The long-lived MCV of 10–13 June 2003: A possible example of an incipient tropical disturbance over land?

The purpose of this presentation is to document the structural evolution of the long-lived mesoscale convective vortex (MCV) of 10–13 June 2003 occurred during the field phase of the Bow Echo and MCV Experiment (BAMEX). This MCV began over New Mexico at 0600 UTC 10 June as a downward extension of potential vorticity (PV) to midlevels from an upper-level disturbance that was embedded in an unusually strong subtropical jet (STJ). By 0000 UTC 11 June, the MCV entered Oklahoma and triggered a mesoscale convective system (MCS). As the MCV moved eastward across Oklahoma during 0000–1200 UTC 11 June, it acquired warm-core characteristics as it expanded horizontally and grew vertically and developed an attendant surface cyclonic circulation. The warm-core MCV triggered another round of convection over Missouri, Arkansas and Kentucky at 1800 UTC 11 June. This new convective precipitation that formed within the MCVs cyclonic circulation moved to the north side of the MCV center and acquired stratiform characteristics. As the MCV continued to move northeast toward the Great Lakes, it attached itself to a surface baroclinic zone along the southern shore of Lake Erie, effectively transitioning into a “Norwegian-like” surface frontal cyclone via a very unconventional pathway.

This MCV was noteworthy for its: (1) longevity, (2) development of a surface cyclonic circulation and associated -2–4 hPa sea-level pressure perturbation, and (3) transition from a warm-core MCV to a cold-core frontal cyclone with Norwegian cyclone model characteristics. Another noteworthy aspect of this MCV was the development of characteristic structures (e.g., surface cyclonic circulation associated with a low-level PV maximum beneath a midlevel diabatically-induced positive temperature anomaly) that are similar to incipient tropical disturbances (TDs). There have been several instances documented in the literature of incipient TDs stemming from long-lived continental mesoscale convective vortices (MCVs) that moved offshore (e.g., Johnstown, Pennsylvania, MCV of July 1977). These continental long-lived MCVs were of substantial intensity at middle and low levels, and had gone through several convective retriggering episodes.

The focus of this presentation is to document the structural evolution of this long-lived MCV of 10–13 June 2003 that occurred during the field phase of BAMEX. In particular, the physical processes that led to the development of a surface cyclonic circulation beneath the midlevel MCV during 0000–1200 UTC 11 June will be discussed using detailed WSR-88D wind analyses and surface mesoanalyses. This surface-based cyclonic circulation remained in place beneath the midlevel MCV for two consecutive subsequent diurnal heating cycles. Given that the deep-layer (850–200 hPa) wind shear decreased to less than 12.5 m s–1 during 0600 UTC 11–1800 UTC 12 June, the approximate surface (800 hPa) tangential winds were near 5–10 (15–20) m s–1, and the 850–700 hPa PV (850 hPa ) was near 2.0 PV units (14 x 10-5 s-1), it is hypothesized that this MCV (at its fully mature stage) could have developed into a TD had it been situated over a warm ocean.