Search Results

You are looking at 1 - 10 of 23 items for :

  • Plains Elevated Convection At Night (PECAN) x
  • All content x
Clear All
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 and Russ S. Schumacher

buoyancy gradient above the equilibrium layer, while positive vorticity is generated below. This results in favorable kinematic lifting above the equilibrium layer on the downshear side. The intrusion below the equilibrium layer is also less dense than its surroundings, leading to upward buoyant forces. Below the equilibrium layer, the vorticity pairing is unfavorable for vertical motion, but generates an acceleration vector that points to the right around the equilibrium level. In the case where mean

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

simulation without this effect (No_ULand). To explain how the urban land leads to a stronger convection initiation, the dynamics, thermodynamics, and kinematics are examined in ULandAero and No_ULand at 2120 UTC as shown in Fig. 7 . The urban land provides a temperature increase of 2°–3°C at 45 m AGL (lowest model level) over the city as well as over a large area downwind due to the southerly low-level wind resulting in warm air advection ( Figs. 7a–c ). This temperature increase extends to about 0

Restricted access
Brian J. Carroll, Belay B. Demoz, David D. Turner, and Ruben Delgado

retrievals, kinematic profilers, rawinsondes, and surface observations on a forecast of a nocturnal convection initiation event during the PECAN field campaign . Mon. Wea. Rev. , 147 , 2739 – 2764 , . 10.1175/MWR-D-18-0423.1 Degelia , S. K. , X. Wang , D. J. Stensrud , and D. D. Turner , 2020 : Systematic evaluation of the impact of assimilating a network of ground-based remote sensing profilers for forecasts of nocturnal convection initiation

Restricted access
Rachel L. Miller, Conrad L. Ziegler, and Michael I. Biggerstaff

. Convective systems may also evolve to become more or less elevated due to changes in the system-relative mesoscale inflow environment ( Corfidi 2003 ). The following case study of the 25–26 June 2015 MCS will analyze a combination of radar observations and in situ surface and sounding observations to examine the relationships between kinematics and reflectivity morphology of the MCS and the characteristics of the mesoscale NBL environment. Two unique aspects of the present study are the radar wind

Free access
David M. Loveless, Timothy J. Wagner, David D. Turner, Steven A. Ackerman, and Wayne F. Feltz

studies, however, are not necessarily representative of the phenomenon of bores as there is likely a selection bias toward extraordinary cases. The typical changes that bores make to the boundary layer and atmospheric stability have not yet been discussed beyond a case study. The present work seeks to address this issue by compositing the thermodynamic and kinematic profiles from a set of eight bores, each in a different stage of its life cycle, observed during the Plains Elevated Convection at Night

Full access
David J. Bodine and Kristen L. Rasmussen

causes of these propagation changes by examining internal and external factors to MCS evolution, and to explore thermodynamic, microphysical, and kinematic changes within the MCS. Internal factors such as an intensifying cold pool or rear-inflow jet could lead to a faster propagating MCS. External factors, such as discrete propagation events, could also cause faster MCS propagation. The present study examines a nocturnal MCS on 6 July 2015 in South Dakota that occurred during the Plains Elevated

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

convection-allowing ensemble data assimilation (DA) and forecast system for nocturnal convection. They performed real-time numerical predictions for nocturnal convection during the Plains Elevated Convection at Night (PECAN) experiment and found that their ensemble forecasts initialized at 1200 UTC were nearly unbiased regarding the timing of nocturnal CI. The assimilation of synoptic- and mesoscale observations can improve the analyses of convergent boundaries, as well as the thermodynamic and kinematic

Full access
Stanley B. Trier, James W. Wilson, David A. Ahijevych, and Ryan A. Sobash

interpolated pressure among the three locations. In (2) we use a kinematic lower boundary condition, where , , and are the average surface wind, terrain height gradient, and density within the triangle, to estimate the effects of terrain-following flow at and below on vertical motion at . Though there is uncertainty in this estimate, the diagnosed values of ~−0.5 to −1.3 s −1 , which reflect upslope flow, are relatively small. However, much larger errors in can accumulate when there are

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

.7) yields the late afternoon buoyancy profile as The kinematic pressure perturbation [ , where is pressure, is the reference pressure profile at a fixed x location (so ), and is a constant value of density] satisfies the hydrostatic equation in the initial state ( ) and in the postsunset motion ( ). Since is independent of x , is independent of x . Equivalently, is independent of z . We therefore determine at any height from its distribution in the free atmosphere, which we

Full access