shawn m. milrad, department of geography university of kansas eyad h. atallah and john r. gyakum...

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)


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)


Future Work

From Nicosia et al. (2009)


Future Work

From Nicosia et al. (2009)

Nicosia et al. (2009)Impacts in

Pennsylvania


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


Future Work


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)



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.


(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


Radar Imagery

t=-3 h (1510 UTC) t=-2 h (1610 UTC)


***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)



Radar Imagery

t=+1 h (1910 UTC) t=+2 h (2010 UTC)



Case Overview: MeteogramsOttawa, ON (CYOW): 28 January 2010


Case Overview: MeteogramsMassena, NY (KMSS): 28 January 2010


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


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


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)


t=-6 h (1200 UTC) t=-3 h (1500 UTC)




t=0 h (1800 UTC) t=+3 h (2100 UTC)




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)



t=-6 h (1200 UTC) t=-3 h (1500 UTC)




t=0 h (1800 UTC) t=+3 h (2100 UTC)




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


t=-6 h (1200 UTC) t=-3 h (1500 UTC)



Lift: Mesoscale


t=0 h (1800 UTC) t=+3 h (2100 UTC)



Lift: Mesoscale


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).


t=-6 h (1200 UTC) t=-3 h (1500 UTC)





t=0 h (1800 UTC) t=+3 h (2100 UTC)





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


Instability: MAUL

t=-18 h (0000 UTC) t=-12 h (0600 UTC)

NARR soundings for Ottawa (CYOW)


Instability: MAUL

t=-6 h (1200 UTC) t=-3 h (1500 UTC)



Instability: MAUL

t=0 h (1800 UTC) t=+3 h (2100 UTC)



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)


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


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


Forecasts: The problem


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


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?


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

shawn m. milrad, department of geography university of kansas eyad h. atallah and john r. gyakum...

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