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A new snow forecasting technique

A new snow forecasting technique. Mike Evans. Outline. Background The technique Local Example - December 30, 2007 Local Example – February 17, 2003 Local Example – January 23, 2005 Local Example – February 14, 2007 Summary. New Technique from the U.S. / Canadian Great Lakes Workshop.

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A new snow forecasting technique

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  1. A new snow forecasting technique Mike Evans

  2. Outline • Background • The technique • Local Example - December 30, 2007 • Local Example – February 17, 2003 • Local Example – January 23, 2005 • Local Example – February 14, 2007 • Summary

  3. New Technique from the U.S. / Canadian Great Lakes Workshop • Being used at Great Lakes offices (MKE, GRR, DTX) • How well does it work here?

  4. F vectors – the change in the temperature gradient following a parcel (using the real wind)

  5. F vectors – In this case, the F vector is all Fn

  6. The magnitude of the Fn vector is frontogenesis

  7. F vectors – Fn vectors converge where frontogenesis forces upward motion

  8. Why look at Fn? Why not just omega? • Omega is dependent on forcing and stability (negative EPV and omega bulls-eyes are often co-located). • Stability is often difficult for models (especially elevated instability). • Forcing (F vector convergence) may be more consistent from run to run. • Fn vectors should highlight frontogenetical forcing zones, which have historically been big snow producing zones.

  9. The dendrite zone • Favored area for snow growth between -12 and -18 degrees C. • Previous techniques indicate that heavy snow areas can be identified by looking for strong upward motion in the dendrite zone.

  10. The new technique • Instead of looking for strong upward vertical motion (negative omega) in the dendrite zone, look for Fn convergence in the dendrite zone. • This technique has caught on at offices in the western and central Great Lakes. • How well does it work around here?

  11. One final note… • Recall from our winter weather drill that the displacement between frontogenesis and lift is dependent on stability. • Therefore, the displacement between Fn convergence and lift is dependent on stability.

  12. Example 1 – December 30, 2007 – 24 hr NAM valid 00z 12/31

  13. December 30, 2007 – 30 hr NAM valid 12/31 06z

  14. December 30, 2007 00z NAM 24-hr QPF valid 12/31 12z

  15. 24 hr cross-section Fn convergence and temperature

  16. 24 hr cross-section – omega and temperature

  17. 24 hour Plan view of Fn Convergence and temperature

  18. 24 hour plan view of omega and temperature

  19. 12 hr NAM valid 12/31 00z

  20. 18 hr NAM valid 12/31 06z

  21. 24 hr NAM 24 hr QPF valid 12/31 12z

  22. 18 hour Fn convergence and temperature

  23. 18 hr omega and temperature

  24. 18 hr plan view Fn convergence and temperature

  25. 18 hr plan view omega and temperature

  26. Radar 00z – 09z

  27. Snowfall

  28. Summary from the 1st case • The Fn vector convergence was north of the max forecast lift in the 24 hour forecast. • The Fn vector convergence showed more run to run consistency than the omega forecast. • The Fn vector convergence would have pointed to more snow, farther north in the earlier run, which was correct.

  29. Example #2 February 17, 2003 Presidents Day Storm

  30. Total Snowfall

  31. 42 hr 500 mb ht and pmsl valid 2/17 18z

  32. 48 hr NAM 24 hr qpf valid 2/18 00z

  33. 42 hr max lift and Fn convergence in the dendrite zone valid 2/17 18z

  34. 42 hr maximum Fn convergence in the dendrite zone valid 2/17 18z

  35. 42 hr maximum lift in the dendrite zone valid 2/17 18z

  36. 18 hr 500 mb height and pmsl valid 2/17 18z

  37. 18 hr 24 hr QPF valid 2/18 00z

  38. 18 hr max lift and Fn convergence in the dendrite zone valid 2/17 18z

  39. 18 hr Fn convergence in the dendrite zone valid 2/17 18z

  40. 18 hr maximum lift in the dendrite zone valid 2/17 18z

  41. President’s Day Summary • Model QPF trended north • Fn convergence / omega fields appeared to be more stable • Fn convergence and omega were co-located in the 42 hour forecast • The lift maximum was north of the Fn convergence maximum in the 18 hour forecast

  42. Example #3 – January 23, 2005

  43. January 22-23 total snowfall

  44. 24 hour forecast 500 mb heights and pmsl valid 1/23/00z

  45. 36 hr NAM 24 hr QPF valid 1/23 12z

  46. 24 hr NAM Fn convergence in the dendrite zone valid 1/23 00z is directly beneath the max lift)

  47. 24 hr maximum Fn convergence in the dendrite zone valid 1/23 00z

  48. 24 hr Maximum lift in the dendrite zone valid 1/23 00z

  49. 12 hour forecast 500 mb heights and pmsl valid 1/23/00z

  50. 18 hr NAM 24 hr QPF valid 1/23 12z

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