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Paul J. Roebber, James M. Frederick, and Thomas P. DeFelice

, the strong composite 500-hPa Pacific jet splits over North America, with the southwesterly (northwesterly) subtropical (polar) jet positioned over the southern United States (northern Canada), leading to confluence downstream of the U.S. midwest. The anomalous nature of this split flow is indicated by the strong positive 500-hPa height anomalies located over Canada ( Figs. 5a and 5b ). Correspondingly, composite surface conditions ( Figs. 6a–d ) were relatively quiescent with broad-scale high

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Melissa M. Hurlbut and Ariel E. Cohen

sample the kinematic characteristics of the jet-enhancing convection if the jet resides north of the international border, which is common during the summer owing to the northward migration of the jet ( Fig. 14 ). As such, a holistic, regional-scale analysis is encouraged in assessing severe weather potential. The position of the mid- and upper-level jet maximum does appear to be operationally meaningful ( Fig. 14 ), as the right-entrance region and curvature downstream of the trough enhance upward

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Joseph A. Rogash and Jonathan Racy

instability and wind shear closely examined. In the calculation of instability parameters, a virtual temperature correction was applied. With respect to the surface and upper troposphere, special attention was directed toward locating such features as surface thermal–moisture boundaries, extratropical cyclone centers, low-level jets, and middle- and upper-tropospheric troughs and jet streaks. As discussed below, lower-tropospheric patterns associated with each episode were generally similar to patterns M

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Hyung Woo Kim and Dong Kyou Lee

in the postchangma period ( Lee et al. 1998 ). Under the latter condition, it is difficult to distinguish indicators of MCS outbreaks from synoptic-scale observations due to their small spatial and temporal scales. According to previous studies ( Lee et al. 1998 ; Sun and Lee 2002 ), favorable conditions for heavy rainfall in Korea are as follows: a southwesterly low-level jet stream (LLJ), cold-air advection associated with upper-level disturbances, potential instability, a warm moisture tongue

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Paul B. Dorian, Steven E. Koch, and William C. Skillman

cold fronts. Synoptic climatological conditions favoring the occurrence of this relatively rare phenomenon are also identified.The LC/CZ appears during the afternoon almost solely over the Great Plains states during spring and autumn.The line convection was found in all but one case to be parallel to, and either along or on the cyclonic side of,a prefrontal 850 mb jet. Although the LC/CZ is usually found on the anticyclonic side of upper-level jet streaks,it does not seem to prefer any

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Ryan P. Aylward and Jamie L. Dyer

locations of jet streaks, as these can all affect storm strength, movement, and precipitation rate in a synoptically forced environment. The goal of this research is to define the synoptic conditions necessary for the generation of a SCEPT event and to establish a definition of an extreme precipitation training event in terms of its duration and precipitation rate. With this information, forecasters will be able to recognize that a life-threatening SCEPT event could potentially occur in their forecast

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Dusanka Zupanski, Milija Zupanski, Eric Rogers, David F. Parrish, and Geoffrey J. DiMego

method in application to a severe-weather event. Indeed, smaller-scale processes (50–100 km) are often mislocated in the forecast results because they are unresolved by the model (scales between meso- α and meso- β are actually resolved). Nevertheless, the method is capable of producing realistic larger-scale precursors of tornadic activity [e.g., low- and upper-level jet streaks, convective available potential energy (CAPE), wind shear], 24–36 h in advance of the event, which may serve as a

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Christopher Lucas, Peter T. May, and Robert A. Vincent

characteristics of fronts derived from qualitatively combining wind profilers and Radio Acoustic Sounding Systems compared favorably with the results obtained from more traditional observing systems and allowed for mesoscale features of frontal systems to be resolved on hourly timescales. Browning et al. (1998) combined data from UHF and VHF wind profilers to identify mesoscale characteristics of a cold frontal system in Wales, including the upper-level and low-level jets, the rearward sloping warm

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R. A. Dare and W. F. Budd

the literature so here the following terminology is employed. The term katabatic is defined as a wind that flows downslope (due to negatively buoyant air being acted upon by gravity) with a vertical profile that possesses a near-surface jet, such that the wind speed measured at some level near the surface is greater than the wind speed at the adjacent level above. Generally, a katabatic wind's low-level wind maximum is located within the lowest 100 m of the atmosphere, but the AUW dataset has only

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Joseph A. Rogash and Richard D. Smith

-wave trough over the west-central United States and downstream ridging over the east. A core of maximum winds extends from the Texas panhandle and southwestern Kansas into southern Minnesota. The highest wind speeds (around 80 m s −1 ) are over the Texas panhandle, placing Arkansas in the right exit region of the upper-level jet. The significance of this will be discussed in the next section. The 500-hPa geopotential height field ( Fig. 4 ) shows that the midtropospheric position of the deep trough

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