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 Support provided by the NSF ATM– th Northeast Regional Operational Workshop Albany, NY 3 November 2010

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

NOWrad Areal Coverage ≥45 dBZ I II III 0

NOWrad Areal Coverage ≥45 dBZ 0

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

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

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

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

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

Hourly Climatological Distributions n=110

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

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

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

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

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

18 June persist 24 June 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

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

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

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

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

2000 UTC 18 June 10 - persist SLP (hPa), Surface Temperature (  C), and Surface Mixing Ratio (>18 g kg -1 ) cold pool boundary

1200 UTC 24 June 03 - dissipate SLP (hPa), Surface Temperature (  C), and Surface Mixing Ratio (>18 g kg -1 ) cold pool boundary

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 )

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

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

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

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

°C Buoy  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

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

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 ) B 12 Z - GRB

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

°C Buoy  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

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

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

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

Organizational Type n= % 45.7% 69.2%