scholarly journals Characteristics and Synoptic Environment of Drylines Occurring over the Higher Terrain of Southeastern Wyoming

2015 ◽  
Vol 30 (6) ◽  
pp. 1733-1748 ◽  
Author(s):  
Philip T. Bergmaier ◽  
Bart Geerts
Keyword(s):  
Great Plains ◽  
Rocky Mountains ◽  
Deep Convection ◽  
Potential Temperature ◽  
Warm Season ◽  
Thunderstorm Activity ◽  
Southern Great Plains ◽  
Synoptic Conditions ◽  
Virtual Potential Temperature ◽  
Close Relationship

Abstract Commonly observed over the broadly sloped terrain of the southern Great Plains (SGP), drylines are frequent loci of warm season deep convection and have been the focus of numerous observational, theoretical, and climatological studies over last half century. In this study, a 3-yr (2010–12) analysis of the characteristics and synoptic environment of drylines occurring elsewhere, over the high terrain in southeastern Wyoming just east of the Rocky Mountains, is presented. Observed on ~11% of the days between May and August of the years examined, southeastern Wyoming drylines were often associated with large moisture gradients [~5–10 g kg−1 (100 km)−1], large horizontal virtual potential temperature differences (~2–5 K), and convergent zonal wind flow at the surface. The synoptic conditions leading to their formation and their relationship to thunderstorm activity are also explored in an effort to aid local forecasters in anticipating the development and convective impact of drylines across the region. Similarities exist between these drylines and those found over the SGP, especially with regard to their strength and close relationship to deep convection. However, the frequency at which they occur, some characteristics of their diurnal motion, and the synoptic conditions driving their formation differ noticeably.

scholarly journals A 20-Year Climatology of Nocturnal Convection Initiation over the Central and Southern Great Plains during the Warm Season

2017 ◽  
Vol 145 (5) ◽  
pp. 1615-1639 ◽  
Author(s):  
Dylan W. Reif ◽  
Howard B. Bluestein
Keyword(s):  
Great Plains ◽  
Warm Season ◽  
Thunderstorm Activity ◽  
Surface Boundary ◽  
Initiation Time ◽  
Southern Great Plains ◽  
Surface Data ◽  
Convection Initiation ◽  
Storm Characteristics

Abstract A nocturnal maximum in rainfall and thunderstorm activity over the central Great Plains has been widely documented, but the mechanisms for the development of thunderstorms over that region at night are still not well understood. Elevated convection above a surface frontal boundary is one explanation, but this study shows that many thunderstorms form at night without the presence of an elevated frontal inversion or nearby surface boundary. This study documents convection initiation (CI) events at night over the central Great Plains from 1996 to 2015 during the months of April–July. Storm characteristics such as storm type, linear system orientation, initiation time and location, and others were documented. Once all of the cases were documented, surface data were examined to locate any nearby surface boundaries. The event’s initiation location relative to these boundaries (if a boundary existed) was documented. Two main initiation locations relative to a surface boundary were identified: on a surface boundary and on the cold side of a surface boundary; CI events also occur without any nearby surface boundary. There are many differences among the different nocturnal CI modes. For example, there appear to be two main peaks of initiation time at night: one early at night and one later at night. The later peak is likely due to the events that form without a nearby surface boundary. Finally, a case study of three nocturnal CI events that occurred during the Plains Elevated Convection At Night (PECAN) field project when there was no nearby surface boundary is discussed.

scholarly journals A Mechanistically Credible, Poleward Shift in Warm-Season Precipitation Projected for the U.S. Southern Great Plains?

2017 ◽  
Vol 30 (20) ◽  
pp. 8275-8298 ◽  
Author(s):  
Melissa S. Bukovsky ◽  
Rachel R. McCrary ◽  
Anji Seth ◽  
Linda O. Mearns
Keyword(s):  
Great Plains ◽  
Climate Models ◽  
Climate Model ◽  
Global Climate Model ◽  
Regional Climate ◽  
Warm Season ◽  
Dry Season ◽  
Wet Season ◽  
Southern Great Plains ◽  
Poleward Shift

Abstract Global and regional climate model ensembles project that the annual cycle of rainfall over the southern Great Plains (SGP) will amplify by midcentury. Models indicate that warm-season precipitation will increase during the early spring wet season but shift north earlier in the season, intensifying late summer drying. Regional climate models (RCMs) project larger precipitation changes than their global climate model (GCM) counterparts. This is particularly true during the dry season. The credibility of the RCM projections is established by exploring the larger-scale dynamical and local land–atmosphere feedback processes that drive future changes in the simulations, that is, the responsible mechanisms or processes. In this case, it is found that out of 12 RCM simulations produced for the North American Regional Climate Change Assessment Program (NARCCAP), the majority are mechanistically credible and consistent in the mean changes they are producing in the SGP. Both larger-scale dynamical processes and local land–atmosphere feedbacks drive an earlier end to the spring wet period and deepening of the summer dry season in the SGP. The midlatitude upper-level jet shifts northward, the monsoon anticyclone expands, and the Great Plains low-level jet increases in strength, all supporting a poleward shift in precipitation in the future. This dynamically forced shift causes land–atmosphere coupling to strengthen earlier in the summer, which in turn leads to earlier evaporation of soil moisture in the summer, resulting in extreme drying later in the summer.

Bores Observed during IHOP_2002: The Relationship of Bores to the Nocturnal Environment

2017 ◽  
Vol 145 (10) ◽  
pp. 3929-3946 ◽  
Author(s):  
Kevin R. Haghi ◽  
David B. Parsons ◽  
Alan Shapiro
Keyword(s):  
Great Plains ◽  
Deep Convection ◽  
Horizontal Wind ◽  
Wave Trapping ◽  
Southern Great Plains ◽  
Direction Of Movement ◽  
Low Level Jet ◽  
Relationship Of ◽  
The Relationship ◽  
Scorer Parameter

This study documents atmospheric bores and other convergent boundaries in the southern Great Plains’ nocturnal environment during the IHOP_2002 summer campaign. Observational evidence demonstrates that convective outflows routinely generate bores. Statistically resampled flow regimes, derived from an adaptation of hydraulic theory, agree well with observations. Specifically, convective outflows within the observed environments are likely to produce a partially blocked flow regime, which is a favorable condition for generating a bore. Once a bore develops, the direction of movement generally follows the orientation of the bulk shear vector between the nose of the nocturnal low-level jet and a height of 1.5 or 2.5 km AGL. This relationship is believed to be a consequence of wave trapping through the curvature of the horizontal wind with respect to height. This conclusion comes after analyzing the profile of the Scorer parameter. Overall, these findings provide an impetus for future investigations aimed at understanding and predicting nocturnal deep convection over this region.

scholarly journals Coupling between Large-Scale Atmospheric Processes and Mesoscale Land–Atmosphere Interactions in the U.S. Southern Great Plains during Summer. Part I: Case Studies

2004 ◽  
Vol 5 (6) ◽  
pp. 1223-1246 ◽  
Author(s):  
Christopher P. Weaver
Keyword(s):  
Great Plains ◽  
Large Scale ◽  
Deep Convection ◽  
Individual Case ◽  
Atmospheric Modeling ◽  
Surface Fluxes ◽  
Southern Great Plains ◽  
Atmospheric Processes ◽  
Mesoscale Processes

Abstract This paper is Part I of a two-part study that uses high-resolution Regional Atmospheric Modeling System (RAMS) simulations to investigate mesoscale land–atmosphere interactions in the summertime U.S. Southern Great Plains. The focus is on the atmospheric dynamics associated with mesoscale heterogeneity in the underlying surface fluxes: how shifts in meteorological regimes modulate these diurnal, mesoscale processes, and their overall impact at larger scales and over multiple diurnal cycles. Part I examines individual case study time periods drawn from the simulations that illustrate general points about the key land–atmosphere interactions. The main findings are as follows: The mesoscale processes are embedded within a synoptic-scale organization that controls the background meteorological regime at a given location. During the clear, dry days in the simulated months, heterogeneity in the surface fluxes forces strong, lower-tropospheric, mesoscale circulations that exhibit a characteristic dynamical life cycle over diurnal time scales. In general, the background large-scale flow does not affect the overall intensity of these coherent roll structures, though strong large-scale subsidence can sometimes dampen them. In addition, depending on the thermodynamic profile, the strong vertical motions associated with these circulations are sufficient to trigger shallow or even deep convection, with associated clouds and precipitation. Furthermore, surface heterogeneity sufficient to force such circulations can arise even without heterogeneity in preexisting land cover characteristics such as vegetation, for example, solely as a result of spatial variability in rainfall and other atmospheric processes. In Part II the mesoscale land–atmosphere interactions in these case study periods are placed in the larger context of the full, monthlong simulations.

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