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Richard Seager, Lisa Goddard, Jennifer Nakamura, Naomi Henderson, and Dong Eun Lee

lesser extent, warm tropical North Atlantic sea surface temperature (SST) anomalies ( Schubert et al. 2004a , b ; Seager et al. 2005b ; Herweijer et al. 2006 ; Seager 2007 ). This most recent drought also coincided with a La Niña event. Indeed, a recent study ( Hoerling et al. 2013 ) has concluded that the precipitation reduction over Texas in the summer of 2011 was within the range of natural variability of the atmosphere–ocean–land surface system and made much more likely by the La Niña of 2010

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Paul A. Dirmeyer, Jiangfeng Wei, Michael G. Bosilovich, and David M. Mocko

1. Introduction Rain or snow falling over any particular location is composed of condensed water vapor that entered the atmosphere as surface evaporation from a range of upstream locations. Surface and atmospheric conditions along the paths of moisture advection determine the ultimate sources of evaporative moisture, which generally have a combination of oceanic and terrestrial origins. Knowledge of the sources of moisture supplying precipitation over a particular location could be used to

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Johnna M. Infanti and Ben P. Kirtman

( Ropelewski and Halpert 1986 , 1987 ; Mo and Schemm 2008a , b ; Seager et al. 2009 ). In contrast to Mo and Schemm (2008a) , Seager et al. (2009) concluded that rainfall is more closely related to internal atmospheric variability, particularly in summer. Noise or internal atmospheric variability, for the purposes of this paper, is unpredictable, that is, we cannot relate it to specific forcing or feedback (ocean–atmosphere or atmosphere–land). This unpredictable variability is due to internal

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Hailan Wang, Siegfried Schubert, Randal Koster, Yoo-Geun Ham, and Max Suarez

drought and determining the timing of the drought, sustaining and/or amplifying droughts over the United States involves other factors such as local soil moisture feedback and random atmospheric internal variability (e.g., Koster et al. 2003 ; Ferguson et al. 2010 ). For example, a month with low precipitation leads to a drier-than-average soil, which in turn can lead to lower-than-average evaporation, which may lead to continued low precipitation. Such feedback between the land and atmosphere plays

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M. Hoerling, J. Eischeid, A. Kumar, R. Leung, A. Mariotti, K. Mo, S. Schubert, and R. Seager

May and June ( Fig. 5 , top panels), a zonal ridge of high pressure anomalies inhibited the typical southward push of cold fronts from Canada that often serve to organize widespread rains. July (bottom left) saw a somewhat different pattern, though no less effective in inhibiting rainfall. An intense anticyclone was centered over the northern plains region, preventing frontal incursions while also stabilizing the atmosphere and inhibiting deep convection that typically contributes appreciably to

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John M. Peters, Christopher J. Nowotarski, and Gretchen L. Mullendore

its original formulation, is unrealistically moist in the middle to upper troposphere (e.g., Potvin and Flora 2015 ). To add thermodynamic variability to our simulations, we used two different boundary layer moisture values of 14 and 16 g kg −1 , yielding two different convective available potential energy (CAPE) values and mixed-layer depths (0–1-km mean CAPE values of 1729 and 2744 J kg −1 , respectively). Runs with 14 and 16 g kg −1 are referred to as LOWCAPE and HICAPE, respectively. Fig . 1

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Sujay V. Kumar, Christa D. Peters-Lidard, David Mocko, Rolf Reichle, Yuqiong Liu, Kristi R. Arsenault, Youlong Xia, Michael Ek, George Riggs, Ben Livneh, and Michael Cosh

several factors, including errors related to variations in snow physical properties, surface, and the atmosphere ( Foster et al. 2005 ; Markus et al. 2006 ; Tedesco and Narvekar 2010 ). The snow retrievals are also prone to large errors in the presence of dense vegetation and water bodies ( Foster et al. 2005 ). Moreover, they have been shown to be less sensitive to thin snow packs (SWE less than around 10 mm) and to saturate for thick snowpacks (SWE above ground 200 mm; Dong et al. 2005 ). The

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