Transcript Cloud Resolving Model Simulation of the Convective

Lake Effect Storms
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
F air
 (bulk
 C Vformulae):
(Heat)
T  T 
H
D
air
water
Fv    CD V  qair  qs ( p, Twater ) 
(Vapor)
FM    CD V V
(Momentum)
Note: CD  1.1x103  4.x105 V
Lidar Observation of Steam Fog
Lidar Observation of Steam
Fog
Lidar Observation of Steam Fog
Lake Effect Storm Types
• Wind/Shear Parallel Bands
• Shore Parallel Bands
– Shore based
– Midlake
• Mesoscale Vortex
Lake
Superior
Lake
Effect
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
Lake Ontario Lake Effects
Lake Erie Shore Parallel Band
December 24, 2001 Buffalo
Lake Erie Shore Parallel Band
December 24, 2001 Buffalo
Lake Michigan Shore Parallel Band
Lake Michigan Shore Parallel Band
Lake Michigan Shore Parallel Band
Lake Michigan Shore Parallel Band
Lake Michigan Shore Parallel Band
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 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)
Wind or Shear Parallel Bands
• Rayleigh Benard Instability
• Relatively shallow, i.e. depth of Boundary
Layer
• So shallow, often can not form a viable
precipitation process
• Long periods of light snow
Lake Michigan
Wind/Shear
Parallel Band
10 and 13 January, 1998
UW Volume Imaging Lidar
at Lake-ICE
Characteristics of Wind Parallel
vs. Shore Parallel Bands
Growth of Planetary Boundary Layer
Across Lake
Visible
Satellite
Loop
• Cloud rolls over
water
• Spectacular Cloud
streets over land
• Effect of lake
shoreline
• Gravity waves
perpendicular to
flow
1704 UTC - 1748UTC
Detailed Study of
Shore Parallel
Bands
Sounding and Hodograph of Winds Incident on Western
Shore
Rayleigh Numbers
Origins
of Bands
Type “B” Waves
Wave Duct
Leading to
Type”B” Bands
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 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
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