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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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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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Peter G. Veals, W. James Steenburgh, and Leah S. Campbell

toward the shoreline as LCAPE increases, with LPE greater near the shoreline than over Tug Hill. This effect reverses with high , suggesting that the effects of LCAPE are overwhelmed by the strong prevailing flow. During high periods, increasing LCAPE instead produces higher LPE rates, displaces the LPE maximum farther inland, and increases AE. Increased forcing for convection plausibly explains the higher LPE rates, and it is possible that it allows the precipitating clouds to survive farther

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

three Center for Severe Weather Research mobile radars operated during IOP2b, their deployment locations and scanning strategies provided little coverage east of Lake Ontario and are not used here. Welsh et al. (2015) describe observations collected by the University of Wyoming King Air W-band cloud radar during a portion of IOP2b, which will be the subject of a future paper. a. Micro Rain Radars (MRRs) To investigate transitions in storm structure over Tug Hill, we utilize observations collected

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Jake P. Mulholland, Jeffrey Frame, Stephen W. Nesbitt, Scott M. Steiger, Karen A. Kosiba, and Joshua Wurman

westerly following the passage of the aforementioned 500-hPa short-wave trough and the approach of a 700-hPa ridge from the west (see section 5a ). Multilake connections are commonly observed across the Great Lakes during instances of northwest BL flow in which a single snow/cloud band may be traced across as many as three lakes (e.g., Byrd et al. 1991 ; Sousounis and Mann 2000 ; Rodriguez et al. 2007 ). The Lake Ontario LLAP band persisted for over 20 h on 6–7 January 2014, even after the upstream

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