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Philip T. Bergmaier and Bart Geerts

(yellow arrow in Fig. 15e ). This is the convergent boundary seen south of the LLAP band in Figs. 8c,f . LBF2 separates warmer lake-modified air to the northwest from cooler air over land that has undergone hardly any upstream modification ( Figs. 14c,e ). Multiple weak CLs also develop over Lake Ontario to the north and west of the primary CL. They appear to be associated with horizontal convective rolls (HCRs). MODIS imagery (not shown) indicates that cloud streets were present over the western

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W. James Steenburgh and Leah S. Campbell

played an unexpectedly prominent role in simulations exploring orographic effects over Tug Hill ( Campbell and Steenburgh 2017 ). In the next section, we describe the datasets and modeling system used for our analysis. Sections 3 – 6 then use operational analyses, Weather Research and Forecasting (WRF) Model simulations, trajectories, and frontogenesis diagnostics to show how the large-scale flow, shape of the Lake Ontario shoreline, and differential surface heating and roughness contribute to the

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

cover all periods with dominant bands in OWLeS with the exception of the 15–16 December 2013 storm. Following the identification of these time periods, reanalysis simulations were generated for each period with the Weather Research and Forecasting (WRF) Model ( Skamarock et al. 2008 ). These reanalyses were generated by assimilating hourly in situ observations (e.g., operational surface, aircraft, and radiosonde data were assimilated; radar reflectivities and OWLeS field observations were not

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Peter G. Veals and W. James Steenburgh

Weather Service Cooperative Observer (COOP) data (1994–2014) increases from 83.7 cm (33.0 in.) at Watertown [WTN (151 m MSL)] just north of Tug Hill to 109 cm (42.9 in.) at Hooker [HKR (448 m MSL)] on Tug Hill (see Fig. 1 for locations). Mean September–May snowfall increases from 288 cm (113 in.) to 571 cm (225 in.), although these sites may not be well situated to identify the orographic precipitation gradient or the area of heaviest snowfall on Tug Hill. In addition to weather impacts

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

-effect forecasts by the National Weather Service and has important repercussions for public safety. Villani et al. (2017) conducted a detailed evaluation of statistical relationships between a number of atmospheric variables and the inland extent of LLAP bands. A key finding is that inland extent is strongly correlated with the band’s connection to an upwind Great Lake, indicating the important influence of upstream modification on LLAP-band inland extent. In addition, the authors develop a 14-variable

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Leah S. Campbell and W. James Steenburgh

constrained, however, by the inherent limitations of the observational datasets and were unable to fully investigate the potential enhancement mechanisms. This paper uses Weather Research and Forecasting (WRF) Model simulations to build on the findings of Minder et al. (2015) , Campbell et al. (2016) , and Welsh et al. (2016) to further our understanding of the mechanisms producing the Tug Hill precipitation maximum during OWLeS IOP2b. We describe the observational datasets and model configuration in

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

spectra . Mon. Wea. Rev. , 132 , 3019 – 3032 , doi: 10.1175/MWR2830.1 . 10.1175/MWR2830.1 Smirnova , T. G. , J. M. Brown , S. G. Benjamin , and J. S. Kenyon , 2016 : Modifications to the Rapid Update Cycle land surface model (RUC LSM) available in the Weather Research and Forecasting (WRF) Model . Mon. Wea. Rev. , 144 , 1851 – 1865 , doi: 10.1175/MWR-D-15-0198.1 . 10.1175/MWR-D-15-0198.1 Sousounis , P. J. , and G. E. Mann , 2000 : Lake-aggregate mesoscale disturbances. Part V

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Philip T. Bergmaier and Bart Geerts

1. Introduction Much attention has been devoted to understanding how large lakes (e.g., the North American Great Lakes) influence the weather and climate of the surrounding region. Lake-effect (LE) convection, which typically ensues when cold air masses migrate over relatively warmer open water during the fall and winter, often leads to heavy snowfall downwind of the lakes impacting local travel and commerce. More than a half century of research related to LE snowstorms has yielded significant

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

multiple authors, L2L bands can produce particularly intense snowfall over and near the downwind lake (i.e., Niziol et al. 1995 ; Sousounis and Mann 2000 ; Rodriguez et al. 2007 ; Ackerman et al. 2013 ). Mann et al. (2002) classified the influences of boundary layer modification from upwind lakes as either “direct” or “synergistic (indirect).” The latter type of influence, whereby regional-scale wind flows are altered by the influence of multiple Great Lakes, affects convective locations and

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

. Soc. , 112 , 335 – 345 , doi: 10.1002/qj.49711247204 . Colle , B. A. , Y. Lin , S. Medina , and B. F. Smull , 2008 : Orographic modification of convection and flow kinematics by the Oregon Coast Range and Cascades during IMPROVE-2 . Mon. Wea. Rev. , 136 , 3894 – 3916 , doi: 10.1175/2008MWR2369.1 . Colle , B. A. , R. B. Smith , and D. A. Wesley , 2013 : Theory, observations, and predictions of orographic precipitation. Mountain Weather Research and Forecasting: Recent

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