel to major axis of lake
  • Air warms from heat flux from water creating a strong land-water air temperature contrast
  • Land Breeze is created forcing a land breeze front and meso-beta scale convergence
  • Meso-beta scale lifting of air to as high as 4 km AGL (compared to 1 km AGL for wind parallel bands) along land breeze front (s)
  • Land breeze fronts usually combine into single convergence line
    • Parallel to shoreline of lake
    • Pushed to downwind shoreline when winds are not completely parallel to shoreline
    • Down center of lake when winds are exactly parallel to shoreline of lake
shore parallel bands2
Shore Parallel Bands
  • Most intense snows of all the different lake-effect snow types, because:
    • Concentrates all of the absorbed moisture and heat along a single narrow band
    • Mesoscale lifting deepens the system to several kilometers allowing precipitation processes to be more efficient
      • Colder than –20 C
      • Deeper layer Bergeron – Findeisen Process
    • Bands extend off shore and drop massive amounts of snow over small region
      • Buffalo, NY (Lake Erie, WSW wind)
      • Gary, Indiana (Lake Michigan, Northerly wind)
predicting shore parallel lake effect storms
Predicting Shore Parallel Lake Effect Storms
  • Wind nearly parallel to long axis of lake
  • Lake temperature minus 850 mb temperature >13C (can occur with less temperature contrast)
  • Wind speed light to high, i.e. > 5 m/s
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