Abstract
The Program for Research on Elevated Convection with Intense Precipitation (PRECIP) field campaign sampled 10 cases of elevated convection during 2014 and 2015. These intense observing periods (IOP) mostly featured well-defined stationary or warm frontal zones, over whose inversion elevated convection would form. However, not all frontal zones translated as expected, with some poleward motions being arrested and even returning equatorward. Prior analyses of the observed data highlighted the downdrafts in these events, especially diagnostics for their behavior: the downdraft convective available potential energy (DCAPE) and the downdraft convective inhibition (DCIN). With the current study, the DCAPE and DCIN are examined for four cases: two where frontal motion proceeded poleward, as expected, and two where the frontal motions were slowed significantly or stalled altogether. Using the Weather Research and Forecasting (WRF) model, a multi-model ensemble was created for each of the four cases, and the best performing members were selected for additional deterministic examination. Analyses of frontal motions and surface cold pools are explored in the context of DCAPE and DCIN. These analyses further establish the DCAPE and DCIN, not only as a means to classify elevated convection, but also to aid in explaining frontal motions in the presence of elevated convection.
Highlights
Elevated thunderstorm complexes pose numerous threats and are well established as producers of heavy rainfall [1,2,3,4], flash flooding [3,4,5], and cloud-to-ground lightning flashes [4,6,7]
Enhanced convection and heavy rainfall were observed where this coolest region interacted with the warm air along and south of the boundary. Cases in which this was observed occurred in environments that were favorable for elevated mesoscale convective systems (MCSs), which is consistent with what was shown by Moore et al [3]
quantitative precipitation forecasts (QPF), a lower bias will indicate an underforecast of QPF, while those models toward the upper left will indicate an overforecast of QPF
Summary
Elevated thunderstorm complexes pose numerous threats and are well established as producers of heavy rainfall [1,2,3,4], flash flooding [3,4,5], and cloud-to-ground lightning flashes [4,6,7]. Colman [11,12] established one definition of elevated convection as a storm that is isolated from surface diabatic effects and found above a frontal inversion He further refined this definition to include that observations must lie on the cold side of an analyzed front with clear contrast in the mass and momentum fields with surrounding stations recording similar conditions. Similar criteria were used by Grant [13], Rochette and Moore [1], Moore et al [14], Moore et al [3], and McCoy et al [4] for studies involving elevated thunderstorms This definition is rather specific, and, while being useful in determining if a given cell is surface-based or elevated by way of synoptic map interrogation, it falls short in defining elevated convection in scenarios where a boundary is not well-defined. Convection can be elevated even when near-surface parcels have positive CAPE, as suggested by Nowotarski et al [17]
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