Rapid Mesoscale Environmental Changes Accompanying Genesis of an Unusual Tornado

Details

• Journal Title:
  Weather and Forecasting
• Personal Author:
  Koch, Steven E. ; Ware, Randolph ; Jiang, Hongli ; Xie, Yuanfu
• NOAA Program & Office:
  OAR (Oceanic and Atmospheric Research) ; ESRL (Earth System Research Laboratory) ; NSSL (National Severe Storms Laboratory) ; CIRES (Cooperative Institute for Research in Environmental Sciences)
• Description:
  This study documents a very rapid increase in convective instability, vertical wind shear, and mesoscale forcing for ascent leading to the formation of a highly unusual tornado as detected by a ground-based microwave radiometer and wind profiler, and in 1-km resolution mesoanalyses. Mesoscale forcing for the rapid development of severe convection began with the arrival of a strong upper-level jet streak with pronounced divergence in its left exit region and associated intensification of the low-level flow to the south of a pronounced warm front. The resultant increase in stretching deformation along the front occurred in association with warming immediately to its south as low-level clouds dissipated. This created a narrow ribbon of intense frontogenesis and a rapid increase in convective available potential energy (CAPE) within 75 min of tornadogenesis. The Windsor, Colorado, storm formed at the juncture of this warm frontogenesis zone and a developing dryline. Storm-relative helicity suddenly increased to large values during this pretornadic period as a midtropospheric layer of strong southeasterly winds descended to low levels. The following events also occurred simultaneously within this short period of time: a pronounced decrease in midtropospheric equivalent potential temperature theta(e) accompanying the descending jet, an increase in low-level theta(e) associated with the surface sensible heating, and elimination of the capping inversion and convective inhibition. The simultaneous nature of these rapid changes over such a short period of time, not fully captured in Storm Prediction Center mesoanalyses, was likely critical in generating this unusual tornadic event.
• Source:
  Weather and Forecasting, 31(3), 763-786.
• DOI:
  https://doi.org/10.1175/WAF-D-15-0105.1
• Document Type:
  Journal Article
• Rights Information:
  Other
• Compliance:
  Submitted
• Download URL:
  https://repository.library.noaa.gov/view/noaa/16492/noaa_16492_DS1.pdf
• File Type:
  [PDF - 7.58 MB]
• Collection(s):
  Office of Oceanic and Atmospheric Research (OAR) ; NOAA Cooperative Institutes
• Main Document Checksum:
  urn:sha256:9edab8be212d07c4a262bcee6447d1fb16ade772354acfc5cb5fa54f6f07ea5d