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Isaque Saes Lanfredi and Ricardo de Camargo

at the initial stage. The maximum amplification occurs under the influence of the Andes mountain range through the ageostrophic cold-air advection on its east side, as stated by Marengo et al. (1997) , in agreement with Gan and Rao (1994) and Seluchi et al. (1998) . According to Xu (1990) , the momentum balance on the eastern side of the Andes is responsible for forcing the cold air mass to move northward through the effect known as mountain channeling. North of 18°S, the mountains show a

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John A. Augustine and Fernando Caracena

-troposphericenvironments that indicate the expected location and degree of nocturnal mesoscale convective system (MCS)development over the central United States. The authors concentrate on two features: 1 ) the forcing for thelow-level jet (LLJ), and 2) the frontogenetic character of lower-tropospheric fronts, or other types of airmassboundaries, with which MCSs are associated. Results show that very large, long-lived, nocturnal MCSs are likelyto mature downwind of a late afternoon surface geostrophic wind maximum if that

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Graham A. Mills and Ian Russell

1992) Between 17 and 22 April 1990 widespread flooding occurred throughout Queensland, New South Wales, andVictoria, with several record rainfalls recorded. This paper investigates the forcing of the rainfall, assesses thequality of the operational numerical weather prediction model guidance during this period, and presents somenumerical sensitivity experiments both to diagnose forcing mechanisms and to identify reasons for modelweaknesses. All diagnostics used in this study could be made

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David M. L. Sills, James W. Wilson, Paul I. Joe, Donald W. Burgess, Robert M. Webb, and Neil I. Fox

at least one adjacent scan angle and on either a previous or subsequent scan (to ensure spatial and temporal continuity). To allow for convergent (divergent) vortices in the lower (upper) portions of the mesocyclone, the inbound and outbound velocity maxima used to calculate MDV did not have to be at the same range from the radar. 4. The prestorm environment a. Synoptic-scale forcing On 3 November, the synoptic-scale environment over the eastern third of Australia was characterized by a

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Stephen F. Corfidi

midpoint of the twentieth century. On the evening of 20 March 1948, a tornado struck Tinker Air Force Base, Oklahoma, without warning, causing more than $10 million in damage and several injuries. The funnel moved diagonally across the airfield, destroying aircraft and shattering the control tower’s windows. The following day, the commanding general of the Oklahoma City Air Materiel Area, Fred S. Borum, directed the base weather officers at work that evening, Major E. J. Fawbush and Captain R. C

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Hui Yu and H. Joe Kwon

upper-level trough could be either favorable or unfavorable to TC development. On the favorable side, it has been suggested that the asymmetric structures of the outflow layer associated with upper-level synoptic-scale systems could produce large-eddy imports of angular momentum. As a result of the small inertial stability in the upper troposphere, the response to external forcing can penetrate to the vortex center ( Holland and Merrill 1984 ). Up until now, many composite and case studies ( McBride

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Paloma Borque, Paola Salio, Matilde Nicolini, and Yanina García Skabar

1. Introduction Environments where mesoscale convective systems (MCSs) develop have some common characteristics, including an upper-level short-wave trough, a quasi-stationary frontal zone, and a strong low-level jet (LLJ) ( Maddox 1983 ; Laing and Fritsch 2000 ). Consistently, organized convection in subtropical South America develops essentially under environmental conditions characterized by synoptic-scale forcing associated with a cold front over northern Patagonia, downstream from a

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Ben C. Bernstein, Tiffany A. Omeron, Frank McDonough, and Marcia K. Politovich

, and location relative to surface weather features. Upper-air maps were tagged for the synoptic-scale forcing mechanisms operating in each area. Forbes et al. (1993) performed a similar study, comparing pilot reports to surface and upper-air charts, sounding data from the National Weather Service (NWS), and the STORM-FEST field program and output from an early nonoperational version of NCEP’s Eta Model ( Messinger et al. 1988 ). That study was limited to data from February to March 1992 and

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Gregory Thompson, Roelof T. Bruintjes, Barbara G. Brown, and Frank Hage

measures used in WRIPEP; however, more testing may be required since the 500-m requirement only encompasses one or two model levels and thus may be too restrictive. c. AFGWC RAOB icing scheme An algorithm developed by the Air Force Global Weather Central ( Knapp 1992 ) for guidance of their flight operations was also included in WRIPEP. This icing algorithm was originally written for use with rawinsonde data but was tested in WRIPEP on model data. The algorithm, shown in Table 3 , has three

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Chanh Q. Kieu, Hua Chen, and Da-Lin Zhang

an area of high oceanic heat content. It deepened 29 hPa in the first 6 h and 54 hPa in the next 6 h. During the rapid intensification episode, a U.S. Air Force reconnaissance flight indicated that the hurricane eye contracted to a diameter of about 3–5 km. The estimated minimum central pressure at the time of peak intensity is 882 hPa, which is the recorded lowest value for TCs in the Atlantic basin. The lack of observational data at these extreme limits puts any statistical PWR at some

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