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Planetary and Synoptic Analysis of Freezing Rain Events in Montreal, Quebec

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Department of Atmospheric and Oceanic Sciences, McGill University ... Events are partitioned according to the location of the long-wave trough axis. West Central East ... – PowerPoint PPT presentation

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Title: Planetary and Synoptic Analysis of Freezing Rain Events in Montreal, Quebec


1
Planetary and Synoptic Analysis of Freezing Rain
Events in Montreal, Quebec
  • Gina M. Ressler, Eyad H. Atallah, and John R.
    Gyakum
  • Department of Atmospheric and Oceanic Sciences,
    McGill University

The 11th Northeast Regional Operational Workshop,
Nov. 4-5th, 2009
Sponsored by Ouranos
2
Motivation
  • Freezing rain is a major environmental hazard
  • Especially common along the St. Lawrence river
    valley
  • Severe events can have a devastating effect on
    people, commerce, and property (1998 Ice Storm)

Median annual hours of freezing rain from 1979 to
1990 (Fig. 2, Cortinas et al. 2004)
3
Motivation
  • Most research has focused on
  • climatology (Stuart and Isaac 1999 Cortinas et
    al. 2004)
  • case studies (Higuchi et al. 2000 Gyakum and
    Roebber 2001)
  • statistical methods for prediction (Cheng et al.
    2004)
  • Fewer synoptic analyses (Cortinas 2000 Rauber et
    al. 2001)

Surface analysis illustrating Rauber's Pattern C
Cyclone-Anticyclone (Fig 5c, Rauber et al. 2001)
4
Objectives
  • Construct a complete list of events
  • Characterize the relevant planetary and synoptic
    features of a Montreal freezing rain event
  • Synoptic archetypes
  • Event causation, duration, and severity

Montreal, Dec. 2008
5
Data
  • Environment Canada hourly surface observations at
    Montreal, Quebec (YUL) for the period 1979-2008
  • National Centers for Environmental Prediction
    (NCEP) North American Regional Reanalysis (NARR)

6
Freezing Rain Events in Montreal, 1979-2008
  • 163 synoptically independent freezing rain events
  • Highest frequency in Dec, Jan, Feb
  • Most are short lived
  • Median 3 hours
  • Severe events are defined as having 6 or more
    hours of freezing rain
  • 46 severe events

7
(No Transcript)
8
Composite Anomalies for Severe (6hr) Events
The sea level pressure composite is consistent
with Rauber et al.'s (2001) Pattern C and Cheng
et al.'s (2004) Type 2, both describing a surface
Cyclone-Anticyclone couplet
9
Synoptic Partitioning
  • Events are partitioned according to the location
    of the long-wave trough axis
  • West Central East

500hPa heights (m contoured) and absolute
vorticity (10-5 s-1 shaded) at the freezing rain
onset time
10
Synoptic Partitioning
Western (blue) Central (green) Eastern (red)
n10 n17 n20
Absolute vorticity maxima for all severe events.
11
Western Cases (n10) MSLP (solid) and
1000-500hPa thickness (dotted) mean composites
12
Central Cases (n17) MSLP (solid) and
1000-500hPa thickness (dotted) mean composites
13
Eastern Cases (n20) MSLP (solid) and
1000-500hPa thickness (dotted) mean composites
14
Synoptic Analysis Preliminary Results
  • Western Cases
  • Long upper-level wavelength
  • Broad region of surface high pressure, and strong
    stationary cyclone near Greenland
  • Duration is 50 longer than both Central and
    Eastern cases
  • Central Cases
  • Similar to Western cases weaker anticyclone
    (Greenland cyclone)
  • Eastern Cases
  • Short upper-level wavelength, negatively tilted
  • Strong surface cyclone two separate anticyclones
  • Deformation zone more frontogenetical

15
Continued Research
  • Anomaly plots for each synoptic group
    statistical significance
  • For each group, investigate
  • Temperature and precipitation evolution
  • Frontogenesis
  • Moisture sources and air mass origins
  • Spatial extent (ie. along the St. Lawrence river
    valley)
  • Case studies for each synoptic group
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