School of Meteorology (Defense)

Moisture and Thermal Characteristics of Southern Plains Ice Storms: Insights from a Regional Climatology and WRF-ARW Sensitivity Study

Esther Mullens
OU School of Meteorology

25 July 2014, 2:00 PM

National Weather Center, Room 2100
(CIMMS Conference Room)
120 David L. Boren Blvd.
University of Oklahoma
Norman, OK

Winter storms, including snowstorms and ice storms, are an infrequent yet significant hazard for the south-central United States. This work examined characteristics of freezing precipitation for the Southern Great Plains (SGP) by developing a regional thermodynamic and synoptic climatology 1993-2011. National Climatic Data Center Storm Event/Storm Data reports, surface weather analyses and local climate summaries were used to identify winter precipitation events and their phase characteristics, while upper air data was sourced from the University of Wyoming sounding archive, and ARM SGP site for Lamont, OK. EOF and composite techniques were used to develop a set of common flow fields prior to and during ice and snow storms, based initially on the amplitude and structure of the 500 hPa geopotential height. Composites for each derived pattern type evaluated temperature, moisture, sea level pressure and winds, with their thermal and dynamical evolutions described and contrasted.
As an extension to this work, and past literature, a hypothesis was proposed suggesting the Gulf of Mexico (GOM) Sea Surface Temperature (SST), as the proximal basin and major moisture source, impacts the severity of ice storms by modulation of the melting layer profile and moisture potential. This assertion was tested using high-resolution nested WRF-ARW sensitivity studies for two synoptically distinct winter storms (December 9-11 2007, January 28-30 2010) and six representations of the GOM SST field. These included the 1981-2010 climatology, a uniform 2 K perturbation to the control (control=real SST), and a physical upper and lower limit SST field for the warmest and coolest event date basin-average anomalies observed during 1981-2011. The control WRF simulation was evaluated against a suite of observations, to determine model efficacy to the observed evolution of key features. Our results indicated discernable and non-linear impacts of SST on the evolution of freezing precipitation for both case studies, even with modest SST changes. Key results, applications and extensions to this work will be discussed.

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