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 air (bulk formulae):

(Heat)

( , ) (Vapor)

(Momentum)

H D air water

v D air s water

M D

F C V T T

F C V q q p T

F C V V

3 5Note: 1.1 10 4. 10 V DC x x

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 BandDecember 24, 2001 Buffalo

Lake Erie Shore Parallel BandDecember 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 Lidarat Lake-ICE

Characteristics of Wind Parallel vs. Shore Parallel Bands

Growth of Planetary Boundary LayerAcross Lake

1704 UTC - 1748UTC

• Cloud rolls over water

• Spectacular Cloud streets over land

• Effect of lake shoreline

• Gravity waves perpendicular to flow

Visible Satellite

Loop

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