Search Results

You are looking at 1 - 10 of 38 items for :

  • Plains Elevated Convection At Night (PECAN) x
  • Refine by Access: All Content x
Clear All
Brian J. Carroll, Belay B. Demoz, David D. Turner, and Ruben Delgado

1. Introduction The Great Plains low-level jet (LLJ) is a primarily nocturnal phenomenon of strong southwesterly winds within the planetary boundary layer (PBL) spanning hundreds of kilometers in width and length, and is most frequent and impactful during the warm-season. LLJs provide major contributions to nocturnal convection in the region, such as mesoscale convective systems (MCSs), via convergence of the wind field and advection of moisture and temperature ( Byerle and Paegle 2003 ; Trier

Restricted access
John M. Peters, Erik R. Nielsen, Matthew D. Parker, Stacey M. Hitchcock, and Russ S. Schumacher

inflow layer (EIL; Thompson et al. 2007 ). We refer to storms within an environment where the lower bound of the EIL (as defined by the aforementioned CAPE and CIN thresholds) is above the earth’s surface as elevated. In this article, we use an observational analysis of an elevated MCS’s near environment to demonstrate how numerical weather prediction (NWP) models’ moisture errors within an MCS’s EIL influence the ability of these models to accurately predict the MCS. Horizontal and temporal

Full access
Yun Lin, Jiwen Fan, Jong-Hoon Jeong, Yuwei Zhang, Cameron R. Homeyer, and Jingyu Wang

al. 2002 ; Shepherd 2005 ; Hubbart et al. 2014 ). Convective storms may be initiated at the UHI convergence zone that is created through a combination of increased temperature and mechanical turbulence resulting from complex urban surface geometry and roughness ( Bornstein and Lin 2000 ; Shepherd 2005 ; Hubbart et al. 2014 ; Liu and Niyogi 2019 ). Urban landscapes can impact sensible and latent heat flux, soil moisture, etc., affecting thunderstorm initiation with a higher frequency in urban

Restricted access
Guo Lin, Coltin Grasmick, Bart Geerts, Zhien Wang, and Min Deng

because of varying ground elevation along flight legs, and the ease with which airborne, surface, and profile observations can be compared. The mean height of the ground surface over the domain of interest is 590 m MSL. CAPE, CIN, and the distance to each parcel’s level of free convection (LFC) are computed following Grasmick et al. (2018) and Lin et al. (2019) . In essence, CRL temperature and moisture at each time step (interval of 3 s) at any height between the ground and flight level are

Restricted access
Stacey M. Hitchcock and Russ S. Schumacher

several different methods of classification, but two distinct categories consistently emerge for events over the central Great Plains. In synoptic-type events, a strong midtropospheric trough and slow moving surface front lead to strong forcing for ascent in a region with southerly flow and associated moisture transport. During the warm season, isentropic ascent of warm, moist air transported by the nocturnal low-level jet (LLJ) can lift an air to saturation on the cool side of a stationary or warm

Free access
Manda B. Chasteen, Steven E. Koch, and David B. Parsons

warm season. During the daytime, an east–west temperature gradient had developed over the southern plains, and a surface low and dryline were located over the Edwards Plateau region of west Texas at 0200 UTC ( Fig. 2 ). A quasi-stationary front, which was characterized primarily by a pronounced wind shift and low-level moisture gradient, extended northeastward from the low pressure center into central Oklahoma. Additionally, an extensive radar fine line had moved into northern Oklahoma, which was

Full access
Samuel K. Degelia, Xuguang Wang, and David J. Stensrud

moist layer that is key to generating nocturnal CI. Peters et al. (2017) connect errors in mesoscale convective system (MCS) forecasts to moisture biases, and in the simulations with negative moisture biases the models produce errors in both CI timing and location due to the parcels requiring additional residence time within the lifting regions. Assimilating kinematic and thermodynamic observations can improve many of the above issues related to forecasting nocturnal CI. Recently, Degelia et al

Full access
Stacey M. Hitchcock, Russ S. Schumacher, Gregory R. Herman, Michael C. Coniglio, Matthew D. Parker, and Conrad L. Ziegler

an elevated layer between 0200 and 0500 UTC ( Trier and Parsons 1993 ). Changes were associated with the southward progression of a shallow surface front, and an increase in moisture advection in conjunction with the onset of the southerly nocturnal LLJ. These observations led to a schematic (Fig. 20 in Trier and Parsons 1993 ) of isentropic ascent of high θ e air associated with the LLJ over a quasi-stationary frontal zone. This has become a relatively common conceptual model for nocturnal

Full access
Joshua G. Gebauer, Alan Shapiro, Evgeni Fedorovich, and Petra Klein

enhances the southerly geostrophic wind. It is likely that the effects described by Holton (1967) , Shapiro and Fedorovich (2009) , and Parish (2016) all contribute to the LLJ intensity and frequency maximum over the Great Plains. The LLJ has long been considered to be a key contributor to the nocturnal precipitation maximum over the Great Plains, although not all mechanisms involved are well understood. A well-defined diurnal oscillation in moisture flux over the region is associated with the

Full access
Tammy M. Weckwerth and Ulrike Romatschke

). The compositing process used in our analyses smoothed out the jet streak structure so the jet coupling is not as prominent as that shown in Squitieri and Gallus (2016) . Significant low-level moisture associated with the LLJ was observed in the region ( Fig. 16a ). The enhanced moisture at 300 mb ( Fig. 15a ) was likely caused by a combination of advection from the southwest and upward moisture transport by the sustained deep convection in the region. Break days also showed 850-mb southerly flow

Free access