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R. Uijlenhoet, J.-M. Cohard, and M. Gosset

hypothesis. Note, however, that this was the first event of the year after a four-month dry period. The atmospheric boundary layer was loaded with a high aerosol concentration from the Sahel during the day. In addition, a southwesterly monsoon flux brought humidity to the lower layers of the atmosphere during the night preceding the rainfall event. These conditions produced significant variations in aerosol concentrations and thermodynamic conditions during the event, which make it difficult to interpret

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Sandra E. Yuter, David A. Stark, Justin A. Crouch, M. Jordan Payne, and Brian A. Colle

enhancement extending 60 km upwind from the coastline (within 150 km from the crest of the Coastal Range) and over the first two peaks in terrain for winter storms. JH2005 found that orographic enhancement was more pronounced under joint conditions when the midlevel (500–700 hPa) flow was strong (>30 m s −1 ), midlevel dewpoint depression was low (<3°C), low-level (900–800 hPa) wind speed was > 20 m s −1 , and low-level stability was > 0 s −1 . Panziera and Germann (2010 , hereafter referred to as PG

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Dusanka Zupanski, Sara Q. Zhang, Milija Zupanski, Arthur Y. Hou, and Samson H. Cheung

variables The WRF model is configured to run in a regional domain with options to add nested inner domains with finer resolutions. The regional forecast runs use lateral boundary conditions from global forecast systems such as the NCEP Global Forecast System (GFS). The large-scale forcing is applied at the outer domain boundaries. In a nested domain run, the inner-domain boundary conditions are provided through the interaction with the outer domain. The cloud-resolving microphysics from GCE model ( Tao

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F. M. Ralph, E. Sukovich, D. Reynolds, M. Dettinger, S. Weagle, W. Clark, and P. J. Neiman

be released before the landfall of major winter storms, is also under development. A crucial step in the flood-control process involves the reservoir operator at Folsom Dam (U.S. Bureau of Reclamation) making decisions about how much water to release from the dam. A major factor compounding the risks is the potential that future climate conditions will reduce snowpack and move the peak runoff season into the earlier part of the spring season, when flooding events are more likely to occur than

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James A. Smith, Gabriele Villarini, and Mary Lynn Baeck

. Fig . 11. Storm total rainfall accumulations (mm) from the 15 Apr 2007 storm based on composite “stage IV” NEXRAD rainfall maps. Storm tracks are based on surface pressure fields from downscaled Weather Research and Forecasting (WRF) simulations. Fig . 12. The 850-hPa specific humidity (g kg −1 ) and wind field (m s −1 ) based on simulations using the WRF model on a 9-km grid with NCEP–NCAR reanalysis fields used for initial and boundary conditions [see Ntelekos et al. (2008 , 2009) and Zhang

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Jian Zhang and Youcun Qi

; Fig. 1b 4 ) as well as underestimation associated with blockage/overshooting (e.g., near 47.5°N, 123.4°W; Fig. 1b 4 ). The BB feature coexisted with orographically enhanced precipitation ( Fig. 1c 4 ). The fifth was the Tropical Storm Gustav event on 3 September 2008 in the southeast, where overestimations associated with a BB (near northern boundary of the domain; Fig. 1b 5 ) was accompanied with underestimations associated with tropical precipitation (southwest of the domain; Fig. 1b 5 ). The

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Masamichi Ohba, Shinji Kadokura, Yoshikatsu Yoshida, Daisuke Nohara, and Yasushi Toyoda

developments for data assimilation and for numerical prediction models. Heavy rainfall events can have various atmospheric origins (e.g., convective rainfall and frontal rainfall) and may be nonlinearly related to many meteorological factors. Synoptic-scale background conditions are one of the dominant origins of continuous heavy rainfall. Classification of such synoptic-scale conditions can be potentially fruitful for understanding the origin of extreme events and improving rainfall forecasting. For

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Youcun Qi, Jian Zhang, Brian Kaney, Carrie Langston, and Kenneth Howard

out by Panziera and Germann (2010) through a study of 106 days of rainfall in the southern part of the European Alps, the upstream wind velocity has the largest impact on the frequency and intensity of the precipitation in the mountainous area, and the direction of the wind determines the spatial distribution and intensity of the precipitation. The airmass stability also determines the intensity of the precipitation, and usually unstable conditions cause more precipitation over a mountainous

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