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Published on October 3, 2007

Author: Janelle

Source: authorstream.com

The Integration of WRF Model Forecasts for Mesoscale Convective Systems Interacting with the Mountains of Western North Carolina Progress Update Jacob Carley:  The Integration of WRF Model Forecasts for Mesoscale Convective Systems Interacting with the Mountains of Western North Carolina Progress Update Jacob Carley What is an MCS?:  What is an MCS? An MCS (mesoscale convective system) is a large system of thunderstorms that generally persist up to several hours. These systems can span several states and are capable of producing large hail, damaging winds, and tornadoes. What is the WRF model?:  What is the WRF model? Weather Research and Forecasting model (WRF). WRF is the new model to be used heavily in forecasting. A mesoscale model that places emphasis on terrain. Is scheduled to replace the Eta/NAM. Can be run at very high resolutions. Less than 2km! Why?:  Why? MCS systems are especially difficult events to forecast in Western North Carolina due to the Appalachian Mountains. Current forecast models have difficulty creating high resolution products while acknowledging this complex terrain. The WRF has the capability to create high resolution products while recognizing unique land features. Criteria for Selecting Events to Study:  Criteria for Selecting Events to Study Crossing. MCS crosses over the mountains while retaining most of its energy. Dissipating. MCS dissipates and/or loses most of its energy upon reaching the mountains. First Event:  First Event April 22nd, 2005. Involves two waves of severe weather. First wave crosses, second dissipates. One tornado report in Pickens County, SC. Second Event:  Second Event May 19th, 2005. MCS crosses over the mountains but is severely weakened. One confirmed F1 tornado in Smyth County, VA. Third Event:  Third Event July 27th, 2005. Very broad and linear line of convection. As the system advances upon the Appalachian Mountains it quickly dissipates. First Event Radar Imagery:  First Event Radar Imagery So far we have been able to run the first event (April 22, 2005) in the WRF model. All radar images are 0.5 degree base reflectivity. Radar data is courtesy of the NCDC. Radar images were made using StormLab with help from Chad Hutchins. April 22 at 18Z. First Wave. :  April 22 at 18Z. First Wave. April 22 at 19Z. First Wave. :  April 22 at 19Z. First Wave. April 22 at 20Z. First Wave. :  April 22 at 20Z. First Wave. April 23 at 01Z. Second Wave.:  April 23 at 01Z. Second Wave. April 23 at 04Z. Second Wave.:  April 23 at 04Z. Second Wave. April 23 at 05Z. Second Wave.:  April 23 at 05Z. Second Wave. First Event WRF Data:  First Event WRF Data This run of WRF was initialized at 06Z April 22 (the day of the event). Map of 500mb vorticity. Vorticity is a good indicator of convection. April 22 at 18Z. First Wave:  April 22 at 18Z. First Wave April 22 at 19Z. First Wave:  April 22 at 19Z. First Wave April 22 at 20Z. First Wave:  April 22 at 20Z. First Wave April 23 at 01Z. Second Wave:  April 23 at 01Z. Second Wave April 23 at 04Z. Second Wave:  April 23 at 04Z. Second Wave April 23 at 05Z. Second Wave:  April 23 at 05Z. Second Wave Radar Data Vs. WRF Forecast:  Radar Data Vs. WRF Forecast Observations with the first wave. WRF appears slow to bring in convection with the first wave. Leaves residual bull's-eyes of vorticity afterward. Observations with the second wave. WRF initially looks mostly on target with onset of front at 01z. However, it does not even show any showers crossing at all at 04Z and 05Z. So How Did The WRF Do?:  So How Did The WRF Do? WRF at first glance has problems with onset of prefrontal convective precipitation. However, it was still surprisingly accurate. The model had problems bringing the actual frontal precipitation across the mountains. Theories or hypotheses? Did the model handle this well because of the synoptic features influencing the event? Changes to make to WRF runs? Initialization time appears to be important. 00Z initialization was very slow. 12Z initialization missed a lot of the convection (ironic).

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