Data that Illustrated the Potential for Thundersnow
9 to 12 hour lead time for first round of thundersnow around 1200 UTC


  • Upper Jet Evolution Supportive of Mesoscale Wave Disturbances (Uccellini and Koch, 1987) - refer to 300 Mb charts from 12/30/00 0000 UTC and 1200 UTC, and Water Vapor Imagery
  • Region in left-exit region of an upper-level jet streak
  • Geostrophic adjustment occurred as upper jet streak strengthened
  • Strengthening of upper-level jet seen as darkening in water vapor imagery (2 jet streaks converged into one jet) (Bader et al. 1995)
  • Upper-level divergence increased in the left-exit region of the upper-level jet
  • Mesoscale Wave Disturbances seen in Water Vapor and Infrared Satellite Imagery (slow loop so labeled info can be read)
  • Line of convection formed over the offshore waters between 0000 UTC and 0600 UTC on 30 December
  • Water temperatures >15C aided in destablizing low levels
  • Increasing southerly low-level winds (in response to thermally indirect circulation of strengthening upper jet (Uccellini and Kocin 1987)), were not resolved in the upper air data network
  • Lightning data showed cloud-to-water strikes well offshore, coinciding with the mesoscale wave disturbances seen in satellite imagery
    • 3 to 6 hour lead time for second round of thundersnow around 1700 UTC


  • Radar Imagery showed the banded precipitation, increasing southeasterly low-level winds over eastern Long Island, northeast winds near New York City, and high reflectivities advecting off the ocean into Long Island and New York City
  • The radar data in addition to the lightning data suggested that once convective elements moved over land, thundersnow was likely
  • Note lightning strikes indicated on Long Island on the 1200-1500 UTC and 1500-1800 UTC frames
  • Note how convective elements advected into Long Island off the ocean (on Infrared satellite imagery) during the same time period
  • Visible satellite imagery showed the mesoscale wave disturbances and convective elements, seen as textured cloudiness wrapping into the center of the surface low

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  • 1800 UTC Upton, NY sounding showed the temperature and moisture profile of the atmosphere proximate to areas that observed thundersnow (Brooks and Doswell 1994)
  • Conditions supportive of possible upright convective thundersnow (after virtual temperature correction, Doswell and Rasmussen 1994) were not evident in the upper air network until this observation, because the airmass that produced the thundersnow originated over the ocean
  • Convective instability and positive Convective Available Potential Energy in an upper air sounding completely below freezing is rarely observed
    • References