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Snowfall was heavy, organized along a narrow swath northwest of the cyclone

Martin, J.E., 1998: The Structure and Evolution of a Continental Winter Cyclone. Part II: Frontal Forcing of an Extreme Snow Event. Mon. Wea. Rev. , 126 , 329–348. Lightning. Snowfall was heavy, organized along a narrow swath northwest of the cyclone. Key questions:

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Snowfall was heavy, organized along a narrow swath northwest of the cyclone

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  1. Martin, J.E., 1998: The Structure and Evolution of a Continental Winter Cyclone. Part II: Frontal Forcing of an Extreme Snow Event.Mon. Wea. Rev., 126, 329–348.

  2. Lightning Snowfall was heavy, organized along a narrow swath northwest of the cyclone Key questions: What dynamic processes forced the precipitation What instabilites led to the narrow banding and convection Total Snowfall Radar reflectivity and 2-5 km mean isentropes

  3. University of Wisconsin–Nonhydrostatic Modeling System Grid 1 (outer grid), grid 2 (middle grid), and grid 3 (inner grid) had horizontal resolutions of 160 km, 80 km, and 40 km Note the inner grid resolution: This grid in a numerical model determines the resolvable scale What types of circulations are resolved at 40 km?

  4. Simple Sine wave example with 40 km gridspacing 0 km 40 km 80 km 120 km Phenomena of 80 km wavelength: Phase is barely resolved, amplitude is lost

  5. Simple Sine wave example with 40 km grid spacing 0 km 200 km 400 km 600 km Phenomena of 400 km wavelength: Amplitude and Phase well resolved

  6. Lightning Key questions: What dynamic processes forced the broad area of precipitation? (question answerable) What instabilities led to the narrow banding and convection? (only inferences can be made based on environment) Total Snowfall Radar reflectivity and 2-5 km mean isentropes Half wavelength = 400 km (broad swath of snow well resolved) Wavelength of narrow bands < 80 km unresolved

  7. Measured snowfall Model Predicted snowfall

  8. The two dimensional frontogenesis function

  9. M and e dark shade PI, light CSI Negative PVe and e Frontogenesis Vertical velocity and RHwrt water

  10. Where the air came from… Parcel 1, originally located at 869 hPa, was lifted to 621 hPa between 0000 and 0600 UTC. Parcel 2 rose from 801 to 599 hPa and parcel 3 from 729 to 632 hPa during that same time interval. Question: was the air lifted so that potential instability was released?

  11. Model sounding from Little Rock Observed sounding from Little Rock Answer: Difficult to determine: distribution of instability very sensistive to initial moisture profile. Model and Little Rock sounding differed sufficiently that it was difficult to draw conclusions

  12. M and e dark shade PI, light CSI Negative PVe and e Frontogenesis Vertical velocity and RHwrt water

  13. Not provided in paper M and e dark shade PI, light CSI Negative PVe and e Vertical velocity and RHwrt water Frontogenesis

  14. Parcel 1 rose from 796 to 591 hPa (1.87 to 4.16 km) Parcel 2 rose from 844 to 622 hPa Parcel 3 rose from 864 to 653 hPa

  15. Model sounding from Paducah Observed sounding from Paducah All parcels were negatively buoyant when lifted using the model sounding but became freely convective when lifted from actual Paducah sounding

  16. The trough of warm air aloft (TROWAL) as defined here by the canyon in equivalent potential temperature

  17. Trajectories in this quadrant of deformation flow Trajectory of air moving relative to the Trowal structure

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