1. Synoptic and Mesoscale Conditions associated with Persisting and Dissipating Mesoscale Convective Systems that Cross Lake Michigan Nicholas D. Metz and Lance F. Bosart Department of Atmospheric and Environmental Sciences University at Albany/SUNY, Albany, NY 12222 E-mail: nmetz@atmos.albany.edu Support provided by the NSF ATM–0646907 12th Northeast Regional Operational Workshop Albany, NY 3 November 2010

2. Motivation Johns and Hirt (1987) Augustine and Howard (1991) Great Lakes region is an area of frequent MCS (MCC and derecho) activity –Important to understand MCS behavior upon crossing the Great Lakes Frequency of Derechos MCC Occurrences 1986

3. NOWrad Areal Coverage ≥45 dBZ I II III 0

4. NOWrad Areal Coverage ≥45 dBZ 0

5. Background Graham et al. (2004) 68% 24% 8%

6. Purpose Present a climatological overview of MCSs that encountered Lake Michigan Examine composite analyses of MCS environments associated with persisting and dissipating MCSs Describe two MCSs, one that persisted and one that dissipated while crossing Lake Michigan, and place them into context of the climatology and composites

7. MCS Selection Criteria Warm Season (Apr–Sep) 2002–2007 MCSs in the study: –are ≥(100  50 km) on NOWrad composite reflectivity imagery –contain a continuous region ≥100 km of  45 dBZ echoes –meet the above two criteria for >3 h prior to crossing Lake Michigan 100 km 50 km

8. Climatology of MCSs MCSs persisted upon crossing Lake Michigan if they: –continued to meet the two aforementioned reflectivity criteria –produced at least one severe report n=110

9. 3.0°C 4.4°C10.8°C 18.9° C 21.6°C19.1°C Monthly Climatological Distributions n=110 LM LWT Climo

10. Hourly Climatological Distributions n=110

11. Synoptic-Scale Composites Constructed using 0000, 0600, 1200, 1800 UTC 1.0° GFS analyses Time chosen closest to intersection with Lake Michigan –If directly between two analysis times, earlier time chosen Composited on MCS centroid and moved to the average position

12. Dynamic Persist vs. Dissipate Persist Dissipate 200-hPa Heights (dam), 200-hPa Winds (m s -1 ), 850-hPa Winds (m s -1 ) n=17 n=31 m s −1 200-hPa 850-hPa

13. Dynamic Persist vs. Dissipate CAPE (J kg -1 ), 0–6 km Shear (barbs; m s -1 ) Persist Dissipate n=17 n=31 J kg −1 CAPE

14. Differences Significant to 99.9th Percentile 850-hPa Wind Climatology n=110 Source: NARR

15. Downstream CAPE/Shear Climatology n=54 Source: UAlbany sounding archive CAPE Differences Significant to 95th Percentile DTX

16. 18 June 2010 - persist 24 June 2003 - dissipate Case Studies – Bow Echoes 9 out of 13 bow echoes (69%) persisted compared with 47 out of 110 (43%) total MCSs in the climatology

17. MCS 1800 UTC 18 June 10 - persist Source: UAlbany Archive 1000 UTC 24 June 03 - dissipate MCS Source: NOWrad Composites

18. Source: UAlbany Archive MCS Source: NOWrad Composites 2000 UTC 18 June 10 - persist 1200 UTC 24 June 03 - dissipate

19. Source: UAlbany Archive MCS Source: NOWrad Composites 2200 UTC 18 June 10 - persist 1400 UTC 24 June 03 - dissipate

20. Source: UAlbany Archive MCS Source: NOWrad Composites 0000 UTC 18 June 10 - persist 1600 UTC 24 June 03 - dissipate

21. 2000 UTC 18 June 10 - persist SLP (hPa), Surface Temperature (  C), and Surface Mixing Ratio (>18 g kg -1 ) 20 23 26 29 32 18 08 04 12 16 cold pool boundary

22. 1200 UTC 24 June 03 - dissipate SLP (hPa), Surface Temperature (  C), and Surface Mixing Ratio (>18 g kg -1 ) 20 18 08 12 16 23 20 cold pool boundary

23. 2200 UTC 18 June 10 - persist Source: 20-km RUC 1400 UTC 24 June 03 - dissipate 200-hPa Heights (dam), 200-hPa Winds (m s -1 ), 850-hPa Winds (barbs; m s -1 )

24. CAPE (J kg -1 ), 0–6 km Shear (barbs; m s -1 ) 2200 UTC 18 June 10 - persist1400 UTC 24 June 03 - dissipate Source: 20-km RUC

25. cold pool B B’ B B 2000 UTC 2200 UTC ∆  (K),  (K), Wind (m s -1 ) 600 700 800 900 B 975-hPa ∆  (K), 0–3-km Shear (m s -1 ) 2-h  differences at 2200 UTC 18 June 10 - persist

26. B’ B ACARS sounding at 2208 UTC 18 June 10 - persist 900 hPa 975-hPa ∆  (K), 0–3 km Shear (m s -1 ) Descent sounding from Madison, WI

27. T, T d, p °C Rockford, Illinois meteogram - persist Source: UAlbany Archive 975-hPa ∆  (K), 0–3 km Shear (m s -1 ) hPa

28. °C Buoy 45007  T=2.9°C Source: NDBC Buoy meteogram - persist 975-hPa ∆  (K), 0–3 km Shear (m s -1 ) hPa T air, T water, p

29. Lake Interactions LWA – South Haven 2130 Z 2200 Z T, T d, p

30. 2-h  differences at 1300 UTC 23 June 03 - dissipate cold pool B B’ B B 1100 UTC 1300 UTC 975-hPa ∆  (K), 0–3-km Shear (m s -1 )∆  (K),  (K), Wind (m s -1 ) 600 700 800 900 B 12 Z - GRB

31. T, T d, p °C Oshkosh, Wisconsin meteogram - dissipate Source: UAlbany Archive 975-hPa ∆  (K), 0–3 km Shear (m s -1 ) hPa

32. °C Buoy 45007  T=3.4°C Source: NDBC Buoy meteogram - dissipate 975-hPa ∆  (K), 0–3 km Shear (m s -1 ) hPa T air, T water, p

33. Later Season Differences Significant to 99th Percentile Surface-Inversion Climatology T 5m - T Sfc n=97 Source: NDBC

34. Conclusions – Climatology/Composite MCSs persisted 43% of the time (47 of 110 MCSs) upon crossing Lake Michigan during warm seasons of 2002–2007 MCSs persisted during all months and hours but favored July and August and evening and overnight MCSs persisted with large downstream CAPE/shear and strong 850-hPa winds and near-surface lake inversions (non-bow echoes) MCSs persisted with a greater frequency as organizational structure increased

35. Conclusions – Case Studies Compared with the MCS that dissipated, the MCS that persisted had: –a deeper, more robust convective cold pool –a near-surface lake inversion of ~equal strength –increased downstream CAPE/shear and a stronger 850-hPa low- level jet stream In these case studies, (and with other bow echoes in the climatology), persistence/dissipation over Lake Michigan appears to be a function of environmental conditions and NOT interactions with Lake Michigan

36. Organizational Type n=110 33.3% 45.7% 69.2%