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Shawn M. Milrad Department of Atmospheric and Oceanic Sciences McGill University Montreal, Quebec, Canada Eyad H. Atallah and John R. Gyakum Department of Atmospheric and Oceanic Sciences McGill University Montreal, Quebec, Canada Slide 2 Outline Motivation and Background Case comparison: Ottawa, ON (28 January 2010) vs. Calgary, AB (3-4 December 2011) Case overviews Synoptic-dynamic analysis Forecasts and warnings Future work Slide 3 Motivation The climatology, dynamics and impacts of lake effect snow squalls (bursts) throughout the U.S. have been well-documented Great Lakes Wiggins (1950); Niziol (1987); Niziol et al. (1995) Great Salt Lake Steenburgh et al. (2000); Steenburgh and Onton (2001) Lake Champlain Payer et al. (2007); Laird et al..(2009) Other studies have examined events dynamically related to snow bursts Thundersnow events (synoptic-scale cyclones) Market et al. (2002); Market et al. (2006); Crowe et al. (2006) C0ld-season severe weather Holle and Watson (1996); Schultz (1999); Hunter et al. (2001); Trapp et al. (2001); van den Broeke et al. (2005); Corfidi et al. (2006) Motivation/Background Case Overviews Dynamics Forecasts Future Work Slide 4 Source: UCAR/COMET Motivation Motivation/Background Case Overviews Dynamics Forecasts Future Work Slide 5 However, few studies have focused on snow bursts that occur outside lake effect regions Snow bursts outside of lake effect regions: Often not associated with a synoptic-scale cyclone Cold-season convection Can produce rapid-onset whiteout conditions hazardous to motorists and aviation Often occur without warning (DeVoir 2004) Not large enough snow accumulations to meet NWS warning or advisory criteria Motivation Motivation/Background Case Overviews Dynamics Forecasts Future Work Slide 6 Nicosia et al. (2009) Impacts in Pennsylvania Previous Work Motivation/Background Case Overviews Dynamics Forecasts Future Work Slide 7 Ottawa, Ontario: 28 January 2010 (Photos are courtesy of the Ottawa Citizen) Motivation/Background Case Overviews Dynamics Forecasts Future Work Slide 8 Calgary, AB: 3 December 2011 (Photo is courtesy of the Calgary Sun) Motivation/Background Case Overviews Dynamics Forecasts Future Work Slide 9 Small snow accumulation: 3.6 cm (1.4 in.) Near-zero visibility Dynamics Synoptic-scale forcing for ascent (Q-vector convergence) Mesoscale forcing for ascent: Arctic front Just enough moisture to create a problem Thermodynamics Very steep low-level lapse rates Convective instability (CI) and Conditional Symmetric Instability (CSI) Soundings: Deep (300-400 hPa) Moist Absolutely Unstable Layer (MAUL) Ottawa: 28 January 2010 Motivation/Background Case Overviews Dynamics Forecasts Future Work Slide 10 Ottawa: 28 January 2010 Motivation/Background Case Overviews Dynamics Forecasts Future Work t=0 h (1800 UTC) Ottawa, ON (CYOW): 28 January 2010 ***Ottawa International Airport (CYOW): black star*** Slide 11 Calgary: 3-4 December 2011 Motivation/Background Case Overviews Dynamics Forecasts Future Work Larger snow accumulation: 8.9 cm (3.5 in.): Below snowfall warning criterion 6.1 cm on 3 December 2.8 cm on 4 December Near-zero visibility Dynamics and Thermodynamics Similarities and differences? Slide 12 t=-1 h (2310 UTC) ***Calgary International Airport (CYYC): black star*** Calgary: 3-4 December 2011 Motivation/Background Case Overviews Dynamics Forecasts Future Work t=+1 h (0110 UTC) Slide 13 Calgary: Meteograms Motivation/Background Case Overviews Dynamics Forecasts Future Work Calgary, AB (CYYC): 3 December 2011 Calgary, AB (CYYC): 4 December 2011 Slide 14 Dynamic Analysis: Strategy Snow bursts are essentially a form of wintertime moist convection Ingredients-based methodology: Moist convection Doswell et al. (1996); Schultz and Schumacher (1999); Wetzel and Martin (2001) Three main ingredients Lift (synoptic-scale and mesoscale)** Moisture Instability** Convective (CI): (d e /dz) < 0 Conditional Symmetric (CSI): MPV * g < 0 Motivation/Background Case Overviews Dynamics Forecasts Future Work Slide 15 t=0 h (1800 UTC 28 January 2010) 850-500 hPa Q-vector divergence (shaded, cool colors convergent), SLP (hPa, solid), 1000-500 hPa thickness (dam, dashed) Lift: Synoptic-scale Motivation/Background Case Overviews Dynamics Forecasts Future Work t=0 h (0000 UTC 4 December 2011) Ottawa Calgary Slide 16 925 (850-700) hPa frontogenesis (K (100 km) -1 (3 h) -1 ), shaded), 925-700 (850-600) hPa lapse rate (K km -1, blue solid contours starting at -8 with an interval of.5), 1000-500 hPa thickness (dam, dashed), and 10 m wind (knots, barbs). Mesoscale lift: Ottawa vs. Calgary Motivation/Background Case Overviews Dynamics Forecasts Future Work t=0 h (1800 UTC 28 January 2010) Ottawa Calgary t=0 h (0000 UTC 4 December 2011) Slide 17 Instability: CI and CSI (Ottawa) Saturated equivalent geostrophic potential vorticity (MPV * g, m 2 s 1 K kg 1, shaded for negative values) and e (K, solid contours). Motivation/Background Case Overviews Dynamics Forecasts Future Work t=0 h (1800 UTC 28 January 2010) Slide 18 Saturated equivalent geostrophic potential vorticity (MPV * g, m 2 s 1 K kg 1, shaded for negative values) and e (K, solid contours). Instability: CI and CSI (Calgary) t=0 h (0000 UTC 4 December 2011) Motivation/Background Case Overviews Dynamics Forecasts Future Work t=+3 h (0300 UTC 4 December 2011) Slide 19 Bryan and Fritsch (2000) argued that a sixth static stability state exists Moist absolutely unstable ( s > s ) Moist Absolutely Unstable Layers (MAULs) Short-lived Rare: 1.1% of 100,000 soundings in Bryan and Fritsch (2000) Often shallow; deep MAULs are defined as at least 100 mb in depth with a dewpoint depression of