Weather systems occurring over Fort Simpson, Northwest Territories, Canada, during three seasons of 1998–1999: 2. Precipitation features

Abstract

[1] Precipitation events were examined at Fort Simpson, Northwest Territories, Canada, during the autumn and winter of 1998 and during the spring of 1999 with a variety of observational tools, including a polarimetric radar. This location is characterized by a relatively small amount of precipitation (annual average of 450 mm), with approximately half being in the form of snow. During the observational periods, precipitation was produced within multilayered cloud systems with heights ranging up to 10 km, and instances of light snow were associated with either low (<2.5 km) or high (up to 10 km) clouds. Precipitation over the observational periods was typically produced in banded structures, was sometimes reduced because of subcloud evaporation or sublimation, and in the winter was often in the form of individual crystals. A state-of-the-art weather forecasting model was often poor at simulating some of the critical features of the precipitation events, such as cloud top height and precipitation amount. In addition, it was shown that with the sensitive CloudSat radar, $17% of overpasses will be associated with the occurrence of detectable precipitation at Fort Simpson, but with the less sensitive Global Precipitation Measurement (GPM) radar, much of the precipitation will be undetected.

Storm Studies in the Arctic (STAR)

“…In fact, one particular event (not shown) had as many as five cloud layers, indicating complex meteorological structures. Stewart et al (2004) also found many cloud layers present during precipitation events in the western Canadian Arctic, at times as many as five.…”

“…Only one major Canadian-led experiment has focused on arctic storms-the 1994 Beaufort and Arctic Storms Experiment (BASE; Hudak et al 1995;Hanesiak et al 1996)-although the Mackenzie Global Energ y and Water Cycle Experiment (GEWEX) Study (MAGS) also carried out some storm observations (Stewart et al 1998). BASE and MAGS took place in the lee of the Western Cordillera, which significantly inf luence storm systems.…”

“…The precipitation efficiency of a system is decreased (increased) when the background static stability is increased (decreased) or when the Coriolis parameter is increased (decreased) . Hudak et al (2004) and Stewart et al (2004) used a variety of field observations during MAGS to characterize cloud and precipitation systems transiting the western Canadian Arctic. Unique features included the prevalence of multilayered systems, the cold temperatures of low clouds, significant sublimation effects, and significant diurnal trends in cloud properties in winter.…”

“…This project, however, was not primarily focused on storms but rather on cloud characteristics/microphysics in relation to radiation. Although not conducted in the Arctic, information from the 1986 and 1992 Canadian Atlantic Storms Program (CASP) field experiments that took place in Atlantic Canada is also relevant (see, e.g., Stewart 1991;Hanesiak and Stewart 1995). Many studies launched from the CASP projects, including the development of conceptual storm models and research into strong winds and low-level jet characteristics, rain-snow boundary structures, and internal feedbacks, and heavy precipitation.…”

A Study of the Meteorological Conditions Associated with Anomalously Early and Late Openings of a Northwest Territories Winter Road

“…Generally, significant precipitation in the MRB is preceded by an extended period during which the tropospheric air becomes saturated with water vapor from precipitation aloft (Lackmann and Gyakum, 1996). However, because air is drier at lower tropospheric levels, sub-cloud evaporation and sublimation reduce the amount of precipitation reaching the ground (Szeto et al, 1997;Smirnov and Moore, 1999;Stewart et al, 2004). Fort Simpson (61˚30; N, 121˚0' W) lacks low-level moisture in the cold season (Liu and Stewart, 2003;Hudak et al, 2004;Stewart et al, 2004) because it is located inland, in the lee of the Rocky Mountains.…”