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Joseph P. Zagrodnik, Lynn McMurdie, and Robert Conrick

saturated everywhere on the coast and windward slopes, except for a few isolated pockets such as the interior Quinault Valley. In the next section, we demonstrate that these profound differences in low-level vertical motions and moisture have major implications for the microphysical precipitation processes in these regions. 5. Microphysical composites Figures 8b–d and 10b–d show SW–NE composite cross sections of the average cloud water + cloud ice mixing ratio ( Figs. 11a,b ), average rainwater

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Robert Conrick and Clifford F. Mass

disdrometers was documented by Jaffrain and Berne (2011) , who demonstrated that number concentration uncertainty was less than 5% and D 0 uncertainty less than 7% at temporal averages exceeding 10 min. Thus, there is confidence that the observing systems used in this study are sufficiently accurate for model evaluation. 3. Results of OLYMPEX wintertime simulations a. Fidelity of incoming moisture flux during the OLYMPEX project Before evaluating model microphysics, it is important to evaluate the

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David J. Purnell and Daniel J. Kirshbaum

precipitation enhancement (OPE) apply to most mountain ranges, including the Olympics. The amplitude of OPE depends on the impinging vertically integrated horizontal moisture flux (or “influx,” I ) (e.g., Neiman et al. 2002 ). Larger I favors increased terrain-forced condensation and, in turn, precipitation. Also, the nondimensional mountain height ( , where is the crest height, and N and U are the mean Brunt–Väisälä frequency and mean cross-barrier wind speed in the subcrest layer) broadly

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

observations from the CloudSat Profiling Radar (CPR), the AMSU-B, and NOAA’s Microwave Humidity Sounder (MHS). More recently, Sims and Liu (2015) used the CloudSat radar and multiple ground-based reanalysis data, including near-surface air temperature, atmospheric moisture, low-level vertical temperature lapse rate, surface skin temperature, surface pressure, and land cover types to diagnose precipitation phase partitioning. This algorithm is deployed in the GPM operational precipitation retrievals

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

, orographic enhancement is negligible on average with no statistically significant differences in precipitation rate between the five OLYMPEX sites ( Fig. 4 ). The lack of moisture and the weak low-level flow evidently limited the ability of this regime to produce strong orographic enhancement, while cold processes above the bright band nevertheless generated medium- to large-sized raindrops. d. Distributions during heavy rain (high N w and large D o ) The highest rain rates observed at the OLYMPEX sites

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Aaron R. Naeger, Brian A. Colle, Na Zhou, and Andrew Molthan

relatively strong low-level moist flow impinging upon the Olympic Mountains that promoted large windward rain accumulations. At 0000 UTC 13 November ( Fig. 1b ), the GFS reanalysis showed a 700-hPa trough was over the Gulf of Alaska, along with a plume of moisture (RH > 90%) from the central Pacific to the Pacific Northwest. At lower levels a950-hPa southwesterly jet (25 m s −1 ) associated with a warm front was advecting the warm, moist air toward the coast ( Fig. 2a ). The warm front propagated over

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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

. Twice, on 13 and 17 November, Lake Quinault rose at a rate of 0.15 m h −1 for 12–18 h and nearly flooded the DOW radar site on the shore of the lake ( Figs. 1 and 2 ). These two storms were “atmospheric rivers,” in which long plumes of moisture in the warm sector just ahead of the cold front are advected by the low-level jet ahead of the front. When this moisture plume intersects the mountains, great enhancement of the frontal precipitation occurs ( Neiman et al. 2008 ; Houze 2012 , 2014

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

lee side is very dry ( Fig. 1 ). In a recent study using OLYMPEX data, Purnell and Kirshbaum (2018 , hereafter PK18 ) used rain gauges and operational National Weather Service radars to show that orographic precipitation distributions are highly sensitive to the upstream static stability, horizontal moisture flux, and the presence of preexisting precipitation associated with the large-scale synoptic storm sectors. McMurdie et al. (2018) found that when the large-scale conditions resembled warm

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Robert Conrick and Clifford F. Mass

statistically different from those observed by the GMI instrument, a result consistent with RH profiles and IVT being realistically simulated. For cloud water ( Figs. 8b,e,h ), the postfrontal sector was most realistically simulated, though some overprediction was present at low values and underprediction at high values. These biases become larger in the warmer, more moisture-rich prefrontal and warm-sector environments. Rain-rate frequencies ( Figs. 8c,f,i ) were similar, with postfrontal sectors having

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

. Sci. , https://doi.org/10.1175/JAS-D-18-0073.1 , in press . 10.1175/JAS-D-18-0073.1 Dutton , J. , and H. A. Panofsky , 1970 : Clear air turbulence: A mystery may be unfolding . Science , 167 , 937 – 944 , https://doi.org/10.1126/science.167.3920.937 . 10.1126/science.167.3920.937 Friedrich , K. , D. E. Kingsmill , C. Flamant , H. V. Murphy , and R. M. Wakimoto , 2008 : Kinematic and moisture characteristics of a non-precipitating cold front observed during IHOP. Part II

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