84th AMS Annual Meeting

Thursday, 15 January 2004
Proximity Sounding Composites of Midwestern Thundersnow Events
Room 4AB
Patrick S. Market, University of Missouri, Columbia, MO; and A. M. Oravetz, D. Gaede, E. Bookbinder, B. Pettegrew, and R. Thomas
Poster PDF (936.4 kB)
Sounding profiles of the atmosphere were generated to get a more accurate picture of the thermodynamics present during thundersnow. Horizontal composite fields (see associated abstract) paint a vivid portrait of an active snowstorm, but fail to distinguish a typical cyclone from those that harbor an electrified cloud and thundersnow. Proximity soundings were found in 12 thundersnow events and are discussed and defined presently. Four of the events occurred at the exact time and location of a sounding. Four of the events occurred at the exact time of a sounding but were not at the exact location the sounding occurred; the location of thundersnow was within 90 nmi (169 km) of the sounding station. The remaining four cases occurred within 90 nmi of the sounding station and the thundersnow report occurred in a window of zero to three hours after the rawinsonde was released.

These profiles add value to the horizontal composites produced previously. The horizontal composite charts revealed that thundersnow events occur in otherwise unremarkable, snowbearing extratropical cyclones. Working on the assumption that some feature (instability) makes these events unique, and that convection resulting from instability is the source of charge separation for lightning production, these profiles were constructed. What appears most clearly is the presence of an elevated layer of potential instability in events northwest of a cyclone center (N=8). While not deep, it generally exists in a region of deep moisture and forcing for ascent. Cases of thundersnow northeast of a cyclone center (N=4) are potentially neutral, but with profiles rich in moisture and again forcing for ascent. Although not statistically significant, these profiles would seem to support the hypothesis of potential instability related convection dominating in thundersnow cases northwest of a cyclone and potential symmetric instability related convection dominating in cases occurring northeast of the cyclone center.

Supplementary URL: