An Investigation of Thundersnow Environment Differences between the Phoenix Metropolitan Area and Columbia, MO from 20-21 February 2013 (88)
Peter Speck, National Weather Service Quad Cities IA/IL, Davenport, IA
Bohumil Svoma, Salt River Project
Thundersnow is simply defined as an observation of snow at the surface associated with lightning and thunder. Although rare in nature, thundersnow has been observed and studied across various regions of the U.S., with most attention being given to the Midwest, Great Salt Lake and Great Lakes. On 20 February 2013, an upper level low with 500-hPa temperatures below 243 K tracked eastward across the Southwestern U.S., bringing a wide swath of precipitation mostly in the form of rain over the low deserts. In the late afternoon, localized snow and graupel accumulations occurred in the Phoenix Metropolitan Area (PMA) around 22:30 UTC, with coincident reports of thunder. Early analysis showed that the causes of this event were likely: 1) increasing intensity of frozen precipitation leading to a deepening of the near-isothermal 0°C layer through the cooling effects of melting and sublimation (allowing frozen precipitation to reach lower altitudes), and 2) the very cold temperatures at 500-hPa increasing atmospheric instability. This system continued east towards the Great Plains, producing severe weather in the Gulf States and additional reports of thundersnow in the Midwest, including Columbia, MO. While it's not uncommon to see thundersnow in the Central U.S. during the winter months, it's unusual in that convective snowfall and snow accumulation at lower elevations of the PMA are extremely rare. This study's objective is to diagnose and compare the likely environments of the PMA, Columbia, MO and locations in between from this storm system.