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Christopher A. Davis and Lance F. Bosart

assimilation as the simulation progressed. The track of the simulated storm appears to agree less well with observations early in the development. Part of this error is due to the fact that the low-level cyclonic circulation was broad and weak. Bosart and Bartlo (1991) show a well-defined low center at 0000 UTC 8 September, but given the distribution of observations and the elongated nature of the pressure trough, there is some uncertainty as to the location and intensity of the incipient cyclone. More

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Craig S. Schwartz, John S. Kain, Steven J. Weiss, Ming Xue, David R. Bright, Fanyou Kong, Kevin W. Thomas, Jason J. Levit, and Michael C. Coniglio

1. Introduction Convection-allowing numerical weather prediction (NWP) efforts in the United States began in the early to mid-1990s, when experimental model predictions with horizontal grid spacing as fine as 3 km were initialized with real data ( Droegemeier et al. 1996a , b ; Xue et al. 1996a , b ). Although these forecasts focused on relatively small geographic domains and limited time scales, they demonstrated the potential value of convection-allowing model forecasts for the short

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David R. Stauffer and Thomas T. Warner

VOLUME II5a. Cold-air damming The geography and topography of the eastern UnitedStates is favorable for cold-air damming, the processby which cold, stable air from a surface anticyclone,with its center located somewhere in the northeasternUnited States, flows southwestward and is channeledalong the Appalachian Mountain chain. The mountains, perhaps acting as a physical barrier to the flow,"trap" or "dam" the air along the eastern slopes, particularly during the winter. As a result, a "nose" ofhigh

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Daniel J. Cecil, Edward J. Zipser, and Stephen W. Nesbitt

found at the boundary of the vortex core and the environmental envelope. The Rossby number is of order unity in this location, which places the SBC near the center of weak hurricanes and farther away in strong hurricanes. The SBC has three components, although all three are not always present: the principal band, the connecting band, and the secondary bands. The SBC may coexist with the eyewall or with concentric eyewalls. The categorizations used in this study are motivated by the three distinct

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John M. Wallace and David S. Gutzler

/ororographic forcing (Hoskins and Karoly, 1981).The observed patterns are characterized by anequivalent barotropic vertical structure. Their horizontal structure at mid-tropospheric levels tends tobe wavelike with multiple centers of action, whereasthe corresponding patterns of the earth's surfacetend to be more localized; in these respectsthe observed patterns also resemble the linear solutions obtained by Hoskins and Karoly. The geographical location of the patterns, depicted in Fig.26, appears to bear some

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VINCENT E. JAKL

be noted that by this time the Lake HIGH was merging into the Atlantic HIGH. The inference is optional, ac-cording to the theory one is inclined to favor, as to whether the SW. to NE. drift was incidental to the Atlantic HIGH and the process of its increment by the Lake HIGH, or that the 3W. to NE. drift was an entity,levels and at the surface wou F d depend on other modifyingdated it. on t R e weather map dissipat,ing in its ad-west that have no pronounce : LOW in their front, to beallel to a

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Caren Marzban, Scott Sandgathe, and Hilary Lyons

forecast). Cluster analysis ( Everitt 1980 ) refers to a set of statistical techniques designed to identify structures in data. The generality of the methodology allows for the objects to be not only two-dimensional (as in a gridded field), but also multidimensional entities that include spatial information as well as other dimensions, including the intensity of the field, or the time at which it is recorded. As such, the verification procedure based on cluster analysis has three desirable features: It

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Wolfgang Koch and Frauke Feser

and Foster (2003) ; they showed these small-scale wind streaks being very closely aligned with the surface wind direction. The present study searches for relationships between wind-induced patterns on SAR images and wind direction at the 10-m height. Both entities are accessible by proxy data. The wind vectors are approximated by a numerical weather model, while the directions of image patterns are approximated by a method that is based on gradients. Although well-processed measurements are

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H. H. Schiesser, R. A. Houze Jr., and H. Huntrieser

selected for our study aretreated in the same manner; that is, they are classifiedaccording to the scheme of HSD. This procedure allowsus to compare the organization of storms occurring inthe mountainous and hilly region of Switzerland withmesoscale convective systems in the generally flat region of Oklahoma.2. Study area, data, and definitionsa. Area and period of study Figure 1 shows the location of the study area. It issituated within the area covered by two operationalweather radars and has a

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Richard A. Anthes, Ying-Hwa Kuo, Stanley G. Benjamin, and Yu-Fang Li

SEPTEMBER 1982 ANTHES, KUO, BENJAMIN AND LI 1187The Evolution of the Mesoscale Environment of Severe Local Storms: Preliminary Modeling Results RICHARD A. ANTHESNational Center for Atmospheric Research, ~ Boulder, CO 80307YING-HWA KUO AND STANLEY G. BENJAMINThe Pennsylvania State University, University Park 16802 YU-FANG LIDepartment of Geography, Hang-zhou University, People

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