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Hunter Coleman and John Marwitz

explanation. Is there a mechanism associated with the diabatic process of melting that can act to focus the release of thermodynamic instability over the SN–FZRA interface? This paper will investigate and describe the detailed kinematic and thermodynamic structure of the SN–FZRA interface region that produces the heaviest snow and freezing rain. In particular, four aspects of the storm were investigated: the temporal evolution of the low-level jet (LLJ), the vertical stability of the various layers, the

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Arnaldo P. Alfonso and Lino R. Naranjo

eastern Gulf of Mexico there was a 300-hPa jet streak interacting with a low-level jet. A hodograph typically associated with supercells or severe squall lines was observed at Key West, Florida. The air mass over the eastern Gulf of Mexico, Florida, and Cuba was conditionally unstable. Instability was enhanced by moist air at the surface interacting with a dry intrusion in the midtroposphere from the Mexican Plateau. Lifting induced by a strong short-wave trough favored the formation a compact squall

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William H. Bauman III, Michael L. Kaplan, and Steven Businger

by 1200 UTC 22 July ( Fig. 5d ). To reveal the 150-mb cold low in a summer subtropical environment, it was necessary to analyze height contours every 20 m and the isotachs every 5 m s −1 , instead of the conventional 120 m and 10 m s −1 intervals, respectively. Propagation of the cold low during the period tightens the height gradient over Florida and Georgia on 21 and 22 July, creating a jet streak of 20 m s −1 by 1200 UTC 22 July ( Fig. 5d ). A climatological study by Fitzpatrick et al

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Thomas L. Mote, Douglas W. Gamble, S. Jeffrey Underwood, and Mace L. Bentley

advection in the forecast of vertical motion fields associated with areas of heavy snowfall across the United States. Vertical motion resulting in heavy snowfall was also discussed in relation to the low-level jet (LLJ) beneath an exit region of an upper-tropospheric jet streak by Uccellini and Kocin (1987) and Kocin and Uccellini (1990) . Kocin et al. (1995) analyzed the role of upper-level jets in the “superstorm” of March 1993. The transverse flow between regions of ascent associated with

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Russell L. Pfost and Alan E. Gerard

speed accurate warnings. The circulation associated with the CHE and a strong rear inflow jet helped spawn small tornadoes in Claiborne County, Mississippi, and wind damage in western Hinds County, Mississippi. The observed damage path from the tornadoes was more than 8 km (5 mi) long but was fortunately through sparsely populated forested areas so that no one was hurt. For much of the track, the tornadoes paralleled the Natchez Trace, a scenic federal highway that extends from Natchez to Nashville

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Stanley F. Rose, Peter V. Hobbs, John D. Locatelli, and Mark T. Stoelinga

convection expected), a forecast of surface boundaries that might initiate convection (such as fronts, drylines, or outflow from previous convection), and a forecast of upper-level features such as 500-hPa troughs or jet streaks (to identify synoptic-scale forcing of vertical motion that may enhance convection over particular regions). The day-1 convective outlook issued at 1630 UTC 20 June 2000 called for a moderate risk of severe thunderstorms over portions of western Missouri, southern and eastern

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Stephen F. Corfidi, Sarah J. Corfidi, David A. Imy, and Allen L. Logan

being investigated. In contrast to Johns et al. (1990) , the grid overlay was aligned along the direction of the predominant forward motion of the MCS, with the center of the grid placed on the centroid of damage and gust reports. This was done to account for the fact that LDDs, like all derechos, occur with a wide range of upper-jet orientations (e.g., from southwesterly to northwesterly; Coniglio et al. 2004 ). Because LDDs tend to move in the direction of the mean cloud-layer flow as do other

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Amanda K. Kis and Jerry M. Straka

some percentage of nocturnal tornadoes form within stable boundary layers, and the likelihood of this scenario must be examined. In addition, low-level jets (LLJ) are common features at night over the Great Plains, and the storm mode may shift from “classic” isolated supercells to quasi-linear convective systems (QLCSs) as LLJs strengthen their vertical wind shear and organize convection into more linear modes. Also, LLJs may impact tornadogenesis by increasing low-level vertical wind shear and

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Mei Hong, Dong Wang, Ren Zhang, Xi Chen, Jing-Jing Ge, and Dandan Yu

level pressure in the region 20°–10°S, 40°–60°E; 2) the Somali low-level jet (SJ), that is, the 850-hPa average longitude wind within the region 5°–15°N, 40°–60°E; 3) the Indian monsoon latent heat flux (FLH), that is, the latent heat flux within the region 12.5°–22.5°N, 80°–100°E; 4) the Tibetan high (eastern type) activity index (TH), that is, the average grid points of 200-hPa geopotential height within the range 25°–30°N, 95°–105°E; and 5) the monsoon circulation index at the Bay of Bengal (J1V

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Morris L. Weisman, Clark Evans, and Lance Bosart

-inflow jet and a deep strip of cyclonic vorticity extending from the northern bookend vortex southward along and within the cold pool, becomes established very early in the evolution of the system. The transition to the occlusion-like stage is, somewhat surprisingly, associated with a weakening of the convective line and associated convective cold pool as the system moves east of the low-level jet (LLJ) into an environment of weaker vertical wind shear and CAPE. These results will then be discussed

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