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Joseph P. Zagrodnik, Lynn A. McMurdie, and Robert A. Houze Jr.

1. Introduction The west coast of North America is frequented by landfalling extratropical cyclones from the Pacific Ocean during the fall through early spring. When these storms pass over coastal mountain ranges, they produce copious precipitation on the windward slopes, frequently contributing to hazards such as flooding and landslides. These storms are also responsible for the accumulation of snow at higher elevations, which is crucial for summer water supply. Understanding the processes

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Robert A. Houze Jr., Lynn A. McMurdie, Walter A. Petersen, Mathew R. Schwaller, William Baccus, Jessica D. Lundquist, Clifford F. Mass, Bart Nijssen, Steven A. Rutledge, David R. Hudak, Simone Tanelli, Gerald G. Mace, Michael R. Poellot, Dennis P. Lettenmaier, Joseph P. Zagrodnik, Angela K. Rowe, Jennifer C. DeHart, Luke E. Madaus, Hannah C. Barnes, and V. Chandrasekar

. Wick , J. D. Lundquist , and M. D. Dettinger , 2008 : Meteorological characteristics and overland precipitation impacts of atmospheric rivers affecting the west coast of North America based on eight years of SSM/I satellite observations . J. Hydrometeor. , 9 , 22 – 47 , doi: 10.1175/2007JHM855.1 . 10.1175/2007JHM855.1 Painter , T. H. , and Coauthors , 2016 : The Airborne Snow Observatory: Fusion of scanning lidar, imaging spectrometer, and physically-based modeling for mapping snow

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Robert Conrick and Clifford F. Mass

mesoscale conditions varying substantially between storm sectors (prefrontal, warm sector, and postfrontal). Because IVT was realistically simulated by the University of Washington (UW) WRF during OLYMPEX (Conrick and Mass 2018, manuscript submitted to J. Hydrometeor. ), we define storm sectors in terms of IVT as in McMurdie et al. (2018) , using values from the North American Regional Reanalysis (NARR; Mesinger et al. 2006 ) grid point nearest to the OLYMPEX NASA S-Band Dual Polarimetric (NPOL

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Hannah C. Barnes, Joseph P. Zagrodnik, Lynn A. McMurdie, Angela K. Rowe, and Robert A. Houze Jr.

( Pobanz et al. 1994 ). KH waves have been observed within midlatitude baroclinic systems in various geographic regions, including off the East Coast of the United States ( Wakimoto et al. 1992 ), the North American Great Plains (e.g., Friedrich et al. 2008 ; Houser and Bluestein 2011 ), and mountainous regions in Europe ( Houze and Medina 2005 ) and the United States (e.g., Geerts and Miao 2010 ; Medina and Houze 2016 ). A large proportion of these studies observed KH waves within or near the

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Robert Conrick and Clifford F. Mass

modest atmospheric river that reached the Olympic Peninsula. The 850-hPa synoptic chart at 1200 UTC 13 November ( Fig. 9a ) indicates a low over the Gulf of Alaska, with strong (45 kt; 1 kt ≈ 0.51 m s −1 ) 850-hPa flow impacting the west coast of North America. The warm sector of this system was characterized by high IVT and a moist–neutral environment, with substantial vertical shear in the lower troposphere ( Fig. 9b ). Following cold frontal passage, precipitation intensity declined in the

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Zeinab Takbiri, Ardeshir Ebtehaj, Efi Foufoula-Georgiou, Pierre-Emmanuel Kirstetter, and F. Joseph Turk

phase detection capabilities over snow-covered surfaces ( Fig. 8 ). The probability of hit for the liquid, mixed, and the solid phase is mostly greater than 0.85 and reaches 0.95 over the high altitudes of North America. However, we observe a relatively lower detection rate of around 0.74 for liquid precipitation over the tropical and subtropical regions such as the rain forest of Amazonian and central Africa. The results show that the low probability of detection for the liquid phase is mostly

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Robert Conrick, Clifford F. Mass, and Qi Zhong

University boundary layer scheme ( Hong et al. 2006 ). Following Barnes et al. (2018) , the NCEP North American Regional Reanalysis (NARR; Mesinger et al. 2006 ) was used to evaluate the simulated synoptic conditions for the two case studies. Figure 2 presents a map of the OLYMPEX observing locations used in this study and the regional terrain. Barnes et al. (2018) and Houze et al. (2017) described the OLYMPEX instrumentation used to observe KH waves, including the NASA polarimetric (NPOL) radar

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Qian Cao, Thomas H. Painter, William Ryan Currier, Jessica D. Lundquist, and Dennis P. Lettenmaier

retrospective forcing in the North American Land Data Assimilation System (NLDAS) project . J. Geophys. Res. , 108 , 8842 , https://doi.org/10.1029/2002JD003118 . Currier , W. R. , T. Thorson , and J. D. Lundquist , 2017 : Independent evaluation of frozen precipitation from WRF and PRISM in the Olympic Mountains . J. Hydrometeor. , 18 , 2681 – 2703 , https://doi.org/10.1175/JHM-D-17-0026.1 . 10.1175/JHM-D-17-0026.1 Daly , C. , R. Neilson , and D. Phillips , 1994 : A statistical topographic

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Joseph P. Zagrodnik, Lynn A. McMurdie, Robert A. Houze Jr., and Simone Tanelli

so that the columns add up to 100%. The variability among storm sectors is readily apparent in the infrared satellite images and overlaid 500-hPa contours shown in Fig. 3 from each of the nine flights used in this study. The three subsections below describe the synoptic conditions that were used to classify the flights into prefrontal ( Figs. 3a–c ), warm sector ( Figs. 3d–f ), and postfrontal ( Figs. 3g–i ) sectors. Fig . 3. GOES-West infrared imagery (filled contours; °C) and North American

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Mircea Grecu, Lin Tian, Gerald M. Heymsfield, Ali Tokay, William S. Olson, Andrew J. Heymsfield, and Aaron Bansemer

electromagnetic-scattering models and use an efficient database-navigation procedure to inversely relate observed radar reflectivities to PSDs. The PSDs are derived from measurements by a two-dimensional stereo probe (2D-S; Lawson et al. 2006 ) and two orthogonally mounted High Volume Precipitation Spectrometers (HVPS-3) on board the University of North Dakota (UND) Cessna Citation airplane during OLYMPEX ( Houze et al. 2017 ) and IPHEX ( Barros et al. 2014 ) using the method of Heymsfield et al. (2018

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