Several annual mesoscale convective complex (MCC) summaries have been compiled since Maddox strictly defined their criteria in 1980. These previous studies have largely been independent of each other and therefore have not established the extended spatial and temporal patterns associated with these large, quasi-circular, and, typically, severe convective systems. This deficiency is primarily due to the difficulty of archiving enough satellite imagery to accurately record each MCC based on Maddox's criteria. Consequently, this study utilizes results from each of the MCC summaries compiled between 1978 and 1999 for the United States in order to develop a more complete climatology, or description of long-term means and interannual variation, of these storms. Within the 22-yr period, MCC summaries were compiled for a total of 15 yr. These 15 yr of MCC data are employed to establish estimated tracks for all MCCs documented and, thereafter, are utilized to determine MCC populations on a monthly, seasonal, annual, and multiyear basis. Subsequent to developing an extended climatology of MCCs, the study ascertains the spatial and temporal patterns of MCC rainfall and determines the precipitation contributions made by MCCs over the central and eastern United States. Results indicate that during the warm season, significant portions of the Great Plains receive, on average, between 8% and 18% of their total precipitation from MCC rainfall. However, there is large yearly and even monthly variability in the location and frequency of MCC events that leads to highly variable precipitation contributions.

A 44-yr climatology of nonconvective wind events (NCWEs) for the Great Lakes region has been created using hourly wind data for 38 first-order weather stations during the months of November through April. The data were analyzed in terms of the two National Weather Service (NWS) criteria for a high-wind watch or warning: sustained winds of at least 18 m s Ϫ1 for at least 1 h or a wind gust of at least 26 m s Ϫ1 for any duration. The results indicate a pronounced southwest quadrant directional preference for nonconvective high winds in this region. Between 70% and 76% of all occurrences that satisfied the NWS criteria for NCWEs were associated with wind directions from 180°through 270°. Within the southwest quadrant, the west-southwest direction is preferred, with 14%-35% of all NCWEs coming from this particular compass heading. This directional preference is borne out in five out of six stations with high occurrences of cold-season NCWEs (Buffalo, New York; Dayton, Ohio; Lansing, Michigan; Moline, Illinois; Springfield, Illinois). Given the geographic spread of these stations, a nontopographic cause for the directional preference of cold-season NCWEs is indicated. The connection between NCWEs and low pressure systems found in this climatology and in case studies suggests that midlatitude cyclone dynamics may be a possible cause of the directional preference.

This study extends investigations of mesoscale convective complexes (MCCs) over subtropical South America (SSA) by describing the physical characteristics of MCCs during the austral warm season (October-May) for 1998-2007 in SSA. Within the nine warm seasons, 330 events were documented. An average of 37 MCCs occurred each warm season and reached a maximum cloud-shield size of 256 500 km 2 , and lasted 14 h on average. Although 85% of the MCC population occurred over the South American continent, the remaining systems that occurred over the adjacent Atlantic Ocean were significantly larger by nearly 30%. These findings show MCCs in SSA are larger and longer-lived than shown in previous work. Compared to the United States, MCCs in SSA are significantly larger with longer durations. Unlike the US systems, these events do not exhibit much poleward migration throughout the warm season. The highest frequency and concentration of MCC cloud shields are centred east of the Andes Mountains between 20°S and 30°S over Paraguay, northern Argentina, and southern Brazil throughout the warm season. As a result, relationships between latitude, and MCC maximum extent or duration are weak or non-existent, respectively. There is, however, a moderate positive relationship between duration and maximum extent. Ultimately, MCCs in SSA are large, long-lasting events that possess great potential for contributing significantly to precipitation totals across the region.

This study uses a database consisting of 330 austral warm-season (October-May) mesoscale convective complexes (MCCs) during 1998-2007 to determine the contribution of MCCs to rainfall across subtropical South America (SSA). A unique precipitation analysis is conducted using Tropical Rainfall Measuring Mission (TRMM) 3B42 version 6 data. The average MCC produces 15.7 mm of rainfall across 381 000 km 2 , with a volume of 7.0 km 3 . MCCs in SSA have the largest precipitation areas compared to North American and African systems. MCCs accounted for 15%-21% of the total rainfall across portions of northern Argentina and Paraguay during 1998-2007. However, MCCs account for larger fractions of the total precipitation when analyzed on monthly and warm-season time scales. Widespread MCC rainfall contributions of 11%-20% were observed in all months. MCCs accounted for 20%-30% of the total rainfall between November and February, and 30%-50% in December, primarily across northern Argentina and Paraguay. MCCs also produced 25%-66% of the total rainfall across portions of west-central Argentina. Similar MCC rainfall contributions were observed during warm seasons. An MCC impact factor (MIF) was developed to determine the overall impact of MCC rainfall on warm-season precipitation anomalies. Results show that the greatest impacts on precipitation anomalies from MCC rainfall were located near the center of the La Plata basin. This study demonstrates that MCCs in SSA produce widespread precipitation that contributes substantially to the total rainfall across the region.

No abstract