Ben Moyer Senior Meteorologist National Weather Service Des Moines, Iowa

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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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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 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 Overview
  • The six cases
  • Methodology
  • Parameters studied
  • Analysis
  • SREF and 5 April 2009 event
  • Conclusions
  • National Weather Service - Des Moines, IA Blizzard Warning Events Used National Weather Service - Des Moines, IA 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 Parameters Studied National Weather Service - Des Moines, IA Sample Spreadsheet National Weather Service - Des Moines, IA 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 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 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 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 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 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 00Z 4 Apr 2009 GFS 500 mb National Weather Service - Des Moines, IA 00Z 4 Apr 2009 GFS 850 mb National Weather Service - Des Moines, IA 00Z 4 Apr 2009 GFS Surface National Weather Service - Des Moines, IA 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 00Z 4 April 2009 Model RunsFor 24 hour period 00Z Apr 5 to 00Z Apr 6 National Weather Service - Des Moines, IA 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 F045 valid 18Z 5 Apr 2009 25 to 30 mph 10 Meter Maximum Wind (MPH) From Any Member National Weather Service - Des Moines, IA 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 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 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 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 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 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 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 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 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 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 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 00Z-18Z 5 Apr 2009 National Weather Service - Des Moines, IA Regional Radar Loop National Weather Service - Des Moines, IA 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 Final Snowfall Map National Weather Service - Des Moines, IA 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 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 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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