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David A. Lavers, Ervin Zsoter, David S. Richardson, and Florian Pappenberger

midlatitude regions—namely, western Europe—recent research has built on predictability assessments of variables most relevant for predicting extreme precipitation ( Lavers et al. 2014 ) to show that vertically integrated horizontal water vapor transport [integrated vapor transport (IVT)], a key driver of extreme events (e.g., Ralph et al. 2006 ; Lavers et al. 2011 ), can provide earlier awareness of extreme precipitation occurrence ( Lavers et al. 2016a ). In the study, the European Centre for Medium

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Jason M. Cordeira and F. Martin Ralph

). The primary goal of this study is to quantify the skill of the National Centers for Environmental Prediction (NCEP) Global Ensemble Forecast System (GEFS) forecasts of enhanced integrated water vapor transport (IVT) along the U.S. West Coast that is commonly observed during landfalling ARs during October–April 2017–20. b. Background on AR-related forecast skill A majority of cool-season precipitation forecasts over the western United States likely inherently account for landfalling ARs through the

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Robert A. Mazany, Steven Businger, Seth I. Gutman, and William Roeder

desired 90-min lead time ( NCDC 1996 ). The KSC false alarm rate is 43.2%. There is room for improvement in these statistics, particularly in reducing the false alarm rate. a. GPS and the role of water vapor The water molecule has an asymmetric distribution of charge that results in a permanent dipole moment. This unique structure results in the large latent heat associated with changes of phase, it makes possible the phenomena of lightning, and also makes possible the ability to monitor integrated

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Brett T. Hoover, David A. Santek, Anne-Sophie Daloz, Yafang Zhong, Richard Dworak, Ralph A. Petersen, and Andrew Collard

from observation impact metrics employing a model adjoint technique used at other centers (e.g., Gelaro et al. 2010 ), aircraft observations have demonstrated significant impact on the 24-h forecast error in adjoint-based investigations as well ( Langland and Baker 2004 ; Cardinali 2009 ). Early attempts to derive automated moisture observations from aircraft sensors included the Water Vapor Sensing System (WVSS), which used a thin-film capacitor to measure relative humidity (RH; Fleming 1996

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Agnes H. N. Lim, James A. Jung, Sharon E. Nebuda, Jaime M. Daniels, Wayne Bresky, Mingjing Tong, and Vijay Tallapragada

or water vapor gradients from consecutive satellite images taken 30 minutes apart ( Menzel 2001 ). Both polar-orbiting and geostationary satellites use this technique to derive AMVs. Geostationary satellites are able to generate AMVs at higher temporal resolution than polar satellites due to their orbital and scanning geometry ( Velden et al. 2005 ). Numerical weather prediction (NWP) centers such as the European Centre for Medium-Range Weather Forecasts (ECMWF), the Met Office, the Bureau of

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Irina Mahlstein, Jonas Bhend, Christoph Spirig, and Olivia Martius

strong topographical forcing, which can be used as a basis to build an early flood alert system. In Switzerland, a relationship exists between extreme vertically integrated water vapor transport [IVT; see e.g., Lavers et al. (2012) for the computation of IVT] and major flood events ( Martius et al. 2006 ; Froidevaux and Martius 2016 , hereafter FM16 ). Exceptionally high IVT directed perpendicularly to the main mountain chains was present for 10 out of 14 major flood events in Switzerland in the

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S. A. Ackerman, A. S. Bachmeier, K. Strabala, and M. Gunshor

UTC, which displays a more dramatic (and perhaps unexpected) signature of the low temperature and humidity characteristics of this air mass. The low total column water vapor content and the strong contrast in surface temperature between the unfrozen northern Great Lakes and the surrounding snow-covered land surface in Canada allow surface features (the northern coastline of the Great Lakes) to be detected in this “water vapor channel” imagery; even hints of the boundary layer LES cloud bands over

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W. F. Feltz, K. M. Bedka, J. A. Otkin, T. Greenwald, and S. A. Ackerman

. In some cases, the existence of clear-air turbulence associated with mountain waves is “validated” by aircraft that experience the turbulence ( Clark et al. 2000 ), incidents which can cause serious injury to crew/passengers and damage to the aircraft itself. High-resolution satellite water vapor imagery from the Moderate Resolution Imaging Spectroradiometer (MODIS) allows forecasters to identify the presence of mountain waves and infer the potential for hazardous turbulence. Mountain waves are

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William H. Gemmill and Vladimir M. Krasnopolsky

surface) and by the sea surface temperature (SST). The propagation of the microwave radiation through the atmosphere is influenced by the integrated amounts of water vapor and liquid water in the atmospheric column ( Wentz 1992 , 1997 ). As a result the brightness temperatures carry signals from all these geophysical parameters and can then be converted into geophysical parameters (surface wind speed, columnar water vapor, columnar liquid water, and SST) using retrieval algorithms. DMSP satellites

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Deborah E. Hanley

suggest that PV signatures alone may not be suitable as forecast methods ( HMK ). The high percentage of intensifying superposition cases observed by HMK suggests that identification of such interactions by numerical guidance or by satellite imagery could improve the forecasting of intensity change during this type of interaction. The relationship between water vapor and PV has been shown by several investigators (e.g., Appenzeller and Davies 1992 ; Appenzeller et al. 1996 ; Mansfield 1997

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