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R. Romero, C. A. Doswell III, and R. Riosalido

anticipate the capability of high-resolution numerical prediction in the context of a future operational forecasting setting, where fine-grid mesoscale models are likely to be run. Mesoscale models applied to convective flash flood events under the current feasible conditions (grid lengths of 20–30 km and moderately sophisticated physical parameterizations) have already shown their potential for locating the general centers of heavy precipitation, especially in those areas where the orographic forcing is

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Moti Segal, Zaitao Pan, and Raymond W. Arritt

1. Introduction A large amount of the summer rainfall over the central United States is related to diurnal variation of radiative forcing at the surface (e.g., Wallace 1975 ; Fritsch et al. 1986 ; Dai et al. 1999 ). Development of the daytime convective boundary layer (CBL) commonly provides conducive thermodynamical conditions for deep convection. Mesoscale diurnally forced systems, such as nocturnal low-level jets and thermally induced slope circulations in the high plains, provide an

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Donald R. Johnson and Louis W. Uccellini

870 MONTHLY WEATHER REVIEW VOLUME 111A Comparison of Methods for Computing the Sigma-Coordinate Pressure Gradient Force for Flow over Sloped Terrain in a Hybrid Theta-Sigma Model DONALD R. JOHNSONUniversity of Wisconsin, Department of Meteorology and Space Science and Engineering Center, Madison, WI 53706 LOUIS W. UCCELLINIGoddard Laboratory

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David A. Rahn and Thomas R. Parish

described in Bond et al. (1996) and Nuss (2007) . Strong ridging from the surface to about 700 hPa is present over the Pacific Northwest and extends southward to northern California in the days prior to the onset of a CTWR. There is evidence that in some cases the thermal low situated over the desert southwest may migrate westward in response to the large-scale ridging to the north. This is often associated with a large area of a weak horizontal pressure gradient force (PGF) over the coastal

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Wei Wang and Thomas T. Warner

DECEMBER1988 WEI WANG AND THOMAS T. WARNER 2593Use of Four-Dimensional Data Assimilation by Newtonian Relaxation and Latent-Heat Forcing to Improve a Mesoscale-Model Precipitation Forecast: A Case Study WEI WANG AND THOMAS T. WARNERDepartment of Meteorology, The Pennsylvania State University, University Park, Pennsylvania(Manuscript received 3 February 1988, in final form 16 June

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W. James Steenburgh and Leah S. Campbell

complimentary contributions in lake-effect situations” (p. 1039). The relative contributions of differential thermal and roughness forcing are, however, situationally dependent. In real-data numerical simulations of snowbands over the English Channel and Irish Sea, Norris et al. (2013) found that differential roughness (and orography) was less important than thermal forcing for band formation, but did affect location and morphology. Idealized numerical simulations suggest land-breeze-forced ascent during

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Andrea Schneidereit, Dieter H. W. Peters, Christian M. Grams, Julian F. Quinting, Julia H. Keller, Gabriel Wolf, Franziska Teubler, Michael Riemer, and Olivia Martius

.g., Labitzke 1987 ; van Loon and Labitzke 1987 ), zonally asymmetric ozone changes (e.g., Peters et al. 2015 ), El Niño–Southern Oscillation (ENSO) (e.g., Butler and Polvani 2011 ), and the Madden–Julian oscillation (MJO) (e.g., Garfinkel et al. 2012 ; Liu et al. 2014 ). All these processes change the forcing of planetary waves in the troposphere or change the wave propagation into and in the stratosphere (mainly wavenumbers 1–3; Charney and Drazin 1961 ; Dickinson 1969 ). The strong mean

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Sam Hardy, David M. Schultz, and Geraint Vaughan

upper-level forcing, or different phasing between the PV anomaly and cyclone, would have produced a higher-impact flooding event across the United Kingdom or whether the verifying solution represented the highest-impact event possible for this synoptic setup. The question is answered by using piecewise PV inversion to design a suite of model simulations with the strength and position of the PV anomaly modified in the initial conditions, following a similar method to previous studies by Huo et al

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Angela Benedetti and Marta Janisková

cloud optical depths were compared to sets of different independent observations. Figure 15 shows some of the results for the shortwave and longwave cloud forcings (SWCF and LWCF, respectively) at the top of atmosphere (TOA) and for precipitation averaged over the tropical belt between 20°N and 20°S for April 2006. The TOA radiative forcings obtained from the model runs were compared against the Clouds and the Earth’s Radiant Energy System (CERES) products ( Wielicki et al. 1996 ). The surface

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Bart J. Wolf and Donald R. Johnson

APmL 1995 WOLF AND JOHNSON 1059The Mesoscale Forcing of a Midlatitude Upper-Tropospheric Jet Streak by a Simulated Convective System. Part I: Mass Circulation and Ageostrophic Processes BART J. WOLF* AND DONALD R. JOHNSONtSpace Science and Engineering Center, University of Wisconsin-Madison, Madison, Wisconsin(Manuscript received 26 July 1993, in final form 18 May

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