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Ben Moyer Senior Meteorologist National Weather Service Des Moines, Iowa

Basic Blizzard Ingredients Unmasked and a Review of the 5 April 2009 Non-Blizzard Through the Eyes of the SREF. Ben Moyer Senior Meteorologist National Weather Service Des Moines, Iowa. The Why. Snowcrystals.com. Snowcrystals.com.

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Ben Moyer Senior Meteorologist National Weather Service Des Moines, Iowa

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  1. Basic Blizzard Ingredients Unmasked and a Review of the 5 April 2009 Non-Blizzard Through the Eyes of the SREF Ben Moyer Senior Meteorologist National Weather Service Des Moines, Iowa National Weather Service - Des Moines, IA

  2. The Why Snowcrystals.com Snowcrystals.com • Verification of last 6 Blizzard Warning events in central Iowa lower than expectation • 5 April 2009 case was impetus • Credible warnings important to many users • Study of past blizzard research did not discuss basic meteorological parameters needed • Can a study of these events reveal any clues? National Weather Service - Des Moines, IA

  3. Overview • The six cases • Methodology • Parameters studied • Analysis • SREF and 5 April 2009 event • Conclusions National Weather Service - Des Moines, IA

  4. Blizzard Warning Events Used National Weather Service - Des Moines, IA

  5. Methodology • Reviewed the 6 cases on the Weather Event Simulator (mimics AWIPS) • GFS, NAM, and SREF model forecast data • For the model run forecaster was using to make Blizzard Warning decision • Reviewed observational data • Radar • Surface observations • RUC model initializations National Weather Service - Des Moines, IA

  6. Parameters Studied National Weather Service - Des Moines, IA

  7. Sample Spreadsheet National Weather Service - Des Moines, IA

  8. Surface Analysis Common values for blizzards with falling snow • Low pressure center sub-990 mb • Deepening to less than 985 mb • Minimum 6-hour intensification of 5 mb • Max pressure gradient across Iowa of at least 18 – 19 mb (300-400 miles) National Weather Service - Des Moines, IA

  9. Max 6-Hour SFC Low Central Pressure Change and Iowa Gradient H PH 984 mb 983 mb 1002 mb 1012 mb 994 mb National Weather Service - Des Moines, IA

  10. 850 mb Analysis Common values for blizzards • Low height center deepening and preferably less than 1300 meters • Minimum 6-hour intensification of 40 meters • Maximum wind at least 45 knots (mixing) • 1-2 Mar 2007 as high as 60 knots • Cold advection at the rate of at least 10 degrees Celsius per 12 hours National Weather Service - Des Moines, IA

  11. 500 mb Analysis Common values for blizzards • Not as definitive • Rapidly deepening negatively tilted cyclone • Also open waves (22 Jan 2005) and positively tilted waves (29 Jan 2008) National Weather Service - Des Moines, IA

  12. Best Correlations for Iowa Blizzards • Surface low pressure • Intensity • Trends • Gradient • 850 mb Height • Intensity and trends • 850 mb Winds National Weather Service - Des Moines, IA

  13. 5 April 2009 Winter Storm • Blizzard Watch issued 36-48 hours in advance • Blizzard Warning issued 24 hours in advance National Weather Service - Des Moines, IA

  14. 00Z 4 Apr 2009 GFS 500 mb National Weather Service - Des Moines, IA

  15. 00Z 4 Apr 2009 GFS 850 mb National Weather Service - Des Moines, IA

  16. 00Z 4 Apr 2009 GFS Surface National Weather Service - Des Moines, IA

  17. 5 April 2009 Winter Storm • How did model data at warning decision time correspond to blizzard values shown in this study? National Weather Service - Des Moines, IA

  18. 00Z 4 April 2009 Model RunsFor 24 hour period 00Z Apr 5 to 00Z Apr 6 National Weather Service - Des Moines, IA

  19. SREF Winter Weather Fields • Focus on period when forecaster was making the Blizzard Warning decision • 21Z 3 Apr 2009 model run (from SPC) National Weather Service - Des Moines, IA

  20. F045 valid 18Z 5 Apr 2009 25 to 30 mph 10 Meter Maximum Wind (MPH) From Any Member National Weather Service - Des Moines, IA

  21. F039 valid 12Z 5 Apr 2009 Snow becomes likely precipitation type 09-12Z 5 Apr 2009 – 9 to 12 hours into the valid time of the Blizzard Warning! Likely Precipitation Type National Weather Service - Des Moines, IA

  22. F030 valid 03Z 5 Apr 2009 Best near MN border, but before probability of snow became likely. Mean Depth Dendrite Growth Zone >= 50 mb National Weather Service - Des Moines, IA

  23. F042 valid 15Z 5 Apr 2009 Max shifted east and probability decreased. (Turned out to be too far north.) Mean Depth Dendrite Growth Zone >= 50 mb National Weather Service - Des Moines, IA

  24. F030 valid 03Z 5 Apr 2009 Never more than 10 to 30% and before snow became likely. 50 mb and 100 mb charts infer than an abundance of heavy snowfall was unlikely in Blizzard Warning area. Mean Depth Dendrite Growth Zone = 100 mb National Weather Service - Des Moines, IA

  25. F039 valid 12Z 5 Apr 2009 Probability only 25% Mean 32F contour (dashed blue) not even into central IA until now – 12 hours into valid time of Blizzard Warning. Calibrated 6 Hour Probability New Snow or Ice on Roads National Weather Service - Des Moines, IA

  26. F045 valid 18Z 5 Apr 2009 Probability decreased through the morning. After 12Z, 32F contour (dashed blue) moved a little farther southeast, but then retreated by 18Z. Calibrated 6 Hour Probability New Snow or Ice on Roads National Weather Service - Des Moines, IA

  27. F039 valid 12Z 5 Apr 2009 Note Mean 32F contour Equal to above normal chances of snow accumulating on the roads. But, remember it is early April. Already somewhat anomalous to have snowfall. Chance S/IP/ZR Detection on Road National Weather Service - Des Moines, IA

  28. F042 valid 15Z 5 Apr 2009 Barely got to 10 and only after 12Z. Wetter than normal snow – not likely to blow around much. Mean Estimated Snow to Liquid Equivalent Ratio National Weather Service - Des Moines, IA

  29. F036 valid 09Z 5 Apr 2009 Only 10 to 30% over northern Iowa and again before snow became likely. Again, heavy snowfall seemed unlikely. Probability Snowfall Rate >= 1”/Hour National Weather Service - Des Moines, IA

  30. SREF Summary • Several signs in SREF output showed attaining true blizzard conditions would be difficult • Warm ground and air temperatures • Wetness of snow • Unlikelihood of sustained heavy snowfall • 10m winds of less than 35 mph National Weather Service - Des Moines, IA

  31. What Happened? • It eventually snowed in central Iowa. • Surface temps were too warm for light snow to accumulate much. • A heavy band did set up…but mainly outside of Blizzard Warning area • Wet snow precluded any true blizzard conditions. • Any 35 mph winds were very short duration. National Weather Service - Des Moines, IA

  32. 00Z-18Z 5 Apr 2009 National Weather Service - Des Moines, IA

  33. Regional Radar Loop National Weather Service - Des Moines, IA

  34. Max Potential Blizzard Time?10Z 5 Apr 2009 • Significant portion had very little snow • What did fall had little chance to accumulate • SREF was on to something! • Heavy band of snow farther south had brief 35 mph winds • Low pressure 1001 mbnorth of St. Joseph, MO National Weather Service - Des Moines, IA

  35. Final Snowfall Map National Weather Service - Des Moines, IA

  36. Conclusion • Model forecasts were in fairly good agreement • Some magnitudes off slightly, but trends verified well • Basic thresholds for blizzard potential established • SREF output an excellent resource for corroboration • Other parameters like mixed layer wind (gust potential), character of falling snow or antecedent snow cover, and depth of snow already on ground, not included in this study National Weather Service - Des Moines, IA

  37. Conclusion • Using a combination of basic meteorological parameter thresholds, and • Observing trends in the SREF winter weather fields and impact graphics, • Forecasters should be able to make higher confidence forecasts and more easily discern the validity of issuing a Blizzard Warning National Weather Service - Des Moines, IA

  38. Acknowledgements • Karl Jungbluth, SOO – NWS Des Moines, IA • Dan Baumgardt, SOO – LaCrosse, WI • SPC SREF website: http://www.spc.noaa.gov/exper/sref/frames.php?run=latest National Weather Service - Des Moines, IA

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