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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

the 7–9 January event is given in section 3 . Section 4 presents the airborne radar observations and a comparison of these observations with corresponding model cross sections. A model analysis of the mesoscale forcing and inland penetration of the band is given in section 5 . The results of the study are discussed and summarized in sections 6 and 7 , respectively. 2. Data and methods a. Airborne measurements A significant portion of this study focuses on airborne radar data from the

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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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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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Seth Saslo and Steven J. Greybush

events by altering wind fields and creating local orographic lift ( Onton and Steenburgh 2001 ; Alcott and Steenburgh 2013 ). This can result in localized precipitation enhancement ( Veals and Steenburgh 2015 ), although the mechanisms associated with this are still under investigation ( Minder et al. 2015 ; Campbell et al. 2016 ). It follows that an accurate LES precipitation forecast needs to account for large-scale synoptic forcing, as well as local features and mesoscale variables. As a result

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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

(WCR) dual-Doppler analysis showed a solenoidal circulation pattern with near-surface convergence over each lake, buoyant updrafts about 1 km deep, and divergence aloft ( Bergmaier and Geerts 2016 ). Near the downwind shores light snowfall became more widespread as a result of orographic ascent and band interactions with more complex terrain. OBSERVED PROCESSES AND PHENOMENA. Mesoscale band circulation patterns. Previous studies have found that surface buoyant forcing over the relatively warm

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

( Sinclair et al. 1997 ; Neiman et al. 2002 ). Similar to the effects of mesoscale and synoptic-scale forcing on orographic precipitation, the mesoscale organization of lake-effect precipitation systems may affect the ratio of upland to lowland LPE. Single, organized bands (LLAP and shoreline) generally feature the most intense LPE rates and ascent, and the location of their associated LPE/ascent maxima may supersede any orographically induced ascent to produce a lowland LPE maximum or a nearly equal

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Daniel T. Eipper, Steven J. Greybush, George S. Young, Seth Saslo, Todd D. Sikora, and Richard D. Clark

extends farther inland than its thermodynamic forcing. This pattern suggests a Lagrangian evolution of the band’s mesoscale circulation in which the thermal contrast across the band (i.e., the thermal forcing) equilibrates sooner than does the kinematic response, as can be expected from conservation of momentum. Notwithstanding this temporal/spatial lag, the kinematic circulation nevertheless weakens with distance inland so that the band’s reflecitivity structure is eventually dominated by upper

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Leah S. Campbell and W. James Steenburgh

strengthened the precipitation maximum over Tug Hill. 7. Conclusions Using WRF simulations, this study has examined the mechanisms responsible for the lake-effect precipitation maximum observed over Tug Hill during IOP2b of the Ontario Winter Lake-effect Systems (OWLeS) field campaign. Our analysis shows that both nonorographic and orographic mechanisms contribute to the maximum, including the mesoscale forcing produced along a quasi-stationary land-breeze front (LBF2), precipitation enhancement processes

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

of convective vertical motions have been found for other cases in which air moved over a relatively warm surface. Nonlocal entrainment would be expected to increase as a result of nonlocal surface thermal forcing (i.e., intensified vertical motions enhancing mixing at the PBL top; e.g., Stull 1988 ; Young and Sikora 2003 ; etc.), consistent with the observed deepening of the OPBL. In principle, a gravity wave train could be generated by surface changes upwind of the shore (such as over Lake

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