Wednesday, 9 January 2013: 5:15 PM
Room 15 (Austin Convention Center)
Snowbands associated with winter cyclones can feature intense rates of snowfall in excess of 2.5 cm (1 in) h-1, and heavy snow accumulations greater than 15 cm (6 in). This snowfall can impact travel across large swaths of the central United States. Many of these snowbands can be less than 100 km in width, resulting in large gradients of snowfall, and thus creating a challenging forecast. Banded snowfall has been observed in multiple locations with respect to the surface cyclone. While many snowbands occur to the northwest of the cyclone along the trough of warm air aloft (TROWAL), snowbands can also occur to the northeast of the cyclone along the traditional warm front. This study examines the variability of cold-season banded snowfall environments associated with central United States cyclones. Understanding the different environments in which forcing for ascent and instability can occur will help forecasters to better anticipate situations where heavy banded snow is probable. In order to document the different environments associated with the development of heavy snowbands, the winters of 2006-2007 through 2010-2011 were examined. Any event with snowfall greater than 10 cm (4 in.) in 24 h between the lee of the Rocky Mountains and the windward side of the Appalachians was included in the study. Radar and surface data were examined and the following characteristics were recorded for each event: band duration, location of both banded and non-banded snow with respect to the cyclone, the latitude and longitude of both the snow band and the cyclone center, and the length and width of the snowband. Over 1020 cases were identified over the 5-year period. Cases were divided into five categories for compositing: 1) snowband located northeast of the cyclone with southwest flow, 2) snowband located northeast of the cyclone with northwest flow , 3) snowband located northwest of the cyclone with southwest flow, 4) non-snowband event in northwest flow, and 5) non-snowband in southwest flow. System-relative composites were created for each category using the North American Regional Reanalysis (NARR) dataset. A comparison of both synoptic and mesoscale features including mixing ratios, frontogenesis, and equivalent potential vorticity (EPV) will highlight the differences in moisture, lift, and instability present in each category.
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