1. Assessing the Predictability of Band Formation and Evolution during Three Recent Northeast U.S. Snowstorms David R. Novak NOAA/ NWS Eastern Region Headquarters, Scientific Services Division, Bohemia, New York Stony Brook University, State University of New York, Stony Brook, New York Brian A. Colle Stony Brook University, State University of New York, Stony Brook, New York © New York Times

2. Motivation High-resolution models are capable of simulating mesoscale snowbands

3. 1800 UTC 25 Dec 2002 Dual Doppler 4 km MM5 Radar Reflectivity (shaded, dBZ) 3 km winds

4. 1815 UTC Dual Doppler 4 km MM5 Radar Reflectivity (shaded, dBZ) 3 km winds

5. 1830 UTC Dual Doppler 4 km MM5 Radar Reflectivity (shaded, dBZ) 3 km winds

6. 1845 UTC Dual Doppler 4 km MM5 Radar Reflectivity (shaded, dBZ) 3 km winds

7. 1900 UTC Dual Doppler 4 km MM5 Radar Reflectivity (shaded, dBZ) 3 km winds

8. 1915 UTC Dual Doppler 4 km MM5 Radar Reflectivity (shaded, dBZ) 3 km winds

9. 1930 UTC Dual Doppler 4 km MM5 Radar Reflectivity (shaded, dBZ) 3 km winds

10. 1945 UTC Dual Doppler 4 km MM5 Radar Reflectivity (shaded, dBZ) 3 km winds

11. 2000 UTC Dual Doppler 4 km MM5 Radar Reflectivity (shaded, dBZ) 3 km winds

12. 2015 UTC Dual Doppler 4 km MM5 Radar Reflectivity (shaded, dBZ) 3 km winds

13. 2030 UTC Dual Doppler 4 km MM5 Radar Reflectivity (shaded, dBZ) 3 km winds

14. 2045 UTC Dual Doppler 4 km MM5 Radar Reflectivity (shaded, dBZ) 3 km winds

15. 2100 UTC Dual Doppler 4 km MM5 Radar Reflectivity (shaded, dBZ) 3 km winds

16. Motivation High-resolution models are capable of simulating mesoscale snowbands An ensemble of high-resolution models may provide useful band predictability information However, in the words of Rich Grumm: “high- resolution deterministic forecasts can be highly detailed, but highly inaccurate.”

17. Objectives Demonstrate ability of a high-resolution ensemble to provide qualitative band predictability information during three recent snowstorms Explore sources of band uncertainty 25 Dec 2002 12 Feb 2006 14 Feb 2007

18. Ensemble Design -multi-model (MM5 v3 /WRF-ARW v 2.2) -multi-initial condition (GFS/NAM/SREF) -multi-physics (Microphysics/Convective) MemberModelIC/BCMicrophysicsConvectivePBL NAM-MM5MM5NAMSimpleGrellMRF GFS-MM5MM5GFSSimpleGrellMRF GFS-MM5-R2MM5GFSReisner2GrellMRF SREF_N1-MM5MM5SREF_N1SimpleGrellMRF SREF_N2-MM5MM5SREF_N2SimpleGrellMRF SREF_P1_MM5MM5SREF_P1SimpleGrellMRF SREF_P1- MM5-KFMM5SREF_P1SimpleKain FritchMRF SREF_P2-MM5MM5SREF_P2SimpleGrellMRF NAM-WRFWRFNAMWSM-3GrellMRF GFS-WRFWRFNAMWSM-3GrellMRF GFS-WRF-ThomWRFGFSThompsonGrellMRF SREF_N1-WRFWRFSREF_N1WSM-3GrellMRF SREF_N2-WRFWRFSREF_N2WSM-3GrellMRF SREF_P1_WRFWRFSREF_P1WSM-3GrellMRF SREF_P1- WRF-KFWRFSREF_P1WSM-3Kain FritchMRF SREF_P2-WRFWRFSREF_P2WSM-3GrellMRF Initialized 15-21 h prior to band formation

19. Band Definition Model band = simulated reflectivity feature which has an aspect ratio (length/width) of 4:1 or greater, with an intensity of at least 30 dBZ, maintained for at least 2 h. No BandBand

20. Feb 14 2007

21. 14 Feb 2007 Surface Cyclone Depth

22. ObservedEnsemble Storm Total Precipitation

23. Band Occurrence 16 of 16 members (100%) had bands at some time during event

24. Band Timing Band formation among members ranged from 14 UTC to 00 UTC Band dissipation among member ranged from 22 UTC to 3 UTC

25. Band Location Formation

26. Band Location Maturity

27. Band Location Dissipation

28. Feb 14 2007 Summary Band Characteristic SpreadConfidence Occurrence16/16 membersHigh Timing~ 8 hModerate Location~100 kmHigh

29. Dec 25 2002

30. 25 Dec 2002 Surface Cyclone Depth

31. ObservedEnsemble Storm Total Precipitation

32. Band Occurrence 15 of 16 members (94%) had bands at some time during event

33. Band Timing Band formation among members ranged from 17 to 23 UTC Band dissipation among members ranged from 20 UTC to 2 UTC

34. Band Location Formation

35. Band Location Maturity

36. Band Location Dissipation

37. 25 Dec 2002 Summary Band Characteristic SpreadConfidence Occurrence15/16 membersHigh Timing~6 hModerate Location~250 kmModerate

38. 12 Feb 2006

39. 12 Feb 2006 Surface Cyclone Depth

40. ObservedEnsemble Storm Total Precipitation

41. Band Occurrence 12 of 16 members (75%) had bands at some time during event

42. Band Timing Band formation among members ranged from 10 to 20 UTC Band dissipation among members ranged from 13 UTC to 0 UTC

43. Band Location Formation

44. Band Location Maturity

45. Band Location Dissipation

46. Band Location After Dissipation

47. 12 Feb 2006 Summary Band Characteristic SpreadConfidence Occurrence12/16 membersModerate Timing~9 hLow Location~400 kmLow

48. Band occurrence was favored in the ensemble for each case However the specific timing and location of the bands had considerable spread, especially in the 25 Dec 2002 and 12 Feb 2006 cases. Why?

49. Location Difference (GFS errored left, NAM errored right) 14 Feb 2007

50. 36 km NAM 0000 UTC GFS NAM - GFSR ~475 – 250 mb PV -1 0 1 2 3 4 PVU-1 0 1 2 3 4 -2 -1 0 1 PVU

51. 36 km NAM 0600 UTC GFS NAM - GFSR ~475 – 250 mb PV -1 0 1 2 3 4 PVU-1 0 1 2 3 4 -2 -1 0 1 PVU

52. 36 km NAM 1200 UTC GFS NAM - GFSR ~475 – 250 mb PV -1 0 1 2 3 4 PVU-1 0 1 2 3 4 -2 -1 0 1 2 PVU

53. 36 km NAM 1800 UTC GFS NAM - GFSR ~475 – 250 mb PV -1 0 1 2 3 4 PVU-1 0 1 2 3 4 -2 -1 0 1 2 PVU

54. Location Difference (SREF_N1 errored left, GFSR errored right) 25 Dec 2002

55. 36 km GFSR 0000 UTC SREF_N1 SREF_N1 - GFSR ~475 – 250 mb PV -1 0 1 2 3 PVU-1 0 1 2 3 4 -2 -1 0 1 PVU

56. 36 km GFSR 0600 UTC SREF_N1 SREF_N1 - GFSR ~475 – 250 mb PV -1 0 1 2 3 PVU-1 0 1 2 3 -2 -1 0 1 PVU

57. 36 km GFSR 1200 UTC SREF_N1 SREF_N1 - GFSR ~475 – 250 mb PV -1 0 1 2 3 PVU-1 0 1 2 3 -2 -1 0 1 PVU

58. 36 km GFSR 1800 UTC SREF_N1 SREF_N1 - GFSR -1 0 1 2 3 PVU-1 0 1 2 3 -2 -1 0 1 2 PVU

59. Location Difference (GFSR errored left, SREF-N1 errored far right) 12 Feb 2007

60. 36 km SREF_N1 1200 UTC GFS ~475 – 250 mb PV SREF - GFSR -1 0 1 2 3 4 PVU -2 -1 0 1 2 PVU -1 0 1 2 3 4

61. 36 km SREF_N1 1800 UTC GFS ~475 – 250 mb PV SREF - GFSR -1 0 1 2 3 4 PVU -2 -1 0 1 2 PVU -1 0 1 2 3 4

62. 36 km SREF_N1 0000 UTC GFS ~475 – 250 mb PV SREF - GFSR -1 0 1 2 3 4 PVU -2 -1 0 1 2 3 PVU -1 0 1 2 3 4

63. 36 km SREF_N1 0600 UTC GFS ~475 – 250 mb PV SREF - GFSR -1 0 1 2 3 4 PVU -2 -1 0 1 2 3PVU -1 0 1 2 3 4

64. 36 km 1200 UTC GFS ~475 – 250 mb PV SREF_N1 -1 0 1 2 3 4 PVU -2 -1 0 1 2 PVU -1 0 1 2 3 4 SREF - GFSR

65. Summary A simple 16-member 12-km multi-model,-initial condition, and -physics ensemble can identify favored time periods and corridors of band formation threat. Although band occurrence was favored in the ensemble for each case, the specific timing and location of the bands had considerable spread. -suggests that answering whether a band will occur may be easier to answer than when or where it will occur, even at 12-24 h forecast projections. Spread of variables differed markedly amongst the three cases – appeared to be related primarily to IC uncertainty. -suggests the largest improvements in band prediction may occur with targeted initial condition improvements.

66. Model Comparison

69. Spread Where is the spread coming from? -Examine 24 h forecast MSLP spread (max MSLP minus min MSLP) for each sub ensemble 25 Dec12 Feb14 FebMean IC10.0 mb8.5 mb11.09.8 mb Model6.4 mb2.1 mb3.6 mb4.0 mb Physics1.5 mb0.3 mb3.8 mb1.8 mb IC uncertainty dominates

70. MSLP Spread Method MemberModelIC/BCMicrophysicsConvectivePBL NAM-MM5MM5NAMSimpleGrellMRF GFS-MM5MM5GFSSimpleGrellMRF GFS-MM5-R2MM5GFSReisner2GrellMRF SREF_N1-MM5MM5SREF_N1SimpleGrellMRF SREF_N2-MM5MM5SREF_N2SimpleGrellMRF SREF_P1_MM5MM5SREF_P1SimpleGrellMRF SREF_P1- MM5-KFMM5SREF_P1SimpleKain FritchMRF SREF_P2-MM5MM5SREF_P2SimpleGrellMRF NAM-WRFWRFNAMWSM-3GrellMRF GFS-WRFWRFNAMWSM-3GrellMRF GFS-WRF-ThomWRFGFSThompsonGrellMRF SREF_N1-WRFWRFSREF_N1WSM-3GrellMRF SREF_N2-WRFWRFSREF_N2WSM-3GrellMRF SREF_P1_WRFWRFSREF_P1WSM-3GrellMRF SREF_P1- WRF-KFWRFSREF_P1WSM-3Kain FritchMRF SREF_P2-WRFWRFSREF_P2WSM-3GrellMRF IC Spread= (MSLP spread of MM5 members with simple ice and Grell physics) + (MSLP spread of WRF members with simple ice and Grell physics) / 2 Members involved in calculation are highlighted

71. MSLP Spread Method MemberModelIC/BCMicrophysicsConvectivePBL NAM-MM5MM5NAMSimpleGrellMRF GFS-MM5MM5GFSSimpleGrellMRF GFS-MM5-R2MM5GFSReisner2GrellMRF SREF_N1-MM5MM5SREF_N1SimpleGrellMRF SREF_N2-MM5MM5SREF_N2SimpleGrellMRF SREF_P1_MM5MM5SREF_P1SimpleGrellMRF SREF_P1- MM5-KFMM5SREF_P1SimpleKain FritchMRF SREF_P2-MM5MM5SREF_P2SimpleGrellMRF NAM-WRFWRFNAMWSM-3GrellMRF GFS-WRFWRFNAMWSM-3GrellMRF GFS-WRF-ThomWRFGFSThompsonGrellMRF SREF_N1-WRFWRFSREF_N1WSM-3GrellMRF SREF_N2-WRFWRFSREF_N2WSM-3GrellMRF SREF_P1_WRFWRFSREF_P1WSM-3GrellMRF SREF_P1- WRF-KFWRFSREF_P1WSM-3Kain FritchMRF SREF_P2-WRFWRFSREF_P2WSM-3GrellMRF Model Spread= [(NAM-MM5 minus NAM-WRF)+(GFS-MM5 minus GFS-WRF) + (GFS-MM5-R2 minus GFS-WRF-R2) + (SREF_N1-MM5 minus SREF_N1-WRF)+etc..] / 8 Members involved in calculation are highlighted

72. MSLP Spread Method MemberModelIC/BCMicrophysicsConvectivePBL NAM-MM5MM5NAMSimpleGrellMRF GFS-MM5MM5GFSSimpleGrellMRF GFS-MM5-R2MM5GFSReisner2GrellMRF SREF_N1-MM5MM5SREF_N1SimpleGrellMRF SREF_N2-MM5MM5SREF_N2SimpleGrellMRF SREF_P1_MM5MM5SREF_P1SimpleGrellMRF SREF_P1- MM5-KFMM5SREF_P1SimpleKain FritchMRF SREF_P2-MM5MM5SREF_P2SimpleGrellMRF NAM-WRFWRFNAMWSM-3GrellMRF GFS-WRFWRFNAMWSM-3GrellMRF GFS-WRF-ThomWRFGFSThompsonGrellMRF SREF_N1-WRFWRFSREF_N1WSM-3GrellMRF SREF_N2-WRFWRFSREF_N2WSM-3GrellMRF SREF_P1_WRFWRFSREF_P1WSM-3GrellMRF SREF_P1- WRF-KFWRFSREF_P1WSM-3Kain FritchMRF SREF_P2-WRFWRFSREF_P2WSM-3GrellMRF Physics Spread= [(GFS-MM5 minus GFS-MM5-R2)+(GFS-WRF minus GFS-WRF-Thom)+(SREF_P1-MM5 minus SREF_P1- KF)+(SREF_P1-WRF minus SREF_P1-WRF-KF)] / 4 Members involved in calculation are highlighted