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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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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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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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Samuel M. Bartlett and Jason M. Cordeira


Atmospheric rivers (ARs) are synoptic-scale phenomena associated with long, narrow corridors of enhanced low-level water vapor transport. Landfalling ARs may produce numerous beneficial (e.g. drought amelioration and watershed recharge) and hazardous (e.g. flash flooding and heavy snow) impacts that may require the National Weather Service (NWS) to issue watches, warnings, and advisories (WWAs) for hazardous weather. Prior research on WWAs and ARs in California found that 50–70% of days with flood-related and 60–80% of days with winter weather-related WWAs occurred on days with landfalling ARs in California. The present study further investigates this relationship for landfalling ARs and WWAs during the cool seasons of 2006–2018 across the entire western U.S. and considers additional dimensions of AR intensity and duration. Across the western U.S., regional maxima of 70–90% of days with WWAs issued for any hazard type were associated with landfalling ARs. In the Pacific Northwest and Central regions, flood-related and wind-related WWAs were also more frequently associated with more intense and longer duration ARs. While a large majority of days with WWAs were associated with landfalling ARs, not all landfalling ARs were necessarily associated with WWAs (i.e., not all ARs are hazardous). For example, regional maxima of only 50–70% of AR days were associated with WWAs issued for any hazard type. However, as landfalling AR intensity and duration increased, the association with a WWA and the “hazard footprint” of WWAs increased quasi-exponentially across the western U.S.

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Kenneth L. Pryor and Gary P. Ellrod

) evaluation, it was found that corresponding precipitable water and stability indices were significantly improved when the GFS model was used as a first guess instead of the Eta Model. The improvement was most apparent in moist atmospheric conditions when convection was most likely. The internal NESDIS study, which compared Eta and GFS model first-guess profiles, also found that a larger root-mean-square error (rmse) for low-level temperature (e.g., 950 mb) existed in the Eta Model first guess. The

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Dan Bikos, Daniel T. Lindsey, Jason Otkin, Justin Sieglaff, Louie Grasso, Chris Siewert, James Correia Jr., Michael Coniglio, Robert Rabin, John S. Kain, and Scott Dembek

of low-level water vapor convergence ( Chesters et al. 1983 ), providing potentially useful information on convective initiation locations before any clouds have formed. An example of this difference is provided in section 3 . 3. Examples Five examples are shown to highlight representative strengths and weaknesses of using synthetic imagery from the NSSL 4-km WRF-ARW for severe thunderstorm forecasting. The example in section 3d utilizes the CIMSS forward model, while the examples in the other

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Viel Ødegaard

resistance to vertical motion ( Fabry and Zawadzki 1995 ). a. Parameterization scheme 1) Condensation–precipitation parameterization The control condensation scheme treats condensation and precipitation, from large-scale (model resolved) and subgrid-scale convective processes. Convection is parameterized according to a modified version of the Kuo scheme, including modeling of large-scale instability processes. Rain is a diagnostic variable, while cloud liquid water and water vapor are prognostic

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