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

, (d) 0700, (e) 0800, and (f) 0900 UTC 7 Jan 2014. As the short-wave trough departs the region to the northeast and the midlevel short-wave ridge approaches, BL winds back from northwest (NW) to west (W), forcing the Georgian Bay band northward ( Fig. 18 ). Eventually, the winds back sufficiently for the connection to be lost ( Fig. 18d ). The shear zone and associated string of misovortices over Lake Ontario may have been influenced by this connection, at least during a portion of this event

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

band organization is lesser or absent. This accentuates the role of lifting by these alternate mechanisms in the absence of strong convective forcing. Fig . 4. Data from radiosondes released nearly simultaneously from (a) Oswego, (b) SC, and (c) NR (locations shown in Fig. 2 ), plotted on a skew T –log p diagram. The wind is plotted on the right of each diagram (long barb = 5 m s −1 ). (d) Corresponding virtual potential temperature ( θ υ ) profiles. This research focuses on observations

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

of convection was largest near the lake shore and decreased inland to Tug Hill ( Figs. 13 , 14a–c , 15 ). These factors enabled precipitation rates to be nearly as high in the coastal lowlands as over Tug Hill ( Fig. 13a ). We note, however, that there is a weak downstream broadening of the LLAP bands, so that snowfall occurs over a larger area as one moves inland over Tug Hill. In contrast, during nonbanded periods, the mesoscale forcing is weaker and there is a clear increase in echo

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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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