s rm o ffect St e E ak L

Transcription

1 Lake Effect Storms

2 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): F ( ) H = ρc D V T air T water (Heat) F ( (, )) v = ρc D V q air q s pt water (Vapor) F = ρc VV (Momentum) M D Note: C = 1.1 x x 10 5 V D

3

4 Lidar Observation of Steam Fog

5 Lidar Observation of Steam Fog

6 Lidar Observation of Steam Fog

7 Lake Effect Storm Types Wind/Shear Parallel Bands Shore Parallel Bands Shore based Midlake Mesoscale Vortex

8 Lake Superior Lake Effect

9 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

10 Lake Ontario Lake Effects

11 Lake Erie Shore Parallel Band December 24, 2001 Buffalo

12 Lake Erie Shore Parallel Band December 24, 2001 Buffalo

13 Lake Michigan Shore Parallel Band

14 Lake Michigan Shore Parallel Band

15 Lake Michigan Shore Parallel Band

16 Lake Michigan Shore Parallel Band

17 Lake Michigan Shore Parallel Band

18 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

19 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)

20 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

21 Lake Michigan Wind/Shear Parallel Band

22 10 and 13 January, 1998

23 UW Volume Imaging Lidar at Lake-ICE

24 Characteristics of Wind Parallel vs. Shore Parallel Bands

25 Growth of Planetary Boundary Layer Across Lake

26 Visible Satellite Loop Cloud rolls over water Spectacular Cloud streets over land Effect of lake shoreline Gravity waves perpendicular to flow 1704 UTC UTC

27 Detailed Study of Shore Parallel Bands

28 Sounding and Hodograph of Winds Incident on Western Shore

29 Rayleigh Numbers

30

31 Origins of Bands

32 Type B Waves

33 Wave Duct Leading to Type B Bands

34 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)

35 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

36 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