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R. H. SIMPSON, NEIL FRANK, DAVID SHIDELER, and H. M. JOHNSON

,haract.er of the ITC became evident, and some investi-gators (e.g. Palmer 1201) went so far as to suggest, thatthe ITC is in realit,y only a statistical entit,y, day-to-dayweather distributions in the equatsorial t-rough consistingonly of t.hat weather associated with a succession of eddycirculations. The meteorological satellite has show1 in-controvertibly that, the 1C frequently involves a single,narrow, sometimes continuous band of convection in itseasbwest ext,ent, over several thousand miles.' At. ot

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David W. Reynolds

. Their conclusion was that an objective method for severestorm identification could be developed using current radar information and tropopause heights forgiven geographic regions. This paper reports on a method, using properlyenhanced GOES imagery, to identify damaging hailstorms over the High Plains. During the summer of1978 almost $100 million in damage from severe hailstorms occurred over the High Plains from Montanato New Mexico. One particular hailstorm was observed over Miles City, Montana

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Jason E. Nachamkin

event, information regarding the general model performance can be statistically determined. At the most basic level, it is important to know if the model can systematically reproduce a distribution of events that is similar in size and geographical location to the observations. The number distributions of the predicted and observed mistrals on the native model grid can be used for this comparison. In the 18-h forecasts, for example ( Fig. 3 ), the shapes of the distributions were slightly different

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Louis W. Uccellini

.g., Petterssen, 1956b;Newton, 1967). The tendency has been to treatlow-level jets (LLJ's) and upper tropospheric jetstreaks as separate entities. However, Reiter (1969)and Uccellini and Johnson (1979) present evidencewhich indicates that, in some cases, upper and lowertropospheric jets are a coupled entity. Results fromthe Uccellini and Johnson case study show that 1) aLLJ beneath the exit region of an upper troposphericjet streak is embedded in the lower branch of anindirect circulation, 2) the development

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Brian E. Mapes and Robert A. Houze Jr.

(OLR), which has the advantage of being measured globally by polar-orbitingsatellites. In addition to indicating the location of convective activity, and hence precipitation and latentheating, the upper-tropospheric cloudiness itself has aprofound effect on the local radiation budget (Websterand Stephens 1980). The reliability, availability, and geographical stationarity of IR imagery from geosynchronous satellites Corresponding author address.' Dr. Robert A. Houze, Jr., Depart.ment of

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Kimberly L. Elmore and Michael B. Richman

large range over the domain will emphasize those locations with a large variance. For example, an eigenanalysis based on a covariance matrix of Northern Hemisphere sea level pressure will emphasize those geographic locations that exhibit large variance (midlatitudes) and de-emphasize those geographic locations with small variance (tropical regions). A cross products (covariance without removing the means) similarity matrix also preserves units, and results are sensitive to the magnitudes of the

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Christopher Davis, Barbara Brown, and Randy Bullock

geographical location, but is displaced in time, the error is one of timing. If the forecast system correctly predicts its temporal centroid, but predicts the spatial centroid in the wrong geographical location, the error is spatial. If everything propagates at the same speed c , such that x − ct = constant, for example, then either the “ x ” or “ t ” dimension can be considered redundant, and the dimensionality reduces to two. Verification in this reduced-dimensional space was considered in Davis et

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T. N. Carlson, S. G. Benjamin, G. S. Forbes, and Y-F. Li

indicated by a dot-dashed line.The western edge of the lid formed by the Mexican desert airstream isshown by the scalloped line. The light shading is meant to show thewestern edge of a low stratus deck. Small hatched regions near AMAdenote the location of the first tornadoes which began about 1930 GMTon 10 April.layer with warmer air to the west of the lid edge, asopposed to the gradient at lower levels. The coldfront, shown to lie west of Midland (MAF) in Fig. 10,was a distinctly separate entity from

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L. Ronald Johnson, Paul L. Smith, Thomas H. Vonder, and Donald Reinke

this kind exists, but the samplewas quite small and further investigation was called for.This paper reports on the part of that extended investigation in which the infrared threshold used to definethe cloud area for SATI calculations for a given geographic location is held fixed. The results, however,suggest a need for different thresholds for locationswith differing dominant precipitation mechanisms.2. Analysis of data collected during CCOPE and NDCMP projects Radar surveillance scans

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Thibaut Montmerle

the opposite, it must be noted that, in the current operational configuration, the very weak coupling between humidity and divergence is somehow alleviated in the case of a simultaneous use of radial velocities and reflectivities from Doppler radar. 3. Use of a heterogeneous matrix in a 3DVar The purpose the heterogeneous formalism is to allow a simultaneous use of different matrices that correspond to different geographical locations in a DA system. Its detailed formulation is already given

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