Weather and Climate Systems
A Regional Climatology and Synoptic Pattern Analysis of Winter Storms in the Southern Great Plains 1993-2011
OU School of Meteorology / CIMMS
30 October 2013, 1:00 PM
National Weather Center, Room 3902
120 David L. Boren Blvd.
University of Oklahoma
Winter storms in the southern United States can have significant impacts on infrastructure and the economy. Between 2000-2010 several damaging winter storms, the majority of which involved accumulation of freezing rain, produced in excess of $500 million in aid expenditure to Oklahoma alone. In this study, National Climatic Data Center Storm Event database and local climate summaries are used to develop a spatial and synoptic climatology for freezing precipitation (inclusive of freezing rain, drizzle and ice pellets) and snowfall over the Southern Great Plains during 1993-2011. One of the key aims is to differentiate the common synoptic evolutions of storms exhibiting an area of freezing rain versus those primarily producing snowfall to the region. The spatial distribution of freezing precipitation and snowfall is evaluated by estimating the average number of days per year that precipitation of said type was observed to have occurred. Subsequently, a subset of 33 (42) freezing precipitation (snowfall) events are selected, based on a series of criteria determining the dominant phase of precipitation, and rotated principal component analysis performed for the 500 hPa height field at the approximate onset time of precipitation. The five most frequently observed patterns are retained for each precipitation type. Composites of temperature, moisture, pressure and wind-fields are constructed for each pattern, and extended 24-hours prior to and after precipitation initiation to track average storm evolutions. All circulation fields involve a mid-level trough, which is typically located somewhat further west in the majority of freezing precipitation events. Two-of-five snowfall patterns involve a deeper surface cyclone, while all freezing precipitation composites reveal southward propagation of an arctic anticyclone 24-hours ahead of event onset, this higher sea level pressure being found to be statistically distinct from snowfall-dominant storms. High impact ice storms in the region often exhibit slow moving upper level flow, persistent isentropic ascent over a surface quasi-stationary front, in the presence of significant positive moisture anomalies, with melting layer airmass trajectories originating over the Gulf of Mexico. The results are preliminary, and are based on a small sample size. However, this work is intended to be of value for forecasters as an aid in predicting the evolution of precipitation within Southern Plains winter storms.
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