Observed radar and environmental properties of United States warm season bow echo convective modes

The radar evolution of warm season 381 bow echoes that occurred over the United States between the months of April through September from 2003 to 2004 was examined. Special attention was given to the radar reflectivity characteristics during the bowing stages. The results demonstrate that five primary bowing modes exist: (i) stratiform classic bow echo (ii) no stratiform classic bow echo (iii) bowing squall line (iv) multiple bowing squall line (v) bowing single cell. The diversification of modes is aided by measuring the bowing convective line lengths which show a preferred scale for all bow echoes to be an average of 75 km with a 35 km standard deviation. Thus, the two classic bow echo modes in this study are set between 40 km and 110 km.

Examination of the evolutionary properties of the bowing modes reveals that the no stratiform classic bow echo most closely resembles the original model of Fujita (1978). Comparing initial convective modes to bowing convective modes reveals that ordinary or multicells favor the formation of stratiform classic bow echoes while mixed supercells and multicells favor the formation of no stratiform classic bow echoes. Bowing squall lines and multiple bowing squall lines are almost always formed from trailing stratiform (TS) squall lines.

The observed bowing modes demonstrate differences in longevity, with bowing squall lines being the longest lived and bowing single cells being the shortest lived. Further examination of U.S. locations, diurnal variability, severe weather production, along with the thermodynamical environments that produce each mode is presented.