Characteristics of Precipitation Particles and Microphysical Processes during the 11–12 January 2020 Ice Pellet Storm in the Montréal Area, Québec, Canada

Lachapelle, Mathieu et Thériault, Julie Mireille (2022). « Characteristics of Precipitation Particles and Microphysical Processes during the 11–12 January 2020 Ice Pellet Storm in the Montréal Area, Québec, Canada ». Monthly Weather Review, 150(5), pp. 1043-1059.

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Freezing rain and ice pellets are particularly difficult to forecast when solid precipitation is completely melted aloft. This study addresses this issue by investigating the processes that led to a long-duration ice pellet event in Montreal, Québec, Canada, on 11–12 January 2020. To do so, a benchmark model initialized with ERA5 data is used to show that solid precipitation was completely melted below the melting layer, which discards partial melting from the possible ice pellet formation processes. Macro photography of precipitation reveals that small columnar crystals (∼200 μm) and ice pellets occurred simultaneously for more than 10 h. The estimation of ice crystal number concentration using macro photographs and laser-optical disdrometer data suggests that all supercooled drops could have refrozen by contact freezing with ice crystals. Rimed ice pellets also indicate ice supersaturation in the subfreezing layer. Given these observations, the formation of ice pellets and ice crystals was probably promoted by secondary ice production and the horizontal advection of ice crystals below the melting layer, as we illustrate using a conceptual model. Overall, these findings demonstrate how ice nucleation processes at temperatures near 0°C can drastically change the precipitation phase and the impact of a storm. Significance Statement Ice pellets are generally formed when snow particles partially melt while falling through a warm layer aloft before completely refreezing in a cold layer closer to the surface. Ice pellets can also be formed when snow particles completely melt aloft, but freezing rain is often produced in such conditions. On 11–12 January 2020, ice pellets were produced during more than 10 h in Montreal, Quebec, Canada. Macro photographs of the precipitation particles show that ice pellets occurred simultaneously with small ice crystals. Most of the ice pellets were produced while snow particles were completely melted aloft. The supercooled drops probably refroze due to collisions with the ice crystals that could have been advected by the northeasterly winds near the surface.

Type: Article de revue scientifique
Informations complémentaires: © 2022 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy ( Content that is immediately available upon publication as open access.
Mots-clés ou Sujets: Cloud microphysics, Freezing precipitation, Ice crystals, Radars/radar observations, Ice particles
Unité d'appartenance: Centres institutionnels > Centre pour l'étude et la simulation du climat à l'échelle régionale (ESCER)
Faculté des sciences > Département des sciences de la Terre et de l'atmosphère
Déposé par: Julie Mireille Thériault
Date de dépôt: 27 sept. 2022 10:39
Dernière modification: 09 oct. 2022 23:10
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