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

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

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

Source: UCAR/COMET Motivation Motivation/Background Case Overviews Dynamics Forecasts Future Work

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

Nicosia et al. (2009) Impacts in Pennsylvania Previous Work Motivation/Background Case Overviews Dynamics Forecasts Future Work

Ottawa, Ontario: 28 January 2010 (Photos are courtesy of the Ottawa Citizen) Motivation/Background Case Overviews Dynamics Forecasts Future Work

Calgary, AB: 3 December 2011 (Photo is courtesy of the Calgary Sun) Motivation/Background Case Overviews Dynamics Forecasts Future Work

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 ( hPa) Moist Absolutely Unstable Layer (MAUL) Ottawa: 28 January 2010 Motivation/Background Case Overviews Dynamics Forecasts Future Work

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***

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?

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)

Calgary: Meteograms Motivation/Background Case Overviews Dynamics Forecasts Future Work Calgary, AB (CYYC): 3 December 2011 Calgary, AB (CYYC): 4 December 2011

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): (dθ e /dz) < 0 Conditional Symmetric (CSI): MPV * g < 0 Motivation/Background Case Overviews Dynamics Forecasts Future Work

t=0 h (1800 UTC 28 January 2010) hPa Q-vector divergence (shaded, cool colors convergent), SLP (hPa, solid), 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

925 ( ) hPa frontogenesis (K (100 km) -1 (3 h) -1 ), shaded), ( ) hPa lapse rate (K km -1, blue solid contours starting at -8 with an interval of.5), 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)

Instability: CI and CSI (Ottawa) Saturated equivalent geostrophic potential vorticity (MPV * g, m 2 s −1 K kg −1, shaded for negative values) and θ e (K, solid contours). Motivation/Background Case Overviews Dynamics Forecasts Future Work t=0 h (1800 UTC 28 January 2010)

Saturated equivalent geostrophic potential vorticity (MPV * g, m 2 s −1 K kg −1, shaded for negative values) and θ 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)

Bryan and Fritsch (2000) argued that a sixth static stability state exists Moist absolutely unstable (γ s > Γ 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 <= 1˚C throughout Occur in close proximity to moist convection Indications of (and caused by) intense mesoscale vertical motion Instability: MAUL Motivation/Background Case Overviews Dynamics Forecasts Future Work

t=0 h (1800 UTC) Ottawa (CYOW): 28 January 2010 Instability: MAUL (Ottawa) Motivation/Background Case Overviews Dynamics Forecasts Future Work

t=0 h (0000 UTC) Calgary (CYYC): 4 December 2010 Instability: MAUL (Calgary) t=+6 h (0600 UTC) Motivation/Background Case Overviews Dynamics Forecasts Future Work

Synoptic-dynamic Conclusions: Calgary Dynamics Synoptic-scale forcing: *descent* Mesoscale forcing: Arctic front (frontogenesis) Just enough moisture to create a problem Upslope flow? Thermodynamics: Unstable, no matter how you slice it Very steep low-level lapse rates Convective instability (CI) Conditional Symmetric Instability (CSI) Soundings: Deep ( hPa) Moist Absolutely Unstable Layer (MAUL), especially after t=0 h Motivation/Background Case Overviews Dynamics Forecasts Future Work

Upslope flow? Motivation/Background Case Overviews Dynamics Forecasts Future Work t=0 h (0000 UTC) t=+3 h (0300 UTC)

Forecasts and Warnings From limited research (a few case studies), the models appear to do a decent job in predicting these events (not shown) The real problem is that despite the high impact of snow burst events, they often do NOT meet warning or advisory criteria in the United States Snow accumulations too low Winds not high enough for severe criteria Not the season for “convection” Not in lake effect regions In Canada, however…. Motivation/Background Case Overviews Dynamics Forecasts Future Work

Forecasts: Snowsquall Warning WarningOpen-water Location Threshold Criteria National, except extreme Northern Quebec* When, down wind of large bodies of water, like the Great Lakes,snow squalls are imminent or occurring with one or more of the following conditions being produced:snow squalls Localized, intense snowfall producing snowfall amounts of 15 cm or more in 12 hours or less. Reduced visibility (less than 400 metres) caused by heavy snow with or without blowing snow for 3 hours or more.visibilityblowing snow Note that local snow accumulations may be significant.snow Frontal Location Threshold Criteria National, except extreme Northern Quebec* When there is a brief period (less than one hour) of very poor visibility (400 metres or less), caused by heavy snow and blowing snow, and accompanied by strong, gusty winds of 45 km/hr or greater, is expected to occur with the passage of a cold front.visibilityblowing snowcold front Motivation/Background Case Overviews Dynamics Forecasts Future Work

Forecasts: Calgary From the Prairie and Arctic Storm Prediction Center: FORECASTS FOR SOUTHERN ALBERTA AND THE MOUNTAIN PARKS ISSUED BY ENVIRONMENT CANADA AT AM MST SATURDAY 3 DECEMBER 2011 FOR TODAY AND SUNDAY. CITY OF CALGARY. TODAY..SNOW. AMOUNT 5 CM. WIND NORTHWEST 40 KM/H GUSTING TO 70. HIGH PLUS 2. TONIGHT..SNOW. AMOUNT 5 CM. BLOWING SNOW WITH VISIBILITY LESS THAN 1 KILOMETRE THIS EVENING. WIND NORTH 50 KM/H GUSTING TO 70 DIMINISHING TO 30 GUSTING TO 50 THIS EVENING. LOW MINUS 9. But, no snowsquall warning Motivation/Background Case Overviews Dynamics Forecasts Future Work

Important questions: What is the frequency of occurrence of snow burst events? Are they more prevalent in certain regions? What are the favorable large-scale meteorological conditions? What are the favored instability regimes? Predictability: Model forecasts Objectives: Assemble an event climatology at representative stations in the northern U.S. and southern Canada Dynamic analysis and synoptic typing Index and forecast decision tree development Future Work Motivation/Background Case Overviews Dynamics Forecasts Future Work