Meteorology Commons^™

Synoptic Typing And Precursors Of Heavy Warm-Season Precipitation Events At Montreal, Québec, Shawn M. Milrad, Eyad H. Atallah, John R. Gyakum, Giselle Dookhie

Shawn M. Milrad

A precipitation climatology is compiled for warm-season events at Montreal, Québec, Canada, using 6-h precipitation data. A total of 1663 events are recorded and partitioned into three intensity categories (heavy, moderate, and light), based on percentile ranges. Heavy (top 10%) precipitation events (n = 166) are partitioned into four types, using a unique manual synoptic typing based on the divergence of Q-vector components. Type A is related to cyclones and strong synoptic-scale quasigeostrophic (QG) forcing for ascent, with high-θe air being advected into the Montreal region from the south. Types B and C are dominated by frontogenesis (mesoscale QG forcing …

A Meteorological Analysis Of Important Contributions To The 1999-2005 Canadian Prairie Drought, Lisa M. Hryciw, Eyad H. Atallah, Shawn M. Milrad, John R. Gyakum

Shawn M. Milrad

Drought is a complex natural hazard that is endemic to the Canadian prairies. The 1999–2005 Canadian prairie drought, which had great socioeconomic impacts, was meteorologically unique in that it did not conform to the traditional persistent positive Pacific–North American (PNA) pattern and west coast ridging paradigm normally associated with prairie drought. The purpose of this study is to diagnose the unique synoptic-scale mechanisms responsible for modulating subsidence during this drought. Using 30-day running means of the percent of normal precipitation from station data, key severe dry periods during 1999–2005 are identified. Analysis of the mean fields from reanalysis data shows …

A Thermodynamic Analysis Of An Intense North American Arctic Air Mass, Jessica K. Turner, John Gyakum, Shawn M. Milrad

Shawn M. Milrad

Northwestern Canada is a genesis region of arctic air masses often considered to be formed primarily through radiative processes. However, the details of their life cycle are poorly understood. This paper examines the formation, maintenance, and dissipation of an intense and long-lived arctic air mass, using a thermodynamic budget analysis.

The airmass formation is characterized by a deep-layer, multistage process that begins with snow falling into a nascent air mass. Radiative cooling from cloud tops begins the process. After the snow abates and clear skies are observed, the surface temperature drops rapidly, aided by the high emissivity of fresh snow …