The Effects of Lake Michigan on Mature Mesoscale Convective Systems 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 Great Lakes Operational Meteorology Workshop Toronto, Ontario 23 March 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 behavior of MCSs when crossing the Great Lakes Frequency of Derechos MCC Occurrences 1986

Areal Coverage ≥45 dBZ I II III 0

Areal Coverage ≥45 dBZ 0

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

Purpose Present a climatology 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 the lake if they: –continued to meet the two aforementioned reflectivity criteria –produced at least one severe report n=110 Persist Dissipate

Intersection Time after Formation n=110 Persist Dissipate

Monthly Distributions n= °C 4.4°C10.8°C 18.9° C 21.6°C19.1° C Persist Dissipate

Hourly Distributions (UTC) n=110 Persist Dissipate

Synoptic-Scale Composites Constructed using 0000, 0600, 1200, 1800 UTC 1° 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 vs. Progressive Dynamic Progressive Johns (1993)

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

Progressive Persist vs. Dissipate 200-hPa Heights (dam), 200-hPa Winds (m s -1 ), 850-hPa Winds (m s -1 ) Persist Dissipate n=30n=32 m s −1 200-hPa 850-hPa

Progressive Persist vs. Dissipate n=32 n=30 CAPE (J kg -1 ), 0–6 km Shear (barbs; m s -1 ) Persist Dissipate n=30n=32 J kg −1 CAPE

7–8 June persist 4–5 June dissipate Case Studies

MCS 2105 UTC 7 June 08 - persist Source: UAlbany Archive 1600 UTC 4 June 05 - dissipate MCS Source: NOWrad Composites

Source: UAlbany Archive MCS Source: NOWrad Composites 2304 UTC 7 June 08 - persist 1800 UTC 4 June 05 - dissipate

Source: UAlbany Archive MCS Source: NOWrad Composites 0001 UTC 8 June 08 - persist 1900 UTC 4 June 05 - dissipate

Source: UAlbany Archive MCS Source: NOWrad Composites 0104 UTC 8 June 08 - persist 2000 UTC 4 June 05 - dissipate

Source: UAlbany Archive MCS Source: NOWrad Composites 0302 UTC 8 June 08 - persist 2200 UTC 4 June 05 - dissipate

2000 UTC 7 June 08 - persist SLP (hPa), Surface Temperature (  C), and Surface Mixing Ratio (>18 g kg -1 ) Source: UAlbany Archive MCS

SLP (hPa), Surface Temperature (  C), and Surface Mixing Ratio (>16 g kg -1 ) Source: UAlbany Archive MCS 1800 UTC 4 June 05 - dissipate

0000 UTC 8 June 08 - persist Source: 20-km RUC 2100 UTC 4 June 05 - dissipate 200-hPa Heights (dam), 200-hPa Winds (m s -1 ), 850-hPa Winds (barbs; m s -1 )

Source: 20-km RUC CAPE (J kg -1 ), 0–6 km Shear (barbs; m s -1 ) 0000 UTC 8 June 08 - persist2100 UTC 4 June 05 - dissipate Source: 20-km RUC

4-h  differences at 2300 UTC 7 June 08 - persist 975-hPa ∆  (K), 0–3-km Shear (m s -1 )∆  (K),  (K), Wind (m s -1 ) cold pool A A’ A A 1900 UTC 2300 UTC A Courtesy: M. Weisman Weisman and Rotunno (2004)

975-hPa ∆  (K), 0–3-km Shear (m s -1 ) cold pool A’ A A 2300 UTC A 905 hPa 4-h  differences at 2300 UTC 7 June 08 - persist

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

°C hPa T air, T water, p Buoy hPa ∆  (K), 0–3 km Shear (m s -1 )  T=6.2°C Source: NDBC Buoy meteogram

2-h  differences at 1900 UTC 4 June 05 - dissipate cold pool B B’ B B 1700 UTC 1900 UTC 975-hPa ∆  (K), 0–3-km Shear (m s -1 )∆  (K),  (K), Wind (m s -1 ) B

cold pool B’ B B 975-hPa ∆  (K), 0–3-km Shear (m s -1 ) B 935 hPa 2-h  differences at 1900 UTC 4 June 05 - dissipate

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

°C hPa T air, T water, p Buoy  T=2.1°C Source: NDBC Buoy meteogram 975-hPa ∆  (K), 0–3 km Shear (m s -1 )

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

Later Season Weak LLJ Differences Significant to 95th Percentile Surface-Inversion Climatology T 5m - T Sfc n=110 Persist Dissipate Source: NDBC

All Months Phase Space - Warm Season Source: NARR/NDBC n=110 Persist Dissipate

AMJ JAS Phase Space - Early Season Phase Space - Late Season n=46 n=64 Persist Dissipate Persist

Conclusions – Climatology MCSs persisted 43% of the time (47 of 110 MCSs) upon crossing Lake Michigan during warm seasons of 2002–2007 MCSs persisted and dissipated at a wide range of times after formation MCSs persisted during all months and hours but favored July and August and evening and overnight MCSs persisted with stronger 850-hPa winds and near- surface lake inversions, especially from April to July

Conclusions – Composites/Case Studies Compared to MCSs that dissipated, MCSs persisted in environments that contained: –stronger 200-hPa and 850-hPa jet streams –larger amounts of CAPE and 0–6-km shear –similar looking synoptic-scale patterns –stronger, deeper convective cold pools –more stable marine layers