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2024 Hennepin County All -Jurisdiction Hazard Mitigation Plan <br />Volume 2 — Hazard Inventory <br />4.3.2.9. Indications and Forecasting <br />National responsibility for developing tornado indications and forecasts rests with the National Oceanic <br />and Atmospheric Administration/National Weather Service's Storm Prediction Center (SPC) in Norman, <br />Oklahoma. The SPC issues daily Convective Weather Outlooks. These outlooks give general categories that <br />explain the chances/risk of tornadoes each day. As conditions look to develop more favorable for tornadic <br />storms to occur, the SPC will issue Mesoscale Discussions (MDs). MDs contain a graphical depiction of the <br />mesoscale convective developments, an area affected line, concerning line, valid time, a summary <br />paragraph summary, and a paragraph for a technical discussion. There are five categories of concern <br />issued with the MD: <br />• Severe Potential... <br />Watch Unlikely (5 or 20%) <br />• Severe Potential... <br />Watch Possible (40 or 60%) <br />• Severe Potential... <br />Watch likely (80 or 95%) <br />• Severe Potential... <br />Tornado Watch likely (80 or 95%) <br />• Severe Potential... <br />Severe Thunderstorm Watch Likely (80 or 95%) <br />• Severe Potential... <br />Watch Needed Soon (95%) <br />After an MD is issued, SPC will monitor conditions and if tornadic potential still is likely, they will issue a <br />tornado watch. A tornado watch is issued when atmospheric conditions are favorable for the <br />development of severe thunderstorms capable of producing tornadoes. On average, Hennepin County is <br />included in 4 tornado watches each year. In addition to the SPC's information about potential for <br />tornadoes, the National Weather Service Forecast Office will issue Hazardous Weather Outlook (HWO) <br />based on their thoughts for the potential of tornadoes occurring. In this discussion, they will highlight the <br />best time, and generally geographic location for storms to occur. <br />4.3.2.10. Detection and Warning <br />National responsibility for detection and warning of tornadoes falls on the local National Weather <br />Service's Weather Forecast Offices (WFO). The local WFO for Hennepin County is in Chanhassen, MN. One <br />of the systems the WFO uses to detect tornadoes is RADAR. There are two RADAR sites that the <br />Chanhassen WFO uses, the NEXRAD WSR-88D and the Terminal RADAR. The NEXRAD WSR-88D is located <br />at the Chanhassen WFO office, and the Terminal RADAR is in Woodbury and is used daily for incoming <br />aircraft. There are many different products that the NWS can use from these RADARS that help them <br />detect whether a storm has a tornadic signature to it. <br />Another avenue that the WFO uses are spotter reports, or reports from emergency managers. In the <br />metro region, there is an organized amateur radio group called Metro SKYWARN that teach SKYWARN <br />spotter classes to amateur radio operators so they can make reports directly to the local WFO. Hennepin <br />County Emergency Management also trains internal SKYWARN spotters to report to the Hennepin County <br />Emergency Operations Center during activations or directly to the local WFO. <br />If the WFO sees evidence that there is a tornado either on the ground, or the potential, they will issue a <br />tornado warning. A tornado warning means a severe thunderstorm has developed and has either <br />produced a tornado or radar has indicated the presence of atmospheric conditions conductive to tornado <br />development. On average, Hennepin County is in a tornado warning between 30 and 45 minutes a year. <br />Once a tornado warning has been issued, there are a variety of notification systems that notified <br />78 <br />