An investigation of thundersnow environment differences between the Phoenix metropolitan area and Columbia, MO from an analytical and modeling perspective

Abstract

Thundersnow (TSSN) is linked to increased snowfall intensity and accumulation totals within cyclones. Although rare, TSSN has been observed and studied across various regions of the U.S., although most attention has been given to the Midwest, Great Salt Lake and Great Lakes regions. On 20 February 2013 an upper level low with 500- hPa temperatures below 243 K tracked slowly eastward across the Southwestern U.S. and brought with it 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), with coincident reports of thunder. The Earth Network Total Lightning Network (ENTLN) confirmed lightning strikes in the area. This is an unusual event in that convective snowfall and snow accumulation at lower elevations of the PMA are extremely rare. Initial analysis of 3-km High Resolution Rapid Refresh (HRRR) output showed an isolated region of instability over the PMA (e.g., surface CAPE greater than 500 J kg-1 per the HRRR simulations) along with warm temperatures at the lower levels and the surface. This suggests that enough of an updraft was present to initiate charge separation, and that the event was likely surface based in nature. Temperatures likely cooled due to cooling effects of melting, evaporation and sublimation as precipitation fell, and allowed for a deepening of the 0[degrees]C isotherm and for frozen precipitation to reach the surface. This upper level storm continued eastward towards the central Great Plains on 21 February 2013, and produced more TSSN across the panhandles of Texas and Oklahoma, Kansas and Missouri, including Columbia, MO.