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Case 1: 4-5 February 1995 snowstorm

Nicosia, D.J., and R.H. Grumm, 1999: Mesoscale Band Formation in Three Major Northeastern United States Snowstorms. Wea. Forecasting , 14 , 346–368. Case 1: 4-5 February 1995 snowstorm. Case 2: 14-15 November 1995 snowstorm. Snowfall in cm. Snowfall in cm.

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Case 1: 4-5 February 1995 snowstorm

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  1. Nicosia, D.J., and R.H. Grumm, 1999: Mesoscale Band Formation in Three Major Northeastern United States Snowstorms.Wea. Forecasting, 14, 346–368.

  2. Case 1: 4-5 February 1995 snowstorm Case 2: 14-15 November 1995 snowstorm Snowfall in cm Snowfall in cm Case 3: 12-13 January 1996 snowstorm Snowfall in cm

  3. Case 1: 4-5 February 1995 snowstorm Case 2: 14-15 November 1995 snowstorm Case 3: 12-13 January 1996 snowstorm Example radar reflectivity display for each case study showing mesoscale bands

  4. Meso Eta forecast – initial time 00 UTC 4 Feb 95 6 hr forecast 12 hr forecast 18 hr forecast 24 hr forecast 300-hPa heights (dark, 120-m interval), and 1000-hPa heights (light, 30-m interval) Case 1: 4-5 February 1995 snowstorm

  5. Meso Eta forecast – initial time 00 UTC 4 Feb 95 0 hr forecast 6 hr forecast Note developing frontogenesis region north of the cyclone center followed by frontolysis 12 hr forecast 24 hr forecast 700-hPa heights (heavy contours, 30-m interval) and 700-hPa frontogenetic function [light contours, contour interval 2 K (100 km)−1 (3 h)−1]: (solid) frontogenesis, (dashed) frontolysis. Case 1: 4-5 February 1995 snowstorm

  6. Meso Eta forecast – initial time 00 UTC 4 Feb 95 0 hr forecast 6 hr forecast Note negative EPV in region of strong frontogenesis Indicative of CSI Coincident with region of mesoscale band on 4 Feb 95 12 hr forecast 24 hr forecast frontogenetic function [heavy contours, contour interval 1 K (100 km)−1 (3 h)−1] saturation equivalent potential temperature (dashed, contour interval 2 K) equivalent potential vorticity [negative values shaded, shading interval of 3 × 10−7 K (Pa s)−1 Case 1: 4-5 February 1995 snowstorm

  7. Meso Eta forecast – initial time 15 UTC 14 Nov 95 3 hr forecast 12 hr forecast 21 hr forecast 18 hr forecast 300-hPa heights (dark, 120-m interval), and 1000-hPa heights (light, 30-m interval) Case 2: 14-15 November 1995 snowstorm

  8. Meso Eta forecast – initial time 15 UTC 14 Nov 95 3 hr forecast 12 hr forecast Note developing frontogenesis region north of the cyclone center followed by frontolysis 18 hr forecast 700-hPa heights (heavy contours, 30-m interval) and 700-hPa frontogenetic function [light contours, contour interval 2 K (100 km)−1 (3 h)−1]: (solid) frontogenesis, (dashed) frontolysis. Case 2: 14-15 November 1995 snowstorm

  9. Meso Eta forecast – initial time 15 UTC 14 Nov 95 3 hr forecast 12 hr forecast Note negative EPV in region of strong frontogenesis Indicative of CSI Coincident with region of mesoscale band on 4 Feb 95 18 hr forecast frontogenetic function [heavy contours, contour interval 1 K (100 km)−1 (3 h)−1] saturation equivalent potential temperature (dashed, contour interval 2 K) equivalent potential vorticity [negative values shaded, shading interval of 3 × 10−7 K (Pa s)−1 Case 2: 14-15 November 1995 snowstorm

  10. Meso Eta forecast – initial time 15 UTC 12 Jan 96 3 hr forecast 6 hr forecast 9 hr forecast 12 hr forecast 300-hPa heights (dark, 120-m interval), and 1000-hPa heights (light, 30-m interval) Case 3: 12-13 January 1996 snowstorm

  11. Meso Eta forecast – initial time 15 UTC 12 Jan 96 0 hr forecast 6 hr forecast Note developing frontogenesis region north of the cyclone center followed by frontolysis 12 hr forecast 24 hr forecast 700-hPa heights (heavy contours, 30-m interval) and 700-hPa frontogenetic function [light contours, contour interval 2 K (100 km)−1 (3 h)−1]: (solid) frontogenesis, (dashed) frontolysis. Case 3: 12-13 January 1996 snowstorm

  12. Meso Eta forecast – initial time 15 UTC 12 Jan 96 3 hr forecast 6 hr forecast Note negative EPV in region of strong frontogenesis Indicative of CSI Coincident with region of mesoscale band on 4 Feb 95 12 hr forecast 18 hr forecast frontogenetic function [heavy contours, contour interval 1 K (100 km)−1 (3 h)−1] saturation equivalent potential temperature (dashed, contour interval 2 K) equivalent potential vorticity [negative values shaded, shading interval of 3 × 10−7 K (Pa s)−1

  13. Meso Eta forecast – initial time 15 UTC 12 Jan 96 6 hr forecast 1800 UTC 4 Feb 95 12 hr forecast 0300 UTC 15 Nov 95 Case 1: 4-5 February 1995 snowstorm Case 2: 14-15 November 1995 snowstorm 6 hr forecast 2100 UTC 12 Jan 96 Where does negative EPV come from? In model negative EPV is generated at leading edge of dry slot. Case 3: 12-13 January 1996 snowstorm Generation of equivalent potential vorticity (K2 m−2) (negative dashed, contour every 1 × 10−11) at 500 hPa, 500-hPa winds barbs (kt) 500-hPa relative humidity greater than 60% (shaded) from the Meso Eta.

  14. The ageostrophic vertical circulation about fronts cannot generate EPV In frictionless, adiabatic flow is conserved and in saturated flow , is conserved. Ageostrophic Circulation rotates pattern but does not generate SCAPE. Tilt of boxes will change, but area (EPV) will not Generation of negative EPV: Frictional generation Generation of EPV Diabatic generation What is this term?

  15. Thermal wind (shear vector) Advection of two fields during frontogenesis will differ. Since EPV is sensitive to moisture distribution, EPV can change locally as moister or drier air is moved into a region.

  16. Process by which CSI is generated. Conceptual model depicting the frontogenesis region and zone of equivalent potential vorticity reduction within the context of the major components of a developing extratropical cyclone.

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