Climatology of and Factors Contributing to Occurrences of Near-0C Temperatures and Associated Precipitation At and Near Terrace, British Columbia, Canada

Occurrences of near-0 degrees C temperatures (-2 degrees C <= T <= 2 degrees C) are common in cold regions such as Canada, and these conditions can lead to freeze-thaw events and hazardous precipitation. Many locations in the Coast Mountains within the Canadian province of British Columbia (BC) are especially prone to near-0 degrees C conditions. This study examines the factors that promote anomalously persistent near-0 degrees C conditions, often with precipitation, in Terrace, a small industrial city within the Coast Mountains of northwestern BC. The climatology of near-0 degrees C conditions and associated precipitation over the 1956-2020 period was developed using a combined network of weather stations and field data to study the atmospheric conditions and precipitation during periods of near-0 degrees C conditions. Events with continuous near-0 degrees C conditions generally had long durations, with a climatological mean of 11 h, which increases substantially if accompanied by precipitation (18 h), and even more if accompanied with freezing precipitation (38 h). The longest near-0 degrees C event lasted 233 h and was associated with long-lasting snow and rain. By combining the field data information, large-scale weather conditions and long-term climatology, several factors that contribute to near-0 degrees C conditions at Terrace were identified. These include the ocean's proximity, the surrounding topography, persistent cloudiness, and diabatic processes associated with melting and freezing, although local factors linked with topographic features are also important. Collectively, this study has characterized and improved our understanding of Terrace's near-0 degrees C conditions and its associated precipitation, and these insights can be used for improved forecasting of hazardous events in the area. [Traduit par la redaction] Les temperatures proches de 0 degrees C (-2 degrees C <= T <= 2 degrees C) sont courantes dans les regions froides comme le Canada, et ces conditions peuvent entrainer des phenomenes de gel-degel et des precipitations dangereuses. De nombreux endroits de la chaine cotiere de la province canadienne de la Colombie-Britannique sont particulierement exposes a des conditions proches de 0 degrees C. Cette etude se penche sur les facteurs qui favorisent des conditions anormalement persistantes proches de 0 degrees C, souvent accompagnees de precipitations, a Terrace, une petite ville industrielle situee dans la chaine cotiere du nord-ouest de la Colombie-Britannique. La climatologie des conditions proches de 0 degrees C et des precipitations associees sur la periode 1956-2020 a ete elaboree au moyen d'un reseau combine de stations meteorologiques et de donnees de terrain afin d'etudier les conditions atmospheriques et les precipitations pendant les periodes de conditions proches de 0 degrees C. Les evenements avec des conditions continues proches de 0 degrees C ont generalement une longue duree, avec une moyenne climatologique de 11 heures, qui augmente considerablement s'ils sont accompagnes de precipitations (18 heures), et encore plus s'ils sont accompagnes de precipitations verglacantes (38 heures). Le plus long episode de temperatures proches de 0 degrees C a dure 233 heures et a ete associe a des chutes de neige et de pluie de longue duree. En combinant les donnees de terrain, les conditions meteorologiques a grande echelle et la climatologie a long terme, plusieurs facteurs contribuant a des conditions proches de 0 degrees C a Terrace ont ete recenses. Il s'agit notamment de la proximite de l'ocean, de la topographie environnante, de la nebulosite persistante et des processus diabatiques associes a la fonte et au gel, bien que les facteurs locaux lies aux caracteristiques topographiques soient egalement importants. Cette etude a permis de caracteriser et d'ameliorer notre comprehension des conditions de Terrace proches de 0 degrees C et des precipitations associees, et ces connaissances peuvent servir a ameliorer la prevision des phenomenes meteorologiques dangereux dans la region.