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David Novak

An Investigation of Model-Simulated Band Placement and Evolution in the 25 December 2002 Northeast U.S. Banded Snowstorm. David Novak

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David Novak

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  1. An Investigation of Model-Simulated Band Placement and Evolution in the 25 December 2002 Northeast U.S. Banded Snowstorm David Novak NOAA/ NWS Eastern Region Headquarters, Scientific Services Division, Bohemia, New York Stony Stony Brook University, State University of New York, Stony Brook, New York Brian Colle Stony Brook University, State University of New York, Stony Brook, New York Daniel Keyser University at Albany, State University of New York, Albany, New York

  2. Previous Work Compare Eta, MM5, and WRF forecasts to observations • Models initialized with EDAS at 0000 UTC 25 Dec 2002 • 36/12/4 km one-way nest for MM5/WRF

  3. MSLP Time Series

  4. 1800 UTC 12 km MM5 12 km WRF • Simulated Radar Reflectivity (shaded, dBZ) • 700-hPa height (thick solid, m) • 700-hPa 2D Miller Frontogenesis (thin solid, °C 100 km-1 h-1)

  5. 2000 UTC 12 km MM5 12 km WRF • Simulated Radar Reflectivity (shaded, dBZ) • 700-hPa height (thick solid, m) • 700-hPa 2D Miller Frontogenesis (thin solid, °C 100 km-1 h-1)

  6. 2200 UTC 12 km MM5 12 km WRF • Simulated Radar Reflectivity (shaded, dBZ) • 700-hPa height (thick solid, m) • 700-hPa 2D Miller Frontogenesis (thin solid, °C 100 km-1 h-1)

  7. 0000 UTC 12 km MM5 12 km WRF • Simulated Radar Reflectivity (shaded, dBZ) • 700-hPa height (thick solid, m) • 700-hPa 2D Miller Frontogenesis (thin solid, °C 100 km-1 h-1)

  8. 2000 UTC 4 km MM5 4 km WRF • 700-hPa 2D Miller Frontogenesis (shaded, °C 100 km -1 h-1) • 700-hPa temperature (thick solid, C) • 700-hPa wind barbs

  9. Motivation • Why did the MM5 and WRF models forecast the band too far to the southeast? • Is the deformation/frontogenesis farther northwest? • Can the modeled sharp 700-hPa trough and attendant intense frontogenesis be verified? • What accounts for the different band evolution forecasts in the WRF and MM5? • MM5: one single band that dissipates early • WRF: correct event length but two separate bands

  10. Analyses and Observations • RUC and EDAS used for analysis, with supplemental tropospheric observations

  11. Analyses and Observations 18 UTC 700 mb Height (red, 15 m) 700 mb Temp (shaded, 2°C) Analysis Winds (white barb) Observed Winds (black barb) RUC

  12. RUC vs. EDAS 18 UTC EDAS RUC

  13. Analyses and Observations 19 UTC 700 mb Frontogenesis (red, °C 100 km-1 h-1) 700 mb Temp (shaded, 2°C) Analysis Winds (white barb) Observed Winds (black barb) RUC

  14. Analyses and Observations 22 UTC 700 mb Frontogenesis (red, °C 100 km-1 h-1) 700 mb Temp (shaded, 2°C) Analysis Winds (white barb) Observed Winds (black barb) RUC

  15. Analyses and Observations 00 UTC 700 mb Frontogenesis (red, °C 100 km-1 h-1) 700 mb Temp (shaded, 2°C) Analysis Winds (white barb) Observed Winds (black barb) RUC

  16. RUC vs. EDAS 00 UTC EDAS RUC

  17. MM5 and WRF 19 UTC MM5 WRF

  18. MM5 and WRF 22 UTC MM5 WRF

  19. MM5 and WRF 01 UTC MM5 WRF

  20. Features of Note • Sharp 700-hPa trough, attendant winds and frontogenesis can be verified • Trough and associated frontogenesis farther northwest than models forecast • Easterly flow forecast in WRF run over CT was not observed

  21. Potential Vorticity • PV is the product of the • Absolute vorticity • Static stability • High values of PV associated with • Cyclonic flow • High static stability • Low tropopause • Upper trough • Low values of PV associated with • Anticyclonic flow • Low static stability • High tropopause • Upper ridge Figures from Thorpe (1985) for Northern Hemisphere Slide courtesy Dr. Mike Brennen (NCSU)

  22. 12 UTC Dynamic Tropopause Pressure and winds on the PV=2 PVU surface (shaded) MM5 WRF

  23. 15 UTC Dynamic Tropopause MM5 WRF

  24. 16 UTC Dynamic Tropopause MM5 WRF

  25. 17 UTC Dynamic Tropopause MM5 WRF

  26. 18 UTC Dynamic Tropopause MM5 WRF

  27. 19 UTC Dynamic Tropopause MM5 WRF

  28. 20 UTC Dynamic Tropopause MM5 WRF

  29. 21 UTC Dynamic Tropopause MM5 WRF

  30. 22 UTC Dynamic Tropopause MM5 WRF

  31. 23 UTC Dynamic Tropopause MM5 WRF

  32. 00 UTC Dynamic Tropopause MM5 WRF

  33. 01 UTC Dynamic Tropopause MM5 WRF

  34. 02 UTC Dynamic Tropopause MM5 WRF

  35. PV and Latent Heating • PV generated below level of maximum heating • Warming increases static stability • Pressure falls  convergence  increases absolute vorticity PV- PV+ • Opposite occurs above level of maximum heating where PV is reduced • PV growth rate determined by vertical gradient of LHR Slide courtesy Dr. Mike Brennen (NCSU)

  36. Model PV - Reflectivity Comparison 12 UTC Pressure/winds on the DT (shaded) and reflectivity contoured > 32 dBZ MM5 WRF

  37. Model PV - Reflectivity Comparison 15 UTC MM5 WRF

  38. Model PV - Reflectivity Comparison 16 UTC MM5 WRF

  39. Model PV - Reflectivity Comparison 17 UTC MM5 WRF

  40. Model PV - Reflectivity Comparison 18 UTC MM5 WRF

  41. Model PV - Reflectivity Comparison 19 UTC MM5 WRF

  42. Model PV - Reflectivity Comparison 20 UTC MM5 WRF

  43. Model PV - Reflectivity Comparison 21 UTC MM5 WRF

  44. Model PV - Reflectivity Comparison 22 UTC MM5 WRF

  45. Model PV - Reflectivity Comparison 23 UTC MM5 WRF

  46. Model PV - Reflectivity Comparison 00 UTC MM5 WRF

  47. PV Cross Sections 21 UTC MM5 WRF

  48. 800-600 mb PV 21 UTC WRF MM5

  49. PV Findings • Model-simulated bands appear downwind of PV filaments • PV filaments appear to be created by diabatic processes occurring in southeast sector of cyclone • Simulated band evolution was particularly sensitive to diabatically-generated lower-tropospheric PV anomaly over Long Island

  50. Conclusions and Implications • Southeast band position error appears to be due to a misplacement of the sharp 700-hPa trough and associated frontogenesis • Although both the MM5 and WRF successfully predicted band formation, respective band evolution appears to be sensitive to convection occurring in the southeast sector of the cyclone • Suggests the likelihood of banding may be more predictable than exact timing, location, and evolution

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