Shawn M. Milrad, Department of Geography
University of Kansas
Eyad H. Atallah and John R. GyakumDepartment of Atmospheric and Oceanic
SciencesMcGill University
Montreal, Quebec, Canada
Jennifer F. SmithEnvironment Canada
Dartmouth, Nova Scotia, Canada
OutlineMotivationBackgroundOttawa, Ontario: 28 January 2010Case overviewSynoptic-dynamic analysis
Forecasts and warningsFuture work
MotivationThe climatology, dynamics and impacts of lake effect
snow squalls (bursts) throughout the U.S. have been well-documentedGreat 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 burstsThundersnow 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 Ottawa: Overview Dynamics Forecasts Future Work
Source: UCAR/COMET
MotivationMotivation Background Ottawa: Overview 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
MotivationMotivation Background Ottawa: Overview Dynamics Forecasts
Future Work
Ottawa, Ontario: 28 January 2010
(Photos are courtesy of the Ottawa Citizen)
Motivation Background Ottawa: Overview Dynamics Forecasts Future Work
Lundstedt et al. (1993): NWS Eastern Region technical bulletinDevelopment of Wintertime Instability Index (WINDEX)Low-level lapse rates (instability), boundary
layer relative humidity (moisture), 12-hour change in lifted index (instability)
Ever implemented operationally?Weakness: No criterion directly associated
with lift
Previous WorkMotivation Background Ottawa: Overview Dynamics Forecasts
Future Work
DeVoir (2004) and Nicosia et al. (2009)Impacts in PennsylvaniaLittle to no warning (below advisory/warning
criteria)
Previous WorkMotivation Background Ottawa: Overview Dynamics Forecasts
Future Work
From Nicosia et al. (2009)
Previous WorkMotivation Background Ottawa: Overview Dynamics Forecasts
Future Work
From Nicosia et al. (2009)
Nicosia et al. (2009)Impacts in
Pennsylvania
Previous WorkMotivation Background Ottawa: Overview Dynamics Forecasts
Future Work
Pettegrew et al. (2009): Eastern Iowa/North Central Illinois in 20034 cm (1.6 in) of snow> 50 kt winds (exceeds “severe” warning
criteria)Near-whiteout conditionsArctic front passage Intense frontogenesisConvective instabilitySteep lapse rates (momentum mixing)Convection rooted in the boundary layer
Previous WorkMotivation Background Ottawa: Overview Dynamics Forecasts
Future Work
Previous WorkMotivation Background Ottawa: Overview Dynamics Forecasts
Future Work
From Pettegrew et al. (2009)
In association with the passage of an arctic cold front, two intense snow bursts (SB1 and SB2) moved through eastern Ontario and western QuebecSnow accumulation at Ottawa
(CYOW) : 3.6 cm (1.4 in.)
BUTVERY low visibility Dozens of automobile accidents in the
Ottawa region (Ottawa Citizen 2010)At least one critical injury (13-year old
boy)
Ottawa, Ontario: 28 January 2010
Motivation Background Ottawa: Overview Dynamics Forecasts Future Work
Milrad, S. M., E. H. Atallah, J. R. Gyakum, and J.F. Smith, 2011: A diagnostic examination of the eastern Ontario and western Quebec wintertime convection event of 28 January 2010. Wea. Forecasting,
in press.
Ottawa, Ontario: 28 January 2010
(Photo courtesy of the Ottawa Citizen)
DataRadar Imagery
Environment Canada online historical radar database
MeteogramsEnvironment Canada and Iowa State University
online climate dataFor all analyses, t=0 h defined as hour first
snow burst (SB1) moved through CYOW1800 UTC 28 January
Motivation Background Ottawa: Overview Dynamics Forecasts Future Work
Radar Imagery
t=-3 h (1510 UTC) t=-2 h (1610 UTC)
Motivation Background Ottawa: Overview Dynamics Forecasts Future Work
***Ottawa International Airport (CYOW): black star******Massena, NY (KMSS): purple star***
***SB1 (blue arrow), SB2 (red arrow)***
Radar Imagery
t=-1 h (1710 UTC) t=0 h (1810 UTC)
Motivation Background Ottawa: Overview Dynamics Forecasts Future Work
***Ottawa International Airport (CYOW): black star******Massena, NY (KMSS): purple star***
Radar Imagery
t=+1 h (1910 UTC) t=+2 h (2010 UTC)
Motivation Background Ottawa: Overview Dynamics Forecasts Future Work
***Ottawa International Airport (CYOW): black star******Massena, NY (KMSS): purple star***
Case Overview: MeteogramsOttawa, ON (CYOW): 28 January 2010
Motivation Background Ottawa: Overview Dynamics Forecasts Future Work
Case Overview: MeteogramsMassena, NY (KMSS): 28 January 2010
Motivation Background Ottawa: Overview Dynamics Forecasts Future Work
Dynamic Analysis: StrategySnow bursts are essentially a form of
wintertime moist convectionUse “ingredients-based” methodology for
moist convectionDoswell et al. (1996); Schultz and Schumacher
(1999); Wetzel and Martin (2001)Three main ingredients
Lift (synoptic-scale and mesoscale)**MoistureInstability**
Convective (CI): (dθe/dz) < 0 Conditional Symmetric (CSI): MPV*
g < 0
Motivation Background Ottawa: Overview Dynamics Forecasts Future Work
DataNational Centers for Environmental
Prediction (NCEP) North American Regional Reanalysis (NARR)
32 km horizontal resolution 3-hourly
For all analyses, t=0 h defined as hour first snow burst (SB1) moved through CYOW1800 UTC 28 January
Motivation Background Ottawa: Overview Dynamics Forecasts Future Work
Lift: Synoptic-scale
t=-18 h (0000 UTC) t=-12 h (0600 UTC)
850-500 hPa Q-vector divergence (shaded, cool colors convergent), SLP (hPa, solid), 1000-500 hPa thickness (dam, dashed)
Motivation Background Ottawa: Overview Dynamics Forecasts Future Work
t=-6 h (1200 UTC) t=-3 h (1500 UTC)
850-500 hPa Q-vector divergence (shaded, cool colors convergent), SLP (hPa, solid), 1000-500 hPa thickness (dam, dashed)
Lift: Synoptic-scale
Motivation Background Ottawa: Overview Dynamics Forecasts Future Work
t=0 h (1800 UTC) t=+3 h (2100 UTC)
850-500 hPa Q-vector divergence (shaded, cool colors convergent), SLP (hPa, solid), 1000-500 hPa thickness (dam, dashed)
Lift: Synoptic-scale
Motivation Background Ottawa: Overview Dynamics Forecasts Future Work
t=-18 h (0000 UTC) t=-12 h (0600 UTC)
θ on the dynamic tropopause (2 PVU surface, K, shaded), 10 m winds (knots, barbs), and coupling index (θDT – θe 850) (contoured every 4 K from 0 to +16)
Lift: Synoptic-scale
Motivation Background Ottawa: Overview Dynamics Forecasts Future Work
t=-6 h (1200 UTC) t=-3 h (1500 UTC)
θ on the dynamic tropopause (2 PVU surface, K, shaded), 10 m winds (knots, barbs), and coupling index (θDT – θe 850) (contoured every 4 K from 0 to +16)
Lift: Synoptic-scale
Motivation Background Ottawa: Overview Dynamics Forecasts Future Work
t=0 h (1800 UTC) t=+3 h (2100 UTC)
θ on the dynamic tropopause (2 PVU surface, K, shaded), 10 m winds (knots, barbs), and coupling index (θDT – θe 850) (contoured every 4 K from 0 to +16)
Lift: Synoptic-scale
Motivation Background Ottawa: Overview Dynamics Forecasts Future Work
t=-18 h (0000 UTC) t=-12 h (0600 UTC)
925 hPa frontogenesis (K (100 km)-1 (3 h)-1), shaded), 925-700 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).
Lift: Mesoscale
Motivation Background Ottawa: Overview Dynamics Forecasts Future Work
t=-6 h (1200 UTC) t=-3 h (1500 UTC)
925 hPa frontogenesis (K (100 km)-1 (3 h)-1), shaded), 925-700 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).
Lift: Mesoscale
Motivation Background Ottawa: Overview Dynamics Forecasts Future Work
t=0 h (1800 UTC) t=+3 h (2100 UTC)
925 hPa frontogenesis (K (100 km)-1 (3 h)-1), shaded), 925-700 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).
Lift: Mesoscale
Motivation Background Ottawa: Overview Dynamics Forecasts Future Work
Instability: CI and CSI
t=-18 h (0000 UTC) t=-12 h (0600 UTC)
Saturated equivalent geostrophic potential vorticity (MPV*g, m2 s−1 K kg−1, shaded
for negative values) and θe (K, solid contours).
Motivation Background Ottawa: Overview Dynamics Forecasts Future Work
t=-6 h (1200 UTC) t=-3 h (1500 UTC)
Saturated equivalent geostrophic potential vorticity (MPV*g, m2 s−1 K kg−1, shaded
for negative values) and θe (K, solid contours).
Motivation Background Ottawa: Overview Dynamics Forecasts Future Work
Instability: CI and CSI
t=0 h (1800 UTC) t=+3 h (2100 UTC)
Saturated equivalent geostrophic potential vorticity (MPV*g, m2 s−1 K kg−1, shaded
for negative values) and θe (K, solid contours).
Motivation Background Ottawa: Overview Dynamics Forecasts Future Work
Instability: CI and CSI
Bryan and Fritsch (2000) argued that a sixth static stability state existsMoist absolutely unstable (γs > Γs)
Occurrences of this sixth state are called Moist Absolutely Unstable Layers (MAULs)Short-livedRare: 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 convectionIndications of (and caused by) intense mesoscale
vertical motion
Motivation Background Ottawa: Overview Dynamics Forecasts Future Work
Instability: MAUL
t=-18 h (0000 UTC) t=-12 h (0600 UTC)
NARR soundings for Ottawa (CYOW)
Motivation Background Ottawa: Overview Dynamics Forecasts Future Work
Instability: MAUL
t=-6 h (1200 UTC) t=-3 h (1500 UTC)
NARR soundings for Ottawa (CYOW)
Motivation Background Ottawa: Overview Dynamics Forecasts Future Work
Instability: MAUL
t=0 h (1800 UTC) t=+3 h (2100 UTC)
NARR soundings for Ottawa (CYOW)
Motivation Background Ottawa: Overview Dynamics Forecasts Future Work
Instability: MAUL
Conclusions: DynamicsDynamics
Synoptic-scale forcing for ascentArctic front
Mesoscale ascent-focusing mechanism Mesoscale forcing for ascent (frontogenesis)
Just enough moisture to create a problemThermodynamics
Very unstable, however you slice it Very steep low-level lapse rates Convective instability (CI) Conditional Symmetric Instability (CSI) Soundings: Deep (300-400 hPa) Moist Absolutely Unstable
Layer (MAUL)
Motivation Background Ottawa: Overview Dynamics Forecasts Future Work
Forecasts: The problemFrom limited research (a few case studies), the
models appear to do a decent job in predicting these eventsProbably as accurate as warm-season squall line
forecastsThe real problem is that despite the high impact
of snow burst events, they often do NOT meet warning or advisory criteriaSnow accumulations too lowWinds not high enough for severe criteriaNot the season for “convection”Not in lake effect regions
Motivation Background Ottawa: Overview Dynamics Forecasts Future Work
NWS winter weather advisory: “A Winter Weather Advisory will be issued when 2 to 4 inches of snow, alone
or in combination with sleet and freezing rain, is expected to cause a significant inconvenience, but not serious enough to warrant a warning.”
NWS Blizzard Warning: “A Blizzard Warning means that the following conditions are occurring or
expected within the next 12 to 18 hours.1) Snow and/or blowing snow reducing visibility to 1/4 mile or less for 3 hours or longer
AND 2) Sustained winds of 35 mph or greater or frequent gusts to 35 mph or greater.”
Environment Canada Snowsquall Warning: “When, to the lee of the Great Lakes or other large lakes, snow squalls are
expected and 15 cm or more of snow is likely to fall within 12 hours, OR the visibility is likely to be near zero for four or more hours, even without warning level accumulations of snow.”
Forecasts: The problem
Motivation Background Ottawa: Overview Dynamics Forecasts Future Work
Forecasts: The problem
Motivation Background Ottawa: Overview Dynamics Forecasts Future Work
Forecasts: Ottawa CaseThe Environment Canada Ontario Storm Prediction
Center Accurately called for 2-4 cm of snow throughout much of
eastern Ontario on the day of the snow bursts However, the forecast implied gradual “flurries over the course
of the day.”
A special weather statement was issued for CYOW twenty minutes before the first snow burst hit the city“Narrow but intense bands of snow are moving through
southeastern Ontario…Because of the short duration, snowfall accumulations are not expected to be significant, however visibilities may be reduced to a few hundred metres or less at times”
But did anyone actually see the special weather statement?http://www.weatheroffice.gc.ca/canada_e.html
Motivation Background Ottawa: Overview Dynamics Forecasts Future Work
Shortly after both squalls were evident on radar and moving through eastern Ontario, the Quebec Storm Prediction Centre (QSPC) issued a ‘snowsquall warning’ for western Quebec.Forecaster judgment supersedes warning
criteria?
Motivation Background Ottawa: Overview Dynamics Forecasts Future Work
Forecasts: Ottawa Case
t=+1 h (1910 UTC) t=+2 h (2010 UTC)
DeVoir (2004) pointed out that for the United States, no warning or advisory exists that is specific to a high-impact, but short-duration and low-precipitation event such as the Ottawa snow bursts
But what do you do?New warning/advisoryIssue a “winter weather advisory” etc. even if criteria is not metChange current advisory/warning criteriaSpecial weather statements: Are these well enough
disseminated?How do you get the message out?
NWS State College: PENNDOT cooperation (Nicosia et al. 2009)Contact emergency managers?Radio/Weather radio?Text messages?
Forecasts: Potential SolutionsMotivation Background Ottawa: Overview 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
Objectives:Assemble an event climatology at representative
stations in the northern U.S. and southern CanadaDynamic analysis and synoptic typingIndex and forecast decision tree development
Future WorkMotivation Background Ottawa: Overview Dynamics Forecasts
Future Work
Objectives:Assemble an event climatology at representative
stations in the northern U.S. and southern Canada Surface observations Radar data
Dynamic analysis and synoptic typing Group similar events using different sets of dynamic
parameters or thresholds Composite analysis of groups Case studies
Index and forecast decision tree development Update to/revamping of WINDEX Lake-effect snow decision tree (Niziol et al. 1987) Disseminate to operational community
Future WorkMotivation Background Ottawa: Overview Dynamics Forecasts
Future Work
Motivation Background Ottawa: Overview Dynamics Forecasts Future Work