Interannual Variations in Mesoscale Convective System Precipitation Patterns

Mesoscale Convective Systems (MCSs) are crucial components to the precipitation budget in the central United States. A modified version of the Whitehall (2014) infrared satellite image processing algorithm is used to identify MCSs over a 14-year period (2002-2015). This algorithm is completely automated and graph-based, which allows it to identify, track, and characterize complex MCS lifecycles over the central United States. Stage IV precipitation data are then integrated into the output of this algorithm, which produces precipitation profiles for each MCS. In this work, these precipitation profiles are examined for interannual variations in diurnal and seasonal patterns, as well as total precipitation and extreme precipitation events.

For locations in the central United States, MCS system frequency and precipitation contribution vary wildely from year to year, by a factor of 5 or more in some instances. Consequently, the percentage of total annual precipitation produced by MCSs for some locations can range from 10% to 60% in consecutive years. Previous studies have found that year to year variations in MCS precipitation are primarily represented in seasonal and geographic shifts, rather than changes across the entire domain. This work quantifies the annual and season-specific interannual variations for the total domain and regional subsets. It confirms that most of the interannual variation is due to geographical shifts in the favored location for MCS occurrence for each year and the seasonal timing of peak activity.

The total domain and geography-specific interannual variations in MCS frequency and precipitation are quantified for the central United States. These patterns are evaluated in terms of local dynamics involving the low level jet and stationary waves, and teleconnections such as ENSO. Furthermore, interannual variations in seasonality and their impacts on MCS contributions are examined. While the convection relating to MCSs is mesoscale by definition, MCS climatology is strongly influenced by these synoptic and global dynamic influences.