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: [email protected]Support provided by the NSF ATM–0646907 12th Northeast Regional Operational Workshop
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Nicholas D. Metz and Lance F. Bosart Department of Atmospheric and Environmental Sciences
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 - PowerPoint PPT Presentation
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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
• 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 IIIIII
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°C 10.8°C 18.9°C 21.6°C 19.1°C
Monthly Climatological Distributionsn=110
LM LWT Climo
Hourly Climatological Distributionsn=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
• 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