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Peter Knippertz and Jonathan E. Martin

1. Introduction A number of studies have related extraordinary cool season precipitation events in western North America to bands of enhanced moisture transport from low latitudes in connection with landfalling extratropical cyclones from the Pacific Ocean (e.g., Higgins et al. 2000 ; Cavazos and Rivas 2004 ; Ralph et al. 2004 ; Bao et al. 2006 ). The fairly frequent bands connecting Hawaii with the Pacific Northwest region are widely known as the “pineapple express.” Methodically, the

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Eric A. Aligo, William A. Gallus Jr., and Moti Segal

forecasts are sensitively dependent on the soil moisture initial condition uncertainty. Therefore, they suggested adding initial soil moisture perturbations to the existing suite of atmospheric perturbations and/or different models to improve ensemble spread. They used the Weather Research and Forecasting (WRF) Advanced Research WRF (ARW) model to show that two initial soil moisture analyses were different enough to produce 24-h rainfall differences at 5-km horizontal grid spacing that were similar to

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Guiting Song, Robert Huva, Yu Xing, and Xiaohui Zhong

representation of unresolved cloud processes in WRF. In Australia Prasad and Kay (2020) illustrated the difficulty of the WRF-Solar model to appropriately capture location and timing of clouds under partly cloudy conditions, while in Southern California López-Coto et al. (2013) tested 72 different configurations of the WRF Model and found overestimation of irradiance, in general, with a tendency for underprediction of temperature and moisture through the vertical. To reduce bias, or more broadly error

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Rich F. Coleman, James F. Drake, Michael D. McAtee, and Leslie O. Belsma

). After the transition to ARW, a similar warm bias was observed in ARW forecasts. It was thought that in both cases, the warm bias could be attributed to insufficient latent heat flux due to the model failing to include moisture resulting from human activities. Research was undertaken to identify and quantify the sources of anthropogenic moisture in southern California, and to develop a method of incorporating these moisture sources into the WRF modeling system. As precipitation falls through the

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Paul A. Dirmeyer and Subhadeep Halder

1. Introduction It is accepted that the state of the land surface can influence the atmosphere across a range of time scales, thanks to a number of weather and climate modeling studies. Most studies have focused on soil moisture, as it has the largest impact on subseasonal-to-seasonal time scales. Furthermore, the focus has been on time scales of weeks or months, out to seasonal scales, as it has been assumed that weather forecasts (on the order of hours to a few days) are an atmospheric

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S. B. Trier, M. A. LeMone, F. Chen, and K. W. Manning

1. Introduction Land surface conditions including soil moisture and green vegetation fraction can impact deep convective precipitation (e.g., Pielke 2001 ). This results from their effect on the daytime sensible and latent heat fluxes, which influences local conditional instability (e.g., Betts and Ball 1995 ; James et al. 2009 ) and mesoscale circulations arising from surface heterogeneity (e.g., Pielke and Segal 1986 ; Lanicci et al. 1987 ; Segal and Arritt 1992 ). Recent simulations (e

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Yun Fan and Huug van den Dool

1. Introduction Precipitation ( P ) and 2-m surface air temperature (T2m) are two meteorological variables that have most important impacts on human society. For soil moisture, the so-called sea surface temperature (SST) has also been considered important for weather and climate prediction, in particular during the warm season when the land and atmosphere are more tightly coupled ( Dirmeyer 2000 ; Kanamitsu et al. 2003 ; Koster et al. 2003 ; Van den Dool et al. 2003 ; Zhang and Frederikson

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Xuefeng Cui, Douglas J. Parker, and Andrew P. Morse

positive feedback from the recirculation of precipitation through the soil moisture reservoir may lead to prolonged persistence of anomalous wet or dry spells ( Betts et al. 1996 ; Taylor and Lebel 1998 ). Understanding the role of the feedback cycle between soil moisture, surface evaporation, and precipitation on continental scales has been featured in all of the Intergovernmental Panel on Climate Change (IPCC) reports, including the most recent (Fourth Assessment Report, AR4), along with the ability

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Andrew C. Winters and Jonathan E. Martin

of the Caribbean Sea, facilitated much of the anomalous moisture transport out of Central America and into the southern Mississippi River valley. Furthermore, they noted that this moisture transport strengthened over the northern Gulf of Mexico and southern Mississippi River valley in the hours preceding the second day of the event (their Fig. 6). This finding was also noted in subsequent studies of the Nashville flood ( Durkee et al. 2012 ; Lackmann 2013 ; Lynch and Schumacher 2013 ). These

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Stephen M. Jessup and Arthur T. DeGaetano

) classify flash flood events and describe the synoptic and mesoscale characteristics of each type. Doswell et al. (1996) take a fundamental approach, identifying the root cause of flash flooding as the combination of ample atmospheric moisture and a means of precipitating a large amount of this moisture over a single basin. In general, the lifting mechanisms to produce vigorous convection and, consequently, substantial precipitation include low-level convergence (often associated with frontal or

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