Outline

1. Examining the Role of Mesoscale Features in the Structure and Evolution of Precipitation Regions in Northeast Winter Storms Matthew D. Greenstein, Lance F. Bosart, and Daniel KeyserDepartment of Earth and Atmospheric SciencesUniversity at Albany, Albany, NY 12222 David J. NicosiaNational Weather ServiceBinghamton Weather Forecast Office, Johnson City, NY 13790 November 2, 2005

2. Outline • Introduction • Selection of cases • Precipitation patterns • Data analysis • Preliminary results • Additional thoughts • Future work

3. Introduction • Forecasters can predict likely areas of precipitation • Forecasters cannot always skillfully predict mesoscale precipitation signatures within these areas • Forecasting mesoscale details adds value to a forecast • Precipitation patterns have multiple modes (forms) • Goal is to examine the three main ingredients … • Moisture • Stability Regime • Lifting Mechanism • … that operate together to produce heavy snow in a variety of modes

4. Selection of Cases • Cases occur in area bounded by36.5°N, 50°N, 65°W, and 85°W • Within U.S. radar coverage • 1 October – 30 April • No warm sector precipitation • P–type predominantly snow • “Heavy snow” = 15+ cm in 12 h over an area the size of CT • No lake effect snows and enhancements • Past three winters (2002–3, 2003–4, 2004–5)

5. 20 Cases • 26–27 Nov 2003 • 4–6 Dec 2002 • 25–26 Dec 2002 • 2–5 Jan 2003 • 6–7 Feb 2003 • 15–18 Mar 2003 • 6 Mar 2003 • 5–8 Dec 2003 • 13–15 Dec 2003 • 14–15 Jan 2004 • 27–28 Jan 2004 • 16–17 Mar 2004 • 18–19 Mar 2004 • 19–20 Jan 2005 • 22–23 Jan 2005 • 24–25 Feb 2005 • 28 Feb–2 Mar 2005 • 8–9 Mar 2005 • 11–13 Mar 2005 • 23–24 Mar 2005

6. Precipitation Modes • Uniform • Fractured • Banded • – Solid bands (with or without gaps between them) • – Broken bands • – Band segments • During a storm life cycle and even at one time, multiple modes may be present • Blob-like • Grainy • Unclassified

7. Precipitation Modes: Uniform

8. Precipitation Modes: Fractured / Band Segments

9. Precipitation Modes: Broken Band

10. Precipitation Modes: Fractured

11. Precipitation Modes: Segments? Blobs? Grainy?

12. Data Analysis • 32–km North American Regional Reanalysis (NARR) • How to evaluate the stability regime? • Previous research: frontogenesis in the presence of weak moist symmetric stability yields bands • Negative saturation equivalent potential vorticity (EPV*) indicates slantwise and/or upright instability • Upright dominates slantwise instability • Debate continues on EPV* or EPV* • Stability diagnostic: EPV* < 0.25 PVU g

13. Data Analysis: Diagnostic plot • Depth of the EPV* < 0.25 PVU layer in hPa • Examine 50 hPa layers above 850 hPa • [Number of layers] x 50 hPa = Depth • CI overlay • If saturation equivalent potential temperature (Θes) decreases upward in a 50 hPa layer • 700 hPa Miller 2D frontogenesis overlay • What does this diagnostic plot show for banding cases?

14. Data Analysis: 0000 UTC 26 Dec 2002

15. Data Analysis: 0000 UTC 26 Dec 2002

16. Data Analysis: 1500 UTC 5 Dec 2002

17. Data Analysis: 1500 UTC 5 Dec 2002

18. Data Analysis: 2100 UTC 14 Dec 2003

19. Data Analysis: 2100 UTC 14 Dec 2003

20. Preliminary Results • Examined first 13 cases (2002–3 & 2003–4 winters) • No apparent correlation found between depth and mode • Band seems to be associated with EPV* depth gradients … but gradients still exist with other modes • Uniform: gradients, frontogenesis poleward of snow, almost no CI • CI  broken or fractured … but not the converse • Gradients not well defined for broken bands, band segments, and fractured modes • Fractured: no frontogenesis nearby • Bands with spaces between them have at least some CI

21. Additional Thoughts • This diagnostic approach roughly works, but … more ingredients are needed! • EPV* alone is not sufficient! Neither is EPV* + frontogenesis! • Combine STABILITY REGIME and MESOSCALE LIFTING MECHANISM (frontogenesis) with … • … SYNOPTIC-SCALE LIFTINGMECHANISMS… MOISTURE (mean layer RH?)… MICROPHYSICS (dendritic growth) • Synoptic-scale forcing • Warm advection  smoother • Differential cyclonic vorticity advection  more jagged

22. Future Work • Separate depths of weak moist symmetric stability (and instability) and CI • Depth of weak moist symmetric stability layer that satisfies omega and/or dendritic growth criteria • Depth of frontogenetical layer • Ratio of synoptic-scale forcings • Various overlay combinations of synoptic-scale forcing, frontogenesis, EPV* < 0.25 depth, omega, and dendritic growth criteria • Magnitude of EPV* < 0.25 depth gradient • Further investigate any EPV* depth / mode correlations

23. Ultimate Goal • Develop diagnostics for determining modes of heavy snow based on… • Synoptic-scale and mesoscale forcings • Stability regimes • Microphysics • Similar to tables for modes of convection (wind shear and CAPE parameters) • Possibility of transforming diagnostic into a Smart Tool for AWIPS

24. Special thanks to … • David Ahijevych (NCAR) for making gridded WSI NOWrad composite data available • Anantha Aiyyer (UAlbany) for help with FORTRAN scripts to work with gridded NARR data Questions? Comments? e-mail: greenstein@atmos.albany.edu