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Ernest Agee and Erin Jones

of significant strength (F2/EF2–F4/EF4) can be produced by a number of mechanisms including the tilting of solenoidal horizontal vorticity by a cold pool, and by rear-inflow jets (RIJs) in quasi-linear convective systems (QLCS) ( Taylor et al. 2002 ; Trapp and Weisman 2003 ; Weisman and Trapp 2003 ; Trapp et al. 2005 ), as well as by bookend vortices (BEVs) in bow echoes (also see Fujita 1978 ). Even nonsupercell tornadoes of the landspout variety can achieve intensities as high as F2 (see

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Michael J. Brennan, Gary M. Lackmann, and Kelly M. Mahoney

useful tool in the forecast process. For example, plots of potential temperature on the dynamic tropopause [most often defined as a PV isosurface of value between 1 and 2 PVU: 1 potential vorticity unit (PVU) = 10 −6 m 2 s −1 K kg −1 ] can be extremely useful because PV surfaces intersect the core of all major upper-level jet streams, even those centered at different altitudes ( Morgan and Nielsen-Gammon 1998 ). However, it is our sense that PV has not gained widespread acceptance within the

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Maximiliano Viale and Federico A. Norte

storm obtained from the coastal soundings are shown in more detail in Fig. 9 . The early stage of the storm featured a significant increase with height in the cross-barrier profile at the lowest levels, producing a strong vertical shear below 900 hPa ( Fig. 9a ). This strong cross-barrier shear was coincident with a near-surface along-barrier jet, showing peak speeds of 15 m s −1 , and with a very stable near-surface layer (i.e., an isothermal layer in Fig. 7a and the largest values of N m 2 in

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Shawn M. Milrad, John R. Gyakum, Kelly Lombardo, and Eyad H. Atallah

back to the Q vector and thus QG vertical motion using where Q is the Q vector, p is the pressure, p o is some reference pressure, R is the gas constant for dry air, and κ is R divided by c p , the specific heat at constant pressure. Frontogenesis and frontolysis are indicated when Q points to warmer and colder air, respectively (e.g., Sanders and Hoskins 1990 ). Figure 4 shows that CSB1 occurs in the left-exit region of a straight northwest–southeast-upper-tropospheric jet

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Russ S. Schumacher and Richard H. Johnson

rainfall amounts that far surpassed that threshold. The results to be presented will establish that there are several characteristics common to such extreme rain events associated with midlevel vortices, including the presence of a low-level jet (LLJ). Additionally, the idealized findings of Raymond and Jiang (1990) and Trier et al. (2000a) do not address another important component of extreme local rainfall production: the organization of the convective system. The organization is crucial in

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Brian A. Colle, Kelly A. Lombardo, Jeffrey S. Tongue, William Goodman, and Nelson Vaz

the 20 NYC–LI cases reveals that there were 7 Appalachian lee trough events, 6 cold front events, 5 warm front events, 1 stationary front event, and 1 tropical cyclone event (Hurricane Bob 1991). Although Long Island tornadoes develop under a variety of scenarios, several important ingredients are common to many of the events. In the composite, at 1 day prior to the tornado event ( T − 24 h), a 300-hPa westerly jet extends across the northeastern tier of the United States ( Fig. 3a ). By the time

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Steven G. Decker and David A. Robinson

. Although there is no critical level in these soundings (except BUF), the presence of a low-level jet within the inversion (again, except BUF) implies that the shear vector reverses direction, which has been proposed to act like a critical level ( Durran 1986 ). The layered structure to the potential temperature field is also favorable for mountain wave activity ( Klemp and Lilly 1975 ). However, the distance from these soundings to High Point calls into question their representativeness. Thompson et

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Douglas K. Miller, David Hotz, Jessica Winton, and Lukas Stewart

heavy precipitation in the PRB. Air parcels originating in an environment having high background precipitable water values did not have to travel far while undergoing lift in southeasterly flow, orthogonal to the mean ridgeline. Favorable lift of high-humidity parcels remained in place over the southern Appalachians for long periods as the low-level system was cut off from the primary large-scale upper-tropospheric jet. Thus, for the extreme events with no AR, both ingredients of a large average

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Shawn M. Milrad, Eyad H. Atallah, John R. Gyakum, Rachael N. Isphording, and Jonathon Klepatzki

( Fig. 6d ). The DT metric also highlights the subtropical jet stream through high frequency bands in the North Pacific and North Atlantic ( Fig. 6d ). All of these secondary maxima were found as secondary closed/cutoff cyclone hotspots ( Bell and Bosart 1989 ), and regions of frequent AWB ( Bowley et al. 2019 , all AWB mentions henceforth refer to their Fig. 5). Furthermore, both the Alberta and western Europe Floods occurred during spring in regions highlighted by regional flow reversal maxima

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Chung-Chieh Wang, Chu-Ying Kung, Cheng-Shang Lee, and George Tai-Jen Chen

1. Introduction During the early summer rainy season, called the mei-yu season in Taiwan (May–June), there are a number of important synoptic and mesoscale phenomena such as the mei-yu front, low-level jets (LLJs), mesoscale convective systems (MCSs), mesolows–mesocyclones, and orographic effects (e.g., Chen 1992 , 1994 , 2004 ; Chen and Chen 1995 ; Wang and Chen 2002 ; Wang et al. 2005 ; Chen et al. 2003 , 2008 ). During this period, organized MCSs often develop along or near the mei

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