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Philip T. Bergmaier and Bart Geerts

across this boundary, especially during the intense archetype, because of stronger winds. Downstream over the lake, the cross-band baroclinity weakens and buoyancy (or thermal) forcing becomes more prominent, due to latent heating in cloud, mixing of heat from the surface layer, and cloud-top entrainment in a deepening convective BL. This allows the main updraft to deepen and the secondary circulation to become more symmetric, with two counterrotating vortices ( Fig. 19 ). This transition is more

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David A. R. Kristovich, Luke Bard, Leslie Stoecker, and Bart Geerts

often the result of the combined influence of both the local lake and upwind lakes [as evidenced by so-called lake-to-lake (L2L) bands; Rodriguez et al. 2007 ]. This study seeks to improve our understanding of these L2L interactions through analyzing some of the first detailed observations of lake-effect convection over Lake Erie influencing lake-effect snowbands over Lake Ontario. Lake-effect cloud bands extending from one of the Laurentian Great Lakes to another have been noted since early in the

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David A. R. Kristovich, Richard D. Clark, Jeffrey Frame, Bart Geerts, Kevin R. Knupp, Karen A. Kosiba, Neil F. Laird, Nicholas D. Metz, Justin R. Minder, Todd D. Sikora, W. James Steenburgh, Scott M. Steiger, Joshua Wurman, and George S. Young

, M. Hoshimoto , N. Orikasa , Y. Yamada , H. Mizuno , K. Hamazu , and H. Watanabe , 2004 : The characteristics and evolution of orographic snow clouds under weak cold advection . Mon. Wea. Rev. , 132 , 174 – 191 , doi: 10.1175/1520-0493(2004)132<0174:TCAEOO>2.0.CO;2 . 10.1175/1520-0493(2004)132<0174:TCAEOO>2.0.CO;2 Laird , N. F. , D. A. R. Kristovich , X. Z. Liang , R. W. Arritt , and K. Labas , 2001 : Lake Michigan lake breezes: Climatology, local forcing, and

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Justin R. Minder, Theodore W. Letcher, Leah S. Campbell, Peter G. Veals, and W. James Steenburgh

, we are motivated to better understand these mechanisms, both as a fundamental science question regarding the response of shallow convection to surface forcing, and also to aid in the critical evaluation of conceptual and numerical models used to forecast these high-impact storms. Here, we focus specifically on how convective clouds evolve as they transition onto land and rise over Tug Hill. Our primary observations come from an east–west transect (black dots in Fig. 1b ) of four vertically

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W. James Steenburgh and Leah S. Campbell

complimentary contributions in lake-effect situations” (p. 1039). The relative contributions of differential thermal and roughness forcing are, however, situationally dependent. In real-data numerical simulations of snowbands over the English Channel and Irish Sea, Norris et al. (2013) found that differential roughness (and orography) was less important than thermal forcing for band formation, but did affect location and morphology. Idealized numerical simulations suggest land-breeze-forced ascent during

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Philip T. Bergmaier and Bart Geerts

lower boundary layer over the water. Over time (or with “fetch”), the depth of the boundary layer increases, either through continued modification by the lake or by other processes such as thermally driven surface convergence or even synoptic forcing, to the point that clouds and precipitation form. Over the North American Great Lakes, a lake-to-850-hPa temperature difference of at least 13 K (i.e., the dry adiabatic lapse rate) is typically required for the development of LE precipitation ( Holroyd

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Philip T. Bergmaier, Bart Geerts, Leah S. Campbell, and W. James Steenburgh

-level moisture convergence is sustained by solenoidal forcing. Numerical simulations have shown a lake-scale solenoidal circulation in LLAP bands ( Ballentine et al. 1998 ). The present study is the first, to our knowledge, to document this circulation with detailed observations in the vertical plane across a LLAP band. In this paper, we examine the secondary solenoidal circulation within a LLAP band observed during intensive observing period 2b (IOP2b) of the Ontario Winter Lake-effect Systems (OWLeS

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Scott M. Steiger, Tyler Kranz, and Theodore W. Letcher

typical organizations] occur when a continental/maritime polar (cP/mP) air mass is modified via heat and moisture fluxes by a large body of water (in this case, Lake Ontario), leading to the development of moist convection. The surface-based convective cloud tops generally range between 1 and 4 km above ground level (AGL), and the storms form in bands that are approximately 10–25 km wide and parallel to the mean boundary layer wind direction. b. Lake-effect lightning Winter lightning has been observed

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Leah S. Campbell and W. James Steenburgh

producing orographic precipitation enhancement during lake-effect storms have yet to be fully elucidated. Minder et al. (2015) summarize some potential mechanisms for the precipitation maxima found over topographic features during lake-effect storms. These mechanisms include the following: 1) lifting of the inversion layer and subsequent invigoration of convection through increased updraft speed and/or cloud depth (e.g., Murakami et al. 1994 ), 2) broadening of the scale of existing convective cells

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Dan Welsh, Bart Geerts, Xiaoqin Jing, Philip T. Bergmaier, Justin R. Minder, W. James Steenburgh, and Leah S. Campbell

advection of cooler air not modified by the lake, aids in layer lifting. Additionally, frictional convergence during the lake-to-land transition and remnants of the cross-band thermally direct circulation over the lake may also aid in ascent over land. A separation of the individual contributions of these processes is impossible, yet in concert these processes cause widespread lifting, referred to collectively as stratiform ascent, leading to low-level clouds over land, and supporting snow growth. Fig

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