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Gary P. Ellrod, James P. Nelson III, Michael R. Witiw, Lynda Bottos, and William P. Roeder

available at least once every 6 h to provide coverage for the United States territory of Puerto Rico, and the state of Hawaii. Downburst products consist of Sounder-derived numerical values or color-coded boxes displayed at retrieval locations, superimposed on a visible (VIS), IR, or water vapor (WV) image from the GOES Imager at various resolutions. WINDEX and TED use VIS imagery as a background during daylight, and IR at night. Visible imagery is especially useful to show the presence of low

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Brian J. Squitieri and William A. Gallus Jr.

layer) of atmospheric water vapor mixing ratio, total wind magnitude, and mass convergence, along with most unstable convective available potential energy (MUCAPE) and the associated most unstable convective inhibition (MUCIN). RUC analyses were used for observed quantities for all atmospheric variables for the composites, and compared to output from all six WRF configurations after filtering and regridding (mentioned earlier). The MCS-centered compositing methods used in Coniglio et al. (2010

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Yuh-Lang Lin, Sen Chiao, Ting-An Wang, Michael L. Kaplan, and Ronald P. Weglarz

and cold advection east of storm area combine to intensify thickness and pressure gradients. The low-level wind flow maximizes near sunset. 2) A narrow band of conditionally unstable (lifted index = −4 to −7) and unusually moist (water vapor mixing ratio of 13–15 g kg −1 ) air moves southward and westward behind the polar front ( Figs. 2c and 2d ). This air mass is capped by a temperature inversion near 700 mb ( Figs. 3c and 3d ). 3) Orographic lifting provides the mechanism needed to release the

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Peter Knippertz and Jonathan E. Martin

approaches employed to describe and analyze transports of water vapor (WV) differ with respect to the usage of Eulerian, Lagrangian, or pseudo-Lagrangian perspectives. Eulerian approaches usually involve a consideration of water vapor fluxes (WVFs) q · v , with q and v being, respectively, specific humidity and the horizontal vector wind at a given pressure level. Often WVFs are integrated over the depths of the atmosphere to get vertically integrated water vapor fluxes (IWVFs). Given the almost

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Samuel M. Bartlett and Jason M. Cordeira

1. Introduction Atmospheric rivers (ARs) are synoptic-scale phenomena which are associated with long, narrow corridors of enhanced low-level water vapor transport ( American Meteorological Society 2018 ). Landfalling ARs often produce a wide variety of coastal and inland impacts worldwide, that may range from beneficial precipitation for drought amelioration ( Dettinger 2013 ) to hazardous precipitation leading to flooding ( Ralph et al. 2006 ). These beneficial precipitation events associated

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Winston Hao and Lance F. Bosart

31 August 1980 the average daily evaporation amountedto 8 mm for a 4 X l0s kin: region centered over Oklahoma. On individual days the evaporation was as high as10-15 mm. Strong diurnal variations were computed in the water vapor flux, vertical velocity and horizontal divergencefields. These variations, when superimposed over persistent large-scale subsidence, yielded enhanced subsidence,low-level divergence and anticyclonic vorticity production by day and weakened subsidence by night

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Mark J. Mitchell, Raymond W. Arritt, and Ken Labas

conventionalnetwork to detect strong LLJs points to the utility of the profilers in forecasting severe weather and implies thathydrologic budgets computed from conventional radiosonde data are likely to underestimate the atmosphericflux of water vapor over the central United States.1. Introduction The nocturnal low-level jet is an important factorin the development and sustenance of mesoscale convective systems over the Great Plains. The relationshipbetween the low-level jet (LLJ) and deep convectionhas been

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Peter M. Klein, Patrick A. Harr, and Russell L. Elsberry

storm as extratropical. Based on Klein (1997) and review of all 30 ET cases that occurred in the western North Pacific from 1 June through 31 October during 1994–98, the transformation stage of ET is defined to begin when visible, (IR), and water vapor imagery suggest an asymmetric appearance of clouds and, especially, a widespread decrease of deep convection in the western quadrant of the tropical cyclone. Simultaneously, the outermost edge of the tropical cyclone circulation is impinging on a

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Young-Chan Noh, Hung-Lung Huang, and Mitchell D. Goldberg

Abstract

To maximize the contribution of the Cross-track Infrared Sounder (CrIS) measurements to the global weather forecasting, we attempt to choose the CrIS channels to be assimilated in the National Centers for Environmental Prediction (NCEP) Global Forecast System (GFS). From pre-selected 431 CrIS channels, 207 channels are newly selected using a one-dimensional variational (1D-Var) approach where the channel score index (CSI) is used as a figure of merit. Newly selected 207 channels consist of 85 temperature, 49 water vapor, and 73 surface channels, respectively. In addition, to examine how the channels are selected if the forecast error covariance is differently defined depending on the latitudinal regions (i.e., Northern and Southern Hemispheres, and tropics), the same selection process is carried out repeatedly using three regional forecast error covariances. From three regional channel sets, two-channel sets are made for the global data assimilation. One channel set is made with 134 channels overlapped between three regional channel sets. Another channel set consists of 277 channels that is the sum of three regional channel sets. In the global trial experiments, the global CrIS 207 channels have a significant positive forecast impact in terms of the improvement of GFS global forecasting, as compared with the forecasts with the operational 100 channels as well as the overlapped 134 and the union 277 channel sets. The improved forecast is mainly due to the additional temperature/water vapor channels of the global CrIS 207 channels that are selected optimally based on the global forecast error of operational GFS.

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Laurel L. DeHaan, Andrew C. Martin, Rachel R. Weihs, Luca Delle Monache, and F. Martin Ralph

Abstract

Accurate forecasts of atmospheric rivers (ARs) provide advance warning of flood and landslide hazards, as well as greatly aid effective water management. It is therefore critical to evaluate the skill of AR forecasts in numerical weather prediction (NWP) models. A new verification framework is proposed leveraging freely available software and metrics previously used for different applications. Specifically, AR detection and statistics are computed for the first time using the Method for Object-based Diagnostic Evaluation (MODE). In addition, the measure of effectiveness (MoE) is introduced as a new metric for understanding AR forecast skill in terms of size and location. The MoE provides a quantitative measure of the position of an entire forecasted AR compared to observation, regardless of whether the AR is making landfall. In addition, the MoE can provide qualitative information about the evolution of a forecast by lead time with implications about the predictability of an AR. We analyze AR forecast verification and skill using 11 years of cold season forecasts from two NWP models, one global and one regional. Four different thresholds of integrated vapor transport (IVT) are used in the verification revealing differences in forecast skill based on the strength of an AR. In addition to MoE, AR forecast skill is also addressed in terms of intensity error, landfall position error, and contingency table metrics.

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