An Assessment of Environments Supportive of Discreetly Propagating Mesoscale Convective Systems in the Great Basin

Mesoscale Convective Systems (MCS) occur most frequently from the central Plains through the Ohio Valley in environments supportive of significant convective instability and a very moist boundary layer.  MCSs also occur on a less frequent basis across the remainder of the country, including the interior Great Basin. Corfidi et al. identified a small subset of derecho events which occur in environments with limited low level moisture which they termed Low-Dewpoint Derechos (LDD). Interior Great Basin MCSs are often associated with drier environments with less instability than other areas of the country and bear resemblance to LDDs.  In higher moisture environments, the maintenance of MCSs is attributable to an achieved balance between instability and vertical shear.  This balance allows redevelopment of new convection along an advancing cold pool. Across the Great Basin this balance is considerably more difficult to achieve, as often a deep, dry boundary layer results in a very strong cold pool which surges out and away from the parent convection. In some cases, new updrafts will develop along this surging boundary downstream from the original convection.  This process can repeat itself over time as the MCS propagates discretely downstream with a series of convective bursts re-enforcing the advancing cold pool.

The environmental conditions associated with several Great Basin MCSs will be examined. Analysis will include interrogation of large-scale atmospheric conditions, as well as mesoscale environments using RAP derived proximity soundings soundings to analyze common severe weather parameters such as CAPE and shear. Conditions associated with MCS events where successive pulses of convection develop on MCS generated outflow boundaries will be identified. These conditions will be compared and contrasted to those correlated with LDDs. In addition, radar analysis will be conducted on the events and a conceptual model of storm morphology will be discussed.